Energy Instrumentation and Information Analysisjnujprdistance.com/assets/lms/LMS JNU/MBA/MBA - Energy Management/Sem IV/Energy...This book is a part of the course by Jaipur National

Energy Instrumentation and Information Analysis

This book is a part of the course by Jaipur National University, Jaipur.This book contains the course content for Energy Instrumentation and Information Analysis.

JNU, JaipurFirst Edition 2013

The content in the book is copyright of JNU. All rights reserved.No part of the content may in any form or by any electronic, mechanical, photocopying, recording, or any other means be reproduced, stored in a retrieval system or be broadcast or transmitted without the prior permission of the publisher.

JNU makes reasonable endeavours to ensure content is current and accurate. JNU reserves the right to alter the content whenever the need arises, and to vary it at any time without prior notice.

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Index

ContentI. ...................................................................... II

List of FiguresII. ........................................................... V

List of TablesIII. ......................................................... VII

AbbreviationsIV. ......................................................VIII

Case StudyV. .............................................................. 110

BibliographyVI. ......................................................... 115

Self Assessment AnswersVII. ................................. 1157

Book at a Glance

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Contents

Chapter I ....................................................................................................................................................... 1Energy Audit Instruments ........................................................................................................................... 1Aim ................................................................................................................................................................ 1Objectives ...................................................................................................................................................... 1Learning outcome .......................................................................................................................................... 11.1 Introduction .............................................................................................................................................. 21.2 Generalised Measurement System ........................................................................................................... 21.3 Characteristics of Measurement Systems ................................................................................................ 4 1.3.1 Static Characteristics ................................................................................................................ 4 1.3.2 Dynamic Characteristics ......................................................................................................... 71.4 Basic Measurements ................................................................................................................................ 7 1.4.1 Pressure ................................................................................................................................... 9 1.4.1.1 Elastic Pressure Sensors .......................................................................................... 10 1.4.1.2 Electrical Pressure Sensors ..................................................................................... 12 1.4.2 Temperature and Heat Flux .................................................................................................... 15 1.4.3 Flow Rate ............................................................................................................................... 20 1.4.3.1 Volumetric Flow Meters ......................................................................................... 21 1.4.3.2 Quantity Meters or Total Flow Meters .................................................................... 25 1.4.4 Velocity .................................................................................................................................. 27 1.4.5 Vibrations ............................................................................................................................... 291.5 Instruments Used in Energy Systems..................................................................................................... 31 1.5.1 Load and Power Factor ......................................................................................................... 31 1.5.2 Power ..................................................................................................................................... 34 1.5.3 Flue Gas Analysis ................................................................................................................. 39 1.5.4 Air Quality Analysis .............................................................................................................. 44 1.5.5 Thermal Conductivity ............................................................................................................ 451.6 Errors in Measurement ........................................................................................................................... 47 1.6.1 Systematic Errors .................................................................................................................. 47 1.6.2 Gross Errors ........................................................................................................................... 47 1.6.3 Random Errors ....................................................................................................................... 47Summary ..................................................................................................................................................... 48References ................................................................................................................................................... 48Recommended Reading ............................................................................................................................. 48Self Assessment ........................................................................................................................................... 49

Chapter II ................................................................................................................................................... 51Control Systems ......................................................................................................................................... 51Aim .............................................................................................................................................................. 51Objectives .................................................................................................................................................... 51Learning outcome ........................................................................................................................................ 512.1 Introduction ............................................................................................................................................ 522.2 Signal Conditioning ............................................................................................................................... 522.3 Analog to Digital Conversion ................................................................................................................ 53 2.3.1 Successive Approximation Method ....................................................................................... 54 2.3.2 Voltage-to-frequency Conversion Method ............................................................................. 55 2.3.3 Dual-slope Convertor ............................................................................................................. 56 2.3.4 Sigma-delta ADC ................................................................................................................... 572.4 Microcontroller ...................................................................................................................................... 57 2.4.1 Architecture ............................................................................................................................ 58 2.4.2 Selection Criteria for Microcontrollers .................................................................................. 59 2.4.3 89C Series .............................................................................................................................. 592.5 Display Devices and Recorders ............................................................................................................. 63 2.5.1 Digital Instruments ................................................................................................................ 63

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2.5.2 Recorders ............................................................................................................................... 63 2.5.2.1 Graphic Recorders ................................................................................................... 64 2.5.2.2 X-Y recorder............................................................................................................ 652.6 Data Acquisition System ........................................................................................................................ 65 2.6.1 Single Channel DAS ............................................................................................................. 67 2.6.2 Multi-Channel DAS .............................................................................................................. 672.7 Data Logger ........................................................................................................................................... 68Summary ..................................................................................................................................................... 70References .................................................................................................................................................. 70Recommended Reading ............................................................................................................................. 70Self Assessment ........................................................................................................................................... 71

Chapter III .................................................................................................................................................. 73Computer for Energy Management ......................................................................................................... 73Aim .............................................................................................................................................................. 73Objectives .................................................................................................................................................... 73Learning outcome ........................................................................................................................................ 733.1 Introduction ........................................................................................................................................... 743.2 The Structure of Energy Analysis Programmes .................................................................................... 74 3.2.1 Space Loads .......................................................................................................................... 74 3.2.2 System Loads ........................................................................................................................ 74 3.2.3 Central Plant Loads ................................................................................................................ 75 3.2.4 Economic Calculations .......................................................................................................... 753.3 The Difference Between Load Calculations and Energy Analysis ........................................................ 753.4 Typical Program Output ......................................................................................................................... 76Summary ..................................................................................................................................................... 78References .................................................................................................................................................. 78Recommended Reading ............................................................................................................................. 78Self Assessment ........................................................................................................................................... 79

Chapter IV ................................................................................................................................................. 81Management Information Systems .......................................................................................................... 81Aim ............................................................................................................................................................. 81Objectives .................................................................................................................................................... 81Learning outcome ........................................................................................................................................ 814.1 Introduction ........................................................................................................................................... 824.2 What is Information? ............................................................................................................................ 824.3 Management Information System .......................................................................................................... 834.4 Barriers .................................................................................................................................................. 83 4.4.1 Managerial ............................................................................................................................ 83 4.4.2 Technical ............................................................................................................................... 834.5 Getting the Most Out of Your System ................................................................................................... 834.6 Who Uses the Information? .................................................................................................................. 83 4.6.1 What information do Senior Managers Need? ...................................................................... 84 4.6.2 What Information do Middle Managers Need? .................................................................... 84 4.6.3 What Information do Key Personnel Need? ......................................................................... 84 4.6.4 What Information do General Staff Need? ........................................................................... 84 4.6.5 What Information do Energy Managers Need? .................................................................... 844.7 An Energy Management Information System ....................................................................................... 854.8 Typical format for paper industry .......................................................................................................... 94Summary ..................................................................................................................................................... 97References ................................................................................................................................................... 97Recommended Reading ............................................................................................................................. 97Self Assessment ........................................................................................................................................... 98

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Chapter V .................................................................................................................................................. 100Writing User-friendly Energy Audit Reports ........................................................................................ 100Aim ............................................................................................................................................................ 100Objectives .................................................................................................................................................. 100Learning outcome ...................................................................................................................................... 1005.1 Introduction ......................................................................................................................................... 1015.2 What Is a User-friendly Audit Report? ............................................................................................... 1015.3 Guidelines for Writing User-friendly Audit Report ............................................................................. 101 5.3.1 Know Your Audience ........................................................................................................... 101 5.3.2 Use a Simple, Direct Writing Style ..................................................................................... 101 5.3.3 Simplify Your Writing by Using the Active Voice .............................................................. 101 5.3.4 Consider that You are Addressing the Report to One or More Individuals ........................ 101 5.3.5 Avoid Technical Terminology that Your Reader May Not Understand ............................. 102 5.3.6 Present Information Visually .............................................................................................. 102 5.3.7 Make Calculation Sections Helpful .................................................................................... 102 5.3.8 Use Commonly Understood Units ...................................................................................... 102 5.3.9 Make Your Recommendations Clear .................................................................................. 102 5.3.10 Explain Your Assumptions ................................................................................................ 102 5.3.11 Be Accurate and Consistent .............................................................................................. 102 5.3.12 Be Consistent Throughout the Report ............................................................................... 103 5.3.13 Proofread Your Report Carefully ...................................................................................... 1035.4 Report Section ...................................................................................................................................... 103 5.4.1 Title Page ............................................................................................................................. 103 5.4.2 Table of Contents ................................................................................................................. 103 5.4.3 Auditor Firm and Audit Team Details & Certification ........................................................ 104 5.4.4 Executive Summary ............................................................................................................. 104 5.4.5 Introduction to Energy Audit and Methodology .................................................................. 104 5.4.6 Description of the Plant ....................................................................................................... 104 5.4.7 Action Plan Preparation ....................................................................................................... 105 5.4.8 Suppliers/Vendors/Contractor List ....................................................................................... 105 5.4.9 Appendices ........................................................................................................................... 1055.5 Short Form Audit Report .................................................................................................................... 1055.6 Feedback ............................................................................................................................................. 1065.7 Conclusion ........................................................................................................................................... 106Summary ................................................................................................................................................... 107References ................................................................................................................................................. 107Recommended Reading ........................................................................................................................... 107Self Assessment ......................................................................................................................................... 108

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List of Figures

Fig. 1.1 Generalised measurement system ..................................................................................................... 2Fig. 1.2 Functional elements of filled system thermometer ........................................................................... 3Fig. 1.3 Block diagram for a filled system thermometer ............................................................................... 3Fig. 1.4 Linearity ............................................................................................................................................ 5Fig. 1.5 Hysteresis.......................................................................................................................................... 6Fig. 1.6 Input-Output curve ........................................................................................................................... 6Fig. 1.7 Input-Output curve ........................................................................................................................... 7Fig. 1.8 Types of active transducers ............................................................................................................... 8Fig. 1.9 Types of passive transducers ............................................................................................................ 8Fig. 1.10 Different forms of diaphragm ....................................................................................................... 10Fig. 1.11 Bellows ..........................................................................................................................................11Fig. 1.12 Different forms of bourdon tube ....................................................................................................11Fig. 1.13 Resistive pressure transducer ........................................................................................................ 12Fig. 1.14 Inductive pressure transducer ....................................................................................................... 13Fig. 1.15 Capacitive pressure transducer ..................................................................................................... 14Fig. 1.16 Piezoelectric pressure transducer .................................................................................................. 14Fig. 1.17 A typical construction of RTD ...................................................................................................... 15Fig. 1.18 Various types of thermistor ........................................................................................................... 16Fig. 1.19 Seeback effect ............................................................................................................................... 17Fig. 1.20 Basic infrared thermometer .......................................................................................................... 19Fig. 1.21 Heat flux through a thermal resistance layer ................................................................................ 19Fig. 1.22 Different types of flow meters ...................................................................................................... 20Fig. 1.23 Cross-section of electromagnetic flow meter ............................................................................... 22Fig. 1.24 Typical hot wire element in an anemometer ................................................................................. 23Fig. 1.25 Schematic arrangement of Doppler flow meter ............................................................................ 24Fig. 1.26 Schematic arrangement of time of flight ultrasonic flow meter ................................................... 25Fig. 1.27 Nutating disc type flow meter ...................................................................................................... 26Fig. 1.28 Solid flow measurement ............................................................................................................... 27Fig. 1.29 Moving magnet type velocity transducer ..................................................................................... 28Fig. 1.30 DC tachometer .............................................................................................................................. 29Fig. 1.31 Basic vibration measurement system ........................................................................................... 29Fig. 1.32 Seismic accelerometer .................................................................................................................. 30Fig. 1.33 Installation considerations for an accelerometer .......................................................................... 31Fig. 1.34 Power factor triangle .................................................................................................................... 31Fig. 1.35 Measurement of active and reactive power with a multi-meter ................................................... 33Fig. 1.36 Internal construction of an electrodynamometer .......................................................................... 35Fig. 1.37 Simplified electrodynamometer wattmeter circuit ....................................................................... 36Fig. 1.38 Wattmeter connections .................................................................................................................. 37Fig. 1.39 Power measurement with instrument transformer ........................................................................ 38Fig. 1.40 Two-wattmeter method for 3-phase system .................................................................................. 39Fig. 1.41 Schematic diagram of the electro-chemical sensor ...................................................................... 41Fig. 1.42 Schematic diagram of an oxygen sensor ...................................................................................... 43Fig. 1.43 Block schematic diagram of a gas chromatograph ....................................................................... 45Fig. 1.44 Typical thermal conductivity cell ................................................................................................. 46Fig. 2.1 Typical industrial control system .................................................................................................... 52Fig. 2.2 Signal conditioning process ............................................................................................................ 52Fig. 2.3 A/D conversion using successive approximation technique ........................................................... 54Fig. 2.4 Voltage to frequency ADC .............................................................................................................. 55Fig. 2.5 Dual slope integration and discharge times .................................................................................... 56Fig. 2.6 Sigma-delta ADC ............................................................................................................................ 57Fig. 2.7 Components of a typical fully featured microcontroller ................................................................ 58Fig. 2.8 Block diagram of AT89C51 ............................................................................................................ 60Fig. 2.9 Pin configuration of 89C51 ............................................................................................................ 61

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Fig. 2.10 Classification of recorders ............................................................................................................ 64Fig. 2.11 Strip chart recorder ....................................................................................................................... 64Fig. 2.12 Data acquisition system ................................................................................................................ 66Fig. 2.13 Single channel DAS ...................................................................................................................... 67Fig. 2.14 Multi channel DAS using single A/D converter ........................................................................... 68Fig. 2.15 Block schematic diagram of data logger ...................................................................................... 69Fig. 4.1 Information system ......................................................................................................................... 82Fig. 4.2 Specific energy Consumption Trends ............................................................................................. 96

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List of Tables

Table 1.1 Types of thermocouples ............................................................................................................... 18Table 1.2 Typical power factors of electric devices ..................................................................................... 33Table 1.3 Thermal conductivity of selected gases ....................................................................................... 46Table 2.1 Advantages and disadvantages of successive approximation method ......................................... 55Table 2.2 Advantages and disadvantages of voltage-to-frequency conversion method .............................. 56Table 2.3 Advantages and disadvantages of dual-slope convertor............................................................... 56Table 2.4 Advantages and disadvantages of Sigma-delta ADC ................................................................... 57Table 2.5 Alternate functions of port 3 of 89C51 ........................................................................................ 62


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Abbreviations

ACC - AccumulatorADC - Analog to Digital ConvertorALE - Address Latch EnableCMOS - Complementary Metal-oxide Semiconductor CNG - Compressed Natural GasCPU - Central Processing UnitDAC - Digital Acquisition and Control DPM - Digital Panel MeterEA - EnableECO - Energy Conservation OpportunityEEPROM - Electrically Erasable Programmable Read-Only MemoryEM - ElectromagneticEMIS - Energy Management Information SystemEMO - Energy Management OpportunityEMR - Energy Management RecommendationEPROM - Erasable Programmable Read-Only MemoryFSD - FullScaleDeflectionGND - GroundHHS - Hot Heavy StockHSD - High Speed DieselHSHS - High Sulphur Heavy StockHVAC - Heating Ventilation and Air Conditioning I/O - Input-Output IC - Integrated CircuitIR - InfraredIRT - Infrared ThermometerLCD - Liquid Crystal DiodeLED - Light Emitting DiodeLPG - LiquefiedPetroleumGasesLSB - LeastSignificantBitLSD - Light Diesel OilLSHS - Low Sulphur Heavy StockLVDT - Linear Variable Differential TransformerMIS - Management Information SystemMSB - MostSignificantBitNTC - NegativeThermalCoefficientOp-amps - OperationalAmplifierPEROM - Flash Programmable and Erasable Read Only MemoryPIC - Peripheral Interface ControllerPNG - Piped Natural GasPROG - Programme Pulse InputPSEN - Programme Store EnablePTC - PositiveThermalCoefficientRAM - Random Access MemoryROM - Read-Only Memory RST - Reset

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RTD - Resistance Temperature DetectorSFR - Special Function RegisterSPI - Serial Peripheral InterfaceTPS - Thermal Power stationTTL - Transistor-Transistor LogicUART - Universal Asynchronous Receiver-TransmitterUSART - Universal Synchronous Asynchronous Receiver-TransmitterVCC - Supply VoltageVFD - Vacuum Fluorescent Diode

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Chapter I

Energy Audit Instruments

Aim

The aim of the chapter is to:

introduce the concept of measurement•

explore the basic measurements in energy systems•

state the instruments used in energy systems•

Objectives

The objectives of this chapter are to:

explain generalised measurement system•

state the characteristics of measurement•

discuss the errors in measurements •

Learning outcome

At the end of this chapter, the students will be able to:

explain the various types of static and dynamic characteristics of measurement•

definethedifferenttypeselectricalandmechanicaltransducers•

discussquantitymetersortotalflowmeters•


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1.1 IntroductionMeasurement is a comparison of a given unknown quantity with one of its predetermined standard values adopted as a unit. As two quantities are compared, the result of any measurement is a numerical value. This numerical value is thenumberoftimestheunitstandardfitsintothequantitybeingmeasured.Thenumericalvalueisalwaysfollowedbyaunit,whichidentifiesthecharacteristicorpropertymeasured.

Measurement is a process by which one can convert physical parameters to numbers. Thus, measurement provides us with a means of describing a natural phenomenon in quantitative terms.

The parameter required to be measured is generally termed as measurand although the term variable is also used, astheparameterisnotfixed.Variablesareoftwodistincttypes:

floworthroughvariableslikeflowrate,current,charge,etcwhicharesinglepointidentifiable•acrossvariableswhichrequireareferencepointforidentificationlikepressure,voltage,velocity,etc.•

Themethodsofmeasurementarebroadlyclassifiedinto:Direct methods•Indirect methods•

In the direct type, measurement is directly indicated by the instrument designed for the purpose although the instrument itself needs calibration for standardisation. An example is measuring length with a vernier calliper. In the indirect type, the measurement of a parameter is made which is a known function of the actual measurement. Thus, a conversion process is involved in these methods. A thermocouple used for temperature measurement is an example. A measurement system, especially its sensing part may be invasive as in a thermocouple or non-invasive as in a radiation pyrometer.

1.2 Generalised Measurement SystemA measurement system contains various parts that perform prescribed functions in converting a variable quantity or condition into a corresponding indication. Thus, the operation of a measuring system can be described in a generalised manner in terms of functional elements. A block diagram for the same is shown below:

Fig. 1.1 Generalised measurement systemTheprimarysensingelementisthat,whichfirstreceivesenergyfromthemeasuredmediumandproducesan•output corresponding to the value of the measurand.The variable conversion element converts the output signal from the primary sensor (which is some physical •variable like voltage or displacement) into a more suitable variable, while preserving the information content of the original signal. It should be noted that every instrument or system need not include a variable conversion element while some require several.The variable manipulation element manipulates the signal presented to it, preserving the original nature of the •signal. Manipulation here means only a change in the numerical value of the signal. A variable manipulation

Primary Sensing Element

Data Presentation

Element

Variable Conversion

Element

Data Transmission

Element

Variable Manipulation

Element

Measurand

Presented

Data

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element does not necessarily follow a variable conversion element; it may precede it, appear elsewhere in the chain or not appear at all. The data transmission element transmits the data from one element to other. It may be as simple as a shaft and •bearing assembly or as complicated as a telemetry system.The data presentation element conveys the information about the measurand to the person handling the •instrument or the system for monitoring, analysis and control. It may be a simple pointer or recording of pen over a chart. It must be noted that the elements described do not necessarily appear in all measurement systems. •A given instrument may involve the basic functions in any number and combination- they need not appear •always in the same order. Afilled system thermometerwith thevarious functional elements forprocess temperaturemeasurement is•shown below.

Fig. 1.2 Functional elements of filled system thermometer

Primary Sensing Element

Data Presentation

Element

Variable Conversion

Element

Variable Manipulation

Element

Data Transmission

Element

Variable Conversion

Element

Temperature

Temperature Tube

Scale and Pointer Linkage Gear Bourdon Tube

Tubing

Pressure

Motion

Pressure

Fig. 1.3 Block diagram for a filled system thermometer

The liquidor gasfilled temperaturebulb acts as a primary sensing andvariable conversion element since thetemperature range causes a pressure change in the bulb. This pressure is transmitted through the capillary tube (data transmission) to a spiral, bourdon type pressure gauge (variable conversion), which converts pressure into displacement. This displacement is manipulated by the linkage and gearing (variable manipulation) to give a large pointer motion. The pointer and scale indicates the temperature (data presentation).


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1.3 Characteristics of Measurement SystemsMeasurementplaysasignificantrole inachievingthegoalsandobjectivesofengineeringbecauseoffeedbackinformation supplied by them. The main characteristics of measurement system is divided into two categories

Static characteristics•Dynamic characteristics•

1.3.1 Static CharacteristicsStatic characteristics of the system are those that must be considered when the system is used to measure a condition that is constant with respect to time. The various static characteristics are explained below.

Accuracy:Itisdefinedasthedegreeofclosenesswithwhichthemeasuredvalueapproachesthetruevalue.It•isadesirablecharacteristic.Inusualpractice,accuracyisspecifiedaspercentdeviationorinaccuracyofthemeasurement from the true value.

Accuracyoftheinstrumentcanbespecifiedinthefollowingforms:

E.g. if a voltmeter with a range of 1000 V has an accuracy of ±1% and a true value of 100 V is to be measured, then thevoltmeterwillread90to110ifaccuracyisspecifiedaspercentoffullscaledeflection(f.s.d.).However,itwillread99to101ifaccuracyisspecifiedaspercentofTV.

Precision: It indicates the repeatability or reproducibility of an instrument (but does not indicate accuracy). If •an instrument is used to measure the same input, but at different instants, spread over the whole day, successive measurements may vary randomly. A precision instrument indicates that the successive reading would be very close,orinotherwords,thestandarddeviationσeofthesetofmeasurementswouldbeverysmall.Quantitatively,the precision can be expressed as:

The difference between precision and accuracy needs to be understood carefully. Precision means repetition of successive readings, but it does not guarantee accuracy; successive readings may be close to each other, but far from the true value. On the other hand, an accurate instrument has to be precise also, since successive readings must be close to the true value (that is unique).

Repeatability:Itisdefinedastheabilityoftheinstrumenttoreproducetheoutputwhenthesameinputisapplied•repeatedly over a short period of time, with the same measurement conditions, same instrument, same observer, same location and same conditions maintained throughout. Thus, it describes the spread of output readings for the same input if the measurement conditions are constant.Sensitivity:Itisdefinedastheratioofthemagnitudeofresponse(outputsignal)tothemagnitudeofquantity•being measured (input signal), at steady state conditions. This ratio is expressed in the units of measurement of output and input.

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Thus, sensitivity indicates the factor by which the output changes for a unit change in measurand i.e. input.Forexample:Ifapressureof2barproducesadeflectionof10degreesinapressuretransducer,thesensitivityoftheinstrumentis10/2=5degrees/bar(assumingthatthedeflectioniszeroforthezeropressureapplied).

Linearity: It is actually a measure of non-linearity of the instrument. When sensitivity is considered it is assumed •that the input/output characteristic of the instrument are approximately linear. But in practice, it is normally non-linear.Thelinearityisdefinedasthemaximumdeviationf

Where, ∆O=max (∆O1, ∆O2)

Output

O1

O2

Input

OMIN

OMAx

IMIN IMAx

Fig.1.4 Linearity(Source: http://nptel.iitm.ac.in/courses/Webcourse-contents/IIT Kharagpur/Industrial Automation control/pdf/L-

03(SS) (IA&C) ((EE) NPTEL).pdf)

RangeorSpan:Itdefinesthemaximumandminimumvaluesoftheinputsortheoutputsforwhichtheinstrument•is recommended to use. For example: For a temperature measuring instrument the input range may be 100-500oC and the output range may be 4-20 mAResolution:Itisdefinedasthesmallestchangeinthemeasuredvaluethatcanbedetectedwithcertaintyby•the instrument. Thus, resolution implies the smallest measurable change in the input. The least count of any instrument is taken as the resolution of the instrument.For example: A ruler with a L.C. of 1mm. may be used to measure with the nearest 0.5 mm. by interpolation. Therefore, its resolution is 0.5 mm. Similarly, the resolution of a watch is 1sec. as that is the smallest change in time that is observable.Reliability:Itisdefinedastheprobabilitythatitwillperformitsassignedfunctionsforaspecificperiodoftime•under given conditions. Maintainability:Itisdefinedastheprobabilitythatintheeventoffailure,maintenanceactionunderthegiven•conditionswillrestorethesystemwithinaspecifiedtime.Hysteresis:Hysteresisexistsnotonlyinmagneticcircuits,butininstrumentsalso.Forexample,thedeflection•of a diaphragm type pressure gauge may be different for the same pressure, but one for increasing and other for decreasing,asshowninfigure.Thehysteresisisexpressedasthemaximumhysteresisasafullscalereading


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Fig. 1.5 Hysteresis(Source: http://nptel.iitm.ac.in/courses/Webcourse-contents/IIT Kharagpur/Industrial Automation control/pdf/L-

03(SS) (IA&C) ((EE) NPTEL).pdf)

Backlash:Itisdefinedasthemaximumdistanceoranglethroughwhichanypartofthemechanicalsystemmay•be moved in one direction without causing motion of the next part.DeadzoneorDeadband:Itisdefinedasthelargestchangeinthemeasurandi.e.,inputtowhichtheinstrument•does not respond.

output

input

threshold

Dead Band

Fig.1.6 Input-Output curve

Forexample:Theinputappliedmaynotbesufficienttoovercomethefrictionandassuch,theoutputwillnotmove.It will move when the input is such that it produces a driving force which can overcome friction.

Deadtime:Itisdefinedasthetimerequiredbyameasurementsystemtobegintorespondtoachangeinmeasured.•It is in fact the time before the instrument begins to respond after the measured quantity has changed. Drift:Itisdefinedasthegradualvariationoftheoutputoveraperiodoftime,forthegiveninputwhentheother•measurement conditions are constant. This is caused due to the change in sensitivity of the instrument to certain interfering inputs like temperature changes, component instabilities, etc. referred to as sensitivity drift. It is also caused due to a change in the zero reading due to a change in ambient conditions called zero drift.

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Sensitivity drift

Zero drift

Nominal curve

Total error due to sensitivity and zero drift

output

input

Drift curve

Fig.1.7 Input-Output curve

Therearemanyenvironmentalfactorsthatcausedrift.Theymaybestrayelectricandmagneticfields, thermalemfs, temperature changes, mechanical vibrations, wear and tear, and high mechanical stresses developed in some parts of the system.

Calibration: The process called calibration obtains all the performance characteristics of the instrument in one •formorother.Calibrationisdefinedasthecomparisonofspecificvaluesofinputandoutputofaninstrumentwith a reference standard so as to obtain a scale range of measurement. The standard used may be a primary standard, secondary standard with a higher accuracy or an instrument known as accuracy.

1.3.2 Dynamic Characteristics Dynamic characteristics of an instrument are those that must be considered when the instrument is used to measure and analyse a condition varying with time. The various dynamic characteristics are elucidated below.

Speedofresponse:Itisdefinedasthespeedwithwhichaninstrumentrespondstochangeinmeasurand.Itis•characterised by the time constant of a system. Measuring lag: It is the retardation or delay in the response of an instrument to changes in measurand. •Fidelity:Itisdefined,asadegreetowhichaninstrumentindicateschangesinameasuredvariablewithout•dynamic error. Dynamicerror:Itisdefinedasthedifferencebetweenthetruevalueofthequantitychangingwithtimeandthe•value indicated by the instrument, if no static error is assumed. It is also referred to as measurement error. Dynamicrange:Itisdefinedastheratioofthelargesttothesmallestdynamicinputthattheinstrumentwill•faithfully measure. This value is usually given in decibels. Dynamic response: The dynamic response is the evaluation of the system’s ability to faithfully transmit and •present all the pertinent information included in the input signal and exclude all else.

