Table of Contents 1274

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Measurement andInstrumentationPrinciples

Alan S. Morris

: UTTERWORTHEINEMANN

AMSTERDAM BOSTON HEIDELBERG LONDON NEW YORK OXFORD ~PARIS SAN DIEGO SAN FRANCISCO SINGAPORE SYDNEY TOKYO (LlRC ''\lVICAST ,/,/


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PrefaceAcknowledgements

Contents

Part 1: Principles of Measurement1 INTRODUCTION TO MEASUREMENT

1.1 Measurement units1.2 Measurement system applications1.3 Elements of a measurement system1.4 Choosing appropriate measuring instruments

2 INSTRUMENT TYPES AND PERFORMANCECHARACTERISTICS2.1 Review of instrument types2.1.1 Active and passive instruments2.1.2 Null-type and deflection-type instruments2.1.3 Analogue and digital instruments2.1.4 Indicating instruments and instruments with asignal output2.1.5 Smart and non-smart instruments2.2 Static characteristics of instruments2.2.1 Accuracy and inaccuracy (measurement uncertainty)2.2.2 Precisionlrepeatability/reproducibility2.2.3 Tolerance2.2.4 Range or span2.2.5 Linearity

2.2.6 Sensitivity of measurement2.2.7 Threshold2.2.8 Resolution2.2.9 Sensitivity to disturbance2.2.10 Hysteresis effects2.2.11 Dead space

2.3 Dynamic characteristics of instruments

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1212121314151616161717181919202020222323


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,"'.vi Contents".3.1 Zero order instrument 252.3.2 First order instrument 25

2.3.3 Second order instrument 282.4 Necessity for calibration 292.5 Self-test questions 30

3 ERRORS DURING THE MEASUREMENT PROCESS 323.1 Introduction 323.2 Sources of systematic error 33

3.2.1 System disturbance due to measurement 333.2.2 Errors due to environmental inputs 373.2.3 Wear in instrument components 383.2.4 Connecting leads 38

3.3 Reduction of systematic errors 393.3.1 Careful instrument design 393.3.2 Method of opposing inputs 393.3.3 High-gain feedback 393.3.4 C ~ b r a t i o n 413.3.5 Ma ual correction of output reading 423.3.6 I n t e l l i g ~ n t instruments 42

3.4 Quantification ofwstematic errors 423.5 Random errors 42

3.5.1 S t a t i s ~ c a l ' a n a l y s i s of measurements subject torandom e ~ o r s 433.5.2 Graphical"Clata analysis techniques - frequencydistributions 46

3.6 Aggregation of measurement system errors 563.6.1 Combined effect of systematic and random errors 563.6.2 Aggregation of errors from separate measurementsystem components 563.6.3 Total error when combining multiple measurements 59

3.7 Self-test questions 60References and further reading 634 CALIBRATION OF MEASURING SENSORS AND

INSTRUMENTS 644.1 Principles of calibration 644.2 Control of calibration environment 664.3 Calibration chain and traceability 674.4 Calibration records 71References and further reading 72

5 MEASUREMENT NOISE AND SIGNAL PROCESSING 735.1 Sources of measurement noise 73

5.1.1 Inductive coupling 745.1.2 Capacitive (electrostatic) coupling 745.1.3 Noise due to multiple earths 74


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5.1.4 Noise in the form of voltage transients 755.1.5 Thermoelectric potentials 755.1.6 Shot noise 765.1. 7 Electrochemical potentials 765.2 Techniques for reducing measurement noise 765.2.1 Location and design of signal wires 765.2.2 Earthing 775.2.3 Shielding 775.2.4 Other techniques 775.3 Introduction to signal processing 785.4 Analogue signal filtering 785.4.1 Passive analogue filters 815.4.2 Active analogue filters 855.5 Other analogue signal processing operations 865.5.1 Signal amplification 875.5.2 Signal attenuation 885.5.3 Differential amplification 895.5.4 Signallinearization 905.5.5 Bias (zero drift) removal 915.5.6 Signal integration 925.5.7 Voltage follower (pre-amplifier) 925.5.8 VoJtage comparator 925.5.9 Phase-sensitive detector 935.5.10 Lock-in amplifier 945.5.11 Signal addition 945.5.12 Signal multiplication 955.6 Digital signal processing 955.6.1 Signal sampling 955.6.2 Sample and hold circuit 975.6.3 Analogue-to-digital converters 975.6.4 Digital-to-analogue (D/A) conversion 995.6.5 Digital filtering 1005.6.6 Autocorrelation 100

