Instrumentation and Measurement Introduction

8/18/2019 Instrumentation and Measurement Introduction

1/18

U-ECE

NEE4304 Instrumentation & Measurement

2/11/201

ond 2015-2016tructor: Nasser Ismail

ENEE4304Instrumentation and

MeasurementsL1

Introduction

Introduction to Measurements

Measurement techniques have beenof immense importance ever sincethe start of human civilization,

When measurements were firstneeded to regulate the transfer ofgoods in barter trade to ensure that

exchanges were fair.

The industrial revolution during thenineteenth century brought about arapid development of newinstruments and measurementtechniques to satisfy the needs ofindustrialized production techniques.

http://www.google.jo/imgres?imgurl=http://4.bp.blogspot.com/-VH8jKYdsQY0/TctHg0iaspI/AAAAAAAAARw/Ws0ap_GWGnk/s1600/Online-Measurement-Tools.jpg&imgrefurl=http://iwasafatbride.blogspot.com/2011/05/measurements.html&usg=__yj3GxiPM0yWN4k1GP4lXgy3MIcE=&h=600&w=900&sz=364&hl=ar&start=9&zoom=1&tbnid=1FpOv4yIVD5DUM:&tbnh=97&tbnw=146&ei=hGyJTs_PDujd4QSf6LyKDw&prev=/search?q=measurements&um=1&hl=ar&sa=N&tbm=isch&um=1&itbs=1http://www.google.jo/imgres?imgurl=http://4.bp.blogspot.com/-VH8jKYdsQY0/TctHg0iaspI/AAAAAAAAARw/Ws0ap_GWGnk/s1600/Online-Measurement-Tools.jpg&imgrefurl=http://iwasafatbride.blogspot.com/2011/05/measurements.html&usg=__yj3GxiPM0yWN4k1GP4lXgy3MIcE=&h=600&w=900&sz=364&hl=ar&start=9&zoom=1&tbnid=1FpOv4yIVD5DUM:&tbnh=97&tbnw=146&ei=hGyJTs_PDujd4QSf6LyKDw&prev=/search?q=measurements&um=1&hl=ar&sa=N&tbm=isch&um=1&itbs=1


2/18

U-ECE


2/11/201


Applications of Measurement Systems1. Regulating trade

2. Monitoring to allow human beings to take someaction accordingly

3. Use as part of automatic feedback controlsystems

Remember The Five Senses

See

Hear

Touch

Taste

Smell


3/18

U-ECE


2/11/201


Standardization of Units

Establishment of standards for themeasurement of physical quantitiesproceeded in several countries atbroadly parallel times, and inconsequence, several sets of unitsemerged for measuring the samephysical variable.

An internationally agreed set ofstandard units (SI units or Syst`emesInternationales d ’Unit ´es) has been

defined, and strong efforts are beingmade to encourage the adoption ofthis system throughout the world.

Standard Units

http://www.google.jo/imgres?imgurl=http://www.beaconlearningcenter.com/weblessons/measuringtools/groc_scale.jpg&imgrefurl=http://www.beaconlearningcenter.com/weblessons/measuringtools/default.htm&usg=__t6f5VssfotwsLgjdQgH8FHPFb0w=&h=364&w=264&sz=18&hl=ar&start=7&zoom=1&tbnid=RLiydr43jbvEQM:&tbnh=121&tbnw=88&ei=IneJTpH4Caje4QSFmeC9Dw&prev=/search?q=measuring+weight&hl=ar&sa=N&gbv=2&tbm=isch&itbs=1http://www.google.jo/imgres?imgurl=http://www.beaconlearningcenter.com/weblessons/measuringtools/groc_scale.jpg&imgrefurl=http://www.beaconlearningcenter.com/weblessons/measuringtools/default.htm&usg=__t6f5VssfotwsLgjdQgH8FHPFb0w=&h=364&w=264&sz=18&hl=ar&start=7&zoom=1&tbnid=RLiydr43jbvEQM:&tbnh=121&tbnw=88&ei=IneJTpH4Caje4QSFmeC9Dw&prev=/search?q=measuring+weight&hl=ar&sa=N&gbv=2&tbm=isch&itbs=1


4/18

U-ECE


2/11/201


Fundamental Units andSupplementary Fundamental Units

Derived Units


5/18

U-ECE


2/11/201


Purpose and performance ofmeasurement systems

• We begin by defining a process as a system which generates information .• Examples are a chemical reactor, a jet fighter, a gas platform, a submarine,

a car, a human heart, and a weather system.• Table lists information variables which are commonly generated by

processes:• For example: a car generates displacement, velocity and acceleration

variables, and a chemical

• We then define the observer as a person who needs thisinformation from the process.

• This could be the car driver, the plant operator or the nurse.• The purpose of the measurement system is to link the observer to

the process,• Here the observer is presented with a number which is the current

value of the information variable.• We can now refer to the information variable as a measured

variable .• The input to the measurement system is the true value of the

variable; the system output is the measured value of the variable.• In an ideal measurement system, the measured value would be

equal to the true value.