1.4 Basic MeasurementsEvery measurement system will have a transducer/sensor as a primary block converting the measured energy into someotherconvenientformformanipulationanddisplay.A‘transducer’isdefinedasadevicethatacceptsenergyfrom one system and transmits it to another, often in a different form. It provides a usable output in response to a specificmeasurand,whichmaybeaphysicalormechanicalquantity,propertyorcondition.

Transducersarebroadlyclassifiedintotwotypes:Electrical �Mechanical �


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Electrical transducersAn electrical transducer is a sensing device by which the physical, mechanical or optical quantity to be measured is transformed directly by a suitable mechanism into an electrical voltage or current proportional to the input. Electrical Transducersarefurtherclassifiedintotwotypes:

Active transducers•Active transducers are self generating type of transducers. These transducers develop an electrical parameter (i.e., voltage or current) which is proportional to the quantity under measurement. These transducers do not require any externalsourceorpowerfortheiroperation.Theyareclassifiedasfollows:

Photovoltaic Thermoelectric Electromagnetic Piezoelectric

Active Transducers

Fig. 1.8 Types of active transducersPassive transducers•

Passive transducers do not generate any electrical signals by themselves. To obtain an electrical signal from such transducers, an external source of power is essential. Passive transducers depend upon the change in an electrical parameter (R, L, & C). They are also known as externally power driven transducers. They can be subdivided into following categories

Passive transducers

Opto electronic

Photo junctions

Photo conductors

Strain gauge

Photo emissive

Variable reactance

Variable resistance

Thermistor

Fig. 1.9 Types of passive transducers

Mechanical transducersA mechanical transducer is a sensing device by which any quantity to be measured is transformed directly by a suitable mechanism into a mechanical signal like displacement, motion, etc. proportional to the input measurand.

Selection criterion for transducersThe following points should be given acute consideration while selecting a transducer for any specific application.

Purpose of signal detection (measurement, monitoring, control, etc.) •Physical compatibility with its intended application •

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Operating range of detection required •Maintenance, operation, installation, construction considerations •Loading on the source •Sensitivitychosentoallowsufficientoutput•Ruggedness – ability to withstand overloads with safety stops for overload protection •Convenient instrumentation– sufficientlyhighanalogoutput signalwithhigh signal tonoise ratio,digital•output preferable High stability and reliability – minimum error in measurement unaffected by temperature, vibration or other •environmental changes Linearity and repeatability •Dynamic response •Signal compatibility with the controller/ indicator •Accuracy and precision •Speed of response •Adaptability to different input sizes i.e. range change, scale expansion, etc. •Ergonomic considerations i.e. human interpretation, ease of operation, etc. •Suitability of interconnection with existing systems •Specificationsoftheprocess•Electrical parameters – length and type of cable required •Power supply requirements •Availability and maintainability •Ease in calibration when needed •Safety •Cost•

1.4.1 Pressure Themeasurementandcontroloffluidpressure(liquidandgas)isoneofthemostcommonofallprocessindustries.Due to the great variety of conditions, ranges and materials, for which pressure must be measured; there are many types of pressure sensor designs. In the discussion to follow, we will see that the pressure measurement is often accomplished by the conversion of the pressure information into some intermediate form such as displacement which is then measured by a sensor to determine pressure.

Pressureisdefinedastheforceperunitareathatthefluidexertsonthesurroundings.Whenthefluidisinequilibrium,the pressure at a particular point is identical in all directions and is independent of orientation. This is explicitly trueforafluidnotmovinginspace,notpumpedthroughpipesorflowingthroughachannel.Thispressureincaseswherenomotionoccursisreferredtoas‘staticpressure’.Ifafluidisinmotion,thepressurethatitexertsonthesurrounding depends on the motion, is referred to as ‘dynamic pressure’.

Absolute pressure: It is the actual total pressure including the atmospheric pressure acting on a surface. It is the fluidpressureabovethereferencevalueoftheperfectvacuumorabsolutezero.Gaugepressure:Itisthevalueofpressure above the reference value of atmospheric pressure (zero implies atmospheric pressure) i.e., it is the difference between the actual and atmospheric pressure.

Pgauge = Pabs – Patm Vacuum pressure: It represents the amount by which the atmospheric pressure exceeds the absolute pressure i.e., it indicates pressure below relative zero (atmospheric pressure). Pvacuum = Patm – Pabs


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1.4.1.1 Elastic Pressure SensorsElastic elements when subjected to pressure get deformed. This deformation when measured, gives an indication of pressure. These elements may be in the form of diaphragms, capsules, bellows, bourdon tube, etc. They are made up of elastic metal alloys such as bronze, phosphor bronze, beryllium copper, stainless steel, etc.Let us see few of these elements

Diaphragm: It is essentially a thin circular plate stretched and fastened on its periphery. The structure of the •diaphragmmaybeflatorcorrugatedasshowninthefigurebelow.Onapplicationofpressure,thediaphragmproducesadeflection‘x’whichcanbemeasuredaccordingly.Thus,pressureisconvertedintodisplacement.

Pressure Pressure

Fig. 1.10 Different forms of diaphragm

Aback-to-backarrangementofdiaphragmsshowninfig.1.10isreferredtoasacapsule.Theoutputofthecapsulewill be obviously displacement in response to pressure. As is evident from the diagram, one of diaphragms is provided with a central reinforced port to admit the pressure to be measured. The pressure difference over any diaphragm surface is given by

( )

Where,r–Deflectiontothicknessratio–(x/t)t – Thickness of diaphragm D– Diameter of diaphragm E – Modulus of elasticity µ – Poisson’s ratio.

If 0.488r3 << r then, “P is proportional to ‘r’ hence “P is prop to x/t Therefore“Pisproportionaltothedeflection‘x’‘x’ should be less than 1/3 of thickness for working within elastic limits.

Bellows: Bellows are essentially thin walled cylindrical shells with deep convolutions and are sealed at one •end.Itisaone-pieceexpansibleandaxiallyflexiblemember.Thesealedendmovesaxiallywhenpressureisappliedattheotherendasshowninfigure.Thus,pressureissensedasachangeindisplacement.Thenumberof convolutions varies from 0 to 20 depending upon the pressure range, displacement required and the operating temperature.

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P

Fig. 1.11 Bellows

Thedeflection‘x’ofbellowforapressure‘P’isgivenby,

Where,n – Number of convolutionsA – Effective area r – Average radius of bellow E – Modulus of elasticity t – Thickness of wall

Bourdon tube: It is essentially a curved or twisted metal tube having an elliptical cross section and it is sealed •atoneend.Thetubetendstostraightenupontheapplicationofpressureandtheangulardeflectionofthefreeend is taken as a measure of pressure.

ThedifferentconfigurationsemployedforthisdeviceareC–shaped,twisted,andhelicalasshowninthefigurebelow. The C shaped tube has a total angle of curvature of 1800 to 2700 and the displacement is usually measured withamechanicalpointeroveracalibratedscale.ThehelicalissimilarinitsdeflectionbehaviourtoaCtubeexceptthatthetubeiscoiledintoamulti-turnhelixwith5to10turns.Thetwistedversionisbasicallyaflattenedtubetwisted along its central axis throughout its length

PP

P

Fig. 1.12 Different forms of bourdon tube

TheangulardeflectionofaCtypebourdontubeisgivenby

Where, ϕ = angle of rotation ϕ0= total angle of tube


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P = pressure in pascals r = radius of tubet = thickness of wall E = modulus of elasticity b = minor axis measured from middle of one wall to other

1.4.1.2 Electrical Pressure SensorsThe electrical transducer is a device, which converts physical quantity or condition or mechanical output into an electrical signal. Most of the methods of converting mechanical output into an electrical signal work equally well for the bellow, diaphragm and bourdon tube. Generally electrical pressure transducers consist of three elements which are:

pressure sensing element such as bellow, diaphragm or bourdon tube•primary conversion element•secondary conversion element•

Resistive: Resistive transducers are those in which resistance changes due to a change in some physical •phenomena. Any variation in the input variable is sensed or detected, as a change in resistance. Resistive transducers are essentially passive transducers. Strain gauge is a common type of resistive transducer whose electrical resistance changes when it is stretched or compressed. It can be attached to a pressure-sensing diaphragm asshowninthefollowingfigure.

P

R1 R2 R3 R4

Diaphragm

Fig. 1.13 Resistive pressure transducer

Inductive: Inductive transducers are those in which inductance changes due to a change in some physical •phenomena. Any variation in the input variable is sensed or detected, as a change in inductance. They can be self-generating or passive type.

LVDT is basically a passive inductive transducer used to convert linear displacement into an electrical �signal. This displacement can be obtained from a pressure sensing bellow or bourdon tubes thus, facilitating the �LVDT to measure pressure. The basic operating principle is that, when the coupling between two coils change, the reluctance between �them also change. A bellow or a bourdon tube can be used to change the coupling between two coils by moving one part of a �magnetic circuit. This motion changes the voltage induced by one coil in the other. Thechangeintheinducedvoltagecanbeinterpretedasachangeinpressure.ThefigurebelowshowsLVDT �as a pressure transducer with the bellow as a sensing element. The bellow is connected to the core of an LVDT. LVDT basically consists of a primary winding and two �secondary windings. They are arranged concentrically next to each other, wound over a hollow cylindrical former, made of non-magnetic and insulating material.

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A ferromagnetic core usually made up of Cu – Ni alloy slides freely within the hollow former, thus affecting �the magnetic coupling between the primary and the secondary. AC excitation is applied across the primary and the movable core varies the coupling between it and the �two secondary windings. When the core is in the centre position, the coupling to two secondary coils is equal. As the core moves �away from the centre position, the coupling and voltage of one secondary increases, whereas the coupling and voltage of the other secondary decreases.

Primary Output

Bellow

Core

P

x

Secondaries

Fig. 1.14 Inductive pressure transducer

A bellow is connected to the core of the LVDT for the application of pressure. �Anychangeinpressuremakesthebellowsexpandandcontract.Duetothis,adisplacementordeflection �is produced at the output of the bellow which is given to the core of the LVDT. Thus,thedeflectionofthebellowcausesamotiontothemovablecore.Thismotioncausesthevoltageof �one secondary to increase while simultaneously reducing the voltage in other secondary winding. The difference of the two voltages appears at the output which gives a measure of the physical position of �the core and hence the pressure.Thus, pressure is directly converted into an appropriate electrical voltage. �

Capacitive: Capacitive transducers convert pressure into an electrical signal by changing the capacitance. The •basic principle of operation is based upon the familiar capacitance equation

Where, K – dielectric constant A – area of each plated – distance between two plates

Thus, we can say that capacitance is inversely proportional to the distance between two plates. This principle of changing distance between two plates to change the capacitance is used in capacitive pressure transducers to detect pressure changes.


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VoltageCapacitance Bridge

Reference

Pressure

Diaphragm

Fig. 1.15 Capacitive pressure transducer

Itbasicallyconsistsofafixedplateandamovableplatethatisfreetomoveasthepressureappliedchanges.Themovableplateisintheformofadiaphragm,whichexpandsandcontractsduetochangesinpressure.Thefixedplate and diaphragm form a parallel plate capacitor, which is connected as one arm of a capacitive bridge.

Anychangeinpressurewillcauseadeflectiontothediaphragm.This,changesthedistancebetweentwoplatesbetweenthediaphragmandthefixedplate,thuschangingthecapacitance.Thischangeincapacitanceunbalancesthe bridge, producing an appropriate voltage output. Thus, the output voltage corresponds to the pressure applied at the diaphragm plate

Piezoelectric: These utilise the piezoelectric characteristics of certain crystalline and ceramic materials like •quartz to generate an electrical signal.

V

P

Diaphragm

Y1 Y2Charge Amplifier

Fig. 1.16 Piezoelectric pressure transducer

The basic operating principle is that when pressure is applied on piezoelectric crystals, an electrical charge is •generated. Some of the materials that exhibit piezoelectric characteristics are quartz, barium titanate, tourmaline, Rochelle salt, etc.It consists of a diaphragm by which pressure is transmitted to the piezoelectric crystal. This crystal generates •anelectricalsignal,whichisamplifiedbyachargeamplifier.A second piezoelectric crystal Y2 is included to compensate for any acceleration of the device due to vibrations. •This compensation is needed because rapid acceleration creates additional pressure. Asecondchargeamplifieramplifiessignalsfromthecompensationcrystal.Adifferenceamplifierisusedwhich•subtracts pressure, removing all effects of acceleration. Piezoelectric pressure transducers are used to measure very high pressures that change very rapidly, for example: •pressure in a gasoline engine, compressors, rocket motors, etc.They are used to measure pressures in the range of 0 to 50000 psi. However, they cannot measure steady or •static pressure. They respond only to dynamic pressure.

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1.4.2 Temperature and Heat FluxTemperature in a broad sense can be said to be the degree of hotness or coldness of a body or an environment. Temperature is probably the most widely measured and controlled industrial variable. Further it is also a governing factor in thermodynamics and heat transfer. Additionally, it is a fundamental quantity like mass, length and time. Heatfluxistherateofenergytransferperunitarea,expressedinW/m²orW/cm².Heatfluxisoftenconfusedwithtemperature.Althoughtheyarerelated,aheatfluxmeasurementcontainsmore informationthana temperaturemeasurement, and consequently is often more useful.

Temperatureisanindicationoftheinternalenergyofmatter,whereasheatfluxistherateofenergytransferperunitarea.Tosomeextent,heatfluxcanbeconsideredanindicationofwherethetemperatureisheaded.Temperatureisdependentonthematerialpresent;heatfluxmeasurestheenergycrossingaboundaryandthereforeisnotrestrictedby the thermal mass of the system.

There are several simple techniques for the measurement of this common yet important variable starting from the basic expansion thermometers to the more widely used electrical ones and non – contact methods.

Let us have a look on few of these technique.s

Resistance Temperature Detector (RTD)RTD is a temperature transducer in which temperature is sensed as a change in resistance. It has a positive •temperatureco-efficienti.e.,resistanceincreasesastemperatureincreases.The RTD is one of the most accurately reproducible temperature-sensing devices.•The main part of the RTD is the metallic sensing element. The sensing element may be any material that •exhibits a relatively large resistance change in response to temperature. The material used should be stable in itscharacteristicsi.e.neitheritsresistancenortemperaturecoefficientshouldundergoachangewithuse.Some other points to be considered are accuracy, linearity, resistance to contamination and mechanical •strength.The main operating principle is that metals are basically crystalline in structure, comprising of metal ions and •free electrons in equilibrium.Theapplicationofthedcpotentialacrossthemetallicelementresultsinadirectionalflowoftheseelectrons.•During theirmovement, they collidewith themselves andwith the ions, thus restricting theflow,whichsubsequently results in an electrical resistance.As the temperature rises and the mean free path length between collisions decreases due to an increase in the •amplitude of oscillations, it results in an increase in electrical resistance. This basic phenomenon i.e., the change in resistance of various materials, which varies in a reproducible manner •with temperature, forms the basis of resistance thermometers, more commonly referred as to RTD.The metals in common use are Platinum, Copper, Nickel, etc.•

Resistance element (Colt) Hollow ceramic former

Copper leads

Terminal Metal sheath

Protective cement

Fig. 1.17 A typical construction of RTD


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Thetemperaturesensitiveelementisusuallyintheformofafinewire.Thewireofthemetali.e.,Platinumis•wound on the grooved hollow insulating ceramic rod and covered with protective cement.The ends of coils are welded to stiff copper leads that are taken out to be connected in one arm of the Wheatstone •bridge.The entire structure is enclosed in a metal sheath to provide mechanical strength and rigidity.•

Thermistor• Thermistor, a word formed by combining thermal with resistor, refers to a device whose electrical resistance, �or ability to conduct electricity, is controlled by temperature.Thermistor come in two types: �

NTC-Negativethermalcoefficienti. PTC-Positivethermalcoefficientii.

Thermistors are available in a great variety of shapes and sizes having cold resistance ranging from few �ohmstomegaohms.Thevariousconfigurationsareshowninthefigurebelow:

Bead type

Washer type Chip type

Disc typeRod type

Fig. 1.18 Various types of thermistor

The resistance of NTC thermistors decreases proportionally with increase in temperature. They are most �commonly made from the oxides of metals such as manganese, cobalt, nickel and copper. The metals are oxidised throughachemical reaction,ground toafinepowder, thencompressedandsubjected toveryhigh heat. Some NTC thermistors are crystallised from semi-conducting material such as silicon and germanium. PTC thermistors have increasing resistance with increasing temperature. They are generally made by �introducing small quantities of semi-conducting material into a polycrystalline ceramic. When temperature reachesacriticalpoint,thesemi-conductingmaterialformsabarriertotheflowofelectricityandresistanceclimbs very quickly. Unlike the gradual changes in NTC thermistors, PTCs act more like on-off switches. Adjusting the �composition of the thermistors can vary the temperature at which this occurs. Another type of PTC thermistor consists of a slice of plastic with carbon grains embedded in it. When the �plastic is cool, the carbon grains are close enough to each other to form a conductive path. Plastic expands when as it warms; at a certain temperature, it will have expanded enough to push the carbon grains apart and break the conductive path. This on-off behaviour of PTC thermistors is useful in situations where equipmentcanbedamagedbyeasilydefinableevents.Forexample,theycanbeusedtoprotectthewindingsin transformers and electrical motors from excessive heat.

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The temperature resistance relationship of a thermistor is of the exponential type and is given by the �following equation:

[β( )]Where,

R – Resistance at measured temperature T (oK) Ro – Resistance at reference temperature To (

oK) β – Constant for the given thermistor material.

Thermocouple• The thermocouple is a self-generating temperature transducer working on the principle of the thermoelectric •effect.The thermocouple essentially consists of two wires of different metals twisted and brazed or welded together •with each wire covered with insulation.The sensing is based on a principle known as the Seeback effect. It states that when two conductors of dissimilar •metalsAandB, are joined together to forma loop (thermocouple), as shown infig.1.18and twounequaltemperatures T1o and T2oareinterposedatjunctionsJ1andJ2respectively,thenaninfiniteresistancevoltmeterdetects an emf E.The magnitude of E depends on the combination of dissimilar metals and temperatures T1• o and T2o.

T1°C (or°F) COLD

JUNCTION

MILLIVOLT METER

Metal A

Metal B

T2°C (or°F) HOT JUNCTION

Fig. 1.19 Seeback effect

Thus, the emf generated is proportional to the temperature difference in a predictable manner.•E∝(T1-T2)For the convenience of measurements and standardisation, one of the two junctions is maintained at some •known temperature. The measured emf E then indicates the temperature difference relative to the reference temperature such as ice point.

The choice of materials for the thermocouple is governed by the following factors: Ability to withstand the temperatures at which they are used. •Immunity from contamination and oxidation, which ensures the maintenance of precise thermoelectric properties •with continuous usage. Linearity characteristics. •Accuracy required in measurement.•


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Types of thermocouples

Sr. No Type Material (+) Material (-) Temperature Range

1 T Copper Constantan(43% Ni 57% Cu) -200 to +350 oC

2 J Iron Constantan(43% Ni 57% Cu) 0 to 750 oC

3 K Chromel(90% Ni & 10% Cr)

Alumel(94% Ni, 3% Mn, 2% Al, 1% Si)

-200 to +1250 oC

4 E Chromel(90% Ni & 10% Cr)

Constantan(43% Ni 57% Cu) -200 to +900 oC

5 R Platinum-Rhodium(87% Pt & 13% Rh) Platinum 0 to 1500 oC

6 S Rhodium(90% Pt & 10% Rh) Platinum 0 to 1500 oC

Table 1.1 Types of thermocouples

Infrared thermometersInfrared thermometers for non-contact temperature measurement are highly developed sensors, which have •widespread application in industrial processing and research.An infrared thermometer measures temperature by detecting the infrared energy emitted by all materials which •are at temperatures above absolute zero, (0°Kelvin).The most basic design consists of a lens to focus the infrared (IR) energy on to a detector, which converts the •energy to an electrical signal that can be displayed in units of temperature after being compensated for ambient temperature variation.Thisconfigurationfacilitatestemperaturemeasurementfromadistancewithoutcontactwiththeobjecttobe•measured. As such, the infrared thermometer is useful for measuring temperature under circumstances where thermocouples or other probe type sensors cannot be used or do not produce accurate data for a variety of reasons.Some typical circumstances are where the object to be measured is moving; where the object is surrounded by •anEMfield,asininductionheating;wheretheobjectiscontainedinavacuumorothercontrolledatmosphere;or in applications where a fast response is required. As previously stated IR energy is emitted by all materials above 0°K. Infrared radiation is part of the •Electromagnetic Spectrum and occupies frequencies between visible light and radio waves. The IR part of the spectrum spans wavelengths from 0.7 micrometers to 1000 micrometers (microns).Within this wave band, only frequencies of 0.7 microns to 20 microns are used for practical, everyday temperature •measurement. This is because the IR detectors currently available to industry are not sensitive enough to detect the very small amounts of energy available at wavelengths beyond 20 microns A basic infrared thermometer (IRT) design, comprises a lens to collect the energy emitted by the target; a •detector to convert the energy to an electrical signal; an emissivity adjustment to match the IRT calibration to the emitting characteristics of the object being measured; and an ambient temperature compensation circuit to ensurethattemperaturevariationswithintheIRT,duetoambientchanges,arenottransferredtothefinaloutput.Such a concept is illustrated below

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DET.

ATCL

Fig. 1.20 Basic infrared thermometer

Heat flux sensor Aheatfluxsensortypicallyconsistsofathermopileor,sometimesjustapairofthermocouples,inwhichathin•layer of thermal resistance material separates the elements.Under a temperature gradient, the two-thermopile junction layers will be at different temperatures and so will •register a voltage. Theheatfluxisproportionaltothisdifferentialvoltage.•Notice that a temperature gradient must exist; otherwise both thermocouple junction layers will be at the same •temperature and hence record no voltage.The thermal resistance layer is usually as thin as possible to improve the response time of the sensor. •To help insure a proper thermal gradient, heat flux sensors should be designed to have a high thermal•conductivity.

Temperature T1

Temperature T2

Heat Flux q” q”=k(T1-T2)

Upper layer thermocouple junction at T1

Lower layer thermocouple junction at T2

Lower layer thermocouple junction

Upper layer thermocouple junction

Positive thermocouple metal Negative thermocouple metal Thermal resistance layer

Thermal resistance layer with resistivity k

(A)

(B)

Fig. 1.21 Heat flux through a thermal resistance layer

A thermopile is essentially an array of thermocouples. By linking many thermocouples in series, the temperature •sensitivity is increased. Like a thermocouple, the thermopile reads the temperature difference between two points.Foraheatfluxsensor,thesetwopointsarethetopandbottomlayersofthethermopile.•


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1.4.3 Flow Rate

Themeasurementofflowandquantityistheoldestofallmeasurementsofprocessvariablesinthefieldof•instrumentation.Itisbasicallymadefordeterminingtheproportionsandamountofmaterialsflowinginandoutoftheprocess.•Such measurement is often required to be made for steam, water and gas service.Withoutflowmeasurements,plantmaterialbalance,qualitycontrolandeventheoperationofanycontinuous•process would be almost impossible. Manyaccurateandreliablemethodsareavailableformeasuringflow.Someofwhichareapplicableonlyto•liquids, some only to vapours and gases and some others to both.Fluids measured may be clear or opaque, clean or dirty, wet or dry, erosive or corrosive. Flow may be laminar •or turbulent, viscosities may vary, and pressures may vary from vacuum to hundreds of psi.Temperaturemayrangefromcryogenicstohundredsofdegrees,flowratemayrangefromfewdropsperhour•to thousands of gallons per minute, and range abilities may vary.Thus,withthispossibleassortmentofconditionsandrequirements,flowmetersarebroadlydividedintodifferent•categories

Flow meters

Volumetricflowmeter

(Rate meter)

Massflowmeter(Rate meter)

Totalflowmeter(Quantity meter)

Fig. 1.22 Different types of flow meters

Volumetricflowmeasurementsignifies thequantityofafluid (expressedasvolume)flowingperunit time•throughacrosssectionofapipeorchannel.Thereforevolumetricflowisgivenas

Q = V×AWhere,V = velocity in m/s. A = area of cross section in m2 Q=volumetricflowrateinm3/sec

Thevolumetricflowratecanbealsoexpressedinlpm,gpm,etc.Massflowmeasurementsignifiesthequantityofafluid(expressedasmass),flowingperunittimethrougha•cross-sectionofapipeorchannel.Itisthusexpressedinkg/sec,kg/hr,etc.Themassflowratecanbecomputedfromvolumetricratebymultiplyingitwiththefluiddensity.

W = Q × r1Where,Q=volumetricflowrateinr1=densityoffluidinkg/m³W=massflowrateinkg/sec.

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Totalflowmeasurementsignifiestheamountoffluidthatflowspastagivenpointinadefiniteintervaloftime.•Thismeasurementrequiresintegrationwithrespecttothetimeoftheinstantaneousflowrate.Theaverageflowratecanbecomputedbydividingthetotalvolume/massofflowpassedbythetotaltimetaken.

1.4.3.1 Volumetric Flow MetersVolumetricflowmetersarethoseinwhichthefluidpassesthroughtheprimaryelementinacontinuousstream.Themovementoffluidhasaneffectontheprimaryelementaccordingtosomephysicalload.Theflowrateisinferredfromtheeffectsofflowonpressure,force,heattransfer,flowarea,etc.Thus,thesetypesofflowmetersdonotmeasuretheflowdirectly,butinsteadmeasuresomethingassociatedwithflow.Thevarioustypesofvolumetricflowmetersaredescribedbrieflyintheprecedingsections.

Variableheadordifferentialflowmeters:Thisisoneoftheoldestandmostwidelyusedmethodsofindustrialflowmeasurement.Thevariableheadflowmeteroperatesonthebasicprinciplethatarestrictionorobstructioninthelineoftheflowingfluidproducesadifferentialpressureacrosstherestrictionelement,whichisproportionaltotheflowrate.Theproportionalityisnotalinearone,buthasasquarerootrelationship.Thustheflowrateisproportionalto the square root of differential pressure

Thevarioustypesofheadflowmetersareorificeplate,venturytube,flownozzle,Pitottube,etc.

Variableareaflowmeters:Thevariableareaflowmeteroperatesonthebasicprincipleofadjustmentofthesizeofrestriction by an amount necessary to keep the pressure differential constant. The amount of adjustment required is proportionaltoflow.Thisisinexactcontrasttovariableheadmeters,wheretheflowrestrictionisofafixedsizeandthepressuredifferenceacrossitchangeswiththeflowrate.Therotameteristhemostextensivelyusedformofvariableareameter,wheretheadjustmentisprovidedbymeansofafloat,thatmovesfreelyupanddowninthetubewiththeflow.Thus,theflowrateisproportionaltothedisplacementofthefloat.Q∝h

Electromagnetic flow meter

Electro-magneticflowmetersareusedtodeterminethevolumetricflowrateofelectricallyconductingfluids.•Thebasicoperatingprincipleismeasuringtheemfinducedacrossthefluidstreamwhenitpassesthrougha•magneticfield.ThisprincipleisdirectlyanalogoustoFaraday’slawsofElectromagneticInduction.Itstatesthatwheneveraconductormovesthroughamagneticfieldofagivenstrength,avoltageisinducedin•theconductorproportionaltotherelativevelocitybetweentheconductorandthemagneticfield.Theelectricallyconductingliquidactsastheconductorincaseofmagneticflowmeters.Thedirectionofthe•induced emf is given by Fleming’s right hand rule.


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Magnet pole

Plastic pipe

Metal pipeMetal

pipe

Fluid motion

Fluid

Motion(ThuMb)

900

900

Induc ed e.m.i .

