Week 1(Instrumentation and measurement)

7/23/2019 Week 1(Instrumentation and measurement)

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Instrumentation andMeasurement

Department of Mechanical Engineering

Air University


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Subject Title: Measurement and InstrumentationSubject Code:ME 312Credit Hours:2 (2-0-2)

Prerequisites:N/A

Instructor: Akhtar Hanif

Contact Info:

E-mail:[email protected]

Office:Room 202, 2nd Floor, IAA Building

Mobile No:03335594074

Office Hours: ??????

08-Sep-14 ME 312 - Instrumentation and Measurement 2


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Text and Reference Books

Alan S. Morris, Measurement and Instrumentation

Principles, 3rd Edition

R. Figliola, and D. Beasley, Theory and Design for

Mechanical Measurements 5th Edition

Ernest O. Doebelin, Measurement Systems Application

and Design 5th

Edition Alok Barua, Fundamentals of Industrial Instrumentation

308-Sep-14 ME 312 - Instrumentation and Measurement


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Grading Policy

Quizzes 10%

Assignments 10%

Mid Semester Exam 35%

Final Semester Exam 45%

(Grading policy may be revised later. A semester project or an oral presentation maybe included)



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Course Objectives

To provide students with a fundamental understanding of theconcepts, principles, procedure and computations used by

engineers and technologists to analyze, select, specify, design

and maintain modern instrumentation & measurement systems

and develop an appreciation of the various types of devices in

common use in industry.



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Course Outline

Significance of measurement and measurement systems,

calibration, static and dynamic characteristics of instruments,sensitivity, range, accuracy precision, repeatability, and

uncertainty of instruments, measurement errors. Instruments and

sensors for measurement of length, force, torque, frequency,

pressure, flow and temperature, data acquisition through

computers, signal conditioning circuits, smart sensors,

optoelectronic sensors etc.



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Part I : Principles ofMeasurement

Text Book: Alan S. Morris, Measurement

and Instrumentation Principles, Third

Edition


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8

What is

Measurement and

Instrumentation?



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Introduction to Measurement

Importance of measurement techniques in the transfer of

goods in barter trade

Industrial revolution in the 19th century resulted into

development of new instruments and measurement

techniques

In last part of 20th century there has been a rapid growth

in electronics and computers and in turn has required aparallel growth in instruments and measurement

techniques.



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Introduction to Measurement

Modern production techniques dictate working to tighterand tighter accuracy limits and economic forces limit

productions cost.

This has resulted in the requirement of accurate andcheap instruments

In the past few years, the most cost-effective means of

improving instrument accuracy has been found in manycases to be the inclusion of digital computing powerwithin instruments themselves.


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1.1 Measurement Units

First measurement units used in barter trade to quantify theamounts being exchanged and to establish clear rulesabout the relative values of different commodities.

For purposes of measuring length, the human torso was aconvenient tool, and gave units of the hand, the foot andthe cubit.

Such measurement units are imprecise, varying as they dofrom one person to the next.

There has been a progressive movement towardsmeasurement units that are defined much moreaccurately.



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The latest standards for defining the units used for measuringa range of physical variables are:

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Physicalquantity

Standard Unit Definition

Length meter

The length of path travelled by lightin an interval of 1/299 792 458seconds

Mass kilogramThe mass of a platinumiridiumcylinder kept in the InternationalBureau of Weights and Measures,S`evres, Paris



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13

Physicalquantity


Time second

9.192631770 x 109 cycles of radiationfrom vaporized caesium-133 (anaccuracy of 1 in 1012 or 1 second in36 000 years)

Temperature kelvin

The temperature difference between

absolute zero and the triple point ofwater is defined as 273.16 kelvin



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Physicalquantity


Current ampere

One ampere is the current flowingthrough two infinitely long parallelconductors of negligible cross-sectionplaced 1 meter apart in a vacuum andproducing a force of 2 x 10 -7 newtonsper meter length of conductor

Matter mole The number of atoms in a 0.012 kg mass

of carbon-12



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Physicalquantity


LuminousIntensity

Candela

One candela is the luminous intensity in

a given direction from a source emittingmonochromatic radiation at afrequency of 540 terahertz (Hz x 1012)and with a radiant density in thatdirection of 1.4641 mW/steradian. (1steradian is the solid angle which,having its vertex at the center of a

sphere, cuts off an area of the spheresurface equal to that of a square withsides of length equal to the sphereradius)


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The early establishment of standards for the measurementof physical quantities proceeded in several countries atbroadly parallel times, and in consequence, several sets ofunits emerged for measuring the same physical variable.

