Measurement and Instrumentation Principles, First Edition - Alan S Morris PDF

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Measurement and Instrumentation Principles To Jane, Nicola and Julia Measurement and Instrumentation Principles Alan S. Morris OXFORD AUCKLAND BOSTON JOHANNESBURG MELBOURNE NEW DELHI Butterworth-Heinemann Linacre House, Jordan Hill, Oxford OX2 8DP 225 Wildwood Avenue, Woburn, MA 01801-2041 A divisi...

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Measurement and Instrumentation Principles

To Jane, Nicola and Julia

Measurement and Instrumentation Principles Alan S. Morris

OXFORD AUCKLAND BOSTON

JOHANNESBURG MELBOURNE

NEW DELHI

Butterworth-Heinemann Linacre House, Jordan Hill, Oxford OX2 8DP 225 Wildwood Avenue, Woburn, MA 01801-2041 A division of Reed Educational and Professional Publishing Ltd A member of the Reed Elsevier plc group First published 2001  Alan S. Morris 2001

All rights reserved. No part of this publication may be reproduced in any material form (including photocopying or storing in any medium by electronic means and whether or not transiently or incidentally to some other use of this publication) without the written permission of the copyright holder except in accordance with the provisions of the Copyright, Designs and Patents Act 1988 or under the terms of a licence issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court Road, London, England W1P 9HE. Applications for the copyright holder’s written permission to reproduce any part of this publication should be addressed to the publishers British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library ISBN 0 7506 5081 8

Typeset in 10/12pt Times Roman by Laser Words, Madras, India Printed and bound in Great Britain

Contents Preface Acknowledgements Part 1: Principles of Measurement 1 INTRODUCTION TO MEASUREMENT 1.1 Measurement units 1.2 Measurement system applications 1.3 Elements of a measurement system 1.4 Choosing appropriate measuring instruments 2 INSTRUMENT TYPES AND PERFORMANCE CHARACTERISTICS 2.1 Review of instrument types 2.1.1 Active and passive instruments 2.1.2 Null-type and deflection-type instruments 2.1.3 Analogue and digital instruments 2.1.4 Indicating instruments and instruments with a signal output 2.1.5 Smart and non-smart instruments 2.2 Static characteristics of instruments 2.2.1 Accuracy and inaccuracy (measurement uncertainty) 2.2.2 Precision/repeatability/reproducibility 2.2.3 Tolerance 2.2.4 Range or span 2.2.5 Linearity 2.2.6 Sensitivity of measurement 2.2.7 Threshold 2.2.8 Resolution 2.2.9 Sensitivity to disturbance 2.2.10 Hysteresis effects 2.2.11 Dead space 2.3 Dynamic characteristics of instruments

xvii xx 1 3 3 6 8 9

12 12 12 13 14 15 16 16 16 17 17 18 19 19 20 20 20 22 23 23

vi

Contents

2.4 2.5

2.3.1 Zero order instrument 2.3.2 First order instrument 2.3.3 Second order instrument Necessity for calibration Self-test questions

3 ERRORS DURING THE MEASUREMENT PROCESS 3.1 Introduction 3.2 Sources of systematic error 3.2.1 System disturbance due to measurement 3.2.2 Errors due to environmental inputs 3.2.3 Wear in instrument components 3.2.4 Connecting leads 3.3 Reduction of systematic errors 3.3.1 Careful instrument design 3.3.2 Method of opposing inputs 3.3.3 High-gain feedback 3.3.4 Calibration 3.3.5 Manual correction of output reading 3.3.6 Intelligent instruments 3.4 Quantification of systematic errors 3.5 Random errors 3.5.1 Statistical analysis of measurements subject to random errors 3.5.2 Graphical data analysis techniques – frequency distributions 3.6 Aggregation of measurement system errors 3.6.1 Combined effect of systematic and random errors 3.6.2 Aggregation of errors from separate measurement system components 3.6.3 Total error when combining multiple measurements 3.7 Self-test questions References and further reading

25 25 28 29 30 32 32 33 33 37 38 38 39 39 39 39 41 42 42 42 42 43 46 56 56 56 59 60 63