6/18

U-ECE


2/11/201


Elements of a Measurement Systems

In simple cases, the system can consistof only a single unit that gives anoutput reading or signal according tothe magnitude of the unknown.

However, in more complexmeasurement situations, a measuringsystem consists of several separateelements.

These components might be containedwithin one or more boxes, and theboxes holding individual measurement

elements might be either closetogether or physically separate.


In simple cases, the system canconsist of only a single unit thatgives an output reading or signalaccording to the magnitude ofthe unknown.

However, in more complexmeasurement situations, a

measuring system consists ofseveral separate elements.

These components might becontained within one or moreboxes, and the boxes holdingindividual measurementelements might be either closetogether or physically separate.

http://www.google.jo/imgres?imgurl=http://www.beaconlearningcenter.com/weblessons/measuringtools/groc_scale.jpg&imgrefurl=http://www.beaconlearningcenter.com/weblessons/measuringtools/default.htm&usg=__t6f5VssfotwsLgjdQgH8FHPFb0w=&h=364&w=264&sz=18&hl=ar&start=7&zoom=1&tbnid=RLiydr43jbvEQM:&tbnh=121&tbnw=88&ei=IneJTpH4Caje4QSFmeC9Dw&prev=/search?q=measuring+weight&hl=ar&sa=N&gbv=2&tbm=isch&itbs=1http://www.google.jo/imgres?imgurl=http://www.beaconlearningcenter.com/weblessons/measuringtools/groc_scale.jpg&imgrefurl=http://www.beaconlearningcenter.com/weblessons/measuringtools/default.htm&usg=__t6f5VssfotwsLgjdQgH8FHPFb0w=&h=364&w=264&sz=18&hl=ar&start=7&zoom=1&tbnid=RLiydr43jbvEQM:&tbnh=121&tbnw=88&ei=IneJTpH4Caje4QSFmeC9Dw&prev=/search?q=measuring+weight&hl=ar&sa=N&gbv=2&tbm=isch&itbs=1


7/18

U-ECE


2/11/201


Elements of a Measurement Systemscomparison from different references

MeasuredVariable

“ Measurand ”

Sensor Variable

ConversionElement

SignalProcessing

Or Conditioning

Use of Measurement atRemote Location

SignalTransmission

Presentation /Recording Unit

Output


[Figliola, Theory and Design of Mechanical Measurements]


8/18

U-ECE


2/11/201


Single Channel Measuring System

Structure of Measuring System

Sensing Element (Sensor):This is in contact with the process and gives an output whichdepends in some way on the variable to be measured (measurand)If there is more than one sensing element in a system, the elementin contact with the process is termed the primary sensing element ,the others secondary sensing elements .For most but not all sensors, this function is at least approximatelylinear.


9/18

U-ECE


2/11/201


Instrumentation 17

Different measurement systems

Sensing PrinciplesThe interaction of physical parameters with each other —most notably electricity withstress, temperature and thermal gradients, magnetic fields, and incident light —yieldsa multitude of sensing techniques which may be applied in measurements

Transductive ( ي ل و (ح

Piezoelectric

Thermoelectric

Photoelectric

etc.

Constitutive ( س) س

Resistive

Capacitive

Inductive

Etc.

Pressure

Temperature

Light

Current

Voltage

Other.

Transducer

Pressure

Temperature

Light

R, C. L, etc

Sensor


10/18

U-ECE


2/11/201


Examples Sensors

Liquid Mercury

Input: Temperature

Output: Mercury volume

Are these linear sensors?

Thermocouple

Input: Temperature

Output: Voltage

Strain gauge

Input: Strain

Output: Electric resistance

Examples Sensors

Liquid Mercury Thermometer

Measured Variable: Temperature

Sensor: Liquid Mercury

Variable Conversion Element: Stem

Signal Presentation Element: Display Scale


11/18

U-ECE


2/11/201


Signal conditioning elementThis takes the output of the sensing element and converts it into aform more suitable for further processing, usually a d.c. voltage, d.c.current or frequency signal.

Improve the quality of the output of a measurement system.Examples are:

Deflection bridge which converts an impedance change into a voltage change Amplifier which amplifies millivolts to voltsOscillator which converts an impedance change into a variable frequencyvoltage.

Other signal processing element are those that filter out inducednoise and remove mean levels etc. In some devices, signalprocessing is incorporated into a transducer, which is then known as

a transmitter.

Signal processing elementThis takes the output of the conditioning element and converts it intoa form more suitable for presentation.Examples are:

Analogue-to-digital converter (ADC) which converts a voltageinto a digital form for input to a computer Computer (digital signal processor “DSP ” , Microcontroller , FieldProgrammable Gate Array “FPGA ” )which calculates themeasured value of the variable from the incoming digital data.

Typical calculations are:Computation of total mass of product gas from flow rate anddensity data Integration of chromatograph peaks to give thecomposition of a gas streamCorrection for sensing element non-linearity.