5.6.7 Other digital signal processing operations 101References and further reading 1016 ELECTRICAL INDICATING AND TEST INSTRUMENTS 102

6.1 Digital meters 1026.1.1 Voltage-to-time conversion digital voltmeter 1036.1.2 Potentiometric digital voltmeter 1036.1.3 Dual-slope integration digital voltmeter 1036.1.4 Voltage-to-frequency conversion digital voltmeter 1046.1.5 Digital multimeter 1046.2 Analogue meters 1046.2.1 Moving-coil meters 1056.2.2 Moving-iron meter 1066.2.3 Electrodynamic meters 107


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6.2.4 Clamp-on meters 1086.2.5 Analogue multimeter 1086.2.6 Measuring high-frequency signals 1096.2.7 Thermocouple meter 1106.2.8 Electronic analogue voltmeters 1116.2.9 Calculation of meter outputs for non-standardwaveforms 112

6.3 Cathode ray oscilloscope 1146.3.1 Cathode ray tube 1156.3.2 Channel 1166.3.3 Single-ended input 1176.3.4 Differential input 1176.3.5 Timebase circuit 1176.3.6 Vertical sensitivity control 1176.3.7 Display position control 1186.4 Digital storage oscilloscopes 118References and further reading 118

7 VARIABLE CONviRSION ELEMENTS 1197.1 Bridge circuits i .. 1197.1.1 Null-tyP'f1, d.c. bridge (Wheatstone bridge) 1207.1.2 D e f l e c t i o ~ - t y p e d.c. bridge 1217.1.3 Error @alysis 1287.1.4 A.c. b r i d ~ s 1307.2 Resistance measurement 1347.2.1 D.c. bridge circuit 1357.2.2 Voltmeter-ammeter method 1357.2.3 Resistance-substitution method 1357.2.4 Use of the digital voltmeter to measure resistance 1367.2.5 The ohmmeter 1367.2.6 Codes for resistor values 137

7.3 Inductance measurement 1387.4 Capacitance measurement 1387.4.1 Alphanumeric codes for capacitor values 1397.5 Current measurement 1407.6 Frequency measurement 1417.6.1 Digital counter-timers 1427.6.2 Phase-locked loop 1427.6.3 Cathode ray oscilloscope 1437.6.4 The Wien bridge 1447.7 Phase measurement 1457.7.1 Electronic counter-timer 1457.7.2 X-Y plotter 1457.7.3 Oscilloscope 1477.7.4 Phase-sensitive detector 1477.8 Self-test questions 147References and further reading 150


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11 DISPLAY, RECORDING AND PRESENTATION OFMEASUREMENT DATA 20011.1 Display of measurement signals 20011.1.1 Electronic output displays 200

11.1.2 Computer monitor displays 20111.2 Recording of measurement data 20211.2.1 Mechanical chart recorders 20211.2.2 Ultra-violet recorders 20811.2.3. Fibre-optic recorders (recording oscilloscopes) 20911.2.4 Hybrid chart recorders 20911.2.5 Magnetic tape recorders 20911.2.6 Digital recorders 21011.2.7 Storage oscilloscopes 21111.3 Presentation of data 21211.3.1 Tabular data presentation 21211.3.2 Graphical presentation of data 21311.4 Self-test questions 222References and further reading 223!

12 MEASUREMENT RELIABILITY AND SAFETY SYSTEMS 224''',12.1 Reliability \.' 22412.1.1 P r i n c i p l e ~ of reliability 22412.1.2 Laws


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13.9 Ultrasonic transducers 25913.9.1 Transmission speed 26013.9.2 Direction of travel of ultrasound waves 26113.9.3 Directionality of ultrasound waves 26113.9.4 Relationship between wavelength, frequency anddirectionality of ultrasound waves 26213.9.5 Attenuation of ultrasound waves 26213.9.6 Ultrasound as a range sensor 26313.9.7 Use of ultrasound in tracking 3D object motion 26413.9.8 Effect of noise in ultrasonic measurement systems 26513.9.9 Exploiting Doppler shift in ultrasound transmission 26513.9.10 Ultrasonic imaging 267