(Middle finge r)

Field (First finger)

Electrode

EO

S

N

Fig. 1.23 Cross-section of electromagnetic flow meter

Itconsistsofanelectricallyinsulatedornon-conductingpipesuchasfibreglass.•If a metal pipe is used, an electrically insulated liner is provided for the inside of the pipe.•Apermanentmagnetoranelectromagnetismountedaroundthepipe;sothatamagneticfieldisgeneratedin•aplanemutuallyperpendiculartotheaxisofthepipei.e.,theflow.Apairofelectrodesismountedoppositeeachotherandatrightanglestothemagneticfieldforpickingupthe•induced emf.Thedistancebetweentheelectrodesi.e.,pipediameteractsasthelengthoftheconductor,thefluidflowinthe•pipeisatrightanglestotheplaneofthemagneticfluxandinducedemf.Astheliquidpassesthroughthepipesection,italsopassesthroughthemagneticfield,thusinducingavoltage•in the liquid. Electrodes mounted on the pipe wall detect this voltage.Themagnitudeoftheinducedvoltageisproportionaltothevelocityofthefluid.Themagneticcoilsmaybe•energised by ac or dc, though ac is usually preferred as it prevents polarisation of electrodes.AccordingtoFaraday’slaw,thevoltageinducedforconductingfluidsisgivenas:•

E=BLV×10-8VWhere,

B=magneticfluxdensityinV-s/cm2

L = length of conductor in cmV = velocity of conductor in cm/s the effective length of the conductor corresponds to the inner diameter of the pipe.

Hence, L=d

Thevolumetricflowrateisgivenbythecontinuityequationas:Q=A×VTherefore,

E≈ V

Thus, thevolumetricflowrateQisdirectlyproportional to the inducedemfEas longas thefluxdensityBisconstant.

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Turbine flow metersTheturbineflowmeterisusedforthemeasurementofliquid,gasandverylowflowrates.•It derives its name from the operating principle used and is perhaps the most highly developed non-friction, •displacementtypeofmechanicalflowmeter.Itincorporatessomeformofamulti-vanerotordrivenbythemeteringfluid.•Thebasicoperatingprincipleisthatifaturbinewheelisplacedinthepathofaflowingfluid,theimpingingfluid•imparts a force on the rotor. This force sets the rotor in motion with an angular velocity or speed proportional totheflowrate.Byminimisingthebearingfrictionandotherlosses,alinearrelationshipbetweenthevolumetricflowrateand•the speed of rotation can be obtained.Thisdeviceiswidelyusedinweatherstations.Itisalsousedformeasuringflowsindams,riverschannels,•etc.

AnemometerAnemometersarevelocitymeasuringdevices,forobtainingthevelocityofafluidstream,suchasairflowina•ventilatingductorwindtunnelorwaterflowinaclosedchannel,orwindspeedasinmeteorology.Itisadevicemostly used in research applications.Thehotwire anemometer is themostwidelyused type, for themeasurementof themeanandfluctuating•velocitiesinfluidflow.Thefluidcanevenbegaseousathighspeedsornon-conductiveliquidsatlowspeeds•Thebasicoperatingprincipleisthat,whenfluidflowsoveraheatedsurface,heatisdissipatedthroughconvection,•due to which the temperature of the surface reduces.Thisrateofreductionorcoolingisproportionaltothevelocityofthefluidstreamandhencetothevolumetric•flowrate.Theflowsensingelementisasmalllength,finewireofplatinumcoatedtungstenweldedbetweentwoprongs•oftheprobe.Itisschematicallyshowninthefigurebelow:

Wire support

Tungsten wire

Fig. 1.24 Typical hot wire element in an anemometer

Thewireisheatedelectricallyandexposedtothefluidflowwhosevelocityistobedetermined.•The temperature of wire is determined by measuring the resistance with a wheat stone bridge arrangement •The hot wire anemometer can be operated in two modes:•

Constant current mode �Constant temperature mode �

In the constant current mode, a constant current is fed to the hot wire. The value of this current and the resistance •ofthewiredefinethepowerfedtothewire.Duetochangesinfluidvelocity,resistanceofwirechangesareobserved on the circuit.In the constant temperature (or resistance) mode, the current in the hot wire is continuously adjusted to maintain •the wire resistance and hence the wire temperature is at a constant value throughout the range of hot wire operation. The current or voltage across a wire is then a measure of the heat transfer rate and consequently of fluidvelocity.


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Ultrasonic flow metersTheoperatingprincipleofthistypeofflowmetersisbasedontheapparentchangeinthevelocityofpropagation•ofsoundpressurepulsesinafluidwithachangeinvelocityofthefluidflow.The two main types are:•

TheDopplereffectultrasonicflowmeter �Thetimeofflightultrasonicflowmeter �

The Doppler effect ultrasonic flow meterTheDopplereffectultrasonicflowmeterusesreflectedultrasonicsoundtomeasure• thefluidvelocity.The effect of motion of a sound source and its effect on the frequency of the sound was •observedanddescribedbyChristianJohannDoppler.“Thefrequencyofthereflectedsignalismodifiedbythevelocityanddirectionofthefluidflow”.Bymeasuringthefrequencyshiftbetweentheultrasonicfrequencysource,thereceiver,andthefluidcarrier,•the relative motion is measured. The resulting frequency shift is named the Doppler effect.

Transceiver

Receiver

Fig. 1.25 Schematic arrangement of Doppler flow meter

The basic principle of operation employs the frequency shift (Doppler Effect) of an ultrasonic signal when it is •reflectedbysuspendedparticlesorgasbubbles(discontinuities)inmotion.This metering technique utilises the physical phenomenon of a sound wave that changes frequency when it is •reflectedbymovingdiscontinuitiesinaflowingliquid.Ultrasonicsoundistransmittedintoapipewithflowingliquids,andthediscontinuitiesreflecttheultrasonic•wavewithaslightlydifferentfrequencythatisdirectlyproportionaltotherateofflowoftheliquid.Thefluidvelocitycanbeexpressedas:•

Where,f r = received frequency ft = transmission frequency v=fluidflowvelocityφ=therelativeanglebetweenthetransmittedbeamandthefluidflowc=thevelocityofsoundinthefluid

The time of flight ultrasonic flow meterInthetimeofflightultrasonicflowmeterthetimeforthesoundtotravelbetweenatransmitterandareceiver•ismeasured.Thismethodisnotdependableontheparticlesinthefluid.

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Transceiver

Transceiver

Vcosϕ

V

L

ϕ

Fig. 1.26 Schematic arrangement of time of flight ultrasonic flow meterTwo transmitters / receivers (transceivers) are located on each side of the pipe. The transmitters send pulsating •ultrasonicwavesinapredefinedfrequencyfromonesidetotheother.Thedifferenceinfrequencyisproportionaltotheaveragefluidvelocity.•The downstream and upstream pulse transmit time can be expressed as:•

Where, td = downstream pulse transmission timetu = upstream pulse transmission timeL=distance between transceivers

Since the sound travels faster downstream than upstream, the difference can be expressed as:

As v is very small compared to c, therefore,

1.4.3.2 Quantity Meters or Total Flow MetersQuantityflowmetersareusedforthemeasurementoftotalflow.Totalflowsignifiestheamountoffluidthatflowsinaspecificintervaloftime.Thequantityflowmetersaremainlyoftwotypes:

Positive displacement meters •Metering pumps•

Positivedisplacementmetersareessentiallyflowquantitymeters.Thesedevicesworkonthebasicprinciplethat,astheliquidflowsthroughthemeter,itseparatestheflowofliquidintoseparateknownvolumetricincrementsthat are counted and totalled. The sum of increments gives the measurement of the total volume of liquid passed throughthemeter.Thesedevicesaretotalisersanddonotgiveinstantaneousflowrates.Inmostofthesemeters,thetransductionofflowtakesplaceintheformofrotarymotion.Inshort,thesemetersarehydraulicorpneumaticmotors whose cycles of motion are recorded by some form of a counter.


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Thenutatingdisctypeisaformofpositivedisplacementmetershowninthefigurebelow.•It consists of an eccentrically mounted disc on a ball bearing.•The disc wobbles in the metering chamber. An axial pin is attached with the ball, which moves in a circular •motion and drives a shaft connected to a gear train and a totalising register.

Drive shaft to counter mechanism

Nulcting disc (eccentrically mounted)

Spherical ball

Inlet Outlet

Bearing

Fig. 1.27 Nutating disc type flow meter

The top and bottom of the disc maintain tangential contact with the top and bottom of the chamber. The viscosity •of the liquid takes care of sealing and lubrication. Astheliquidflowsthroughthemeter,pressuredropsfromtheinlettooutletcausingawobblingornutating•motion to the disc.Eachnutationofadisccausesaspecificvolumeofliquidtopasstotheoutlet.Thisvolumeisequaltothe•volume of metering chamber minus the volume of disc assembly.The motion of the disc is transmitted by a gear train to the indicating/recording mechanism, which can be •calibrated in terms of discharge

Solid flow measurement

Solidflowmeasurementisrequiredwhenmaterialintheformofsmallparticlessuchascrushedmaterialor•powder; carried by a conveyor belt.Theflowisusuallydescribedbyaspecificationofthemassorweightperunittimeandisexpressedinkg/min.•Inordertomakeameasurementofthemassflow,itisrequiredtocomputethemassorweightofthequantityofmaterialonsomefixedlengthL.A typical system where material is drawn from a hopper and transported by the conveyor is shown in the •followingfigure.

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W

Motor

Hopper

Load cell

L

Fig. 1.28 Solid flow measurement

Assumingthatthematerialflowsfreelyfromthehopper,fastertheconveyorbeltismoved,fasterthematerial•willflowfromthehopperandassuchtheflowratewillbehigher.A load cell measures the mass or weight of the solid material distributed over a length on the conveyor.•Iftheconveyorvelocityisknown,thenthemassflowrateisgivenas•

Where,W=massflowrateinkg/minM = mass or weight of material in kgv = velocity of conveyor in m/minL = length of weighing platform in m.

1.4.4 Velocity

The monitoring of velocity essentially involves the measurement of two variables; linear velocity and angular •velocity.The most commonly used transducer for the measurement of linear velocity is the electro-magnetic •transducer.Thistransducerutilisestheprincipleofvoltageproducedinacoilonaccountofchangeinfluxlinkage,resulting•from change in reluctance.Amovingmagnettypetransducerforthemeasurementoflinearvelocityisshowninfig.1.29.•


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coil

output

velocity

air gap

Mag

net

Fig. 1.29 Moving magnet type velocity transducer

Theconstantmmf(polarisationfield),canbeprovidedbyasolenoidofNturnsandcarryingaconstantcurrent•I,buttheelectromagnetictransducerusesapermanentmagnet,whichprovidesaconstantpolarisingfield.The sensing element is a rod that is coupled to the device whose velocity is being measured. This rod is a •permanent magnet.There is a coil surrounding a permanent magnet. The motion of the magnet induces a voltage in a coil and the •amplitude of the voltage is directly proportional to the velocity.Foracoilplacedinamagneticfield,thevoltageinducedinthecoilisdirectlyproportionaltothevelocity.•The polarity of the output voltage determines the direction of motion. The sensitivity of this transducer is stated •in terms of mV/mm-s.In many cases, the only way to measure linear velocity is to convert it into angular velocity. For example, a •speedometer uses the wheel rotational speed as a measure of the linear road speed.Thedisadvantagewiththemeasurementoflinearvelocityarisesbecauseafixedreferencemustbeusedandif•moving objects have to travel large distances, detection becomes impossible. Hence, angular velocity transducers are used.It consists of a small armature, which is coupled to a machine whose speed is to be measured. This armature •revolvesinthefieldofapermanentmagnet.Theemfgeneratedisproportionaltotheproductoffluxandspeed.Sincethefluxofthepermanentmagnetis•constant, the voltage generated is proportional to speed.The polarity of the output voltage indicates the direction of rotation. This emf is measured with the help of a •moving coil voltmeter having a uniform scale and calibrated directly in terms of speed.The measurement of angular speed is generally done through tachometers, which can be further divided into •many types.

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N

S

Speed to be measured

Permanent Magnet

Commutator

Brushes

Voltmeter

Fig. 1.30 DC tachometer

1.4.5 Vibrations

Vibration is loosely defined as repeated cyclic oscillations of the system and can be caused by applying•acceleration to the system alternately from two sides. The necessity of vibration monitoring is because it can cause •

catastrophic failure when resonance and fatigue are induced due to it �faulty production, by incorrect operation of equipment �excessive wear and tear �discomfort to production/ maintenance people through sound pollution, etc. �

The basic measurement system used for diagnostic analysis of vibrations consists of the three system components •asshowninthefollowingfigure.

Vibration pick up

Pre - amplifier Processing & Display

Fig. 1.31 Basic vibration measurement system

In general, the transducers employed in vibration analyses convert mechanical energy into electrical energy; •that is, they produce an electrical signal that is a function of mechanical vibration. Acceleration is an important parameter in monitoring vibrations. Furthermore, it can be successively integrated •to obtain velocity and displacement.The most common and widely used device for acceleration measurement is a seismic transducer comprising of •a spring-mass system; it is also sometimes referred to as seismic accelerometer.The basic operating principle is to measure the relative motion of mass with respect to base, connected to the •sourceofacceleration.Aschematicdiagramforaseismicaccelerometerisshowninthefiguregivenbelow:


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Accelerating Body

Mass – M

Spring – K

Damper – B

Displacement Transducer

y

x

Fig. 1.32 Seismic accelerometerIt essentially comprises of a mass-m supported on a spring of stiffness-K and a viscous damper with damping •coefficient-B.The base of the device is attached to the body undergoing acceleration. A displacement transducer is also •included, to measure the motion of the mass relative to the base. This is the output of the instrument, that gives the motion of the object i.e. acceleration.In general, a small mass and stiff spring is used for acceleration mode. The mass is constrained to move only •in an axis perpendicular to the base.When the base moves at a constant acceleration, mass M also moves at acceleration and thus some force must •act to produce this.This force is provided by the spring for no relative displacement of the mass with reference to the frame. The •net result is that the mass is displaced by a distance x.The damper reduces the oscillations. Thus acceleration is measured by measuring the force required to accelerate •a given mass. This force is sensed as a change in displacement.The different types of accelerometers employ various displacement-measuring techniques, like potentiometer, •strain gauge, LVDT, piezoelectric, etc.The accelerometers have good sensitivity characteristics and a wide useful frequency range; they are small in •sizeandlightinweightandthusarecapableofmeasuringthevibrationsataspecificpointwithout,ingeneral,loading the vibrating structure.In addition, the devices can be used easily with electronic integrating networks to obtain a voltage proportional •to velocity or displacement. However, the accelerometer mounting, the interconnection cable, and the instrumentation connections are critical factors in measurements employing an accelerometerSome additional suggestions for eliminating measurement errors when employing accelerometers for vibration •measurements are shown in Fig.1.33.Note that the accelerometer mounting employs an isolation stud and an isolation washer. This is done so that •the measurement system can be grounded at only one point, preferably at the analyser.An additional ground at the accelerometer will provide a closed (ground) loop, which may induce a noise signal •that affects the accelerometer output.The sealing compound applied at the cable entry into the accelerometer protects the system from errors caused •by moisture.

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Accelerometer

Sealing compound

Isolation washer

Isolation stud

Fig.1.33 Installation considerations for an accelerometer

Thesecondelementinthevibrationmeasurementsystemisthepreamplifier.•Thisdevice,whichmayconsistofoneormorestages,servestwoveryusefulpurposes:itamplifiesthevibration•pickup signal, which is in general very weak, and it acts as an impedance transformer or isolation device between the vibration pickup and the processing and display equipment.The processing equipment is typically some type of spectrum analyser. The analyser may range from a very •simple device, which yields, for example, the rms value of the vibration displacement, to one that yields an essentially instantaneous analysis of the entire vibration frequency spectrum.

1.5 Instruments Used in Energy SystemsThe instruments used in energy systems are as follows:

1.5.1 Load and Power Factor

Power factor, the ratio of active (real) power to apparent power, is a familiar concept in the power-system •management.It determines how much energy in both work-producing (watts) and reactive (VArs) is required to power a •load.It is never greater than one and is usually given in percentage. •The power factor involves the relationship between these two types of power. Active Power is measured in •kilowatts (kW) and Reactive Power is measured in kilovolt-amperes-reactive (kVAr).Active power and reactive power together make up Apparent Power, which is measured in kilovolt-amperes •(kVA).Thisrelationshipisoftenillustratedusingthefamiliar“powertriangle”thatisshowninfig.1.34.

ϕ

va

watts

vars

Fig. 1.34 Power factor triangle

Real power: Real power is the measure of a circuit’s dissipative elements (R) and is represented by a P, which has aunitmeasureofwatts.Thereareactuallytwodifferenttechniquesthatareusedtomeasurerealpower.Thefirstisto take the time average of the instantaneous product of voltage and current. Another common method is to use the impedance angle depicted in the power triangle above. The cosine of the impedance angle is directly proportional


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to the amount of reactance in a circuit, which is called the power factor (PF). Power Factor = cos(Impedance phase angle) = Real Power/Apparent Power Real Power P = VIcosϕA PF of 1 represents a purely resistive load and power factor less than 1 represents a reactive circuit.

Reactive power: Reactive power is the measure of a circuit’s reactance (X). A purely reactive circuit dissipates zero real power because the power is absorbed by the circuit and returned to the AC source. This circuit results in 90 degrees phase shift between the voltage and current waveforms. A circuit with resistive and reactive components will both dissipate power and return power to the AC source. The current and voltage waveforms will have a phase shift between 0 and 90 degrees. Reactive power is represented with Q and has a unit measure of volt-amps¬reactive (VAR)

Apparent power: Apparent power is the measure of a circuit’s impedance (Z) and is represented by an S, which has a unit measure of volt-amps (VA). Apparent power is the combination of reactive power and real power, without reference to a phase angle. You calculate apparent power by using the following formula:Apparent Power (S) = Vrms× Irms

Understanding power factorThe power factor of a system may be described as lagging if the reactive current is inductive, or leading if the •reactive current is capacitive.A lagging power factor can be corrected by connecting capacitors in parallel with the system. The current in a •capacitorproducesaleadingpowerfactor.Thiscurrentflowsintheoppositedirectiontothatinaninductivedevice. When the two circuits are combined, the effect of capacitance tends to cancel that of the inductance. Most customer loads (particularly motors, but also many lighting circuits) are inductive.•A low power factor can generally be corrected by connecting appropriate capacitors. This is not the case if the •low power factor is caused by harmonics, in which case the installation of capacitors will not help, and may cause a serious problem.In high harmonic situations, expert help should be obtained before attempting to correct power factor •problems. The power factor is the cosine of the phase difference between voltage and current. It is a proportion of the •apparent power, voltage and current that effectively becomes useful power.The lower a power factor, the higher the required electric power supply; therefore an electrical facility becomes •larger. Generally, a power factor lower than 85% is considered a low power factor. •

Devices Power factor (%)Incandescent bulb 100Electric heater 100Electric stove 100Iron 100Colour TV 90-95Stereo 0-95Three-phase induction meter 70-85Fan 65-85Fluorescent light 60-70Motor (sewing machine) 50-80AC welding machine 30-40

Table 1.2 Typical power factors of electric devices

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The power factor in a facility will vary over time. Power factor will also vary with different types of loads, and •the overall mix of various types of loads.Inductive loads, such as motors, will tend to reduce the power factor. Linear loads, such as lighting, will tend •to increase the power factor.Lightly-loaded or varying-load inductive equipment such as HVAC systems, arc furnaces, moulding equipment, •presses, etc. are all examples of equipment that can have a poor power factor. One of the worst offenders is a lightly loaded induction motor (e.g., saws, conveyors, compressors, grinders, etc.). The power factor decreases with the installation of non-resistive loads, such as motors, transformers, lighting •ballasts and other power electronics.

Measurement of reactive powerThe reactive power in a circuit is given by,

Reactive Power, Q = V Isinϕ

It is often convenient and even essential that the reactive power be measured. Such a measurement gives information concerning the nature of the load. It also serves as a check on the power factor measurement. Additionally, apparent power, S determines that the line and generator capacity can be determined from active and reactive power.

Measurement of active and reactive power with a multi-meter A multi-meter can be effectively used for the measurement of active and reactive power, with the aid of a suitable resistorandavariac.Thecircuitschematicdiagramisshowninfig.1.35.

Rload

Xload Variac

Fig. 1.35 Measurement of active and reactive power with a multi-meter

The load is represented by a resistance (Rload) and a reactance (Xload) in series. The series resistor shouldn’t be too large, say 2-10 ohms. Make sure it can dissipate the power. If your load is going to draw 10 amps, and you have a 10-ohm resistor, it is going to dissipate 1000 Watts. In use, you set the output of the variac to get the load voltage to be whatever its rated input voltage is, e.g. 115Volts. To do the calculation, you’ll need the following measurements:The RMS voltage at the load (V1)The RMS voltage out of the variac (V2)The RMS current through the load (I) The resistance of the series resistor (Rseries)


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Calculations: Resistive component of load Rload = ((V2/I)^2 - (V1/I)^2 - Rseries^2)/(2 * Rseries) Reactive Component of Load Xload = sqrt( (V2/I)^2 - Rload^2)(The sign of the reactive component from this measurement)Active power = Rload * I^2Reactive Power = Xload * I^2If the reactive load is capacitive or inductive, you can add a small capacitor or inductor (the reactive impedance must be less than the existing circuit’s) to the circuit, make the measurements again, and see if the X load got bigger or smaller. For instance, if you had measured a reactive impedance of 5 ohms, and then you added a capacitor and got a reactive impedance of 6 ohms, then the original reactive impedance was capacitive. If the reactive impedance decreased, then the original reactive impedance was inductive.

1.5.2 PowerPower in an electric circuit is the product (multiplication) of voltage and current, so any meter designed to measure power must account for both of these variables. Power is essentially the rate at which energy is transformed or made available. It measured in ‘watts’. Power measurements range from direct current to alternating current, including distorted waves, chopped waves and missing pulses. For ac systems, the determination of power is more complex. The voltage and current in an AC circuit periodically changes direction (alternating current). Power measurements are made by measuring the RMS current and voltage and applying the formula.P = Vrms × Irms.

Theory of power: A direct current under the steady state conditions produces power, computed as the product of voltage across the circuit and current in the circuit. This also applies to ac circuits so long as instantaneous values of ‘v’ and ‘i’ are used. The product of ‘v’ and ‘i’ at any instant gives the instantaneous power in ‘watts’. However such ameasurementisunusualanddifficulttomake,andtheresultinginformationisoflimiteduse.‘Averagepower’inan ac circuit is of far more interest, since it is equivalent to dc power and is a measure of mechanical work being done or heat liberated.

The basic equation for power, is derived as follows:

The instantaneous power is given as:p = viIf both voltage and current are sinusoidal, the current lagging in phase by angle, then

The average power over a cycle is given as,

The rms values of sinusoidal voltage and current are

and

Therefore,P=VIcosϕ

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WattmeterItisaninstrumentformeasuringthepowerflowinginacircuitinwatts.•A special meter movement designed especially for power measurement is called the dynamometer movement, and •is similar to a D’Arsonval movement in that a lightweight coil of wire is attached to the pointer mechanism.However, unlike the D’Arsonval movement, another (stationary) coil is used instead of a permanent magnet to •providethemagneticfieldforthemovingcoiltoreactagainst.The voltage in the circuit generally energises the moving coil, while the current in the circuit generally energises •the stationary coil.Wattmeters are often designed around dynamometer meter movements, which employ both voltage and current •coils to move a needle.A dynamometer movement connected in a circuit is elaborated in the next section.•

Electrodynamometer type metersTheelectrodynamometer-typemeterdiffersfromthegalvanometertypesinthattwofixedcoilsareusedto•producethemagneticfieldinsteadofapermanentmagnet.Two movable coils are also used in the electrodynamometer meter. The moving coil moves in a spinning direction •inthemagneticfieldgeneratedbythefixedcoils.Thetorqueappliedtothemovingcoilisproportionaltotheproductofthecurrentsflowinginthefixedand•moving coils.Whenaloadcurrentflowsinthefixedcoilsandasmallcurrentproportionaltotheloadcurrentflowsinthe•moving coil, the torque on the moving coil is proportional to the product of the load current and voltage.For an alternating current, the phase-angles of the currents in both coils (i.e., phase angles of the currents against •the voltages) affect the torque in the same relationship as the power of the load power.This means that the torque is proportional to the electric power whether the current is alternating or direct, and •the power can be indicated by this meter mechanism.The electrodynamometer meter is most commonly found in various types of power meters.•Atypicalinternalconstructionofanelectrodynamometerisshowninfig.1.36.•

Scale

Pointer

Coaxis ofFixed Coils Fixed Coils

Coaxis ofMovable Coils

Movable Coils

SpiralSpring

SpiralSpring

Fig. 1.36 Internal construction of an electrodynamometer


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Thefixedcoilsareconnectedinseriesandpositionedcoaxially(inline)withaspacebetweenthem.•Thetwomovablecoilsarealsopositionedcoaxiallyandareconnectedinseries.Thetwopairsofcoils(fixed•pair and movable pair) are also connected in series with each other.Themovablecoilispivot-mountedbetweenthefixedcoils.Themainshaftonwhichthemovablecoilsare•mountedisrestrainedbyspiralspringsthatrestorethepointertozerowhennocurrentisflowingthroughthecoil.These springs also act as conductors for delivering current to the movable coils. Since these conducting springs •are very small, the meter cannot carry a high value of current.The primary advantage of the electrodynamometer-type meter movement is that, it can be used to measure •alternating as well as direct current.

CURRENTCOIL

CURRENTCOIL

SOURCE

VOLTAGECOIL LOADSR

Fig. 1.37 Simplified electrodynamometer wattmeter circuit

Asimpleschematicdiagramofanelectrodynamometer-typewattmeterisshowninfig.1.37,itconsistsofapair•offixedcoils,knownascurrentcoils,andamovingcoil,calledthevoltage(potential)coil.Thefixedcurrentcoilsarewoundwithafewturnsofarelativelylargeconductor.Thevoltagecoiliswound•withmanyturnsoffinewire.Itismountedonashaftthatissupportedinjewelledbearingssothatitcanturninside the stationary coils.The movable coil carries a needle (pointer) that moves over a suitably graduated scale. Spiral coil springs hold •the needle at the zero position in the absence of a signal. The current coil (stationary coil) of the wattmeter is connected in series with the circuit (load), and the voltage •coil (movable coil) is connected across the line.Whenthelinecurrentflowsthroughthecurrentcoilofawattmeter,afieldissetuparoundthecoil.Thestrength•ofthisfieldisinphasewithandproportionaltothelinecurrent.The voltage coil of the wattmeter generally has a high-resistance resistor connected in series with it.•The purpose for this connection is to make the voltage-coil circuit of the meter as purely resistive as possible.•As a result, current in the voltage circuit is practically in phase with line voltage.•Therefore, when voltage is applied to the potential circuit, current is proportional to and in phase with the line •voltage. Fig. 1.38 shows the proper way to connect a wattmeter into a circuit.

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Watt Meter

Current Coil

Potential CoilSource Load

Single Phase Circuit

+

+

Fig. 1.38 Wattmeter connections

Theactuatingforceofawattmetercomesfromthefieldofitscurrentcoilandthefieldofitspotentialcoil.The•force acting on the movable coil at any instant (tending to turn it) is proportional to the instantaneous values of line current and voltage.