12/18

U-ECE


2/11/201


Data presentation elementThis presents the measured value in a form which can

be easily recognized by the observer.It may be omitted altogether when the measurement isused as part of an automatic control system.

It takes the form either of a signal presentation unit or ofa signal-recording unit.

Examples are:Simple pointer – scale indicator Chart recorder

Alphanumeric displayVisual display unit (VDU) suchas an LCD display

Elements of a Measurement Systems :Variable Coversion Element

Needed where the output variable of aprimary sensor is in an inconvenient formand has to be converted to a moreconvenient form.

The displacement-measuring strain gaugehas an output in the form of a varying

resistance. The resistance change cannotbe easily measured and so it is convertedto a change in voltage by a bridge circuit,which is a typical example of a variableconversion element.

In some cases, the primary sensor andvariable conversion element arecombined, and the combination is knownas a transducer.


13/18

U-ECE


2/11/201


Elements of a Measurement Systems :Signal Transmission

Needed when the observation orapplication point of the output of ameasurement system is somedistance away from the site of theprimary transducer.

It has traditionally consisted ofsingle or multi-cored cable, which isoften screened to minimize signalcorruption by induced electricalnoise.

Fibre-optic cables are being used inever increasing numbers in moderninstallations because of their lowtransmission loss andimperviousness to the effects ofelectrical and magnetic fields.

Elements of a Measurement System

MeasuredVariable

Sensor Variable

ConversionElement

SignalProcessor



14/18

U-ECE


2/11/201



Sensor Variable

ConversionElement

SignalProcessor

SignalTransmission


Transducer

MeasuredVariable


Sensor Variable

ConversionElement

SignalProcessor

SignalTransmission


Transducer

MeasuredVariable

Transmitter


15/18

U-ECE


2/11/201


Choosing appropriate measuring instruments Accuracy, resolution, sensitivity and dynamicperformance.

Environmental conditions that the instrument will besubjected to.

Measurement systems and instruments should bechosen that are as insensitive as possible to theoperating environment.

The extent to which the measured system will bedisturbed during the measuring process is anotherimportant factor in instrument choice.

For example, significant pressure loss can becaused to the measured system in some techniquesof flow measurement.

Instrumentation 30

Data Acquisition and Control• Data acquisition is the process by which physical

phenomena from the real world are transformed intoelectrical signals that are measured and converted into adigital format for processing, analysis, and storage by acomputer .

• In a large majority of applications, the data acquisition(DAQ) system is designed not only to acquire data, but toact on it as well. In defining DAQ systems, it is thereforeuseful to extend this definition to include the controlaspects of the total system .

• Control is the process by which digital control signals from thesystem hardware are convened to a signal format for use bycontrol devices such as actuators and relays. These devicesthen control a system or process. Where a system is referred toas a data acquisition system or DAQ system, it is possible that itincludes control functions as well.


16/18

U-ECE


2/11/201


Instrumentation 31

Physicalworld Sensing S/C ADC

Activation S/C DAC

Display andDecisionMaking

(PC, mP or PIC)

Hardware &Software

I n t e r

f a c e

PC Based Data AcquisitionSystem


17/18

U-ECE


2/11/201


33

Fundamentals of Data Acquisition A data acquisition and control system, built around the power

and flexibility of the PC, may consist of a wide variety of diversehardware building blocks from different equipmentmanufacturers.It is the task of the system integrator to bring together these

individual components into a complete working system.The basic elements of a data acquisition system, as shownin the functional diagram of Figure 1.1, are as follows:

Sensors and transducersField wiringSignal conditioningData acquisition hardware

PC (operating system)Data acquisition software

34

Field wiring and communications cabling/

• Field wir ing

represents the physic a l con nect ion f rom thet ransdu cer s and sensors to the s igna l cond i t ion inghardw are and/or da ta acquis i t ion hardware .

When the signal conditioning and/or data acquisitionhardware is remotely located from the PC, then the fieldwiring provides the physical link between these hardware

elements and the host computer.If this physical link is an RS-232 or RS-485

communications interface, then this component of thefield wiring is often referred to as communicationscabling.


18/18

U-ECE


2/11/201

35

Field wiring and communications cabling/FYI

• Field wir ing

Since field wiring and communications cabling oftenphysically represents the largest component of the totalsystem, it is most susceptible to the effects of externalnoise, especially in harsh industrial environments.The correct earthing and shielding of field wires andcommunications cabling is of paramount importance inreducing the effects of noiseThis passive component of the data acquisition and controlsystem is often overlooked as an important integralcomponent, resulting in an otherwise reliable systembecoming inaccurate or unreliable due to incorrect wiringtechniques.

36

Signal conditioning• Electrical signals generated by transducers often need to

be converted to a form acceptable to the data acquisitionhardware, particularly the A/D converter which convertsthe signal data to the required digital format.

• In addition, many transducers require some form ofexcitation or bridge completion for proper and accurateoperation.

• The principal tasks performed by signal conditioning are:• Filtering• Amplification• Linearization• Isolation• Excitation

Instrumentation and Measurement Introduction

Documents