13.10 Nuclear sensors 26713.11 Microsensors 268References and further reading 270

14 TEMPERATURE MEASUREMENT 27114.1 Principles of temperature measurement 27114.2 Thermoelectric effect sensors (thermocouples) 27214.2.1 Thermocouple tables 27614.2.2 Non-zero reference junction temperature 27714.2.3 Thermocouple types 27914.2.4 Thermocouple protection 28014.2.5 Thermocouple manufacture 28114.2.6 The thermopile 28214.2.7 Digital thermometer 28214.2.8 The continuous thermocouple 28214.3 Varying resistance devices 28314.3.1 Resistance thermometers (resistance temperaturedevices) 28414.3.2 Thermistors 28514.4 Semiconductor devices 286

14.5 Radiation thermometers 28714.5.1 Optical pyrometers 28914.5.2 Radiation pyrometers 29014.6 Thermography (thermal imaging) 29314.7 Thermal expansion methods 294

14.7.1 Liquid-in-glass thermometers 29514.7.2 Bimetallic thermometer 29614.7.3 Pressure thermometers 29614.8 Quartz thermometers 297

14.9 Fibre-optic temperature sensors 29714.10 Acoustic thermometers 29814.11 Colour indicators 29914.12 Change of state of materials 29914.13 Intelligent temperature-measuring instruments 30014.14 Choice between temperature transducers 300


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14.15 Self-test questions 302References and further reading 30315 PRESSURE MEASUREMENT 304

15.1 Diaphragms 30515.2 Capacitive pressure sensor 30615.3 Fibre-optic pressure sensors 30615.4 Bellows 30715.5 Bourdon tube 30815.6 Manometers 31015.7 Resonant-wire devices 31115.8 Dead-weight gauge 31215.9 Special measurement devices for low pressures 31215.10 High-pressure measurement (greater than 7000 bar) 31515.11 Intelligent pressure transducers 31615.12 Selection of pressure sensors 316

16 FLOW MEASUREMENT 31916.1 Mass flow rat6 31916.1.1 Conveyor-based methods 319

16.1.2 Coriolis flowmeter 32016.1.3 T h e r m a l ~ a s s flow measurement 32016.1.4 Joint rr.(easbrement of volume flow rate and fluiddensity 32116.2 Volume flow rate 321

16.2.1 Differential pressure (obstruction-type) meters 32216.2.2 Variable area flowmeters (Rotameters) 32716.2.3 Positive displacement flowmeters 32816.2.4 Turbine meters 32916.2.5 Electromagnetic flowmeters 33016.2.6 Vortex-shedding flowmeters 33216.2.7 Ultrasonic flowmeters 33216.2.8 Other types of flowmeter for measuring volume

flow rate 33616.3 Intelligent flowmeters 33816.4 Choice between flowmeters for particular applications 338References and further reading 339

17 LEVEL MEASUREMENT 34017.1 Dipsticks 34017.2 Float systems 34017.3 Pressure-measuring devices (hydrostatic systems) 34117.4 Capacitive devices 34317.5 Ultrasonic level gauge 34417.6 Radar (microwave) methods 346


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17.7 Radiation methods 34617.8 Other techniques 34817.8.1 Vibrating level sensor 348

17.8.2 Hot-wire elements/carbon resistor elements 34817.8.3 Laser methods 34917.8.4 Fibre-optic level sensors 34917.8.5 Thermography 349

17.9 Intelligent level-measuring instruments 35117.10 Choice between different level sensors 351References and further reading 351

18 MASS, FORCE AND TORQUE MEASUREMENT 35218.1 Mass (weight) measurement 35218.1.1 Electronic load cell (electronic balance) 35218.1.2 Pneumatic/hydraulic load cells 35418.1.3 Intelligent load cells 35518.1.4 Mass-balance (weighing) instruments 35618.1.5 Spring balance 359

18.2 Force measurement 35918.2.1 Use of accelerometers 360 .18.2.2 Vibrating wire sensor 360

18.3 Torque measurement 36118.3.1 Reaction forces in shaft bearings 36118.3.2 Prony brake 36118.3.3 Measurement of induced strain 36218.3.4 Optical torque measurement 364