Wattmeter errorsElectrodynamic wattmeters are subject to errors arising from factors such as temperature and frequency. For •example, heat through the coils eventually causes the small springs attached to the pointer to lengthen and lose tension,whichproducesdeflectionerrors.Largecurrentsthroughthewattmeteralsoproduceanoticeabledeflectionerror.Theseerrorsarecausedbythe•heat (I2R) loss through coils from the application of high currents.Because of this, the maximum current range of electrodynamic wattmeters is normally restricted to approximately •20 amperes.The voltage range of wattmeters is usually limited to several hundred volts because of heat dissipation within •the voltage circuit. However, the voltage range can be extended by the use of voltage multipliers. Good-quality, portable wattmeters usually have an accuracy of 0.2 to 0.25 percent. •

Wattmeter overloadsThe wattmeter consists of two circuits, either of which will be damaged if too much current passes through •them.You should be especially aware of this fact because the reading on the instrument will not tell you whether or •not the coils are being overheated.If an ammeter or voltmeter is overloaded, the pointer will indicate beyond the upper limit of its scale.•In the wattmeter, both the current and potential circuit may carry such an overload that their insulations burn; •yet the pointer may be only part of the way up the scale. This is because the position of the pointer depends upon the power factor of the circuit as well as upon the voltage and current.Therefore, a low power-factor circuit will provide a very low reading on the wattmeter. The reading will be •low, even when the current and voltage circuits are loaded to the maximum safe limit. The safe rating for each wattmeter is always distinctly rated, not in watts, but in volts and amperes.

Instrument transformersPower measurements are made in high voltage circuits connecting the wattmeter to the circuit through current •andpotentialtransformersasshownbelowinfig1.39.


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Supply Load

P.T.

C.T.

C.C.P.C.

Wattmeter

Voltmeter

Fig. 1.39 Power measurement with instrument transformer

The primary winding of the C.T. is connected in series with the load and the secondary winding is in series with •an ammeter and the current coil of the wattmeter.The primary winding of the P.T. is connected across the supply lines and a voltmeter and the potential coil circuit •of wattmeter are connected in parallel with the secondary winding of the transformer.One secondary terminal of each transformer and the casings are earthed.•

Thermal wattmeterThis instrument uses a thermocouple to convert an AC-current into a DC-equivalent current.•When a currentflows through the hotwire, its temperature goes up.A thermocouple is connected to this •hot-wire, so the thermocouple is also heated up.In turn, the thermocouple generates a DC-voltage proportionally to the developed heat at the junction. A moving •coil instrument is used to indicate the result.For measuring power, the rising temperature of the thermocouple is proportional to the square value of the •current and equals the active power.In this case, this instrument uses two thermocouples with a differential circuit.•This instrument can be used to measure both DC and AC.•

Power in poly-phase systemsThe measurement of power in poly-phase systems is governed by ‘Blondel’s theorem’.•It states that, “if a network is supplied through n conductors, the total power is measured by summing the readings •of n wattmeters so arranged that a current element of a wattmeter is in each line and the corresponding voltage element is connected between that line and a common point. If the common point is located on one of the lines, then the total power may be measured by n-1 wattmeters.” Atwowattmetermethodforthemeasurementofthreephasepowerisshowninfig1.40.•

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Watthour Meter 1

Watthour Meter 2

P = Pa + Pb + Pc = P1 + P22 Watthour Meters

P1

P2 Pc

Pb

Pa

aa’

c’

o’

c

b

Fig. 1.40 Two-wattmeter method for 3-phase system

The two-wattmeter method uses two single-phase wattmeters to measure three-phase power. •Thefigure showswattmeasurement of a three-phase three-wireWye(Y) connection load.The sumof the•measurement with two single-phase wattmeters becomes three-phase power in this measuring set-up.In this method, the two current coils are connected to the two wires; each of the two wires of the three-phase •three-wire load. The potential coils are connected between these wires and the rewiring wire. The wattmeter 1 is connected to •the phase ‘a’ and phase ‘c’; the wattmeter 2 is to the phase ‘c’ and phase ‘b’.Each measures the single phase power P1 and P2, respectively. The sum of the two measured values is equal to •the total three-phase power. This is irrespective of whether the load is balanced or not.

1.5.3 Flue Gas Analysis When fuels are burned there remains, besides ash, a certain number of gas components. If these still contain combustion heat, they are called heating gases. As soon as they have conveyed their energy to the absorbing surfaces ofaheatexchanger,theyarecalledflueorstackgases.

Combustion is the act or process of burning. For combustion to occur, fuel, oxygen (air), and heat must be present together.Asperdefinition,combustionisthechemicalreactionofaparticularsubstancewithoxygen.Heatingthefuelaboveitsignitiontemperatureinthepresenceofoxygenstartsthecombustionprocess.Undertheinfluenceofheat, the chemical bonds of the fuel are split. If complete combustion takes place, the elements carbon (C), hydrogen (H) and sulphur (S) react with the oxygen content of the air to form CO2, water vapour, H2O and SO2 and, to a lesser degree, sulphur trioxide SO3.Ifenoughoxygenisnotpresentorthefuel/airmixtureisinsufficient,thentheburninggases are partially cooled below the ignition temperature (too much air or cold burner walls), and the combustion processstaysincomplete.Thefluegasesthenstillcontainburnablecomponents,mainlycarbonmonoxideCO,carbon C (soot) and various hydrocarbons CxHy. Since these components are, along with NOx, pollutants, which harm our environment, measures have to be taken to prevent their formation.

ThecomponentstobefoundinfluegasesareshownbelowintheorderoftheirusualconcentrationsNitrogen (N2): Nitrogen is a colourless, odourless and tasteless gas and it does not take major part in the combustion process.Itisthemaincomponentofair(79%)anditreducestheefficiencyoftheburningprocesssinceitisheatedand blown out of the stack without actual function for the process. Typicalfluegascontent:approx.78to80%


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Carbon dioxide (CO2): Carbon dioxide is also a colourless and odourless gas that is to be found in human breath as well as in every common combustion process. The carbon dioxide level of 1000 ppm will reduce the ability to concentrate by about 30%. Concentrations above 15% (150000 ppm) cause immediate unconsciousness. Typicalfluegascontents:gasburners/boilers10-12%oil burners / boilers 12 - 14%

Oxygen (O2): It plays a very important part without which combustion could not take place. The oxygen content of the air partly reacts with the hydrogen (H2) content of the fuel and forms water (H2O). This water content is, dependentonthefluegastemperature;condensedandcollectedinthewatertraporremainsinthefluegasaswatervapour. The rest of the consumed oxygen reacts with the carbon in the fuel to form carbon dioxide and, less desirably, carbonmonoxide.Theseescapeasheatedgasesthroughthefluepipe.Typicalfluegasoxygenconcentrations:gasburners/boilers2¬3%.Oil burners / boilers 2 - 6 %.

Carbon monoxide (CO): A highly toxic gas which is very nasty because it is also colourless and odourless. The maximumpermittedconcentrationinofficesis50ppm.Typicalfluegascontents:gasburners/boilers70-110ppmOil burners / boilers 70 - 160 ppm.

Nitrogen oxides (NOx): Nitrogen oxides occur in all combustion processes where fossil fuels are burned, partly through oxidation of the nitrogen content of the air, as well as the organic nitrogen content of the fuel. The nitric oxide formed, oxidises with time and forms nitrogen dioxide (NO2). Nitrogen dioxide is a brown, toxic, water-soluble gas that can seriously damage the lungs if inhaled, as well as contributing to acid rain. In connection with the UV-rays in sunlight it helps to form ozone. Typicalfluegascontents:gasburners/boilers50-70ppmOil burners / boilers 50 - 110 ppm.

Sulphur dioxide (SO2): The SO2 content is pretty much dependent on the type and quality of the fuel being used. It is again a toxic gas that contributes to the formation of acid rain. Together with water, sulphurous acid (H2SO3) and sulphuric acid (H2SO4) are formed.Typicalfluegascontents:gasburners/boilers180-250ppm.Whenpoorqualitycoalisbeingfired,theSO2concentrationcansometimesexceed2000ppm.

Hydrocarbons (CXHY): Combustibles like methane (CH4) and butane (C4H10) occur when incomplete combustion takes place. They are to a large extent responsible for global warming. These are part of a chemical family technically known as alkanes.Typicalfluegascontents:oilburners/boilersbelow60ppm.

Soot (smoke): Smoke is another sign of incomplete combustion. It is measured by comparison with the well-known Bacharachscale(0-9).Thesmokeinthefluegaswillcausesoottoformontheinternalpartsoftheburner.Thepresenceofpollutantsinafluegasstreamcanbeexpressedintermsoftheconcentrationsoftheindividualgascomponents.

Units used in flue gas analysisThe following units are the most common: ppm (parts per million): Like the reading “percent (%) “, ppm expresses a ratio. If there is a concentration of 333 ppm CO in a cylinder and you take one million particles out of that cylinder, 333 particles would be carbon monoxide particles. For convenience, higher concentrations are generally expressed as a percentage (%). The conversion is as follows: 10000 ppm = 1 % 1000 ppm = 0.1 % 100 ppm = 0.01 % 10 ppm = 0.001 % 1 ppm = 0.0001 % An oxygen concentration of 21.95 vol.% would equal 219 500 ppm O2, and 10% CO is identical with 100 000ppm CO.

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mg/Nm3 or mg/m3 (milligram per cubic meter): When using the unit mg/Nm3, the standard volume (standard cubic meter,Nm3)isusedasareferenceandthemassconcentrationofthefluegasisgiveninmilligrams(mg).Sincethis unit is pressure and temperature dependent, the volume is expressed at standard conditions. There are different sets of standard conditions used for different purposes. Flue gas analysis commonly uses the standard conditions of temperature at 0 deg.C and pressure at 1013 m.bar.

Sensors in flue gas analysisThefluegasanalyserisbasicallyacollectionofdifferentsensorsandacentralunitthatcollatesalltheresultsandprovides a useful and understandable result. Most of these sensors are designed to measure gas or gas concentration. Additionally sensors for pressure, temperature and humidity are also needed.

Electrochemical sensorsThe standard sensor for toxic gases is still the electrochemical sensor. This sensor acts as a battery, producing •a voltage proportional to the concentration of the gas it is designed to measure.The major elements of toxic gas electrochemical sensors are three coated electrodes (sensing, counter and •reference) and a small volume of an acidic or alkaline solution.Inuse,thegasesdiffusethroughanorificeonthesensingfaceofthesensorontotheelectrodesurfaceandcause•a small electrical current.Thiscurrentisamplifiedandmeasuredbyelectronics.Themeasuredvalueisthendisplayedandavailablefor•printing, storing or downloading to a computer.

Capillary Diffusion Barrier

Sensing Electrode

Reference Electrode

Counter Electrodes

+

-

Flue Gas

Amplifier Circuit

Electrolyte

Fig. 1.41 Schematic diagram of the electro-chemical sensor

In its simplest form, a sensor operating on electrochemical principles requires two electrodes, x a sensing and •a counter x both separated by a thin layer of electrolyte.Gas diffusing to the sensing electrode reacts at the surface of the electrode either by oxidation or reduction. This •reaction causes the potential of the electrode to rise or fall with respect to the counter electrode.With a resistor connected across the electrodes, a current is generated which can be detected and used to determine •the concentration of gas present. One of the conditions required for the above sensor to work accurately is that the potential of the counter electrode should remain constant. In reality, however, the surface reactions at each electrode cause them to polarise. This effect may be small •initially, but it increases with the level of the reactant gas and effectively limits the concentration range the sensor can be used to measure. This effect can be counteracted by the introduction of a reference electrode of stable potential. The reference •electrode is shielded from any reaction, and so maintains a constant potential. Instead of the signal therefore being measured between the counter and sensing electrodes, it can now be more accurately measured between reference and sensing.With this arrangement, the change in potential of the sensing electrode is due solely to the current generated at •the electrode by the reactant gas.


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As the reference electrode must maintain a constant potential for correct operation, it is important that no •current is drawn from this electrode. In order therefore to measure the potential difference between sensing andreference,itisnotsufficientjusttoplacealoadresistoracrossthem,asthiswoulddrawacurrent.Forthisreason, a potentiostatic feedback-operating circuit is used.The oxidation of carbon monoxide, for example, at the sensing electrode can be represented by the equation: •CO + H2O ===> CO2 + 2H+ + 2e¬

The counter electrode acts to balance out the reaction at the sensing electrode by reducing oxygen in air to •water: 1/2O2 + 2H+ + 2e-===> H2O A similar equation can be given for other sensors depending on the reaction of the gas they are designed for on •the sensing electrode: Sulphur dioxide: SO2 + 2H2SO4 ===> CO2 + 2H+ + 2e¬

Nitric oxide: NO + 2H2O ===> HNO3 + 3H+ + 3e¬

Nitrogen dioxide: NO2 + 2H+ + 2e¬ ===> NO + H2O The great advantages of the electrochemical toxic sensor are the relatively low initial price and the small size. •The disadvantages include a limited lifetime and cross-sensitivity problems. •Stability can be ensured by regular calibration, but the sensor requires a minimum level of oxygen and humidity •to operate correctly as well.

Oxygen sensorsThere are many different types of oxygen sensors available, depending on the application, interfering gases •and a few other factors.These range from the expensive paramagnetic sensors to the standard electrochemical sensors with a limited •lifetime.Oxygen sensors, in contrast to the sensors for toxic gases, operate as a current source, not as a voltage source. •Oxygen is not optically active, so it cannot be measured with infrared technology. Oxygen sensors are slightly different. In use, oxygen diffuses through a membrane and the gas contacts the •sensing electrode and the base solution and reacts at the wet surface of the electrode. This reaction consumes the counter electrode. The chemical change in the counter electrode allows a circuit in •the instrument to measure a potential (voltage) between the electrodes.In reality, the oxygen sensor acts as a current source, so the voltage measurement must be carried out over a •load resistor.This should not be large; otherwise the balance of the oxygen circuit will be upset.•

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V

Cathode

Electrolyte

Anode

Air Supply

Load Resistor

Diffusion Barrier

Fig. 1.42 Schematic diagram of an oxygen sensor

All oxygen sensors used are of the self-powered, diffusion limited, metal-air battery type comprising an anode, •electrolyte and an air cathode as shown below.At the cathode, oxygen is reduced to hydroxyl ions according to the equation:•O2 + 2H2O + 4e¬-===> 4OH¬

The hydroxyl ions in turn oxidise the metal anode as follows: •2Pb + 4O H¬ ===> 2PbO + 2H2O + 4e¬

Overall the cell reaction may be represented as: •2Pb + O2 ===> 2PbO

The oxygen sensors used are current generators, and the current is proportional to the rate of oxygen consumption •(Faraday’s Law). This current can be measured by connecting a resistor across the output terminals to produce a voltage signal. If the passage of oxygen into the sensor is purely diffusion limited, this signal is a measure of the oxygen concentration.

Infrared sensorsPortable gas analysis equipment is presently starting to use infrared sensors for certain gases now. This began with thenecessityofmeasuringcertaincomponents,notablycarbondioxide,whichisdifficultorimpossibletomeasureinanyothermanner.Theothercomponentcommonlymeasuredismethane,whichisotherwiseverydifficulttoevaluate. Most of these sensors rely on the absorption of the infrared wavelengths to measure the concentration of the gas present. One of the major disadvantages of infrared sensors is the size required to provide a good resolution to the signal. Longer sensors are needed for lower concentrations. This is sometimes solved by using mirrored chambers and multiple pass systems, but the mirrors are really only an extra surface that can collect dirt and reduce the signal strength.


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Temperature sensorsAmbient temperature is mostly measured using a thermistor. This is a material that changes its resistance proportional to the temperature. The commonest type is probably the platinum thermistor. Flue gas temperature is generally measured with a thermocouple. A thermocouple produces a tiny electrical potential proportional to a temperature difference between two points. There are different types of thermocouples available for different temperature ranges, but most of them cover the combustion gas range.

1.5.4 Air Quality Analysis Analysis of gases to determine the percentage composition of individual constituents has become an essential requirement in many industries. The basic purpose is usually one of the following:

Efficiencyofburningfuelbysensingtheproportionofoxygen,unburnedconstituentsorotherconstituents•resulting from combustion. Gaugingthequalityofaprocessbymeasuringtherelativelevelofspecificconstituentsinthegasorthegas•mixtures emanating from the process. Pollution control by measuring oxides of sulphur, nitrogen, etc. in the gas mixture left in the atmosphere. •

The methods for gas analysis generally fall in two categories: Offlinemethods �Online methods �

Theofflinemethodsareelaboratedinthissection,whereastheonlineonesarediscussedinthenextsectiononthermal conductivity measurement.

ChromatographyChromatography is a physical method of separation of components of a mixture by distribution between two •phases; one of which is stationary and the other is mobile. The process of chromatographic separation involves the transport of a sample of mixture through a column. •The mixture may be in the liquid or gaseous state.The stationary phase may be a solid adsorbent or liquid portioning agent. The mobile phase is a gas or a liquid •and it transports the constituents of the mixture throughout the column.During such transport, the material in the column (stationary phase) exercises selective retardation on various •components of the sample. This retardation may be due to adsorption, solubility, chemical bonding, polarity ormolecularfiltrationofasample.Therefore, the components of the mixture tend to move through at different effective rates resulting in the •separation into different zones or bands. In general, all chromatographic procedures isolate, detect and characterise these bands at some point, usually the column exit.Upon emerging from the column, the mobile phase immediately enters a detector. At this place, individual •components register a series of signals that appear as successive peaks, referred to as the chromatogram.The area under the peak gives a quantitative indication of the particular component and the time delay of the •peak serves to identify the component. Dependingonthenatureofthemobilephase,chromatographyisclassifiedintotwotypes:•

Gas chromatography �Liquid chromatography �

The basic block diagram of a gas chromatograph is shown in Figure 1.43•

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SampleInjector

Injection Port

Detector

Strip chartrecorder

PressureRegulator

FlowRegulator

Carrier Gas

Column

Oven

Temperature Controller

Fig. 1.43 Block schematic diagram of a gas chromatograph

It consists of the following major blocks:Carrier gas supply with pressure and flow regulatorThe mobile phase is formed by a continuous supply of carrier gas usually H2, N2, Ar or He. It is taken from commerciallyavailablecylindersinwhichtheyarestoredatapressureof2500psi.Theflowmonitorandpressureregulatorensuresthatthegaspassesthroughthecolumnatalowrateofflow(typically20ml/min)andpressuresnotmuch greater than atmospheric. The gas is conducted to the sample injection port maintained at temperature T1.

Sample injection systemIt is usually in the form of a syringe and introduces a reproducible quantity of sample into the port where vaporisation takes place. Here the sample vapour mixes instantaneously with the carrier gas and is swept into the chromatographic column. Samples can be introduced in gaseous, liquid or solid state.

Chromatographic columnThe column is the heart of a chromatograph where the fundamental process of separation takes place. It is usually packedwithsolidadsorbingmaterialslikecharcoal,granularsilica,etc.Alternatively,itmaybefilledwithaliquidportioning agent. The different components in the vaporised sample are separated from each other by virtue of their different interaction with column packing. The column is maintained at temperature T2, which determines the time for the passage of the sample.

DetectorDue to the separation in the column, the components of the mixture move at different rates and enter the detector placed at the exit of the column. The detector produces an electrical signal corresponding to the quantity of various constituents in the mixture. The different types of detectors that are commonly employed are thermal conductivity detector,flameionisationdetector,electroncapturedetector,etc.

The detector signal is supplied to a recorder and a plot of time signal amplitude called a chromatogram is obtained. This record determines the identity of the component depending on the time delay and concentration of the component by the peak height.

1.5.5 Thermal ConductivityThe chemical methods described in the previous section are elaborate and time consuming and not suited for online analysis. Such online analysis becomes necessary when a process is to be monitored closely. The most commonly used method is to measure the thermal conductivity and relate it to the quantum of the concerned gas constituent. Thermal conductivity is the ability of a constituent to carry heat by conduction.


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Gas/ Vapour At 00 C At 100 0C

Air 58(1.0) 74Argon(Ar) 39(0.67) 52Carbon monoxide (CO) 53(0.91) --Carbon dioxide (CO2) 34(0.59) 50Hydrogen(H2) 419(7.22) 547Helium(He) 343(5.91) 408Nitrogen(N2) 57(0.98) 73Oxygen(O2) 58(1.0) 76Neon(Ne) 109(1.88) 133Methane(CH4) 73(1.26) --Ethane(C2H6) 43(0.74) 77Propane(C3H8) 36(0.62) --Butane(C4H10) 32(0.55) --

Table 1.3 Thermal conductivity of selected gases

The thermal conductivity of a gas mixture is a function of thermal conductivity of the constituents and the percentage content of the constituents. If the concentration of only one constituent varies or only two of them vary in their relative proportions, the sensed thermal conductivity can be used as a measure of the content of the constituent or ratio of the concerned constituents respectively. Thus, a mixture of air and hydrogen has a relative thermal conductivity of 1 for 0 % hydrogen and 7.22 for 100 % hydrogen. Atypicalthermalconductivitycellisshowninfig.1.44

Outlet connection

Cell

Inlet connection

Main pipe

Spring

Filament

Outlet

Inlet

Fig. 1.44 Typical thermal conductivity cell

Ithasaglasscoatedplatinumfilamentheldunderconstanttension.Thefilamentisinaglassenclosurewithinletandoutletforthegas.Aconstantcurrentispassedthroughthefilamentanditgetsheated.Dependingonthethermalconductivityofthegasinsidethetube,thefilamentattainssteadythermalconditions.Itsresistanceisameasureofthisandhencethethermalconductivityofthegasmix.Changeintheresistanceofthefilamentisconvertedintoan equivalent output voltage using the appropriate signal conditioning. The gas inlet and outlet are connected at thesamesectionandnormaltoit.Thisensuresthatgasflowthroughthecellissolelyduetoconvectionandthusmakesitsoperationindependentoftheflowrate.

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1.6 Errors in MeasurementMeasurement error is the deviation between the measured value and the true value. Depending on the origin the errorscanbebroadlyclassifiedas:

systematic errors �gross errors �random errors �

1.6.1 Systematic ErrorsSystematic errors are those that tend to have the same magnitude and sign for a given set of conditions. As the algebraic sign is the same, they tend to accumulate and hence are sometimes referred to as cumulative errors. Since sucherrorsaltertheinstrumentreadingbyafixedmagnitudeandthesamesign,thiserrorisalsotermedasBIAS.The systematic errors are divided into three categories, which are:

Instrumental errors: These errors arise due to 3 main reasons: •Due to inherent shortcomings in the instrument caused by mechanical structure, poor design/ construction, �calibration or operation of the instrument. Due to misuse of instrument caused by faulty operator, failure to adjust zero, poor initial adjustment, etc. �Due to loading effects. �

Environmental errors: These errors are due to conditions external to the measuring device, including the conditions •in the area surrounding the instrument. These may be the effects of temperature, pressure, humidity, dust, wind forces,vibrations,magneticorelectrostaticfields.Observational errors: These are errors introduced by the observer. The most common error is PARALLAX, •when the line of vision is not exactly above the pointer.

1.6.2 Gross ErrorsGross errors are mainly due to human mistakes in reading instruments, recording and calculating measurement results. The responsibility of the mistake normally lies with the experimenter. For instance due to an oversight, someone reads the temperature as 31.5 while the actual reading is 21.5.

1.6.3 Random ErrorsThese are errors that remain after gross and systematic errors are substantially reduced or at least accounted for. These errors are due to the accumulation of a large number of small effects which change from one measurement to another. They may be of real concern if a high degree of accuracy is required. These errors are due to unknown causes, not determinable in the process of making measurements. Such errors are normally small and follow the laws of probability. As such, they can be treated statistically. As these errors remain even after the systematic errors are taken care of, these errors are sometimes referred as ‘Residual errors’


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SummaryMeasurement is a comparison of a given unknown quantity with one of its predetermined standard values adopted •as a unit. Measurement is a process by which one can convert physical parameters to numbers.In the direct type, measurement is directly indicated by the instrument designed for the purpose although the •instrument itself needs calibration for standardisation.In the indirect type, the measurement of a parameter is made which is a known function of the actual •measurement.Static characteristics of the system are those that must be considered when the system is used to measure a •condition that is constant with respect to time. This includes accuracy, precision, linearity, sensitivity, resolution, hysteresis etc.Dynamic characteristics of an instrument are those that must be considered when the instrument is used to •measure and analyse a condition varying with time. This includes speed of response, measuring lag, dynamic error etc.An electrical transducer is a sensing device by which the physical, mechanical or optical quantity to be measured •is transformed directly by a suitable mechanism into an electrical voltage or current proportional to the input.Active transducers are self generating type of transducers while as passive transducers do not generate any •electrical signals by themselves.RTD is a temperature transducer in which temperature is sensed as a change in resistance.•The thermocouple is a self-generating temperature transducer working on the principle of the thermoelectric •effectVolumetricflowmeasurementsignifies thequantityofafluid (expressedasvolume)flowingperunit time•through a cross section of a pipe or channelMassflowmeasurementsignifiesthequantityofafluid(expressedasmass),flowingperunittimethrougha•cross-section of a pipe or channelPower factor, the ratio of active (real) power to apparent power, is a familiar concept in the power-system •management.Power in an electric circuit is the product (multiplication) of voltage and current, so any meter designed to •measure power must account for both of these variables.Analyses of gases to determine the percentage composition of individual constituents has become an essential •requirement in many industries.Measurement error is the deviation between the measured value and the true value.•

ReferencesSingh, S. K., 2003. • Industrial Instrumentation & Control,2e, Tata McGraw-Hill Education.Rangan, C. S., 1997. • Instrumentation Devices and Systems, 2nd ed. Tata McGraw-Hill Education.Electromechanical Transducers • [Pdf] Available at: <http://www.physics.udel.edu/~yji/PHYS245/lab/Lab%2010.pdf> [Accessed 5 July 2013].Transducers and Applications• [Pdf] Available at: <http://benp2183.mazran.com/download/nota_kelas/chap4_transducers%20ver3.pdf> [Accessed 5 July 2013].Prof. Jana, A. K., 2012. • Mod-01 Lec-36 Lecture-36-Instrumentation: General Principles of Measurement Systems [Video online] Available at: <http://www.youtube.com/watch?v=moSUpIRCKMk> [Accessed 5 July 2013].Prof. Jana, A. K., 2012. • Mod-01 Lec-37 Lecture-37-Instrumentation: General Principles of Measurement Systems (Contd…2) [Video online] Available at: <http://www.youtube.com/watch?v=FVSCMdk-SFQ> [Accessed 5 July 2013].

Recommended ReadingBasic Concepts of Measurement• , CUP Archive.Carstens, R. J., 1993. • Electrical sensors and transducers, Regents/Prentice Hall.Bakshi, A.V. & Bakshi, U. A., 2008. • Electronic Measurements And Instrumentation, Technical Publications.

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Self Assessment____________is a process by which one can convert physical parameters to numbers.1.

Measurementa. Instrumentationb. Mechanismc. Condensationd.

The process called ____________obtains all the performance characteristics of the instrument in one form or 2. other.

measurementa. calibrationb. sizingc. standardisationd.

_____________transducers are self generating type of transducers.3. Passivea. Implicitb. Activec. Explicitd.

______________flowmetersareusedtodeterminethevolumetricflowrateofelectricallyconductingfluids.4. Electro-statica. Electro-mechanicalb. Electricc. Electro-magneticd.

_____________wattmeters are subject to errors arising from factors such as temperature and frequency.5. Electrodynamica. Electro-staticb. Electro-mechanicalc. Electricd.

State which of the following statements is true.6. Active transducers do not generate any electrical signals by themselves.a. Passive transducers do not generate any electrical signals by themselves.b. Passive transducers generate any electrical signals by themselves.c. Passive transducers do not generate any electrostatic signals by themselves.d.

State which of the following statements is false.7. Wattmeterisaninstrumentformeasuringthepowerflowinginacircuitinwatts.a. Precision indicates the repeatability or reproducibility of an instrument.b. Wattmeterisaninstrumentformeasuringthepowerflowinginacircuitinohms.c. Systematic errors are those that tend to have the same magnitude and sign for a given set of conditions.d.


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Whichofthefollowingisdefinedasadegreetowhichaninstrumentindicateschangesinameasuredvariable8. without dynamic error?

Accuracya. Sensitivityb. Speed of responsec. Fidelityd.

Which of the following errors are mainly due to human mistakes?9. Gross errorsa. Random errorsb. Dynamic errorsc. Static errorsd.

Whichofthefollowingisdefinedasthedegreeofclosenesswithwhichthemeasuredvalueapproachesthe10. true value?