4 CALIBRATION OF MEASURING SENSORS AND INSTRUMENTS 4.1 Principles of calibration 4.2 Control of calibration environment 4.3 Calibration chain and traceability 4.4 Calibration records References and further reading

64 64 66 67 71 72

5 MEASUREMENT NOISE AND SIGNAL PROCESSING 5.1 Sources of measurement noise 5.1.1 Inductive coupling 5.1.2 Capacitive (electrostatic) coupling 5.1.3 Noise due to multiple earths

73 73 74 74 74

Contents vii

5.1.4 Noise in the form of voltage transients 5.1.5 Thermoelectric potentials 5.1.6 Shot noise 5.1.7 Electrochemical potentials 5.2 Techniques for reducing measurement noise 5.2.1 Location and design of signal wires 5.2.2 Earthing 5.2.3 Shielding 5.2.4 Other techniques 5.3 Introduction to signal processing 5.4 Analogue signal filtering 5.4.1 Passive analogue filters 5.4.2 Active analogue filters 5.5 Other analogue signal processing operations 5.5.1 Signal amplification 5.5.2 Signal attenuation 5.5.3 Differential amplification 5.5.4 Signal linearization 5.5.5 Bias (zero drift) removal 5.5.6 Signal integration 5.5.7 Voltage follower (pre-amplifier) 5.5.8 Voltage comparator 5.5.9 Phase-sensitive detector 5.5.10 Lock-in amplifier 5.5.11 Signal addition 5.5.12 Signal multiplication 5.6 Digital signal processing 5.6.1 Signal sampling 5.6.2 Sample and hold circuit 5.6.3 Analogue-to-digital converters 5.6.4 Digital-to-analogue (D/A) conversion 5.6.5 Digital filtering 5.6.6 Autocorrelation 5.6.7 Other digital signal processing operations References and further reading 6 ELECTRICAL INDICATING AND TEST INSTRUMENTS 6.1 Digital meters 6.1.1 Voltage-to-time conversion digital voltmeter 6.1.2 Potentiometric digital voltmeter 6.1.3 Dual-slope integration digital voltmeter 6.1.4 Voltage-to-frequency conversion digital voltmeter 6.1.5 Digital multimeter 6.2 Analogue meters 6.2.1 Moving-coil meters 6.2.2 Moving-iron meter 6.2.3 Electrodynamic meters

75 75 76 76 76 76 77 77 77 78 78 81 85 86 87 88 89 90 91 92 92 92 93 94 94 95 95 95 97 97 99 100 100 101 101 102 102 103 103 103 104 104 104 105 106 107

viii

Contents

6.2.4 6.2.5 6.2.6 6.2.7 6.2.8 6.2.9

Clamp-on meters Analogue multimeter Measuring high-frequency signals Thermocouple meter Electronic analogue voltmeters Calculation of meter outputs for non-standard waveforms 6.3 Cathode ray oscilloscope 6.3.1 Cathode ray tube 6.3.2 Channel 6.3.3 Single-ended input 6.3.4 Differential input 6.3.5 Timebase circuit 6.3.6 Vertical sensitivity control 6.3.7 Display position control 6.4 Digital storage oscilloscopes References and further reading

108 108 109 110 111

7 VARIABLE CONVERSION ELEMENTS 7.1 Bridge circuits 7.1.1 Null-type, d.c. bridge (Wheatstone bridge) 7.1.2 Deflection-type d.c. bridge 7.1.3 Error analysis 7.1.4 A.c. bridges 7.2 Resistance measurement 7.2.1 D.c. bridge circuit 7.2.2 Voltmeter–ammeter method 7.2.3 Resistance-substitution method 7.2.4 Use of the digital voltmeter to measure resistance 7.2.5 The ohmmeter 7.2.6 Codes for resistor values 7.3 Inductance measurement 7.4 Capacitance measurement 7.4.1 Alphanumeric codes for capacitor values 7.5 Current measurement 7.6 Frequency measurement 7.6.1 Digital counter-timers 7.6.2 Phase-locked loop 7.6.3 Cathode ray oscilloscope 7.6.4 The Wien bridge 7.7 Phase measurement 7.7.1 Electronic counter-timer 7.7.2 X–Y plotter 7.7.3 Oscilloscope 7.7.4 Phase-sensitive detector 7.8 Self-test questions References and further reading