19 TRANSLATIONAL MOTION TRANSDUCERS 36519.1 Displacement 36519.1.1 The resistive potentiometer 365

19.1.2 Linear variable differential transformer (LVDT) 36819.1.3 Variable capacitance transducers 37019.1.4 Variable inductance transducers 37119.1.5 Strain gauges 37119.1.6 Piezoelectric transducers 37319.1.7 Nozzle flapper 37319.1.8 Other methods of measuring small displacements 37419.1.9 Measurement of large displacements (range sensors) 37819.1.10 Proximity sensors 38119.1.11 Selection of translational measurement transducers 382

19.2 Velocity 38219.2.1 Differentiation of displacement measurements 38219.2.2 Integration of the output of an accelerometer 38319.2.3 Conversion to rotational velocity 38319.3 Acceleration 38319.3.1 Selection of accelerometers 385


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19.4 Vibration 38619.4.1 Nature of vibration 38619.4.2 Vibration measurement 38619.5 Shock 388

20 ROTATIONAL MOTION TRANSDUCERS 39020.1 Rotational displacement 39020.1.1 Circular and helical potentiometers 39020.1.2 Rotational differential transformer 39120.1.3 Incremental shaft encoders 39220.1.4 Coded-disc shaft encoders 39420.1.5 The resolver 39820.1.6 The synchro 39920.1.7 The induction potentiometer 40220.1.8 The rotary inductosyn 40220.1.9 Gyroscopes 40220.1.10 Choice between rotational displacement transducers 40620.2 Rotational velocity 40720.2.1 Digital tachometers 40720.2.2 S t r o b o s ~ o p i c methods 41020.2.3 A n a l o g u ~ tachometers 41120.2.4 Mechani4,1 flyball 41320.2.5 The r a ~ e gyroscope 41520.2.6 F i b r e - O P t i ~ g y r o s c o p e 41620.2.7 Differentia: ion of angular displacement measurements 41720.2.8 Integration of the output from an accelerometer 41720.2.9 Choice between rotational velocity transducers 41720.3 Measurement of rotational acceleration 417References and further reading 418

21 SUMMARY OF OTHER MEASUREMENTS 41921.1 Dimension measurement 41921.1.1 Rules and tapes 41921.1.2 Callipers 42121.1.3 Micrometers 42221.1.4 Gauge blocks (slip gauges) and length bars 42321.1.5 Height and depth measurement 42521.2 Angle measurement 42621.3 Flatness measurement 42821.4 Volume measurement 42821.5 Viscosity measurement 42921.5.1 Capillary and tube viscometers 43021.5.2 Falling body viscometer 43121.5.3 Rotational viscometers 43121.6 Moisture measurement 43221.6.1 Industrial moisture measurement techniques 43221.6.2 Laboratory techniques for moisture measurement 434


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21.6.3 Humidity measurement21.7 Sound measurement21.8 pH measurement21.8.1 The glass electrode21.8.2 Other methods of pH measurement21.9 Gas sensing and analysis21.9.1 Catalytic (calorimetric) sensors21.9.2 Paper tape sensors21.9.3 Liquid electrolyte electrochemical cells21.9.4 Solid-state electrochemical cells (zirconia sensor)21.9.5 Catalytic gate PETs21.9.6 Semiconductor (metal oxide) sensors21.9.7 Organic sensors21.9.8 Piezoelectric devices21.9.9 Infra-red absorption21.9.10 Mass spectrometers21.9.11 Gas chromatographyReferences and further reading

APPENDIX 1 Imperial-metric-SI conversion tablesAPPENDIX 2 Thevenin's theoremAPPENDIX 3 Thermocouple tablesAPPENDIX 4 Solutions to self-test questionsINDEX

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Index

absolute pressure, 304, 305, 307, 310a.c. carrier,.153-4acceleration measurement, 254, 258, 269,