Reliabilitya. Accuracyb. Sensitivityc. Flexibilityd.

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Chapter II

Control Systems

Aim


explain the concept of industrial control system•

discuss various blocks in industrial control system•

explain the concept of analog to digital conversion•

explore microcontroller-basics and architecture•

Objectives


classify the functions of signal conditioning•

describe the types of analog to digital converters•

explain various types of digital systems for indication and recorders•

Learning outcome


explain the concept of signal conditioning •

determine types of ADC and recorders•

state different types of DAC • and data loggers


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2.1 IntroductionControlsysteminfluencespracticallyeveryactivityinourday-to-daylife.Acontrolsystemisonethatmaintainsa prescribed relationship between the output and some reference input. This can be achieved in a variety of ways; however, the most popular is the feedback schematic. The difference between the actual output and the prescribed inputisusedasameansofcontrol.Aschematicdiagramofanindustrialcontrolsystemisshowninfig.2.1.

Indicator/Recorder

Signal Conditioning

Process/ Plant

Sensor

Signal Conditioning

Actuator

Transmitter

Microcontroller

Signal Conditioning

ADC

Signal Conditioning

DAC

Transmitter

Fig. 2.1 Typical industrial control system

A plant is a piece of equipment, perhaps just a set of machine parts functioning together, the purpose of which is to perform a particular operation. The sensor is a device that is used to measure a variable and provide the output in suitable form. The output of a sensor is signal conditioned and transmitted to an analog to digital (ADC), which converts it into a form suitable for use with a microcontroller. The microcontroller is the heart of the system where regulatory decisions are taken and effected to the plant through an actuator. Auxiliary devices like indicators/ recorders are used for monitoring purposes. This chapter focuses on the blocks depicted in Fig. 2.1 and the same are discussed at length in the succeeding sections.

2.2 Signal ConditioningThe signal conditioning circuit is an electronic circuit that converts signals provided by a sensor to useful electric signals.Theseelectricsignalsmustmeetspecificcriteriasothattheyarecorrectlyinterpretedandprocessedbythe rest of the system’s circuitry. The use of Op-amps allows signal conditioning circuits to be more compact and precise in their implementations.

SensorSignal

Conditioning

Physical Phenomenon

Non usable Electrical Signal

Usable Electrical Signal

Fig. 2.2 Signal conditioning process(Source: electron1.eng.kuniv.edu.kw/.../3-Signal%20Conditioning%20Circuits.doc)

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Need for signal conditioningThe signal required by microcontroller or microprocessor cannot be in raw form from input devices like sensors. The signals needs to be converted, this is accomplished by the interface systems, connected between input devices and processors, and processor and output devices. The need for conditioning signals arises from the following reasons:

The processor has to be protected from the erratic input signals of excessive voltage and incorrect polarity.•The processor needs protection from a sudden output signal.•The processor can process the signal that is in a compatible form with the system characteristics.•Theprocessingsystemcanreceivesignalsthathaveratingssuitabletotheirspecifications.•The processor requires noise-free and disturbance-free signals to perform correctly.•The non-linearity in the signal output from the input devices needs to be manipulated to transform it into a •linear signal.

2.3 Analog to Digital ConversionIt is a technique in which a continuously varying (analog) signal is converted into an equivalent multi-level (digital) signal without altering its essential content. The decision as to which type of A/D converter is best suited for a particular application is made based upon speed, accuracy, cost, size, and the inherent noise reduction capability.

A/D convertor terminologyAclearunderstandingofthevariousspecificationsisnecessaryforselectinganA/Dconverterfor therequiredapplication.Followingaresomeofthetermsthataidinunderstandingthespecifications:

Resolution: It is the number of bits that are used to represent the analog input signal. Higher resolution will •reduce quantisation errors. Absolute accuracy: The absolute accuracy error of the converter is the tolerance of the full-scale set point referred •to as an absolute voltage standard. The manufacturer with reference to a recognised voltage standard adjusts the full-scale point of a converter. Acquisition time: The acquisition time is the time taken by a sample-hole circuit to acquire the input signal •withinastatedaccuracy.Sincetheoutputofasample-holdisnotmeaningfuluntilithassettled,thespecificationsshouldnormallyalsoincludethesettlingtimeoftheoutputamplifier.Conversion time: The conversion time refers to the time required for a complete measurement by an analog to •digital converter. Differential linearity: The variation in the analog value of transition between adjacent pairs of digital numbers •overthefullrangeofdigitalinputoroutputinaconverterisspecifiedbydifferentiallinearity.Droop rate: When a sample-hold circuit using a capacitor for storage is in the “hold” mode, the information •cannot be held forever. The rate at which the output voltage changes is termed the droop rate. When using a sample-holdamplifieraheadofanADC,itsdrooprateshouldnotbemorethan0.1LSBduringtheconversiontime of the ADC. Feed through: This refers to the undesirable signal leakage around switches or other devices expected to be •turned off or to provide isolation. Both digital and analog signals can cause feed-through errors. Linearity: Linearity is conventionally equal to the deviation of the performance of the converter from a “best •straightline”fit.Inmanypracticalconverters,thenon-linearityreferredtoisthedeviationfromastraightlinedrawn between the end points after carrying out a normal adjustment and calibration procedure for zero offset and full scale. Monotonicity: In response to a continuously increasing input signal, the output of an A/D converter should not, •at any point, decrease or skip one or more codes. Referred to D/A converters for continuously increasing the input code value, the output should not decrease below the value attained for the previous code. Settling time: Settling time is the time that a DAC takes to settle for a full-scale code change, usually to within •±½ LSB.


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Zero setting: The zero level is set to zero volts at the code corresponding to 0 V in a unipolar DAC. The LSB •transition of an ADC is offset by ½ LSB so that all subsequent transitions ideally occur midway between the nominal code values.

A variety of circuit designs are available for executing the analog to digital conversion, however the most popular of these employ the following techniques:

Successive approximation •Voltage-to-frequency conversion •Dual-slope convertor•Delta-sigma•

2.3.1 Successive Approximation Method

A successive approximation ADC works by using a digital to analog converter (DAC) and a comparator to •performabinarysearchtofindtheinputvoltage.A sample and hold circuit (S&H) is used to sample the analog input voltage and hold (i.e., keep a non-changing •copy) the sampled value while the binary search is performed.Thebinarysearchstartswiththemostsignificantbit(MSB)andworkstowardstheleastsignificantbit(LSB).•For an 8-bit output resolution, 8 comparisons are needed in the binary search, taking a least 8 clock cycles.The sample and hold circuit samples the analog input on a rising edge of the sample signal. The comparator •output is logic 1 if the sampled analog voltage is greater than the output of the DAC, 0 otherwise.

Serial Output

StatusStart

Conversion

Analog Input Sample and Hold

Clock

D/A Converter

Comparator

Shift Register Control Logic

Fig. 2.3 A/D conversion using successive approximation technique

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Table 2.1 Advantages and disadvantages of successive approximation method

2.3.2 Voltage-to-frequency Conversion Method

Voltage-to-frequency ADCs convert the analog input voltage to a pulse train with the frequency proportional •to the amplitude of the input. Thepulsesarecountedoverafixedperiodtodeterminethefrequency,andthepulsecounteroutput,inturn,•represents the digital voltage.Voltage-to-frequency converters inherently have a high noise rejection characteristic, because the input signal •is effectively integrated over the counting interval.Voltage-to-frequency conversion is commonly used to convert slow and noisy signals. •Voltage-to-frequency ADCs are also widely used for remote sensing in noisy environments.•The input voltage is converted to a frequency at the remote location and the digital pulse train is transmitted •over a pair of wires to the counter.This eliminates noise that can be introduced in the transmission lines of an analog signal over a relatively long •distance.

Voltage – to – frequency converter

Timing circuitry

Pulse counter

Vin

Digital pulse train

Digital outputs

Fig. 2.4 Voltage to frequency ADC(Source: http://www.mccdaq.com/PDFs/specs/Analog-to-Digital.pdf)

Advantages Disadvantages

• Capable of high speed and reliable • Higher resolution successive approximation ADC’s will be slower

• Medium accuracy compared to other ADC types • Speed limited to ~5Msps

• Good tradeoffs between speed and cost

• Capable of outputting the binary number in serial (one bit at a time) format


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Simpler than other ADC types since they do not •use DAC Non-linearity•

Good noise rejection and monotonicity• Limited input-voltage dynamic range and •output offset

It is inexpensive, high resolution ADC with •slow conversion rates

Table 2.2 Advantages and disadvantages of voltage-to-frequency conversion method

2.3.3 Dual-slope Convertor

A number of ADCs use integrating techniques, which measure the time needed to charge or discharge a capacitor •in order to determine the input voltage.Awidelyusedtechnique,calleddual-slopeintegration,isillustratedinfig.2.5below.•Itchargesacapacitoroverafixedperiodwithacurrentproportionaltotheinputvoltage.Then,thetimerequired•to discharge the same capacitor under a constant current determines the value of the input voltage.The technique is relatively accurate and stable because it depends on the ratio of rise time to fall time, not on •the absolute value of the capacitor or other components whose values change over temperature and time.

I ∝ Vinput Fixed discharge current

Integration time

Ti

Ti

TdTd

Discharge time

Vinput =Vref

Vca

paci

tor

Fig. 2.5 Dual slope integration and discharge times(Source: http://www.mccdaq.com/PDFs/specs/Analog-to-Digital.pdf)


Input signal is averaged• Slow•

Greater noise immunity than other ADC types• High precision external components required to •achieve accuracy

High accuracy•

Table 2.3 Advantages and disadvantages of dual-slope convertor

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2.3.4 Sigma-delta ADC

A sigma-delta ADC is another type of integrating ADC. It contains an integrator, a DAC, a comparator, and a •summing junction.Like the dual-slope ADC, it’s often used in digital multimeters, panel meters, and data acquisition boards.•Sigma-delta ADCs also require few external components. They can accept low-level signals without much input-•signal conditioning circuitry for many applications, and they don’t require trimming or calibration components because of the DAC’s architecture.TheADCsalsocontainadigitalfilter,whichletsthemworkatahighoversamplingratewithoutaseparate•anti-aliasingfilterattheinput.Sigma-delta ADCs come in 16 to 24-bit resolution, and they are economical for most data acquisition and •instrument applications.

Integrator

VDAC VCO

+Vref 1

-Vref 0

Vin

VS

VIO

VCO

Vref

VCO

VDAC

VDAC DAC

+

–

ƩVout

to digital filter

Fig. 2.6 Sigma-delta ADC(Source: http://www.mccdaq.com/PDFs/specs/Analog-to-Digital.pdf)

Table 2.4 Advantages and disadvantages of Sigma-delta ADC

2.4 MicrocontrollerA microcontroller is a single IC comprising of specialised circuits and functions that are applicable to a wide array of system designs. The advent of microcontrollers has opened up new areas of application to a wide range of control problems. It contains a microprocessor, memory, I/O capabilities and other on-chip resources. It is essentially a microcomputer on a single IC. Some typical examples of microcontrollers are, Atmel’s 89C series, Intel’s MCS 51 and MCS 96 series, Microchip’s PIC series, Motorola’s 6811, etc.

Advantages Disadvantages Sigma delta converters are relatively •inexpensive primarily because they have a single-bit DAC

Slow due to oversampling•

High resolution•No precision external components needed•


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2.4.1 ArchitectureAblockdiagramofatypicalfullyfeaturedmicrocontrollerisshowninfig.2.7.

Fig. 2.7 Components of a typical fully featured microcontroller

ThecomponentsofamicrocontrollerincludetheCPU,inadditiontoafixedamountofRAM,ROM,I/Oports,•serial communication interface, timers, ADCs and DACsThe CPU executes the software stored in ROM and controls all the microcontroller components.•The RAM is used to store the settings and values used by an executing programme•The ROM is used to store the programme and any permanent data.•A designer can have a programme and data permanently stored in ROM provided by the chip manufacturer or •the ROM can be in the form of EPROM or EEPROM, which can be reprogrammed by the user.SoftwarepermanentlystoredinROMisreferredtoas‘firmware’.Theprogrammingdevicescandownloada•compiledmachinecodefilefromaPCdirectlytotheEPROM;usuallyviathePCserialportandspecialpurposepins on the chip. These pins can be used for other purposes once the device is programmed.The data in EPROM is non-volatile, which means the programme can access the data even after power-off.•The I/O ports allow binary data to be transferred to and from the microcontroller. These pins can be used to •read the state of switches and ON¬OFF sensors, to interface external ADC and DAC and to control external actuators.The I/O ports can be also used to transmit signals to and from other microcontrollers to coordinate various •functions. There are various standards or protocols for serial communication like SPI (serial peripheral interface), I2C (inter •integrated circuit), UART (universal asynchronous receiver-transmitter) and USART (universal synchronous asynchronous receiver-transmitter).

Microcontroller

Digital I/O Ports

Serial Communication (SPI, I2C, UART, USART) A/D D/A

Timers

ROM, EPROM or EEPROM (Non- volatile software and data)

RAM(volatile data)CPU

Analog SensorsPotentiometersMonitored Voltages

External EEPROMOther MC’sHost Computer

SwitchesON - OFF S ensorsExternal A/D or D/ADigital DisplaysON - OFF Actuators

Analog ActuatorsAmplifiersAnalog Displays

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2.4.2 Selection Criteria for MicrocontrollersThe following points must be considered:

Itmustmeetthecomputingneedsofthetaskathandefficientlyandcosteffectively.Otherrelatedconsiderations•are:

Speed �Power consumption – this is important in case of battery powered products �Packaging – this is important in terms of space, assembling an prototyping the end product �The amount of ROM and RAM on chip �The number of I/O pins and timer on the chip �The ease of up gradation to new versions �Cost per unit �

Availabilityofsoftwaredevelopmenttoolssuchasassembler,debugger,acodeefficientCcompiler,emulator,•technical support and both in-house and outside expertise. Wide availability and reliable sources of microcontroller; both now and in the future.•

2.4.3 89C Series

The AT89C51 is a low-power, high-performance CMOS 8-bit microcomputer with 4 Kbytes Flash Programmable •and Erasable Read Only Memory (PEROM).The device is manufactured using high-density non-volatile memory technology and is compatible with the •industry standard MCS-51 instruction set and pin-out.Theon-chipflashallowstheprogrammememorytobereprogrammedin-systemorbyaconventionalnon-•volatile memory programmer.By combining a versatile 8-bit CPU with Flash on a monolithic chip, the 89C51 is a powerful microcomputer, •whichprovidesahighlyflexibleandcosteffectivesolutiontomanyembeddedcontrolapplicationsThe AT89C51 provides the following standard features:•

Compatible with MCS-51 products �4Kbytesofin-systemreprogrammableflashmemory �Fully Static Operation: 0 Hz to 24 MHz �Three-Level Programme Memory Lock �128 x 8-Bit internal RAM �32 Programmable I/O lines �Two 16-Bit Timer/Counters �Six interrupt sources �Programmable serial channel �Low power idle and power down modes �Afivevectortwo-levelinterruptarchitecture �A full duplex serial port �On-chip oscillator �Clock circuitry �


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PSENALE/PROG

EA/VPP

RST

Timing and

Control Instruction Register

PSW

ALU

Port 1 Latch

Port 3 Latch

Interrupt, Serial Port,and Timer Blocks

DPTR

Program Counter

PC Incrementer

Port 3 Drivers Port 1 Drivers OSC

TMP2 TMP1

ACCStack

Pointer B

Register

Buffer

Program Address Register

Flash Port 2Latch

Port 0LatchRAMRAM ADDR/

Register

Port 0 Drivers Port 2 Drivers VCC

GND

P0.0 - P0.7 P2.0 - P2.7

P1.0 - P1.7 P3.0 - P3.7

Fig. 2.8 Block diagram of AT89C51(Source: http://datasheetreference.com/component/content/article/ 22-datasheet/143-atmel-89c51-circuit-

diagram.html)

The CPU of 89C51 consists of 8-bit arithmetic and logic unit with associated register like A, B, PSW, SP, 16-bit •programme counter (PC) and data pointer (DPTR).The ALU can perform arithmetic and logic functions on 8-bit variables. The arithmetic unit can perform addition, •subtraction, multiplication and division.The logic unit can perform operations as AND, OR, XOR as well as rotate, clear and complement. The ALU •also looks after the branching decisions.The Accumulator (ACC) is an 8-bit register. It holds the source operand and receives the result of arithmetic •instructions. It can be the source or destination for logical operations and a number of special data movement instructions.In addition to ACC, an 8-bit B-register is available as a general-purpose register. The port structure of 89C51 is •extremelyversatile.Ithas32I/Opinsconfiguredasfour8-bitparallelports(P0,P1,P2,andP3).Allfourportsarebi-directional,i.e.eachpincanbeconfiguredasinputoroutputundersoftwarecontrol.Each port consists of a latch, an output driver and an input buffer. All port pins of Port 3 are multi-functional; •they have special functions as shown below

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ThePinconfigurationsof89C51areshowninfig.2.9withthedescription.

P 1.0P 1.1P 1.2P 1.3P 1.4P 1.5P 1.6P 1.7RSTP 3.0P 3.1P 3.2P 3.3P 3.4P 3.5P 3.6P 3.7

XTAL 2XTAL 1

GND

(RXD)(TXD)(INT0)(INT1)

(T0)(T1)

(WR)(RD)

VCC P 0.0 (AD 0)P 0.1 (AD 1)P 0.2 (AD 2)P 0.3 (AD 3)P 0.4 (AD 4)P 0.5 (AD 5)P 0.6 (AD 6)P 0.7 (AD 7)EA/VPPALE/PROGPSENP 2.7 (A15)P 2.6 (A14) P 2.5 (A13)P 2.4 (A12)P 2.3 (A11)P 2.2 (A10)P 2.1 (A 9)P 2.0 (A 8)

1234567891011121314151617181920

4039383736353433323130292827262524232221

PDIP/Cerdip

Fig. 2.9 Pin configuration of 89C51 VCCSupply voltage

GNDGround

Port 0 Port 0 is an 8-bit open drain bi-directional I/O port. As an output port, each pin can sink eight TTL inputs. When 1s arewrittentoport0pins,thepinscanbeusedashighimpedanceinputs.Port0mayalsobeconfiguredtobethemultiplexed low-order address/data bus during accesses to the external programme and data memory. In this mode, P0 has internal pull-ups. Port 0 also receives the code bytes during Flash programming, and outputs the code bytes duringprogrammeverification.Externalpull-upsarerequiredduringprogrammeverification.

Port 1 Port 1 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 1 output buffers can sink/source four TTL inputs. When 1s are written to Port 1 pins, they are pulled high by the internal pull-ups and can be used as inputs. As inputs, Port 1 pins that are externally being pulled low will source current because of the internal pull-ups. Port 1alsoreceivesthelow-orderaddressbytesduringFlashprogrammingandprogrammeverification.

Port 2 Port 2 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 2 output buffers can sink/source four TTL inputs. When 1s are written to Port 2 pins they are pulled high by the internal pull-ups and can be used as inputs.


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As inputs, Port 2 pins that are externally being pulled low will source current because of the internal pull-ups. Port 2 emits the high-order address byte during fetches from external programme memory and during accesses to external data memory that uses 16-bit addresses (MOVX @ DPTR). In this application it uses strong internal pull-ups when emitting 1s.

During accesses to external data memory that uses 8-bit addresses (MOVX @ RI); Port 2 emits the contents of the P2SpecialFunctionRegister.Port2alsoreceivesthehigh-orderaddressbitsandsomecontrolsignalsduringflashprogrammingandverification.

Port 3 Port 3 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 3 output buffers can sink/source four TTL inputs. When 1s are written to Port 3 pins they are pulled high by the internal pull-ups and can be used as inputs. As inputs, Port 3 pins that are externally being pulled low will source current because of the pull-ups. Port 3 also serves the functions of various special features of the AT89C51 as listed in table 2.5. Port Pin Alternate Functions

Port Pin Alternate FunctionsP3.0 RXD (serial input port)P3.1 TXD (serial output port)P3.2 INT0 (external interrupt 0)P3.3 INT1 (external interrupt 1)P3.4 T0 (timer 0 external input)P3.5 T1 (timer 1 external input)P3.6 WR (external data memory) write strobeP3.7 RD (external data memory) read strobe

Table 2.5 Alternate functions of port 3 of 89C51

RST Reset input. A high on this pin for two machine cycles while the oscillator is running resets the device.

ALE/ PROG Address latch enable output pulse is for latching the low byte of the address during accesses to external memory. Thispinisalsotheprogrammepulseinput(PROG)duringflashprogramming.

In the normal operation, ALE is emitted at a constant rate of 1/6 the oscillator frequency, and may be used for external timing or clocking purposes. Note, however, that one ALE pulse is skipped during each access to external Data Memory.

If desired, ALE operation can be disabled by setting bit 0 of SFR location 8EH. With the bit set, ALE is active only during a MOVX or MOVC instruction. Otherwise, the pin is weakly pulled high. Setting the ALE-disable bit has no effect if the microcontroller is in the external execution mode. PSEN Programme Store Enable is the read strobe to external programme memory. When the AT89C51 is executing code from external programme memory, PSEN is activated twice each machine cycle, except that two PSEN activations are skipped during each access to external data memory.

EA/VPP EA must be strapped to GND in order to enable the device to fetch code from external programme memory locations starting at 0000H up to FFFFH.

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However, note that, if the lock bit 1 is programmed, EA will be internally latched on reset. EA should be strapped to VCC for internal programme executions. This pin also receives the 12-volt programming enable voltage (VPP) duringflashprogramming,forpartsthatrequire12-voltVPP.

xTAL1 Inputtotheinvertingoscillatoramplifierandinputtotheinternalclockoperatingcircuit.

xTAL2 Outputfromtheinvertingoscillatoramplifier.

2.5 Display Devices and RecordersThe last stage of a measurement system is the data presentation stage consisting of data presentation elements like display devices and recorders. The choice between these two depends upon:

the expected use of the output •the information content of the output •

Thefirstfactorconcernswhethertheoutputismeantforhumanobservationoritistobestoredorisgoingasaninputtoadigitalcomputer.Thesecondfactorisinfluencedbywhetherasinglevalueisdesiredortheoutputisneeded as a function of time and also by the frequency content of the output.

2.5.1 Digital Instruments

The digital meters work on the principle of quantisation.•Theanalogquantitytobemeasuredisfirstsub-dividedorquantisedintoanumberofsmallintervalsupto•many decimal places.Theobjectiveistothendetermineinwhichportionofthesub-divisionthemeasurandcanbeidentifiedasan•integral multiple of the smallest unit called the quantum, chosen for that sub-division. The measuring procedure thus reduces to one of counting the number of quantum present in the measurand. Increasing the number of decimal places can increase the reading accuracy.The main advantages of digital instruments are high accuracy and resolution, low power consumption, direct •interface with computers, auto-ranging and low measurement errors.In digital instruments, output devices indicate the value of the measured quantity in decimal digits. This is done •by using different display types like, Segmental type – 7 segment, 14 segment Dot Matrix type – 3 X 5, 5 X 7 Light Emitting Diode – LED display, Liquid Crystal Diode – LCD display, Vacuum Fluorescent Diode – VFD display.

2.5.2 Recorders

It is often necessary to have a permanent record of the state of a phenomenon being investigated. This is •necessarytocontinuouslymonitorthecondition,stateorvalueoftheprocessvariablessuchasflow,pressure,level, etc.A recorder thus records electrical and non-electrical quantities. This record may be written or printed and later •on can be examined and analysed to obtain a better understanding and control of the processes.A permanent record is useful for the following reasons:•

the record may be used by the process operator as a general operating guide, to observe the trends of the �measured variable to provide an overall picture of the performance of the instrument and the process �toprovidedatatotheoperatingmanagementsoastoevaluatethecalibreandefficiencyofitspersonnel �to locate the trouble on the job �


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Abroadclassificationofrecordersisshownbelowinfig.2.10.

Fig. 2.10 Classification of recorders

2.5.2.1 Graphic Recorders

Graphic recorders generally are the devices that display and store a pen and ink record of the history of some •physical event.It essentially consists of:•

a chart for displaying and storing the recorded information �a stylus moving in a proper relationship with paper �a suitable means of interconnection to couple the stylus to the source of information. �

Graphic recorder is again sub divided into following types:•Strip chart recorder – It records one or more variables with respect to time. It is an X – t recorder. �X-Y recorder – It records one or more dependent variables with respect to an independent variable. �

Strip chart recorder

Thebasicconstructionalfeaturesofastripchartrecorderareshowninfig.2.11.•

Stylus

Range Selector

Stylus Drive

System

Information to be recorded Paper Drive

System

Chart Speed

Selector

Chart

Fig. 2.11 Strip chart recorderA strip chart recorder consists of: •

a long roll of graph paper moving vertically �a system for driving the paper at some selected speed. A speed selector switch is generally provided. Chart �

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speeds of 1-100 mm/s are usually used.a stylus for making marks on the moving graph paper. The stylus moves horizontally in proportion to the �quantity being recorded. A stylus driving system that moves the stylus in a nearly exact replica or analog of the quantity being recorded. a range selector switch is used so that input to the recorder drive system is within the acceptable level. �

Most recorders use a pointer attached to the stylus. This pointer moves over a calibrated scale, thus showing the •instantaneous value of the quantity being recorded. An external control circuit for the stylus may be used.

Paper drive system The paper drive system should move the paper at a uniform speed. A spring wound mechanism may be used but in most of the recorders, a synchronous motor is used for driving the paper.

Marking mechanisms There are many types of mechanisms used for making marks on the paper. The ones most commonly used are:

Markingwithinkfilledstylus:Thestylusisfilledwithinkbygravityorcapillaryaction.•Marking with heated stylus: Some recorders use a heated stylus, which writes on a special paper. •Electric stylus marking: This method employs a paper with a special coating which is sensitive to current. •Electric stylus: This method uses a stylus which produces a high voltage discharge thereby producing a permanent •trace on an electro sensitive paper. Optical marking method: This method uses a beam of light to write on a photosensitive paper. •

Tracing systems There are two types of tracing systems used for producing graphic representations:

Curvilinear system •Rectilinear system•

2.5.2.2 x-Y recorder

An X – Y recorder is an instrument which gives a graphic record of the relationships between two variables.•This is done by having one self-balancing potentiometer to control the position of the chart while another self-•balancing potentiometer controls the position of the recording pen (stylus). In some X-Y recorders, one self-balancing potentiometer circuit moves a recording pen (stylus) in the X direction •while another self-balancing potentiometer circuit moves the recording pen (stylus) in the Y direction at right angles to the X direction, while the paper remains stationary. There are many variations of X-Y recorders. The emf, used for the operation of X-Y recorders, may not necessarily •measure only voltages. The measured emf may be the output of a transducer that may measure displacement force pressure; strain, light intensity or any other physical quantity. Thus, with the help of X-Y recorder and appropriate transducers, a physical quantity may be plotted against another physical quantity. An X-Y recorder may have a sensitivity of 10 mV/mm; a slewing speed of 1.5 m/s and a frequency response •about 6 Hz for both the axes. The accuracy of the X-Y recorder is about ± 0.3 %. The use of X-Y recorders in laboratoriesgreatlysimplifiesandexpeditesmanymeasurementsandtests.

2.6 Data Acquisition SystemData Acquisition Systems (DAS) interfaces between the real world of physical parameters, which are analog, •andtheartificialworldofdigitalcomputationandcontrol.With current emphasis on digital systems, the interfacing function has become an important one; digital systems •are used widely because complex circuits are low cost, accurate, and relatively simple to implement.