For instance, length can be measured in yards, meters, orseveral other units. Apart from the major units of length,subdivisions of standard units exist such as feet, inches,

centimeters and millimeters, with a fixed relationshipbetween each fundamental unit and its subdivisions.



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SI units or Syst`emes Internationales dUnites: An

internationally agreed set of standard units. Strongefforts are being made to encourage the adoption

of this system throughout the world.

Imperial system is still widely used, particularly in

America and Britain



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Table 1.2 (a) Fundamental Units.

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Quantity Standard unit Symbol

Length metre m

Mass kilogram kg

Time second s

Electric current ampere A

Temperature kelvin K


Table: Supplementary Fundamental Units


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Table: Supplementary Fundamental Units

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Quantity Standard unit Symbol

Luminous intensity candela cd

Matter mole mol

Plane Angle radian rad

Solid Angle steradian sr



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Table: Derived Units.

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Quantity Standard Unit Symbol Derivation

formula

Area square metre m2

Volume cubic metre m3

Velocity metre per second m/s

Acceleration metre per second

squared m/s2

Angular velocity radian per second rad/s



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formula

Specific volume cubic metre per kilogram m3/kg

Angularacceleration

radian per second squared rad/s2

Density kilogram per cubic metre kg/m3

Mass flow rate kilogram per second kg/s

Volume flow rate cubic metre per second m3/s




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formula

Force newton N kg m/s2

Pressure newton per square metre N/m2

Torque newton metre Nm

Momentum kilogram metre per second kgm/s

Moment of inertia kilogram metre squared kgm2




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formula

Kinematic viscosity square metre per second m2

/s

Moment of inertia kilogram metre squared kgm2

Kinematic viscosity square metre per second m2/s

Dynamic viscosity newton second per square

metre Ns/m2

Work, energy, heat joule J Nm




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formula

Specific energy joule per cubic metre J/m3

Power watt W J/s

Thermal conductivity watt per metre

kelvin W/mK

Electric charge coulomb C As

Voltage, e.m.f., pot.diff.

volt V W/A




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formula

Electric field strength volt per metre V/m

Electric resistance ohm V/A

Electric capacitance farad F As/V

Electric inductance henry H Vs/A

Electric conductance siemen S A/V

Resistivity ohm metre m




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formula

Permittivity farad per metre F/m

Permeability henry per metre H/m

Current density ampere per square

metre A/m2

Magnetic flux weber Wb Vs

Magnetic flux density tesla T Wb/m2

Magnetic field strength ampere per metre A/m




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27

Quantity Standard Unit Symbol Derivatio

n formula

Frequency hertz Hz s-1

Luminous flux lumen lm cd sr

Luminance candela per square metre cd/m2

Illumination lux lx lm/m2

Molar volume cubic metre per mole m3/mol

Molarity mole per kilogram mol/kg

Molar energy joule per mole J/mol




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Application of Measuring Instruments may be classified into:

1. Regulating Trade:Applying instruments that measure physicalquantities such as length, volume and mass in terms of standardunits.

2. Monitoring Functions:Provide information necessary (to allowa human being) to control some domestic or industrialoperation or process e.g. a gardener.

3. Use in feedback Control Systems: Use as part of automaticfeedback control systems. See next two slides for a typicalfeedback block diagram and comments.

1.2Measurement System Applications



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Open Loop System

1.2 Measurement System Applications

Controller ProcessDesiredOutputResponse

Output

Heater RoomDesired

Temperature Temperature



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DesiredOutput

Response

Comparison ProcessOutput

Controller

Measurement

Elements of a simple closed-loop control system.

Closed Loop System



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Response of the closed loop system graphically



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1.2Measurement System ApplicationsA functional block diagram of a simple temperature control system in whichthe temperature Ta of a room is maintained at a reference value Td.



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1.2 Measurement System Applications

The accuracy and resolution with which an output variable of a process iscontrolled can never be better than the accuracy and resolution of themeasuring instruments used



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1.3 Elements of a Measurement System

A measuring system exists to provide information about thephysical value of some variable being measured.