383-6,417-8accuracy, 16-17acoustic thermometer, 298-9, 302active filters, 85-6 .active instruments, 12-13address bus, 167address decoding, 174-5aggregation of measurement errors, 56-9air-vane meter, 337alarms, 241aliasing, 96amplification, 9, 87-8, 89, 101amplifier see operational amplifieramplitude modulation (AM), 153analogue-digital conversion, 95-6, 97-8analogue filters, 78-86analogue instruments, 14-15analogue meters, 104-113angle measurement, 426-7angular motion, 390-418annubar, 322, 327anti-ambiguity track, 396antimony electrode, 439apex bridge-circuit balancing, 129-30ASIC (Application specific integratedcircuit), 184asynchronous transnllssion, 189-90attenuation, 80, 82, 84, 88-9, 101autocorrelation, 100-1band pass filter, 80, 81, 83, 85band stop filter, 80, 81, 83-4, 85bandwidth, 114bathtub reliability curve, 226

beam balance, 356bell-shaped distribution, 48bellows, 307-8, 317bevel protractor, 426bias, 21, 91, 101bimetallic thermometer, 296, 302bimetallic thermostat, 296binary numbers, 168-73Bourdon tube, 308-10, 317box cube, 419bridge circuits, 8, 119-135, 138, 144

a.c., 130-4, 138, 144balancing, 129-30d.c., 119-30, 135error analysis, 128-9British Calibration Service (BCS), 68BS 5750, 66bubbler unit, 342bus network, 194-5calibration, 21, 29-30, 41, 64-72, 179, 182calibration chain, 67-70

calibration frequency, 65documentation, 69-72calipers, 420-2calorimetric sensors, 440Cambridge ring, 195capacitance measurement, 138-9capacitive coupling, 74capacitive sensors, 247, 260, 306, 343,370-1,432catalytic gate FET, 442catalytic sensors, 440cathode ray oscilloscope, 114-8, 143-4,147centrifugal tachometer, 413characteristic impedance, 82


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470 Indexchart recorders, 202-11 f!chi-squared test, 55

...

choice of instrument see instrument choicechromatography, 443clamp-on meter, 108, 141coded disc shaft encoder see shaft encoderscoefficient of viscosity, 429colour codes (resistors and capacitors), 137,

139colour temperature indicators, 299, 302common mode rejection, 88communications, 183-4, 187-99compensating leads, 275compensating resistance, 39computer data logging, 210-1computer networks, 187-99computing principles, 165 - 77confidence tests, 216, 220constant-k filter, 80, 83, 85contention protocol, 195 !continuous thermocouple, 282-3control bus, 167, 175 .conversion tables: imperial-SI u n i t ~ 445-51Coriolis meter, 320, 338 ~corona discharge, 75correlation test, 220-1counter-timer, 142, 145 t,.CPLD (Complex programmable logicdevice), 184crayon temperature indicators, 299creep, 352cross correlation flowmeter, 336cross sensitivity, 384cross talk sensor, 257, 349cumulative distribution function, 48current loop transmission, 152-3, 183current measurement, 140-1current to voltage conversion, 153current transformer, 140curve fitting, 214-21cut off frequency, 79Dall flow tube, 322, 325-6damping ratio, 29, 205-6data analysis, 43-56data bus, 167, 175data logging, 219-1data presentation, 212-21data transmission, 187-99dead space, 23dead weight gauge, 14,312, 317

decibel (dB), 114deflection instruments, 13 -14depth gauge, 425design of instruments see instrument deSigndew point meter, 435dial gauge, 425diaphragm-type pressure transducer,

305-7,317differential amplifier, 89-90differential pressure, 304, 305, 307, 310,318differential transformerslinear, 368rotational, 391digital-analog converter, 99digital filters, 100digital instruments, 14-15digital meters, 102-4, 136, 140, 141, 142digital recorder, 210-1digital (storage) oscilloscope, 118, 211digital thermometer, 270, 282digital voltmeter (DVM), 102-4, 136dimension measurement, 419-27diode temperature sensors, 287dipstick, 340discharge coefficient, 324displacement measurementrotational, 390-407translational, 255, 365-82display of signals, 200-1distributed control system, 187distributed sensors, 254, 259, 282, 298Doppler effect, 265-7, 333draft gauge, 311dual diverse temperature sensor, 301duplex communication, 188DVM see digital voltmeterdynamic characteristics of instruments,

23-9,205-6dynamic viscosity, 429dynamometer, 107-8earthing, 77eddy current sensors, 248electrical signals:measurement, 34-7, 102-18, 119-47recording, 202-11electrochemical cells, 441-2electrochemical potential, 75electrodynamic meter, 107-8electromagnetic balance, 359