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Inaddition,thereisrapidgrowthintheuseofmicrocomputerstoperformdifficultdigitalcontrolandmeasurement•functions.The devices that perform the interfacing function between analog and digital worlds are analog-to-digital (A/D) •and digital-to-analog (D/A) converters, which together are known as data converters.Someofthespecificapplicationsinwhichdataconvertersareusedincludedatatelemetrysystems,pulsecode•modulated communications, automatic test systems, computer display systems, video signal processing systems, data logging systems, and sampled data control systems.Besides A/D and D/A converters, data acquisition and distribution systems may employ one or more of the •following circuit functions:

transducers �amplifiers �filters �nonlinear analog functions �analog multiplexers �sample-holds �

Theinterconnectionofthesecomponentsisshowninthefiguregivenbelow:•

Fig. 2.12 Data acquisition system(Source: http://eu.wiley.com/legacy/wileychi/hbmsd/pdfs/mm452.pdf)

Theinputtothesystemisaphysicalparametersuchastemperature,pressure,flow,acceleration,andposition,•which are analog quantities.Theparameterisfirstconvertedintoanelectricalsignalbymeansofatransducer;onceinelectricalform,all•further processing is done by electronic circuits.Next,anamplifierbooststheamplitudeofthetransduceroutputsignaltoausefullevelforfurtherprocessing•Theamplifierisfrequentlyfollowedbyalow-passactivefilterthatreduceshigh-frequencysignalcomponents,•unwanted electrical interference noise, or electronic noise from the signalThe processed analog signal next goes to an analog multiplexer, which switches sequentially between a number •of different analog input channelsEachinputisinturnconnectedtotheoutputofthemultiplexerforaspecifiedperiodoftimebythemultiplexer•switch.During this connection time, a sample-hold circuit acquires the signal voltage and then holds its value while an •A/D converter converts the value into digital form.The resultant digital word goes to a computer data bus or to the input of a digital circuit.•Thus the analog multiplexer, together with the sample hold shares the A/D converter with a number of analog •input channels timing and control of the complete DAS is done by a digital circuit called a programmer sequencer, which in •turn is under the control of the computer.

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2.6.1 Single Channel DAS

A single channel Data Acquisition System consists of a signal conditioner followed by an analog to digital •(A/D) converter, performing repetitive conversions at a free-running, internally determined rate. A schematic diagramisshowninfig.2.13.

A/D Converter Buffer

convert command

to computer or storage/ print-out

Fig. 2.13 Single channel DAS

The outputs are in digital code words, including over-range indication, polarity information and a status output •to indicate when the output digits are valid.Asshowninfig.2.13,thedigitaloutputsarefurtherfedtoastorageorprintoutdevice,ortoadigitalcomputer•for analysis.The popular digital panel meter (DPM) is a well-known example of this kind, though the sole purpose of •digitising in this case may be only to provide a numerical display.

2.6.2 Multi-Channel DAS

The various sub-systems of the data-acquisition system can be time-shared by two or more input sources. •Depending on the desired properties of the multiplexed system; a number of techniques are employed for such •time-shared measurements. The conventional multi-channel data system has a single A/D converter preceded by a multiplexer, as shown •infig.2.14.Theindividualanalogsignalsareapplieddirectly,orafterpre-amplificationand/orsignal-conditioningwherever•necessary, to the multiplexer; these are further converted to digital signals by the A/D converter sequentially.Forthemostefficientutilisationoftime,themultiplexerismadetoseekthenextchanneltobeconvertedwhile•the previous data stored in the sample-hold (S/H) is converted to the digital form.When the conversion is complete, the status line from the converter causes the S/H to return to the sample mode •and acquires the signal of the next channel. On completion of acquisition, either immediately or upon command, the S/H is switched to the hold mode; or •the conversion begins again the multiplexer switch moves on to the subsequent channel.This method is relatively slower than systems where the S/H outputs or even A/D converter outputs are •multiplexed, but it has the obvious advantage of having a lower cost due to the sharing of a majority of sub-systems.Incaseswherethesignalvariationsareextremelyslow,sufficientaccuracyinmeasurementcanbeachieved•even without the S/H.


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Multiplexer

Analog Signal – 1 Signal Conditioner – 1



Analog Signal – n Signal Condition er – n

to computer or data transmissionLogic

A/D Converter BufferSample &

Hold

Fig. 2.14 Multi channel DAS using single A/D converter

2.7 Data LoggerThe basic function of a data logger is to automatically make a record of the readings of instruments located at •different parts of the plant.Data logger measure and record data effortlessly and quickly, as often and as accurately desired. It can measure •electrical output from virtually any type of transducer and log the value automatically.Automatic data loggers are capable of giving plant performance computation and a logic analysis of alarm •conditions during emergency. Adataloggerprocessesthereadingstorenderthemimmediatelyasrecognisablescientificunits(0C,Kg/cm• 2, KWh,etc).Itcandetectreadingsoutsidethedefinedlimitsandinitiatecorrectiveaction.Itcanalsorecordallor selected readings on a variety of output devices or pass them into a computer for further processing. The measurement range, speed of measurement and the operation of recorders can be different for blocks of •channels and all this is achieved in data loggers by having preset programmes.As loggers handle the data only in digital form, they can manipulate and process the readings without any loss •ofaccuracy.Thebasicblockdiagramofadataloggerisshownbelowinfig.2.15.

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Real Time Clock

Input Scanner

A/D Converter Recorder

Signal Amplifier & Conditioner

Programmer Start

ConvertRecord

Fig. 2.15 Block schematic diagram of data logger

The input scanner is an automatic sequence switch that selects each signal in turn. As it selects only one signal •atatime,thedataloggerrequiresonlyonesignalamplifierandconditioner,oneA/Dconverterandasinglerecorder. The input signals fed to the scanner can be high level signals from pressure sensors, low level signals from •thermocouples, ac signals, pneumatic signals, ON/OFF signals from relays, switches, digital quantities, etc. Independent scanners handle the analog and digital signals.Modern loggers have scanners that scan at a rate of 150 input/s.•Low-levelsignalsarefirstamplifiedand thenconditionedbefore feeding to theA/Dconverter.High-level•signals are directly converted.Theacandpneumaticsignalsarefirstconvertedtodcandthenfedtoaconverter.Acertainamountofprocessing•may be involved in certain cases, such as linearisation of the thermocouple output, etc.Thesignalamplifierandconditionercarryoutallthesefunctions,whichthusprovidealineararrayofsignals•from various transducers.The A/D converts the analog information into a corresponding digital one suitable for driving the recording •equipment.The programmer usually a microprocessor is used to control the sequence operation of various units of the data •logger. The sequential operations, performed by the programmer are as follows:

Setamplifiergainforindividualinputi.e.,thegainhastobesoadjustedthatforamaximumvalueofinput, �the A/D converter records a full-scale reading.Setlinearisationfactorsothattheadjustedoutputfromthesignalamplifierisdirectlyproportionaltothe �measurand. Set high and low alarm limit. �Initiate alarm for abnormal condition. �Select input signal, normally done by a timing pulse. �Start A/D conversion. �Record reading, identify channel and time for use at a later stage. �Reset logger i.e., at the end of the cycle, A/D is reset to its initial condition and the cycle starts again. �

The real time clock is incorporated to automate the system. It commands the programmer to sequence one set of measurements at the intervals selected by the user. Thus, the ‘Data Logger’ represents a classic example of the applicationof‘Microprocessors’inthefieldof‘Instrumentationandcontrol’.


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SummaryThis chapter can be summarised in a nutshell as an introduction to control systems and a discussion on each of •the blocks that comprise a control system.A control system is one that maintains a prescribed relationship between the output and some reference input. •This can be achieved in a variety of ways; however the most popular is the feedback schematic. Signal conditioning is the process of manipulating the output of the sensor/ transducer such that it is suitable •and compatible for indicating, recording, data acquisition or controlling mechanism. A to D conversion is a technique in which a continuously varying (analog) signal is converted into an equivalent •multi-level (digital) signal without altering its essential content. Various types of A to D convertors include Successive approximation, dual slope and voltage to frequency method.A microcontroller is a single IC comprising of specialised circuits and functions that are applicable to a wide •array of system designs.The last stage of a measurement system is the data presentation stage consisting of data presentation elements •like display devices and recorders.An X – Y recorder is an instrument which gives a graphic record of the relationships between two variables.•Data acquisition systems (DAS) are an interface between the real world of physical parameters, which are •analog,andtheartificialworldofdigitalcomputationandcontrol.A single channel Data Acquisition System consists of a signal conditioner followed by an analog to digital (A/D) •converter, performing repetitive conversions at a free-running, internally determined rate.The basic function of a data logger is to automatically make a record of the readings of instruments located at •different parts of the plant.

References Patranabis, D., 2010. • Prin of Industrial Instrumentation 3e, 3rd ed. Tata McGraw-Hill Education.Demler, J. M., 1991. • High-Speed Analog-To-Digital Conversion, Academic Press.Groover, M. P., 2008. • Unit 3 Industrial Control Systems [Pdf] Available at: <http://www.nuigalway.ie/staff-sites/david_osullivan/documents/unit_3_industrial_control_systems.pdf> [Accessed 5 July 2013].Gridling, G. & Weiss, B., 2007. I• ntroduction to Microcontrollers [Pdf] Available at: <http://ti.tuwien.ac.at/ecs/teaching/courses/mclu/theory-material/Microcontroller.pdf> [Accessed 5 July 2013].An Introduction to Microcontrollers• [Video online] Available at: <http://www.youtube.com/watch?v=CmvUY4S0UbI> [Accessed 5 July 2013].Drew, B., 2011. • Control Systems Engineering - Lecture 1 – Introduction [Video online] Available at: <http://www.youtube.com/watch?v=g53tqrBjIgc> [Accessed 5 July 2013].

Recommended ReadingWeiss, J., 2010. • Protecting Industrial Control Systems from Electronic Threats, Momentum Press.Grimble, J. M., 2006. • Robust Industrial Control Systems: Optimal Design Approach for Polynomial Systems, John Wiley & Sons.Lipovski, J. G., 2004. • Introduction to Microcontrollers: Architecture, Programming, and Interfacing for the Freescale 68HC12, 2nd ed. Academic Press.

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Self AssessmentA ______________is one that maintains a prescribed relationship between the output and some reference 1. input.

control systema. input/output systemb. analog systemc. dynamic systemd.

The ____________is a device that is used to measure a variable and provide the output in suitable form.2. integratora. sensorb. samplerc. filterd.

The signal conditioning circuit is an _____________circuit that converts signals provided by a sensor to useful 3. electric signals.

mechanicala. electricalb. electronicc. magnetic.d.

The ____________time refers to the time required for a complete measurement by an analog to digital 4. converter.

laga. acquisitionb. leadc. conversion.d.

State which of the following statements is false.5. Port 2 of the AT89C51also serves the functions of various special features.a. Auxiliary devices like indicators/ recorders are used for monitoring purposes.b. The use of Op-amps allows signal conditioning circuits to be more compact and precise in their c. implementations.The signal required by microcontroller or microprocessor cannot be in raw form from input devices like d. sensors.

State which of the following statements is false.6. A control system is one that maintains a prescribed relationship between the output and some reference a. input.The processor do not require noise-free and disturbance-free signals to perform correctly.b. The signal conditioning circuit is an electronic circuit that converts signals provided by a sensor to useful c. electric signals.Successive approximation is a type of analog to digital convertor.d.


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Which of the following type of ADC converts the analog input voltage to a pulse train with the frequency 7. proportional to the amplitude of the input?

Successive approximationa. Dual-slope convertorb. Voltage- frequency conversion methodc. Sigma-delta d.

Which of the following refers to the time required for a complete measurement by an analog to digital 8. converter?

Measurement timea. Lag timeb. Lead timec. Conversion timed.

Which of the following refers to the time taken by a sample-hole circuit to acquire the input signal within a 9. stated accuracy?

Acquisition timea. Lag timeb. Lead timec. Conversion timed.

Which of the following refers to the number of bits that are used to represent the analog input signal?10. Degreea. Resolutionb. Bitsc. Bytesd.

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Chapter III

Computer for Energy Management

Aim


discuss the use of computers in energy management•

describe the structure of energy analysis programmes•

describe system loads•

Objectives


explain space loads•

state the difference between load calculations and energy analysis•

determine typical program output•

Learning outcome


explain the structure of energy analysis programmes•

differentiate between load calculations and energy analysis •

discuss central plant loads and economic calculations•


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3.1 Introduction Computers have become so inexpensive and a very effective tool for variety of tasks in Energy Management. Data collection, reporting, analysis and monitoring has become extremely easy and user-friendly with computer software. Various software packages are available in the market for performance calculation of utility equipment and systems. Tailor-made software packages can be developed very easily and effectively, using the most commonly available packages such as the excel spreadsheet and Microsoft word. The knowledge of the performance assessment method and input requirements is essential for effectively utilising these software packages. These are very useful for computation and analysis of the data collected during the energy audit of utility systems.

Software for the performance assessment of steam generators, turbines, compressors, pumps, cooling towers, furnaces, heat exchangers, waste heat recovery system, electricity distribution analysis, motor loading, fans and blowers, air conditioning and chiller systems, building energy management, etc. are available and can be effectively used for the quick assessment of performance.

3.2 The Structure of Energy Analysis Programmes All the sophisticated energy analysis programmes perform four basic groups of calculations, which are described here. Different programmes link these calculations in various ways. It is worth your effort to understand the general flowofcalculationsintheprogrammesyouareusing.

The facility’s energy requirements changes continuously, so the sequence of calculations is repeated many times to simulate a full yearly cycle of operation under different conditions of weather, occupancy, etc. At the end, the results of all the repeated calculations are summed to produce the total yearly energy consumption and costs. For input and calculation purposes, the building is divided into “Zones.” Each zone is an area of the building that has particularloadcharacteristics,andisservedbyspecifictypesofconditioning,lighting,andotherenergyconsumingsystems. The programme does most of its calculations separately for each zone.

3.2.1 Space Loads

The programme starts by calculating the end use energy requirements of the spaces.•It calculates heating and cooling loads in the usual way, by adding conduction gains and losses, solar gain, heat •gainedorlostfromoutsideair,humidificationordehumidificationandinternalheatgains.Weather related data needed for these calculations is usually taken automatically from a weather data library.•Solar inputs are calculated by the computer, based on the geographic location and building envelope characteristics •as well as weather data.The programme requires manual input of the physical characteristics of the structure, the sources of internal •heat gain (people and equipment) and temperature settings. The programme also requires manual input of non-weather related loads. These include lighting, electrical •equipment (computers, etc), domestic water heating, specialised process loads, etc. Typically, the user inputs the peak load of each type, along with an hourly schedule of the percentages of peak load. Most energy analysis programmes provide the option of performing these load calculations alone, without the •need to perform the calculations described next.Forexample,indesigninganewbuilding,thespaceloadcalculationsallowthedesignertorefinethebuilding•exteriortoreducesolarcoolingloadsortofindthemosteconomicalamountofwallinsulation.

3.2.2 System Loads

The “systems” loads include the space loads calculated previously, plus the extra energy needed to run the •conditioning equipment, or “systems”. All or most of this extra energy is for fans, in typical systems.The “systems” include air handling systems, fan coil units, air conditioners, radiators, etc, but usually not the •central plant equipment.The programme also calculates energy losses that may be involved in the operation of the systems. The worst •

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of these losses is the reheat losses. For example, if a particular zone is conditioned by an air handling system with reheating terminal units, the programme calculates the fan load, the reheat energy, and the extra cooling energyneededtooffsetthereheat.Thispartoftheprogrammerequiresmanualinputtodescribetheefficiencycharacteristics of the equipment.The equipment operating schedules may also be entered manually, to account for schedules of occupancy. •In some cases, the system's characteristics can be selected from the programmes equipment data library.•The programme will pick out the maximum energy consumption that occurs during the yearly cycle, for each •system. The designer uses these maximum loads to determine the sizing of the conditioning equipment.

3.2.3 Central Plant Loads

Up to this point, the programme has calculated all loads on a zone-by-zone basis.•Next, the programme adds all the zone loads as a total load on the central plant equipment, which includes •boilers, chillers, electric generators, cogeneration plants, thermal storage systems, solar collectors, etc.The programme further adds the energy consumption of central plant auxiliary equipment, such as hydraulic •system pumps and cooling tower fans. For this part of the calculation, the programme requires manual input to describe the plant equipment and its operating schedules.In some cases, plant equipment characteristics can be selected from the program’s equipment data library. This •part of the programme yields the ‘bottom line’ “energy input” to the facility as a whole. This includes energy that is used directly, such as electricity consumption for lighting and receptacle loads.

3.2.4 Economic CalculationsAll the programmes can provide energy cost estimates, as well as raw energy consumption. To do this, the programme requires manual input of energy costs and rate schedules. Some programmes can also calculate the life-cycle costs of alternatives. This requires manual input of equipment and construction costs, at least for the features or equipment beingcompared.Mostprogrammescanincorporatedesiredinterestrates, inflationfactors,andothereconomicvariables in the calculation.

3.3 The Difference Between Load Calculations and Energy AnalysisA load calculation is used primarily to select equipment size based on maximum load condition.•It includes only the space loads discussed above, and it is done only for the single instance of peak load •conditions.For instance, when selecting an air conditioning system for a house, a contractor makes a load calculation to •estimate the peak cooling requirement. This is done by calculating the individual load components and then adding them.For cooling, the load components are solar gain, conduction gain through the walls and roof, the heat gained •byairleakageanddehumidification.The contractor typically uses a one-page worksheet to perform this calculation.•Basic peak-load calculations are simple. They can be done manually, and they are adequate for many •applications.However, manual calculations are not very accurate. One of the causes of error is that all the components of •the load do not reach the peak at the same time. Another limitation is the inability to deal with thermal storage effects. The degree of detail is limited. For example, it is not practical to include the precise orientation of the surfaces in a manual calculation. As a result, a number of computerised load calculation programmes are now available. They provide greater •accuracy, they eliminate the drudgery of arithmetic, and they provide a checklist to make sure that all components of the load are included. There is a range of complexity among computerised programmes, but some are relatively simple. The most detailed load calculations are provided by using the space loads portion of an energy analysis programme, as discussed previously.


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3.4 Typical Program OutputAll the major programmes offer the same types of output information. For calculation, the available output includes:

The input data: The report usually repeats the input data for ease of review. This includes data drawn from the programme’s data libraries, which are discussed below. For example, the output may indicate the outside air temperature and humidity that were assumed for each hour.

Building loads: Loads are divided into heating, cooling, lighting process etc. Some programmes may report the components of these loads. For example, the cooling load may be divided into solar gain, conduction load, internal heat gain and latent load. The loads for individual hours may be displayed. Most programmes report the time of occurrence of each of the peak loads.

Equipment sizing data: Select equipment capacities by using the calculations of peak equipment load. For example, theprogrammemayreportthepeakairflowofairhandlingunits,thepeaksteamflowfromboilers,thepeakenergyinput to individual chillers, etc.

Energy consumption: This can be reported in many ways, including total by energy type: by types of loads (e.g. heating, cooling, lighting, process loads, etc.) by different intervals, including hourly, day type (i.e., weekday, weekend, holiday) monthly and yearly and by system (e.g. chiller plant, air handling units, etc.)

Energy costs: These are derived directly from the consumption calculations, making corrections for variations in prices at different times. The costs can be reported separately by the energy type, e.g. electricity, fuel oil, natural gas, etc.

Life-cycle cost: This is the total cost for energy over a facility’s life cycle, or over a long period of time. This outputincludestheeffectsofchangesinfuelprices,inflation,andinterestrates.Themajorprogrammesallowyouto specify the type of output information you want and the degrees of detail. The programme usually allows you to get output in the same sub-division as input. The loads can usually be displayed by individual zones. Similarly, the characteristics of each system can be displayed separately. All the major programmes can be reported in a variety of tabular and graphical formats. One of the formats is shown in the table below:

Ambient temp. ta DegC 30

Qty. of fuel burnt per hr. mf Kg/hr 25.8

Grosscalorificvalue Kcal/kg 11505.2

Total unburnt combustible loss % 1.500

Loss due to sensible heat in dry FG % 24.24424

Hydrogen % in fuel % 17

Moisture % in fuel % 1.5

Loss due to enthalpy in water vapour % 8.831424

Loss due to moisture in fuel % 0.086583

Loss due to moisture in air % 0.631142

Surface Area m2 7

Surface temperature DegC 75

Radiation Loss % 2.358754

Blow down quantity kg/h r 15

Heat content in blow down kcal/kg 170

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Blow down loss % 0.859066

Total loss % 38.511

ThermalefficiencyonGCV % 61.48879

ThermalefficiencyonNCV % 66.66624

Average % boiler loading % 40

Average radiation loss on daily basis % 5.896886

AverageefficiencyondailybasisonGCV % 57.95066

Calculation of Radiation Loss

Surface area M2 7

Surface Temperature DegC DegC 75

Ambient Temperature DegC 30

Surface Temperature Degc DegC 348

Ambient Temperature DegC 303

Wind velocity MIS 4

1st Factor 358.955

2nd Factor 228.0901

3rd Factor 12.42816

4th factor 3.525359

Radiation Loss Watts 1163.055

Radiation Loss Kcal/hr/m2 1000.227

Total Radiation Loss Kcal/hr/m2 7001.588

%Radiationlosswithfuelfiring % 2.358754


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SummaryComputers have become so inexpensive and a very effective tool for variety of tasks in Energy Management•Data collection, reporting, analysis and monitoring become extremely easy and user-friendly with computer •softwareAll the sophisticated energy analysis programmes perform four basic groups of calculations.•Space loads programme starts by calculating the end use energy requirements of the spaces. It calculates heating •and cooling loads in the usual way, by adding conduction gains and losses, solar gain, heat gained or lost from outsideair,humidificationordehumidificationandinternalheatgain.The “systems” loads include the space loads calculated previously, plus the extra energy needed to run the •conditioning equipment, or “systems”. All or most of this extra energy is for fans, in typical systems.A load calculation is used primarily to select equipment size based on maximum load condition•Manual calculations are not very accurate. Another limitation is the inability to deal with thermal storage •effects.

References Doty, S. & Turner, C. W., 2009. • Energy Management Handbook, 7th ed. The Fairmont Press, Inc.Capehart, L. B., Turner, C. W. & Kennedy, J. W., 2008. • Guide To Energy Management, 6th ed. The Fairmont Press, Inc.Dr. Hui, C. M. S., 2009. • Energy Calculations [Pdf] Available at: <http://www.mech.hku.hk/bse/MEBS6006/mebs6006_0910_05-energy.pdf> [Accessed 5 July 2013].Energy Methods in Structural Analysis• [Pdf] Available at: <http://www.facweb.iitkgp.ernet.in/~baidurya/CE21004/online_lecture_notes/m1l1.pdf> [Accessed 5 July 2013].Structural Analysis by Energy Methods YouTube• [Video online] Available at: <http://www.youtube.com/watch?v=rbDM2ArhXyc> [Accessed 5 July 2013].Structural Analysis by Energy Methods• [Video online] Available at: <http://www.youtube.com/watch?v=AzBS_oucC5A> [Accessed 5 July 2013].

Recommended ReadingCho, H., 1984. • Computer-Based Energy management systems: Technology and Applications: Technology and Applications, Elsevier.Capehart, L. B., Turner, C. W. & Kennedy, J. W., 2002. • Guide to Energy Management, Fourth Edition, 4th ed. CRC Press.Guarracino, F. & Walker, G. H. A., 1999. • Energy methods in structural mechanics: a comprehensive introductlion tomatrixandfinitedelementmehtodsofanalysis, Thomas Telford.

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Self AssessmentA calculation is used primarily to select equipment size based on maximum _________ condition.1.

loada. systemb. plantc. layoutd.

Computers have become so inexpensive and a very effective tool for variety of tasks in _______2. management.

dataa. energyb. companyc. financiald.

The _____________loads include the space loads calculated previously, plus the extra energy needed to run 3. the conditioning equipment, or “systems”.

spacea. plantb. systemsc. layoutd.

Most______________canincorporatedesiredinterestrates,inflationfactors,andothereconomicvariablesin4. the calculation.

programmesa. reportsb. surveysc. analysis reports.d.

State which of the following is false.5. A number of computerised load calculation programmes are now available.a. A load calculation is used primarily to select equipment size based on maximum load condition.b. Loads are divided into heating, cooling, lighting process etc.c. All the sophisticated energy analysis programmes perform only two basic groups of calculationsd. .

State which of the following is true.6. Loads are divided into heating, cooling, lighting process etc.a. Systems are divided into heating, cooling, lighting process etc.b. Plant is divided into heating, cooling, lighting process etc.c. Space system is divided into heating, cooling, lighting process etc.d.

State which of the following is true.7. The facility’s energy requirements changes continuously.a. The facility’s energy requirements do not change continuously.b. The facility’s energy requirements remain constant.c. The facility’s power requirements do not change continuously.d.


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Data collection, reporting, analysis and monitoring become extremely easy and user-friendly with which of the 8. following?

Computer hardwarea. Computer softwareb. Database managementc. Audit reportd.

Which of the following are derived directly from the consumption calculations, making corrections for variations 9. in prices at different times?

Plant costsa. layout costsb. Energy costsc. Building costsd.

Which of the following cost is the total cost for energy over a facility’s life cycle, or over a long period of 10. time?

Long-timea. Load b. Space loadc. Life-cycled.

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Chapter IV

Management Information Systems

Aim

The aim of this chapter is to:

definetheconceptofinformation•

describe the concept of management information system•

discuss technical barriers of energy management information system•

Objectives


discuss the barriers in information•

examine what information is used at different levels in an organisation•

explain energy management information system•

Learning outcome


state the managerial barriers of energy management information system•

answer the question of who uses energy information•

explain the typical format of paper industry•


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4.1 Introduction Goodinformationisindispensableforeffectiveenergymanagement.Butconventionalfinancialaccountsdonotmakevisiblethebenefitsofenergymanagement.Mostorganisationsexaminetheaggregateexpenditureandrevenuerelatedtoeachpartofthebusiness-theyareinterestedinthe‘bottomline’orhowmuchprofitorlosseachdepartmentismaking.Thisisakeyreasonwhyenergymanagershavehaddifficultyinthepastinmaintainingseniormanagementinterestandcommitment.Asthefigurebelowillustrates,weseetheinformationsystemasacyclicalprocess-partof a continuous improvement strategy.

Designing a good information system involves considering the whole process of adequate data input, sensible analysis and appropriate reporting. Until recently, energy information systems have predominately been discussed in terms ofthehardwareandsoftwarespecificationsformonitoringandtargetingsystems.Nowmuchmoreconcernisgiventofindingoutwhatinformationend-usersofsuchsystemsneedandtodesigninginterfacesthatareuserfriendly.Although they may form its core, monitoring and targeting are only part of a comprehensive energy information system.

Fig. 4.1 Information system

4.2 What is Information? Information is a data that has been processed so that it is meaningful to users and helps them make decisions. While designing information systems, the objective is to reduce the amount of data that decision makers receive while increasing the quality of relevant information at their disposal. Instead of producing streams of data, a system should monitor, analyse and produce output tailored for different types of decisions. The questions to ask when you review your existing information systems are:

Who has an interest in the information it produces? •What are they interested in knowing? •Are they getting the right information in the form that is most useful? •

Information needs to be ‘accurate, timely and relevant’. But out of these three requirements, the most important is relevance; information has to be appropriate for the decision to be made. Accuracy and timelines are also important, but they vary with the type of decision. You should always strive for accuracy in the data you gather and the information that you provide, but you need to be realistic about the precision of the data you collect. You can spend considerable time and effort in collecting extremely precise data for no purpose, when other information in the analysis is subject to high levels of uncertainty.

Timelines will also vary with the type of decision making. For energy use data, timing is most often determined by the overall management system. For example, managerial control of most operational issues requires regular reports which correspond with your monthly budgetary cycle. Other kinds of energy management information may be needed for planning purposes and therefore, its timing may be aligned with the organisation’s strategic planning or capital budgeting cycle.

Measure

Data

Analyse

Information

Results

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4.3 Management Information SystemA management information system (MIS) is a system or process that provides the information necessary to •manage an organisation effectively.MIS and the information it generates are generally considered essential components of prudent and reasonable •business decisions.The importance of maintaining a consistent approach to the development, use, and review of MIS systems within •the institution must be an ongoing concern. MISshouldhaveaclearlydefinedframeworkofguidelines,policiesorpractices,standards,andprocedures•for the organisation. These should be followed throughout the institution in the development, maintenance, and use of all MIS.