It can consist of only a single unit or may consist of several

separate elements.



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A dictionary definition of'sensor'is a device that detects

a change in a physical stimulus and turns it into a signalwhich can be measured or recorded

The corresponding definition of'transducer' is a device

that transfers energy from one system to another in the

same or in the different form.

Definition



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The term measuring instrument is commonly used to describe ameasurement system.

The first element in any measuring system is the primary sensor: this

gives an output that is a function of the measurand.




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1.3 Elements of a Measurement System Sensor: For most but not all sensors, this function is at leastapproximately linear.

Examples: Liquid-in-glass thermometer, a thermocouple and a strain

gauge.Mercury-in-glass thermometer is also a complete measurementsystem in itself. However, in general, the primary sensor is only part ofa measurement system.



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Variable Conversion Elementis needed where the output variable ofa primary transducer is in an inconvenient form and needsconversion. For example: the displacement-measuring strain.

In some cases, the primary sensor and variable conversion elementare combined, and the combination is known as a transducer.




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Signal Processing Elementexists to improve the quality of the outputof a measurement system in some way. For example: electronicamplifier.

This element is particularly important where the primary transducerhas a low output. For example: thermocouples.

Some signal processing elements filter out induced noise andremove mean levels etc. In some devices, signal processing isincorporated into a transducer, which is then known as atransmitter.




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Signal transmissionis needed when the observation or applicationpoint of the output of a measurement system is some distance awayfrom the site of the primary transducer.




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The signal transmission element has traditionally consistedof single or multi-cored cable, which is often screened tominimize signal corruption by induced electrical noise.

Fiber-optic cables are being used in ever increasingnumbers in modern installations.




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The final optional element in a measurement system is the pointwhere the measured signal is utilized.

In some cases, this element is omitted altogether. In other cases,

this element in the measurement system takes the form either of asignal presentation unit or of a signal-recording unit. These takemany forms according to the requirements of the particularmeasurement application.




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The starting point in choosing the most suitable instrument isthe specification of the instrument characteristics required;

especially parameters like:

The desired measurement accuracy

Resolution

Sensitivity

Dynamic performance

1.4 Choosing appropriate measuringinstruments



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Environmental conditions must be known that theinstrument will be subjected to.

The Protection reduces the performance of someinstruments, especially in terms of their dynamiccharacteristics.

Provision of this type of information usually requires theexpert knowledge of personnel who are intimately

acquainted with the operation of the manufacturing plantor system in question.




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A skilled instrument engineer should evaluate the possiblelist of instruments in terms of their accuracy, cost andsuitability for the environmental conditions and choosethe most appropriate instrument.

As far as possible, measurement systems and instrumentsshould be chosen that are as insensitive as possible to theoperating environment.

Another important factor in instrument choice is theextent to which the measured system will be disturbedduring the measuring process.




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A good instrumentation engineer must keep abreast of thelatest developments.

The instrument characteristics form the technical basis for a

comparison between the relative merits of differentinstruments. Generally, the better the characteristics, thehigher the cost.

Durability, maintainability and constancy of performanceare also very important in addition to cost and relative

suitability. In consequence of this, the initial cost of an instrument often

has a low weighting in the evaluation exercise.




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Cost is very strongly correlated with the performance of aninstrument, as measured by its static characteristics.

Instrument choice therefore proceeds by specifying theminimum characteristics required by a measurementsituation and then searching manufacturers catalogues tofind an instrument whose characteristics match thoserequired.

To select an instrument with characteristics superior to thoserequired would only mean paying more than necessary fora level of performance greater than that needed.




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As ageneral rule, a good assessment criterion is obtained if

the total purchase cost and estimated maintenance costsof an instrument over its life are divided by the period of itsexpected life. The figure obtained is thus acost per year.

The total costs can only be divided by the period of timethat an instrument is expected to be used for, unless an

alternative use for the instrument is envisaged.




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To summarize therefore, instrument choice is a compromisebetween:

Performance characteristics (Accuracy and Precision)

Simplicity

Resolution

Display and readout

Ruggedness (Environment)

Reliability

Maintenance requirements

Purchase cost.

Availability




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Performance Characteristics



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08-Sep-14ME 312 - INSTRUMENTATION AND MEASUREMENT 51

QUIZ NO: 1

Week 1(Instrumentation and measurement)

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