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472 Indexinertial navigation systems, t03instrument choice, 9-11instrument design, 9-11, 39, 41, 43instumentation amplifier, 87-8instrumentation networks, 187-99integrated circuit transistor sensors, 286intelligent devices, 42, 165-85

in acceleration measurement, 385in dimension measurement, 422, 423in displacement measurement, 399in flow measurement, 178, 338in force and mass measurement, 355in level measurement, 351in pressure measurement, 316in temperature measurement, 300, 302

interfacing, 167, 174-7, 187-99international practical temperature scale(ITPS),271intrinsic safety, 236ionisation gauge, 315ISO-7 protocol, 197, 198-9ISO 9000, 66, 69kinematic viscosity, 429LAN see local area network

!

laser Doppler flowmeter, 258, 337 laser interferometer, 376law of intennediate metals, 275-6law of intennediate temperatures, 277-9least squares regression, 216-20length bar, 424level measurement, 12, 257, 340-51line-type heat detector, 282linear variable differential transfonner((LVDT), 368linearization, 90-1linearity, 19liquid-in-glass thennometer, 26, 295, 302Lisajous patterns, 143-4load cell, 352-6local area network, 187, 190, 192-9lock-in amplifier, 78, 93-4low pass filter, 80, 81, 83, 85lower explosive level, 439LVDT see linear variable differentialtransfonnermagnetic sensors, 247-50, 410magnetic tape recorder, 209-10magnetostrictive tachometer, 410

manometers, 310-1, 317manufacturing tolerances, 53-6MAP (manufacturing automation protocol),

199mass flow rate, see flow measurementmass measurement, 342-9mass spectrometer, 443Maxwell bridge, 131-2McLeod gauge, 314-5mean, 43-4mean-time-between-failures, 225mean-time-to-repair, 225measurement disturbance, 33-8, 125-8,140measurement system design, 8, 37-9measurement uncertainty, 16-17measuring units, 3-6, 445-51mechanical flyball, 413median, 43-4metal oxide gas sensors, 442meters, 102-13metric units, 6metropolitan area network (MAN), 198microbend sensor, 307micrometers, 69-70, 422-3microprocessor, 166micro sensors, 268-70, 306mirror galvanometer, 208modem, 193modifying inputs see environmentallyinduced errorsmoisture measurement, 432-6moving coil meters, 105, 140moving iron meters, 106, 140multimeters, 102, 104, 108-9, 136multiple earths, 74multiplexing, 155, 160multivariable transmitter, 180National Measurement AccreditationService (NAMAS), 68National Standards Organisations, 67 - 70National Testing Laboratory AccreditationScemem (NATLAS), 68natural frequency of instruments, 28-9networks, 192-9neutron moderation, 433noise, 73-8nonnal distribution, 48nonnal probability plot, 54-5notch filter see band pass filter


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nozzle flapper, 373nuclear magnetic resonance (NMR), 433nuclear sensors, 267-8, 319null type instruments, 13-4numerically controlled machine tools, 374,377, 394, 400octal numbers, 170-3ohmmeter, l36one-out-of-two voting, 240one's complement, 168open systems interconnection seven layermodel, 197, 198-9operational amplifier, 87-95optical fibres see fibre opticsoptical incremental shaft encoder, 392-4oplical pyrometer, 289-90optical resonator, 258optical sensors, 252-9optical shaft encoder, 393-4optical tachometer, 408optical wireless telemetry, 160-1organic gas sensors, 442orifice plate, 322-5, 339oscilloscope see cathode ray oscilloscopepaper-tape gas sensor, 441paperless recorder, 211parallax error, 102parallel communication/interface, 187 -8,

190-2parity bit, 189, 190pass band, 79, 82passive filters, 81-5passive instruments, 12-l3PCI (Peripheral component interconnect),174, 184PCM see pulse code modulationpendulum scale, 358pH measurement, 437phase-locked loop, 77, 142-3phase measurement, 145-7

phase-sensitive detector, 93-4, 147photon detector, 290, 292piezoelectric gas sensor, 443piezoelectric transducers, 250-1piezoresistive transducers, 252, 306Pirani gauge, 3l3-4Pitot tube, 322, 326-7platinum resistance thermometer, 284pneumatic signal transmission, 154