MIS is viewed and used at many levels by management. It should be supportive of the institution’s longer term strategicgoalsandobjectives.Totheotherextremeitisalsothoseeverydayfinancialaccountingsystemsthatareusedtoensurebasiccontrolismaintainedoverfinancialrecordkeepingactivities.

4.4 Barriers The main barriers to the use of energy management information are:

4.4.1 Managerial Energy management is marginalised as a technical speciality.

line management is inadequate •thereisinsufficientinterestanddrivingforcefromabove•there is little incentive for departmental managers and general staff to save energy •

4.4.2 Technical

getting accurate data on time is a key problem •monitoringandtargetingisnotintegratedwithfinancialaccounting•output is not reported to either users or senior managers in a form they can readily understand and use•

4.5 Getting the Most Out of Your System The key things you need to keep in mind when developing an effective energy management information system are:

Decide who will use the information and involve them in making a realistic assessment of their needs. •Keep data input and analysis as simple as possible and compatible with achieving your aims. •Ensurethattheoutputmotivatespeopletouseenergyefficiently.•Justify the expense of running the system to the senior management.•

4.6 Who Uses the Information? Thefivemaingroupsofpeoplewhouseenergyinformationare:

Top and senior management •Middle managers (or budget holders) •Key personnel •General staff •Energy managers and coordinators •


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4.6.1 What information do Senior Managers Need? Senior and top management needs to know how much money has been saved by energy management to answer the following questions:

Without energy management, how much more would the organisation have spent on energy last year? •Whattotalamountshouldbeinvestedinenergyefficiencywithashortpaybackinthecomingyear?•Whatmajorenergyefficiencyprojectswithlongerpaybacksshouldbefinancedandwhy?•

4.6.2 What Information do Middle Managers Need? Middle managers, especially those who are budget holders, need to know how well key personnel are managing energy consumption in order to be able to answer the following question:

Is the department meeting its target and /or staying within the budget?•

This needs to be in as simple form as possible, preferably in the same format as any other regular monitoring information they receive.

4.6.3 What Information do Key Personnel Need? Key personnel are those responsible for controlling the plant and premises. They need feedback on their performance in order to be able to answer the following questions:

How much has energy consumption, after taking into account differences in the weather, occupancy, and •production changed compared with last year? What has been the effect, in terms of energy consumed, of any energy management action taken? •What is the trend in energy use?•

4.6.4 What Information do General Staff Need? General staff need simple feedback on how well their department or section is doing in order to answer the question:

Is its consumption of energy improving or getting worse? •What impacts are their actions having on energy use? •

At the very least, this might be in the form of a quarterly or bi-annual bulletin on a notice board, in the company newsletter or pinned up in the entrance lobby.

4.6.5 What Information do Energy Managers Need? In addition to the information above, you and others who manage energy-perhaps on a departmental basis -will also need information to help you answer:

By how much is their department or section improving? •How much effect has their good housekeeping had? •Whatmeasureswouldbringaboutincreasedenergyefficiencyinyourbuildings?Whatistheanticipatedpayback•on these measures? What technical advances in energy management are on the horizon? •

To answer some of these questions, you will need to keep up to date through reading, conferences and training courses, and contact with other colleagues in your own organisation and other energy staff outside.

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4.7 An Energy Management Information System Energy Management Information System (EMIS) is an important element of a comprehensive energy management •program. It provides relevant information to key individuals and departments that enables them to improve energy •performance.An EMIS provides information to appropriate personnel within an organization to help them manage energy •use and costs.An EMIS can be characterized by its deliverables, features, elements and support.•Deliverables include the early detection of poor performance, support for decision making and effective energy •reporting. Features of an EMIS include the storage of data in a usable format, the calculation of effective targets for energy •use, and comparison of actual consumption with these targets. Elements include sensors, energy meters, hardware and software (these may already exist as process and business •performance monitoring systems). Essential support includes management commitment, the allocation of responsibility, procedures, training, •resources and regular audits.

As per the clause (I) of EC Act-2001, every designated consumer has to submit a report in the prescribed form on thestatusoftheenergyconsumptiondataattheendofeveryfinancialyearTheBureauofEnergyEfficiencyispreparingthefollowingthreeformsfordatacollectionandtestingthemonapilot scale.

Form 1 Format for information regarding Total Energy Consumption and Energy Consumption per Unit of Production

Form 2 Format for reporting status of implementation of energy conservation measures based on the business plan of the company

Form 3 ExecutivesummaryofappraisedEnergyConservationpotentialasidentifiedinthe energy auditor’s report

On a pilot scale, these three forms are tested for the three sectors namely: The Engineering sector �The Power sector �Commercial buildings (eg. Hospital) �

For Engineering and Commercial Building Sectors, the Form-1 format is quite exhaustive and needs little •modification.For the power sector, since there is no purchased electricity, coal/oil or gas will be the main inputs. Whereas •there is no column to enter the Auxiliary power consumption for their internal consumption. Auxiliary power consumption is the key energy indicator for comparing different power plant performances. In all these three sectorswe found it difficult to calculate specificpower consumption, because the exact•productionfigurescouldnotbefiguredout.Inthepowersector,thepowergenerationitselfistheproduction.So, we have to enter twice, the generation data both in own generation and production columns. Of course this maynotcreateanyproblemswhilecalculatingspecificpowerconsumption.Wegettheenergycosttowardspower generation in Rs./kWh. Form-2 is simple if we are able to complete Form-3. the only problem with form-2 is to quantify/verify the actual •savings achieved, based on the implementation of the measures suggested by the Energy Auditor. This will be


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difficultunlessthedesignatedconsumerhasaverygoodMonitoringandVerification(M&V)system.Form-3isOK.Butwefinditdifficulttofitsomeofthemeasureslikedemandreduction,etc.inanyofthe•categories.Soitneedssomemodification.Theexhaustivelistof22categoriesissuggestedinthemodifiedform-2, which will cover all most all types of energy conservation measures.

Thetestingofeachformandthecorrespondingcommentsanddifficultiesencounteredduringthefillingoftheseforms are presented in the following section.

Form 1Format for Information regarding Total Energy Consumption and Energy

Consumption per Unit of Production

Name of the Sector : Engineering Sector Name of the company :Full Address :Contact Person :Email address :Telephone/ Fax numbers :Plant Address :Plant Capacity :Plant Capacity Utilisation :Plant year of Commissioning :

A] Power and Fuel consumption

1 Electricity

(a) Purchased

Contract demand (i) 13000 KV

Connected load(ii) A 20000kW

Annual consumption(iii) 280,54,475 kWh

Total cost(iv) 912.27 Rs Lakhs

(b) Own Generation

Through diesel generator (HSD)(i) Annual generationAnnual diesel consumptionTotal fuel costs

38,18.489 kWh980 kilo litres127.28 Lakhs

Through steam turbine/generator(ii) Annual generationFuel used1 kWh

Through Gas turbine(iii) Annual generation kWh

2. Coal

Coal used for(i) Gas production

Quality(Grosscalorificvalue)(ii) 5400kCal/kg

Annual consumption(iii) 2000 Tonnes

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Total coal costs(iv) 40.00 Rs Lakhs

3 Oil

Furnace oil (Boilers)(i) Annual consumptionFurnace oil (Furnaces)Annual consumptionTotal annual costs

1250 kilo litres

kilo litres212.5 Rs Lakhs

Low Sulphur Heavy Stock(LSHS)(ii) Annual consumptionAnnual costs

TonnesRs. Lakhs

4 Diesel Oil

High Speed Diesel (HSD)(i) Annual consumptionAnnual costs

kilo litresRs. Lakhs

Light Diesel Oil (LSD)(ii) Annual consumptionAnnual costs

kilo litresRs. Lakhs

5. Gas

Compressed Natural Gas (CNG)(i) GrosscalorificvalueAnnual consumptionAnnual costs

kCal/NM3

TonnesRs. Lakhs

LiquefiedPetroleumGases(LPG)(ii) GrosscalorificvalueAnnual consumptionAnnual costs

kCal/NM3

TonnesRs. Lakhs

Piped Natural Gas (PNG)(iii) GrosscalorificvalueAnnual consumptionAnnual costs

kCal/NM3

NM3

Rs. Lakhs

6. Biomass

Averagemoisturecontent,asfired(i) %

Averagecalorificvalue,asfired(ii) kCal/kg

Annual consumption(iii) MT

Annual biomass costs(iv) Rs. Lakhs

7. Total Energy

In terms of energy(i) 57226.8 Mill.Kcal

In terms of cost(v) 1292.05 Rs. Lakhs


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B]ProductMixSpecifications

Product Name Source Units

1 Steam Turbines

2 Gas Turbines

3 Generators

4 Heat Exchangers

C]SpecificEnergyConsumptionfigures

Product -1 Kwh/Ton

Product-2 M.Kcal/Ton

Auxiliary power consumption %

Heat Rate Kcal/Kw

Comments on Form 1

Things to be included in the general Category are:

Name of the Sector •Plant Capacity •Plant Capacity Utilisation (to know the effect of under utilisation) •Plant year of Commissioning ( to know the aging effect).•

A] Power and Fuel consumption

Electricity1. Purchased:(a)

Contract Demand normally mentioned in KVA rather than KW.

Own generation: (b) DG set need not be run on Diesel, it can be even HSD. So fuel used needs to be asked.•Power sector people can write their total generation under ‘own generation:•

through steam turbine/generator or �through Gas turbine. �

However for Auxiliary power consumption for internal purposes in the power plants, there is no column in •thepresentform-1.ItshouldbeincludedinaseparateCategory(maybecategory-Cunderspecificenergyconsumptionfigures).If we include this under Annual consumption category of 1 (under purchased Electricity), then we will be •double accounting while calculating total energy cost, because, this Auxiliary power cost is already included in the Annual consumption of either coal or gas.

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OIL 2. Furnace oil consumption can be either in Boilers or Furnaces /kilns. It is suggested to consider oil consumption •for Boiler and Furnaces separately. Hot Heavy Stock (HHS) is not familiar in India, it should be HSHS (High Sulpher Heavy Stock).•

B. Product Mix Itisdifficulttoreportactualproductionintermsof•

Product name 1:…..... �Product name 2:……. �

For a single product, this format is OK. For multi products, even if we know that they are different products, it •isdifficulttocalculatespecificenergyconsumptionperunitofproductfordifferentproducts,becauseweknowonly the total energy consumption and the total energy cost.For example in the engineering industry, with various product mixes, production quantity cannot be added to •get the total production.Similarly for hospitals/hotels /commercial buildings, there is no production. It is better to ask the designated •consumertoreporttheirspecificenergyconsumptionpersq.ftorperpatient,etc.For the power sector, we need to include total power generation once again under product mix.•It is suggested that a code be given to each item in form -1, so that it helps in data entry and subsequent •computerisation and analysis of the data, to get the total energy consumption/cost and also to calculate the specificenergyconsumptionfigures,etc.


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Form -2 (Testing for Engineering Sector)Format for reporting status of implementation of energy conservation measures based on the business plan

of the company

S. No. Description of measure Category Investment (Rs. Lakhs)

Verified savings*

(Rs. Lakhs)

Verified energy savings

Units5 Fuels6

1 Revision of Contract Maximum Demand 1 - 18.70 75,000

2 Incorporation of Lighting Energy Saver 4 6.00 5.00 8,000 kWh E

3 Replacing HPMV 4 3.60 1.50 1,50,484 kWh E

4 Conversion of MG sets to Thyristor Drives 5 7.5 9.00 5,093 kWh E

5 Reduction of compressed Air Leaks 9 1.00 26.00 75,800 kWh E

6Stopping of one Compressor during lunch time

9 - 3.00 86,100 kWh E

7 Stopping of Cooling Tower Fan 11 - 1.57 44,800 kWh E

8 Ceramic Fibre lining for Heat Treatment Furnaces 18 3.00 1.85 28,980 kWh E

9Re-commissioning of So-lar Hot Water system for staff canteen

20 1.50 1.50 43,200 kWh E

10 Incorporation of Welding Energy Savers 22 8.00 10.40 2,98,000 kWh E

11 Use of producer gas for Boilers instead of Foil 19 - 47.20 408 KL 0

Total 30.60 125.72

Useconventionalenergy,volumeormassunitswithproperprefixk=103, M =106, G = 109. State which type of fuel or energy was saved (C = coal, B = biomass, 0 = oil, G = gas, E = electricity).If coal was saved state which grade i.e., C/I = imported, or C/F coal of grade F.

Comments on Form -2 OnceForm-3isreadyinallrespects,thefillingofForm-2iseasyandsimple.•Theanticipatedsavingsidentifiedbytheenergyauditorandtheactual/verifiedsavingsmaybedifferent.•Thequantificationofactualsavingsachievedmaybeverydifficultindividualmeasurewise,withtheabsence•ofapropermonitoringandverificationsystem.Itissuggestedtoaskforclarifications/barriersfromthedesignatedconsumerfornotimplementingsomeof•the suggestions. There should be the provision for incorporating measures implemented also by the designated consumer on •his own.

91/JNU OLE

Use commercial units of litre, kg, tons, and normal cubic metre, kWh or MWh and indicate the unit. Indicate •the anticipated potential in energy savings.Anticipatedcostsavingsinthefirstyearbasedonanticipatedfuelsavings.•Estimatethepredictedlifeofthemeasure,meaningthenumberofyearstheleveloffirstyearenergysavings•or even larger amounts will materialise

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92/JNU OLE

8

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93/JNU OLE

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94/JNU OLE

Comments about Form- 3 Theexecutivesummaryofappraisedenergyconservationpotentialasidentifiedintheenergyauditreport,cannotbefitintothepresentcategoryof13itemsasgiveninform-3.

There are no provisions to include suggestions like demand reduction towards cost savings. •ThereisnoprovisiontoreportefficiencyimprovementinBoilers/Furnaces/DGsets/coolingtowers,etc.•Itissuggestedtoincludemorecategories(foreg.22no’s)assuggestedinthemodifiedFORM-3.•It is suggested including one more column for total savings in “First year cost reduction” because sometimes •we may get energy savings in more than one resource by implementing the same measures. For eg; by reducing excess air in boilers, we get savings both in coal/oil as well as electricity (due to ID fan load reduction). Life cycle years is not understood by many of us. It is suggested asking for the familiar simple payback period •in years. It is suggested adding a total savings row at the end of the table. •It is suggested including reproducing the summary of the energy savings table as it is, as given in the energy •auditor’s report as a separate annexure.

4.8 Typical format for paper industryEnergy ConsumptionThe energy scenario of G. paper industry in the past three years is given below:

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S. No. Description Unit 2002-3 2003-4 2004-5

I. Production of Newsprint

48.8 GSMa) MT 1,00,495 1,09,263 98,749

45 GSMb) MT 0 3,292 13,453Total Production of equivalent 48.8 c) GSM Newsprint MT 1,00,495 1,12,832 98,749

II Total Electrical Energy

Electrical Energy Purchaseda) Lakh kWh 1151 1095 1135

Electrical Energy Generated thro’ TGb) Lakh kWh 932.29 997.75 I 956.57

Electrical Energy Generated thro’ DGc) Lakh kWh 0.71 0.47 1.46

Total Electrical Energy Consumptiond) Lakh kWh 2084 2093.22 2093.03

III Total Coal Consumptiona) MT 1,24,361 2892 1,44,308

Total Furnace oil Consumptionb) KL 2216 1,66,604 2058

IV Energy Cost Details:

Energy cost as % of total cost of pro-a) duction % 32.80 29 30.82

Cost of Electricityb) Rs. Lakhs 5682.51 6125.54 6140.97

Cost of Coalc) Rs. Lakhs 1712.85 2021.13 2095.92

Cost of Furnace oild) Rs. Lakhs 387.09 300.07 302.01

V SpecificElectricalEnergyConsumption/MT of equivalent 48.8 GSM NP:

1) SpecificElectricalEnergy kWh/MT 2073 1855 1847

2) SpecificThermalEnergy Million K Cal/MT 5.32 5.10 4.12

3) SpecificProcessSteam MT IMT 5.82 5.12 4.58

4) SpecificFurnaceOil LIMT 29.2 19.15 4.58

5) SpecificWater KLIMT 116 98.7 95

Continual improvement inspecificenergyconsumptionhasbeenachievedforelectricalenergy,processsteam,furnace oil, water and thermal energy during 2002 to 2005.


96/JNU OLE

Thetrendsofspecificenergyconsumptionfiguresaregraphicallyrepresentedbelow.

2100

2000

1900

1800

17002002-03 2003-04 2004-05

Sp Energy kWh/MT of equivalent 48.8 GSM Newsprint.

2049

1836 1829

2002-03 2003-04 2004-05

6

5

4

32

1

0

Thermal Energy M K Cal/MT

5.32

5.1

4.12

Process Steam: MT/ MT

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5.11

4.58

2002-03 2003-04 2004-05

6

4

2

0

Sp. Furnace Oil: Ltr/ MT29.2

19.15 18.11

2002-03 2003-04 2004-05

30

20

10

0

Specific Water Consumption: KL/MT

2002-03 2003-04 2004-05

150

100

50

0

Colony Energy Consumption:Av.kWh/day

2002-03 2003-04 2004-05

8000

6000

4000

2000

0

65605567 5425

Fig. 4.2 Specific energy Consumption Trends

97/JNU OLE

SummaryGood information is indispensable for effective energy management.•Designing a good information system involves considering the whole process of adequate data input, sensible •analysis and appropriate reporting.Information is data that has been processed so that it is meaningful to users and helps them make decisions.•Information needs to be ‘accurate, timely and relevant.•Senior and top management needs to know how much money has been saved by energy management.•A management information system (MIS) is a system or process that provides the information necessary to •manage an organization effectively.An Energy Management Information System (EMIS) is an important element of a comprehensive energy •management program.Features of an EMIS include the storage of data in a usable format, the calculation of effective targets for energy •use, and comparison of actual consumption with these targets.The chapter also gives different formats to be used for various sectors of industries.•

ReferencesPiercy, N., 1987. • Management Information Systems: The Technology Challenge, Taylor & Francis.Heijden, V. D. H. & Heijden, G. J., 2009. • Designing Management Information Systems, Oxford University Press.Introduction to Management Information Systems• [Pdf] Available at: <http://www.mu.ac.in/mis.pdf> [Accessed 5 July 2013].Harsh, B. S., • MANAGEMENT INFORMATION SYSTEMS [Pdf] Available at: <http://departments.agri.huji.ac.il/economics/gelb-manag-4.pdf> [Accessed 5 July 2013].Prof. Mahanty, B., 2011. • 1 - Introduction – I [Video online] Available at: <http://www.youtube.com/watch?v=5JMkdGQCm4k&list=PLhOZYDWQab_bUIugIkQhacRw0OmKN_HkN> [Accessed 5 July 2013].Prof. Mahanty, B., 2011. • 2 - Introduction – II [Video online] Available at: <http://www.youtube.com/watch?v=JWZ6VAzZ9K0&list=PLhOZYDWQab_bUIugIkQhacRw0OmKN_HkN> [Accessed 5 July 2013].

Recommended ReadingDavis, 2001. • Management Information Systems, Tata McGraw-Hill Education.Shajahan, S., 2004. • Management Information Systems, New Age International.Kelkar, S. A., 2003. • Management Information Systems: A Concise Study, PHI Learning Pvt. Ltd.


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Self Assessment_______________________is a data that has been processed so that it is meaningful to users and helps them 1. make decisions.

Informationa. Reportb. Surveyc. Reviewd.

_________________is viewed and used at many levels by management.2. EISa. MISb. MIPc. IMPd.

__________________management information system is an important element of a comprehensive energy 3. management program.

Financiala. Datab. Energyc. Powerd.

___________can be characterised by its deliverables, features, elements and support.4. MISa. PMISb. EMPSc. EMISd.

_________________provides relevant information to key individuals and departments that enables them to 5. improve energy performance.

EMISa. MISb. PMISc. EMPSd.

A management information system is a system or process that provides the information necessary to manage 6. an/ a _____________effectively.

organisationa. companyb. plantc. instituted.

State which of the following is true.7. Information need not to be accurate, timely and relevant.a. Information needs to be accurate, timely and relevan.tb. Key personnel need simple feedback on how well their department or section is doing.c. General staff are those responsible for controlling the plant and premises.d.

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State which of the following is true.8. Accuracy and timeliness are also important, they do not vary with the type of decision.a. Accuracy is also important, but they vary with the time. b. Accuracy and timeliness are also important, but they vary with the type of decision.c. Accuracy and timeliness are also important, but they vary with the type of organization.d.

Who is responsible for controlling the plant and premises?9. Key personnela. Managerb. Ownerc. Workersd.

Who need simple feedback on how well their department or section is doing?10. Key personnela. managerb. Ownerc. General staffd.


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Chapter V

Writing User-friendly Energy Audit Reports

Aim

The aim of this chapter is to:

understand the concept of audit reports•

state the points to be considered while writing user friendly audit reports•

state the points to be included on the report section•

Objectives


determine why audit reports are required•

examine how to write user-friendly audit report•

examine the short form of audit report•

Learning outcome


recall the concept of audit reports•

follow the guideli• nes to be considered while writing reports

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5.1 IntroductionAnenergyauditisaperiodicexaminationofanenergysystemtoensurethatenergyisbeingusedasefficientaspossible.Itisoneofthefirsttaskstobeperformedintheaccomplishmentofaneffectiveenergycostcontrolprogram.By identifying and minimising wasted energy through an energy audit, you can achieve the following results:

Conserve non-renewable energy resources which are gradually running out.•Protect the environment by burning less fossil fuels, e.g. by reducing power generating requirement, thus •lessening carbon dioxide emissions which contribute to global warming.Save energy and reduce running costs.•

5.2 What Is a User-friendly Audit Report? People generally think of the term “user-friendly” related to something like a computer programme. A user-friendly programmeistheonethathelpsyoutouseitwithaminimumdifficulty.Thesametermisusedforauditreportstomake a report that communicates its information to the user (reader) with a minimum amount of effort on the reader’s part. The report should be such that a reader won’t have to spend his/her valuable time struggling to understand what the report is trying to say. If the report is not clear and easy to follow, the reader is likely to set it down to read later, and “later” may never come.

5.3 Guidelines for Writing User-friendly Audit ReportNumber of points have to be taken into consideration for writing a user-friendly audit report successfully. These points are summarised below:

5.3.1 Know Your Audience

Thefirstthingtokeepinmindwhenyoustartwritinganythingistoknowwhoyouraudienceisandtailoryour•writing to that audience.When writing an industrial audit report, your readers can range from the company president to the head of •maintenance.If recommendations affect a number of groups in the company, each group leader must be given a copy of •the report. Thus, you may have persons of varying backgrounds and degrees of education all looking at the report. The primary decision maker may not be an engineer; the person who implements the recommendations may •not have a college degree.Then provide a detailed section that gives technical supplement. This section of the report includes the calculations •thatsupporttherecommendationsandanyspecificinformationrelatingtoimplementation

5.3.2 Use a Simple, Direct Writing Style Technical writers often feel compelled to write in a third-person, passive, verbose style. Because energy audit reportsaretechnicalinnature,theyoftenreflectthiswritingstyle.Instead,youshouldwriteyourauditreportinclear, understandable language. As noted above, your reader may not have a technical background. Even one who does will not be offended if the report is easy to read and understand.

5.3.3 Simplify Your Writing by Using the Active Voice Writers often are reluctant to take responsibility for their recommendations; they use the passive voice to avoid responsibility, saying “It is recommended …” or “It has been shown …” rather than “We recommend…” or “We have shown.”

5.3.4 Consider that You are Addressing the Report to One or More Individuals Write it as if you were speaking directly to the reader. Use the words “you” and “your”. Make the report plain and simple.


102/JNU OLE

5.3.5 Avoid Technical Terminology that Your Reader May Not Understand Don’t use acronyms such as ECO, EMO or EMR without explaining them. (Energy Conservation Opportunity, Energy Management Opportunity, Energy Management Recommendation).

5.3.6 Present Information Visually Often the concepts we are trying to convey in an audit report are not easy to explain in a limited number of words. Therefore, we often use drawings to show what we mean. For example, we have a diagram that shows how to placethelampsinfluorescentlightingfixtureswhenyouareusingreflectorsandeliminatingtwoofthelampsinafour-lampfixture.Wealsohaveadiagramshowinghowaheatpipeworks.Wepresentourclient’senergyusedatavisually with graphs showing the annual energy and demand usage by month. These graphs give a picture of use patterns. Any discrepancies in use show up clearly.

5.3.7 Make Calculation Sections Helpful Themethodologyandcalculationsusedtodevelopspecificenergymanagementopportunityrecommendationsarepotentially useful in an audit report. Including the methodology and calculations gives technical personnel the ability to check the accuracy of your assumptions and your work. However, not every reader wants to wade through pages describing the methodology and showing the calculations. Therefore, we provide this information in a technical supplement to our audit report. Since this section is clearly labelled as a technical supplement, other readers are put on notice as to the purpose of this section.

5.3.8 Use Commonly Understood Units In your report, be sure to use units that your client will understand. Discussing energy savings in terms of BTUs is not meaningful to the average reader. Kilowatt-hours for electricity or for therms for natural gas are better units because most energy bills use these units.

5.3.9 Make Your Recommendations Clear Some writers assume that their readers will understand their recommendations even if they are not explicitly stated. Although the implied recommendations may often be clear, the better practice is to clearly state your recommendations so that your reader knows exactly what to do.

5.3.10 Explain Your Assumptions A major problem with many reports is a failure to explain the assumptions underlying the calculations. For example, when we use operating hours in a calculation, we show how we got the number. “Your facility operates from 7:30 amto8:00pm,fivedaysaweek,51weeksperyear.Therefore,wewilluse3188hoursinourcalculations.”Whenyou show your basic assumptions and calculations, the reader can make adjustments if those facts change. In our example above, if the facility decided to operate 24 hours per day, the reader would know where and how to make changes in operating hours because we had clearly labelled that calculation.

We use one section of our report to list our standard assumptions and calculations. That way we do not have to repeat the explanations for each of our recommendations. Some of the standard assumptions/calculations included in this section are operating hours, average cost of electricity, demand rate, off-peak cost of electricity and the calculation of the fraction of air-conditioning load attributable to lighting.

5.3.11 Be Accurate and Consistent The integrity of a report is grounded in its accuracy. This does not just mean correctness of calculations. Clearly, inaccurate calculations will destroy a report’s credibility. But other problems can also undermine the value of your report.

103/JNU OLE

5.3.12 Be Consistent Throughout the Report Use the same terminology so your reader is not confused. Make sure that you use the same values. Don’t use two different load factors for the same piece of equipment in different recommendations. This could happen if you calculated the loss of energy due to leaks from a compressor in one recommendation and the energy savings due to replacingthecompressormotorwithahighefficiencymotorinanotherrecommendation.

5.3.13 Proofread Your Report Carefully Typographical and spelling errors devalue an otherwise good product. With computer spell checkers, there is very little excuse for mis-spelt words. Your non-technical readers are likely to notice this type of error, and they will wonderifyourtechnicalcalculationsaresimilarlyflawed.

5.4 Report SectionAfter successfully carried out energy audit a good audit report should be presented to the top management for effective communication and implementation. A typical energy audit reporting contents and format are given in the next section. The following format is applicable for most of the industries. However the format can be suitably modifiedforspecificneedapplicableforaparticulartypeofindustry. Each report shall include the following (in the same sequential order):

Title page•Table of contents•AuditorfirmandauditteamdetailsandCertification•Executive summary•Introduction to the energy audit and methodology•Description about the plant / establishment•Energyconsumptionprofileandevaluationofenergymanagementsystem•Equipment/sectionsspecificreports(Referinstructionmanualsofrelevantequipments)•Summary list of recommendations and action plan•Supplierslistofretrofits/vendors•Appendix•

5.4.1 Title PageThe title page of the report shall contain:

Audit Report title•Date of Report (Month and year)•Auditor Name: The name of the auditor should be written on the title sheet. If the auditor is accredited energy •auditor then ID code of the auditor can also be givenMandatory Audit details: If the energy audit is carried out as a part of mandatory requirement, then it can be •mentioned.