Index 473

pollution monitOring and control, 440positive displacement flowmeter, 328-9,339potentiometers, 25, 3 6 5 ~ 8 , 390,402induction, 402rotational, 390

translational, 365-8preamplifier, 92precession, 403precision, 17presentation of data see data presentationpressure measurement, 12-14,304-18high pressures, 315-6low pressures, 312-5pressure thermometer, 296-7, 302primary fixed point (of temperature), 271primary reference standard, 69probability curve, 47probability density function, 47programming and program execution,

173-4Prony brake, 361protractors, 426-7proximity sensors, 381PRT see platinum resistance thermometerpsychrometer,435pulse code modulation (PCM), 163pulsed temperature sensor, 301pyrometers, 287-93, 301pyrometric cone, 299Q factor (quality factor), l31quantization, 97quartz thermometer, 297, 302radiation pyrometerlthermometer, see

pyrometersradio telemetry, 161-3random access memory (RAM), 166random errors, 33, 42-56range (of instrument), 18-19range measurement, 263, 378-81ratio pyrometer, 292-3read only memory (ROM), 166-7recorders see signal recordersrecording oscilloscopes, 209redundancy, 230reference standards, 67 - 70refractive index measurement, 257refractometer, 433regression techniques, 215-220


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474 Indexrelative humidity, 432 freliability, 224-35

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components in parallel, 229components in series, 228manufacturing systems, 224-31measurement systems, 224-31safety systems, 236-41software, 232-5repeatability/reproducibility, 17resistance measurement, 119-30, 134-7resistance temperature device (RTD),

283-5,301resistance thermometer, 283-5, 301resistive sensors, 247resolution, 20resolver, 398-9resonant-wire pressure sensor, 311-2, 317Reynolds number, 324ring laser gyroscope, 405ring network, 194-5rise time, 114risk analysis, 237

!rogue data points, 55-6rotameter, 327rotary differential transformer, 39


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tabular data presentation, 212-3tachometric generators (tachometers),407-10tank gauge, 341target meter, 337

telemetry, 160-3temperature coefficient, 38, 39, 285, 366temperature measurement, 255-9, 270,271-303thermal detector, 290thermal e.m.f., 75, 272thermal imaging, 293-4, 349thermal mass flow meter, 320-1thermistor, 285-6, 301thermistor gauge, 314thermocouple, 272-83, 300-1thermocouple gauge, 313thermocouple meter, 110thermocouple tables, 276-7, 458-63thermoelectric effect, 75, 272-83thermography, 293-4, 349thermometer (l iquid-in-glass type), 26,295, 302thermopile, 282Thevenin's theorem, 34-7, 125-8,452-7threshold, 20time base circuit, 117time constant, 27tolerance, 17-18,53-6torque measurement, 361-4total measurement error, 56-9touch screens, 201traceability, 67-70transducer, 8transmitter, 9triggering, 117turbine meters, 329-30, 339twisted pair, 76t w o ~ c o l o u r pyrometer, 292-3two-out-of-three voting, 239two's complement, 168UART interface, 174U-tube manometer, 310-1ultrasonic flowmeters, 332-6, 339ultrasonic imaging, 267ultrasonic level gauge, 344

ultrasonic principles, 260-7ultrasonic rule, 420ultrasonic thermometer, 299ultrasonic transducers, 259-67ultraviolet (UV) recorder, 208-9uncertainty, 16-17

Index 475

units of measurement, 3-6, 445-51USB (universal serial bus), 174V24 interface, 190vacuum pressures, 312-5variable area flowmeter, 327-8, 339variable reluctance sensors, 248, 408, 413variance, 44-6variation gauge, 428vee block, 419velocity measurement:rotational, 407 -17translational, 382-3venturi, 322, 323, 325vibrating level sensor, 348vibrating wire force sensor, 360vibration measurement, 386-8viscosity measurement (viscometers),

429-31voltage comparator, 92-3voltage follower, 92voltage to current conversion, 152voltage to frequency conversion, 153-4volume flow rate measurement- see flowmeasurementvolume measurement, 428-9vortex shedding flowmeter, 332, 339weigh beatp., 357weighing see mass measurementWein bridge, 144-5wet and dry bulb hygrometer, 435Wheatstone bridge, 120-1Wide area network, 198wringing (gauge blocks), 424x-y plotter, 145-6zero drift, 21, 37, 91zero order type instruments, 25zirconia gas sensor, 442

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Table of Contents 1274