5.4.2 Table of ContentsA table of contents usually headed simply “Contents,” is a list of the parts of a energy audit report organized in the order in which the parts appear. The contents usually include the titles or descriptions of such as chapter titles in longer works, second level (section level) and (or) third (subsections). Table of contents should be very comprehensive and must include:

Sections and subsections along with page numbers as main content sheet•List of tables along with the table number and corresponding page number•Listoffiguresandgraphsincludingdiagramsandflowchartsifanyalongwithnumberandcorresponding•page numberAbbreviations used in the report.•


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5.4.3 Auditor Firm and Audit Team Details & CertificationThe report shall contain the energy auditor details (such as name, address, phone, fax, email Ids. etc). The report shallalsolisttheenergyauditteaminvolvedinthestudyalongwiththeircertification.Theaccreditedauditorshallsigntheenergyauditreportunderthesealofthefirmgivingalltheaccreditationdetailsalongwithdetailsofenergyauditors employed for conducting energy audit study.Thecertificationshallstatethat:

The data collection has been carried out diligently and truthfully;•Alldatameasuringdevicesareingoodworkingconditionandhavebeencalibratedorcertifiedbyapproved•agencies authorised and no tampering of such devices has occurred. All reasonable professional skill, care and diligence had been taken in preparing the energy audit report and the •contents thereof are a true representation of the facts

5.4.4 Executive SummaryAll information in the executive summary should be drawn from the detailed information in the full report. The executive summary should simple, clear and to the point. The executive summary should contain a brief description of the audit, including:

Name of client, location of facility or plant audited•Objectives of audit•Key systems and equipment analysed•Dates of audit•Summary of recommended energy conservation measures, annual energy savings and cost savings using the •table format below

Sr.No RecommendedMeasure

EstimatedAnnual energy savings

EstimatedAnnual cost savings

Estimatedimplementation cost

Payback period

12

Total

5.4.5 Introduction to Energy Audit and MethodologyThe Introduction to energy audit should include:

Audit objectives and purpose of energy audit: Clearly specify the energy audit objectives and purpose•Scope of work: Brief description of scope of work can be given in this section while detailed scope can be •enclosed as annexureMethodology and approach followed for the audit (techniques - e.g. inspection, measurements, tests, calculations, •analyses and assumptions)Timescheduleforconductingtheenergyaudit–fieldstudyandreportpreparation•Instrumentsused:Detailsofportableenergyauditinstrumentsandspecificonlineinstrumentsusedduringthe•audit (Such as make, model, type, parameters measured, calibration details, etc).

5.4.6 Description of the PlantUnder the description of the plant, energy audit report shall include the information pertaining to:

General overview of the plant which include location details, capacity details, technology used, type of plant, •type of fuel used.Processdescription–briefdescriptionofpowergenerationprocess,processflowdiagram.•Salient features of the plant – facility layout, water sources, fuel source, coal linkages, power evacuation, etc.•

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Brief description about the major equipment such as boiler, turbines, cooling system, pumps and fans – such as •type, make, model, capacity, year etcSalientdesignfeaturesonheatrates,efficiencies,etc•Salient operational features of the plant.•

Energyconsumptionprofileenergymanagementsystems:The following shall be included:

Energy consumption pattern: The audit report shall contain data for the year proceeding to the year for which •energy audit report is being prepared.Efficiencyonthedetailsofenergyconsumedandspecificenergyconsumption/unitofgenerationasapplicable•for TPSSpecificenergyconsumptiondataforunitofproductionintermskcal/kWh,kgoffuel/unitofproduction,etc.•

5.4.7 Action Plan PreparationThe auditor shall summarise all recommendations and provide action plan for implementation where the recommendations are prioritised. This should be discussed with the energy manager or the concerned plant personnel. The action plan shall include:

Preparation of detailed techno-economics of the selected measures in consultation with energy manager / plant •personnelAmonitoringandverificationprotocoltoquantityonannualbasistheimpactofeachmeasurewithrespectto•energy conservation and cost reduction. A time schedule agreed upon by the designated consumer of selected measures taking into consideration •constraintssuchasavailabilityoffinance,resourcesandavailabilityofproposedequipment.

5.4.8 Suppliers/Vendors/Contractor ListThe energy audit report shall provide the source for proposed recommendations such as suppliers / vendors / contractors for implementation of recommendations. The details shall include name and address, contact person, contact details such as phone, fax, email etc.

5.4.9 AppendicesAppendices include background material that is essential for understanding the calculations and recommendations and may include:

Facility layout diagrams•Process diagrams•Referencegraphsusedincalculations,suchasmotorefficiencycurves•Data sets that is large enough to clutter to the text of the report.•Detailedspecifications,designdetails,testcertificates,performancecovers•Detailed calculations.•

5.5 Short Form Audit Report Many energy auditors use a short form audit report. A short report is essential when the cost of the audit is a factor. Writing a long report can be time-consuming and it increases the cost of an audit. The short form report is useful when an on-the-spot audit report is required because the auditor can use a lap-top computer to generate it. It is also an excellent format for preliminary audit reports when the company will have to do further analysis before implementing most of the recommendations.

However, some short form audit reports have drawbacks. When a report is ultra-short and only provides the basic numbers, the reader will not have a memory crutch if he returns to the report sometime after the auditor has left.


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Since some clients do not implement the recommendations immediately, but wait until they gather the necessary capital, an ultra-short form report may lose its value. Therefore, some explanatory text is critical for a user-friendly short form report. The executive summary described above could serve as a model short form audit report.

5.6 Feedback Customer feedback is as appropriate in energy auditing as in any other endeavour. An easy way to get feedback is to give the customer a questionnaire to evaluate the audit service and the report. It is important that the questionnaire beeasytofillout.Ifittakesmuchtimetoreadandfillout,theclientswon’tshowinterestinit.

5.7 ConclusionMany audit reports are not user-friendly. Most often, they are either lengthy documents full of explanations, justificationsandcalculations,ortheyareveryshortwithlittlebackupinformation.Ifareportissolongthatitintimidates your readers by its very size, they may set it aside to read when they have more time. If it is so short that needed information is lacking, the readers may not believe the results. Writing a user-friendly audit report is an important step in promoting implementation of audit recommendations. We hope that some of our report writing suggestions and some of our experiences can help others produce their own successful user-friendly energy audit reports.

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SummaryAnenergyauditisaperiodicexaminationofanenergysystemtoensurethatenergyisbeingusedasefficient•as possible.Thefirstthingtokeepinmindwhenyoustarttowriteanythingistoknowwhoyouraudienceisandtailor•your writing to that audience.Use a simple, direct writing style while preparing an audit report. Simplify the writing by using active voice.•Avoid technical terminology that your reader may not understand while preparing the audit reports.•A major problem with many reports is a failure to explain the assumptions underlying the calculations, therefore •explain your assumption clearly.Typographical and spelling errors devalue an otherwise good product so proofread your report carefully.•Use the same terminology throughout the report so that the reader is not confused.•After successfully carried out energy audit a good audit report should be presented to the top management for •effective communication and implementation.The format for audit report can be suitablymodified for specific need applicable for a particular type of•industry.A short report is essential when the cost of the audit is a factor. Writing a long report can be time-consuming •and it increases the cost of an audit.

ReferencesLampert, M., 2009. • Attention and Recombinance: A Cognitive-Semantic Investigation Into Morphological Compositionality in English, Peter Lang.Thumann, A., Younger, J. W. & Niehus, T., 2010. • Handbook of Energy Audits, 8th ed. The Fairmont Press, Inc.WRITING USER-FRIENDLY ENERGY AUDIT REPORTS• [Pdf] Available at: <http://repository.tamu.edu/bitstream/handle/1969.1/91861/ESL-IE-94-04-31.pdf?sequence=1> [Accessed 5 July 2013].Reporting for Implementation• [Pdf] Available at: <http://www.energy.gov.za/EEE/Projects/Building%20Energy%20Audit%20Training/Training%20Modules/Building%20Energy%20Auditing%20Module%2011_final.pdf>[Accessed5July2013].Types of audit reports Masterclass by Kaplan• [Video online] Available at: <http://www.youtube.com/watch?v=Ffov8F2mNsI> [Accessed 5 July 2013].ACCA F8INT - 1. Audit reports• [Video online] Available at: <http://www.youtube.com/watch?v=ZnZFycIm9oY> [Accessed 5 July 2013].

Recommended ReadingCascarino, E. R., 2012. • Auditor's Guide to IT Auditing, 2nd ed. John Wiley & Sons.Switzer, M. S., 2007. • Internal Audit Reports Post Sarbanes-Oxley: A Guide to Process-Driven Reporting, John Wiley & Sons.Financial Report and Audited Financial Statements• , United Nations Publications.


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Self Assessment____________isaperiodicexaminationofanenergysystemtoensurethatenergyisbeingusedasefficientas1. possible.

Energy audita. Energy reportb. Energy checkc. Energy inspectiond.

The report shall also list the energy audit team involved in the study along with their __________________.2. documentationa. certificationb. credentialsc. qualificationd.

The ______________summary should contain a brief description of the audit.3. manageriala. administrativeb. executivec. directoriald.

Customer ______________is as appropriate in energy auditing as in any other endeavour.4. responsea. outputb. opinionc. feedbackd.

Writing a user-friendly audit report is an important step in promoting implementation of audit 5. _______________.

recommendationsa. correctionsb. alterationc. improvementd.

State which of the following statements is true.6. The name of the auditor should not be written on the title sheet.a. The name of the auditor should be written on the title sheet.b. The name of the auditor should not be included in the report.c. The name of the auditor should be written at the end of the report.d.

State which of the following statements is false.7. Appendices include background material that is essential for understanding the calculations and a. recommendations.When writing an industrial audit report, the readers can range from the company president to the head of b. maintenance.Do not use a simple, direct writing style while preparing an audit report.c. Avoid technical terminology that your reader may not understand while preparing the audit reports.d.

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State which of the following statements is false.8. A short report is essential when the cost of the audit is a factor.a. Typographical and spelling errors devalue an otherwise good product.b. The major problem with many reports is a failure to explain the assumptions underlying the calculations, c. therefore explain your assumption clearly.A short report is essential when the time consumed for the audit is a factor.d.

The title page of the report shall contain which of the following?9. Date of Reporta. Executive summaryb. Table of contentsc. Abbreviationsd.

The executive summary should not include which of the following?10. Name of client, location of facility or plant auditeda. Name of the auditorb. Objectives of auditc. Key systems and equipment analysedd.


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Case Study I

Power & Energy Audit in Commercial Buildings and Corporate Offices

About The InstallationPower & energy audit in buildings like banks, hospitals are getting increasingly popular as these are 24 X 7 and critical in nature, thus uninterruptible power supply and its reliability are the top priority issues. This detailed study iscarriedouttostudypowerqualityandenergyconservationpotentialoftheentirefacilityatCorporateOfficeandmain building of one of the leading public sector bank in India.

Electricity is received at 11 KV from the substation of the state electricity board. The sanctioned contract demand for the facility is 1450 KVA, but in April 2007, the demand has exceeded to 1478 KVA. Present power factor is varying between 0.94 and 0.95.

About The AssignmentPower & Energy Audit has been carried out considering BEE & ECBC guidelines, IS guidelines and IE rules. In this audit, main objective has been to study:

HT/LT substations with DG sets and its adequacy•Installed UPS systems and its performance•Adequacy of the back-up/redundancy•Energy conservation in: air-conditioning, lighting, pumping and any other area•Power quality and associated problems & thoroughly evaluating earthing system•

Overallfocushasbeenonmeasurements,quantificationandanalysisofenergytransmission&usage,identificationandquantificationof losses indistributionsystem,Air-conditioningsystem,pumpingsystemetcandfinally toevolvesolutionstoimproveenergyefficiency.Harmonicstudyhasbeencarriedoutforthemaintransformer&uninterruptible power supply.

ObservationsOverall balance in terms of energy, KWH and cost has been carried out. Variation in KWH consumption, voltage, current and harmonics has been studied.

Findings & RecommendationsAveragebilledpowerfactoris0.94to0.95.SignificantsavingwillbeachievedbyincreasingthePFfrom0.94•to unity (1) at the distribution side by installing additional capacitors. This will results in 7 to 8% savings in the electricity bill with payback in few months.Sometimes it is observed that maximum demand is exceeding the contract demand, therefore it is recommended •to install maximum demand (MD) controller to reduce the MD and hence penalty is avoided and demand charges are reduced.The motors having % loading less than 50 % are recommended to make changeover of connections from delta •to star and replace FTL copper chokes with electronic chokes.Numbers of window air conditioners & split A/C units have been installed as per the requirement. It is •recommended to transfer this air conditioning load to centralized air conditioning system as the KW/TR of window air conditioners is high as compared to water cooled condenser systems. This is possible by installation of additional AHUs. This will result in 5 to 6% saving in total electricity bill with a payback of less than year.The recorded value of percentage THD voltage of about 5 % and percentage THD current of about 38 % for •transformer-1 and 5.2 % and percentage THD current of about 18.2 % for transformer-2, which were recorded under full load conditions are not within the IEEE-519 guidelines for harmonics permits the Vthd upto 3 % and Ithd upto 15 % as reasonable limit, when measurements are carried out with the capacitors switched ON.

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QuestionsIn this audit what are the main objectives that has been studied?1. AnswerThe main objectives studied in this audit are as follows:

Installed UPS systems and its performance.•HT/LT substations with DG sets and its adequacy.•Adequacy of the back-up/redundancy.•Energy conservation in: air-conditioning, lighting, pumping and any other area.•Power quality and associated problems & thoroughly evaluating earthing system.•

What is energy audit?2. AnswerAnenergyauditisaperiodicexaminationofanenergysystemtoensurethatenergyisbeingusedasefficientaspossible.Itisoneofthefirsttaskstobeperformedintheaccomplishmentofaneffectiveenergycostcontrolprogram.

How can be saving achieved in the electricity bill?3. AnswerSignificant savingwillbeachievedby increasing thePF from0.94 tounity (1) at thedistribution sidebyinstalling additional capacitors.

This will results in 7 to 8% savings in the electricity bill with payback in few months.•


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Case Study II

Energy Saving for Fume Exhaust System Blower in 4HI Cold Rolling Mill

Motor rating: 3-ph AC Induction motor of 50 HP, 415 V, 1460 RPMPrevious system was build up with following devices-

Star Delta starter for motor operation•Belt pulley system for power transmission to fan.•

ObservationsBlower fan kept working continuously at a constant speed.•Blower fan working at full speed irrespective of fumes generated or not at rolling mill.•

Process study & ExperimentationFumegenerationwasverylowduringfirstpassrolling.•No fumes generation during coil handling.•Actual rolling duration at full and hence maximum fume generation takes place only 60% of the total duration •of mill operation.Manual control of inlet valve of blower fan was impractical.•

Present SystemAC electronics speed variable drive installed.•Drive operation studied & software designed accordingly, optimise the power consumption during idling of •mill.Further optimisation done to reduce the power consumption in accordance with fumes generation.•

Merits of New SystemSmooth start resulting in increased life of motor and mechanical system.•Energy saving due to speed / voltage variation during idling of the mill.•

Costbenefitsanalysis:Previous System (Without Drive) : Speed=50 Hz, Kw (Consumption)=30•Present System (With Drive) :Speed=0-20-45Hz, Kw (Consumption)=15•Energy Saving per year : 15 Kw X 20 X 300 = 90,000 KwH•Investment : Rs. 1,50,000 /-•Saving in Rupee Terms / Year : 90,000 X 4 = 3,60,000 /-•

Questions:What are the advantages of new system?1. What were the observations with the old system?2. What were the disadvantages of Star Delta starter for motor operation?3.

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Case Study III

Energy Management Information System (EMIS)

IntroductionThe Energy Management Information System (EMIS) demonstration and study when conducted will likely focus on an analysis of the existing electrical system circuits in a facility. Thus, the purpose of the study would be to inspect specificloads,utilizingdigitalmeters,inordertodemonstratetheeconomicandtechnicalvalueofanEMISforthis particular application.

Such analysis can be performed in a variety of ways. An example would be to install electrical measuring devices particularly designed for that purpose on existing circuits.

Kilowatt-Hour UsageKilowatt-hourusagereflectselectricalenergyconsumptiononanhour-by-hourbasis.Italsoactsasaproxyforelectrical demand which is billed monthly on an instantaneous basis, and is measured at the peak load in kilowatts inanygivenfifteenminuteintervalswithinthemonth.Datais takenall throughamonthofMay,whichshowconsistent patterns, and can, therefore, provide some consistent indicators of the behaviour of the electrical loads under examination.

The kitchen utilizes couple of circuits, and the facility may have a laundry that could utilize one. All three meters were connectedtothefeederstothepanels,andreflecttheconsumptionoftheentirepanel,butdonotdirectlymeasureany branch circuit that supplies individual loads. For few days it was observed that some power consumption which appearedtobequitepredictable.Forthekitchen,eachcircuitshowsabaseloadofapproximatelyfivekilowatts(kW) for the late night/early morning hours from 11 p.m. to 5 a.m. Between 5 a.m. and 11 p.m., the load climbs to a base of approximately 15 kW consistently, set of demand peaks of approximately 30 kW, 25 kW and 20 kW that occur around 10:00 a.m., 2 p.m. and 7 p.m.

As the data is relatively consistent on all three days, we can reasonably conclude that the three peaks are a regular phenomena, and are most likely attributable to the presence of an electrical booster that provides sanitary cycle rinse water to the dishwasher at a temperature of 185 degrees Fahrenheit. The domestic water supply is normally maintained at temperatures of 120° to 140° Fahrenheit for the balance of the facility, and must, therefore, be separately boosted in order to achieve the legally mandated higher temperature for dishwashing. As this is done through electrical means, the cost of the power for this individual device can be reasonably determined as follows:

The booster appears to be in use for approximately 9 hours per day with an added demand of some 15 kW. At 11 cents per kWh for energy plus approximately 3 cents for distribution with $4.55 for demand, the cost per hour is 14 cents per kW per hour plus the monthly incremental demand. This calculates to $1.26 per hour or $11.34 per day. On a monthly basis, this adds approximately $351 to consumption with an extra $68.25 for demand. The total effect of this load is approximately $421 per month. If this load were supplied by stored water from a co-generator supplied reserve tank, the monthly expense could possibly be eliminated.

The total expense associated with the kitchen alone is approximately $1400 for consumption (kWh) with and additional $135 attributable to demand for a total monthly cost to be approximately $1535. The laundry was measured as a single circuit and its pattern is quite consistent. The laundry shows a 24 hour base load of approximately 1 kilowatt, increasing to 5 kW for the period from 7 a.m. to 5 p.m. after which the load tapers off gradually to 1 kW somewhere around 10 p.m. This load does not exhibit any unusual peaks and indicates that the machines are used fairly continuously for the bulk of the day.

Calculating the cost of electricity for the laundry, we estimate 1 kW of 24-hour base load with an additional 4 kW of peak load running for 12 hours per day. Using the same kWh, distribution and demand costs, the electrical expense attributable to the laundry is $10.08 per day plus demand contribution of $22.75 each month. This amounts to a monthly expense of approximately $325 based upon the laundry alone. There may be ways to cut this expense, but thiswouldrequireanexaminationofbothlaundryoperationsaswellasmachineefficiency.


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ConclusionThe written analysis provides a sample of the types and quality of information available to a user through an EMIS. For even a limited study such as the one conducted for that site on the kitchen and laundry loads, appropriate use of this information could yield some degree of savings through the ability of the EMIS to pinpoint high consumption patterns or other abnormalities of the electrical load.

This demonstrates that on even a limited basis, the EMIS can act as tool to identify excess energy costs. Identify problem trends as they develop, and act as a cost-center accounting tool to determine the ongoing expense of particular areas of a given facility.

QuestionsWhat is Energy Management Information System?1. Why is EMIS important?2. What are the elements of EMIS?3.

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Bibliography

ReferencesACCA F8INT - 1. Audit reports• [Video online] Available at: <http://www.youtube.com/watch?v=ZnZFycIm9oY> [Accessed 5 July 2013].An Introduction to Microcontrollers [Video online] Available at: <http://www.youtube.com watch?v •=CmvUY4S0UbI> [Accessed 5 July 2013].Capehart, L. B., Turner, C. W. & Kennedy, J. W., 2008. • Guide To Energy Management, 6th ed. The Fairmont Press, Inc.Demler, J. M., 1991. • High-Speed Analog-To-Digital Conversion, Academic Press.Doty, S. & Turner, C. W., 2009. • Energy Management Handbook, 7th ed. The Fairmont Press, Inc.Dr. Hui, C. M. S., 2009. • Energy Calculations [Pdf] Available at: <http://www.mech.hku.hk/bse/MEBS6006/mebs6006_0910_05-energy.pdf> [Accessed 5 July 2013].Drew, B., 2011. • Control Systems Engineering - Lecture 1 – Introduction [Video online] Available at: <http://www.youtube.com/watch?v=g53tqrBjIgc> [Accessed 5 July 2013].Electromechanical Transducers• [Pdf] Available at: <http://www.physics.udel.edu/~yji/PHYS245/lab/Lab%2010.pdf> [Accessed 5 July 2013].Energy Methods in Structural Analysis• [Pdf] Available at: <http://www.facweb.iitkgp.ernet.in/~baidurya/CE21004/online_lecture_notes/m1l1.pdf> [Accessed 5 July 2013].Gridling, G. & Weiss, B., 2007. • Introduction to Microcontrollers [Pdf] Available at: <http://ti.tuwien.ac.at/ecs/teaching/courses/mclu/theory-material/Microcontroller.pdf> [Accessed 5 July 2013].Groover, M. P., 2008. • Unit 3 Industrial Control Systems [Pdf] Available at: <http://www.nuigalway.ie/staff-sites/david_osullivan/documents/unit_3_industrial_control_systems.pdf> [Accessed 5 July 2013].Harsh, B. S., • MANAGEMENT INFORMATION SYSTEMS [Pdf] Available at: <http://departments.agri.huji.ac.il/economics/gelb-manag-4.pdf> [Accessed 5 July 2013].Heijden, V. D. H. & Heijden, G. J., 2009. • Designing Management Information Systems, Oxford University Press.Introduction to Management Information Systems• [Pdf] Available at: <http://www.mu.ac.in/mis.pdf> [Accessed 5 July 2013].Lampert, M., 2009. • Attention and Recombinance: A Cognitive-Semantic Investigation Into Morphological Compositionality in English, Peter Lang.Patranabis, D., 2010. • Prin of Industrial Instrumentation 3e, 3rd ed. Tata McGraw-Hill Education.Piercy, N., 1987. • Management Information Systems: The Technology Challenge, Taylor & Francis.Prof. Jana, A. K., 2012. • Mod-01 Lec-36 Lecture-36-Instrumentation: General Principles of Measurement Systems [Video online] Available at: <http://www.youtube.com/watch?v=moSUpIRCKMk> [Accessed 5 July 2013].Prof. Jana, A. K., 2012. • Mod-01 Lec-37 Lecture-37-Instrumentation: General Principles of Measurement Systems (Contd…2) [Video online] Available at: <http://www.youtube.com/watch?v=FVSCMdk-SFQ> [Accessed 5 July 2013].Prof. Mahanty, B., 2011. • 1 - Introduction – I [Video online] Available at: <http://www.youtube.com/watch?v=5JMkdGQCm4k&list=PLhOZYDWQab_bUIugIkQhacRw0OmKN_HkN> [Accessed 5 July 2013].Prof. Mahanty, B., 2011. • 2 - Introduction – II [Video online] Available at: <http://www.youtube.com/watch?v=JWZ6VAzZ9K0&list=PLhOZYDWQab_bUIugIkQhacRw0OmKN_HkN> [Accessed 5 July 2013].Rangan, C. S., 1997. • Instrumentation Devicesand Systems, 2nd ed. Tata McGraw-Hill Education.Reporting for Implementation• [Pdf] Available at: <http://www.energy.gov.za/EEE/Projects/Building%20Energy%20Audit%20Training/Training%20Modules/Building%20Energy%20Auditing%20Module%2011_final.pdf>[Accessed5July2013].Singh, S. K., 2003. • Industrial Instrumentation & Control,2e, Tata McGraw-Hill Education.


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Structural Analysis by Energy Methods• [Video online] Available at: <http://www.youtube.com/watch?v=AzBS_oucC5A> [Accessed 5 July 2013].Structural Analysis by Energy Methods YouTube• [Video online] Available at: <http://www.youtube.com/watch?v=rbDM2ArhXyc> [Accessed 5 July 2013].Thumann, A., Younger, J. W. & Niehus, T., 2010. • Handbook of Energy Audits, 8th ed. The Fairmont Press, Inc.Transducers and Applications• [Pdf] Available at: <http://benp2183.mazran.com/download/nota_kelas/chap4_transducers%20ver3.pdf> [Accessed 5 July 2013].Types of audit reports Masterclass by Kaplan• [Video online] Available at: <http://www.youtube.com/watch?v=Ffov8F2mNsI> [Accessed 5 July 2013].WRITING USER-FRIENDLY ENERGY AUDIT REPORTS• [Pdf] Available at: <http://repository.tamu.edu/bitstream/handle/1969.1/91861/ESL-IE-94-04-31.pdf?sequence=1> [Accessed 5 July 2013].

Recommended ReadingBakshi, A.V. & Bakshi, U. A., 2008. • Electronic Measurements And Instrumentation, Technical Publications.Basic Concepts of Measurement• , CUP Archive.Capehart, L. B., Turner, C. W. & Kennedy, J. W., 2002. • Guide to Energy Management, Fourth Edition, 4th ed. CRC Press.Carstens, R. J., 1993. • Electrical sensors and transducers, Regents/Prentice Hall.Cascarino, E. R., 2012. • Auditor’s Guide to IT Auditing, 2nd ed. John Wiley & Sons.Cho, H., 1984. • Computer-Based Energy management systems: Technology and Applications: Technology and Applications, Elsevier.Davis, 2001. • Management Information Systems, Tata McGraw-Hill Education.Financial Report and Audited Financial Statements• , United Nations Publications.Grimble, J. M., 2006. • Robust Industrial Control Systems: Optimal Design Approach for Polynomial Systems, John Wiley & Sons.Guarracino, F. & Walker, G. H. A., 1999. • Energy methods in structural mechanics: a comprehensive introduction tomatrixandfiniteelementmethodsofanalysis, Thomas Telford.Kelkar, S. A., 2003. • Management Information Systems: A Concise Study, PHI Learning Pvt. Ltd.Lipovski, J. G., 2004. • Introduction to Microcontrollers: Architecture, Programming, and Interfacing for the Freescale 68HC12, 2nd ed. Academic Press.Shajahan, S., 2004. • Management Information Systems, New Age International.Switzer, M. S., 2007. • Internal Audit Reports Post Sarbanes-Oxley: A Guide to Process-Driven Reporting, John Wiley & Sons.Weiss, J., 2010. • Protecting Industrial Control Systems from Electronic Threats, Momentum Press.

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Self Assessment Answers

Chapter Ia1. b2. c3. d4. a5. b6. c7. d8. a9. b10.

Chapter IIa1. b2. c3. d4. a5. b6. c7. d8. a9. b10.

Chapter IIIa1. b2. c3. a4. d5. a6. a7. b8. c9. d10.


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Chapter IVa1. b2. c3. d4. a5. a6. b7. c8. a9. d10.

Chapter Va1. b2. c3. d4. a5. b6. c7. d8. a9. b10.

Energy Instrumentation and Information Analysisjnujprdistance.com/assets/lms/LMS JNU/MBA/MBA - Energy Management/Sem IV/Energy...This book is a part of the course by Jaipur National

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