119 119 120 121 128 130 134 135 135 135 136 136 137 138 138 139 140 141 142 142 143 144 145 145 145 147 147 147 150

112 114 115 116 117 117 117 117 118 118 118

Contents ix

8 SIGNAL TRANSMISSION 8.1 Electrical transmission 8.1.1 Transmission as varying voltages 8.1.2 Current loop transmission 8.1.3 Transmission using an a.c. carrier 8.2 Pneumatic transmission 8.3 Fibre-optic transmission 8.3.1 Principles of fibre optics 8.3.2 Transmission characteristics 8.3.3 Multiplexing schemes 8.4 Optical wireless telemetry 8.5 Radio telemetry (radio wireless transmission) 8.6 Digital transmission protocols References and further reading

151 151 151 152 153 154 155 156 158 160 160 161 163 164

9 DIGITAL COMPUTATION AND INTELLIGENT DEVICES 9.1 Principles of digital computation 9.1.1 Elements of a computer 9.1.2 Computer operation 9.1.3 Interfacing 9.1.4 Practical considerations in adding computers to measurement systems 9.2 Intelligent devices 9.2.1 Intelligent instruments 9.2.2 Smart sensors 9.2.3 Smart transmitters 9.2.4 Communication with intelligent devices 9.2.5 Computation in intelligent devices 9.2.6 Future trends in intelligent devices 9.3 Self-test questions References and further reading

165 165 165 168 174

10 INSTRUMENTATION/COMPUTER NETWORKS 10.1 Introduction 10.2 Serial communication lines 10.2.1 Asynchronous transmission 10.3 Parallel data bus 10.4 Local area networks (LANs) 10.4.1 Star networks 10.4.2 Ring and bus networks 10.5 Gateways 10.6 HART 10.7 Digital fieldbuses 10.8 Communication protocols for very large systems 10.8.1 Protocol standardization 10.9 Future development of networks References and further reading

176 177 177 179 180 183 184 185 185 186 187 187 188 189 190 192 193 194 195 195 196 198 198 199 199

x

Contents

11 DISPLAY, RECORDING AND PRESENTATION OF MEASUREMENT DATA 11.1 Display of measurement signals 11.1.1 Electronic output displays 11.1.2 Computer monitor displays 11.2 Recording of measurement data 11.2.1 Mechanical chart recorders 11.2.2 Ultra-violet recorders 11.2.3 Fibre-optic recorders (recording oscilloscopes) 11.2.4 Hybrid chart recorders 11.2.5 Magnetic tape recorders 11.2.6 Digital recorders 11.2.7 Storage oscilloscopes 11.3 Presentation of data 11.3.1 Tabular data presentation 11.3.2 Graphical presentation of data 11.4 Self-test questions References and further reading

200 200 200 201 202 202 208 209 209 209 210 211 212 212 213 222 223

12 MEASUREMENT RELIABILITY AND SAFETY SYSTEMS 12.1 Reliability 12.1.1 Principles of reliability 12.1.2 Laws of reliability in complex systems 12.1.3 Improving measurement system reliability 12.1.4 Software reliability 12.2 Safety systems 12.2.1 Introduction to safety systems 12.2.2 Operation of safety systems 12.2.3 Design of a safety system 12.3 Self-test questions References and further reading

224 224 224 228 229 232 236 236 237 238 241 242

Part 2: Measurement Sensors and Instruments

245

13 SENSOR TECHNOLOGIES 13.1 Capacitive and resistive sensors 13.2 Magnetic sensors 13.3 Hall-effect sensors 13.4 Piezoelectric transducers 13.5 Strain gauges 13.6 Piezoresistive sensors 13.7 Optical sensors (air path) 13.8 Optical sensors (fibre-optic) 13.8.1 Intrinsic sensors 13.8.2 Extrinsic sensors 13.8.3 Distributed sensors

247 247 247 249 250 251 252 252 253 254 258 259

Contents xi

13.9

Ultrasonic transducers 13.9.1 Transmission speed 13.9.2 Direction of travel of ultrasound waves 13.9.3 Directionality of ultrasound waves 13.9.4 Relationship between wavelength, frequency and directionality of ultrasound waves 13.9.5 Attenuation of ultrasound waves 13.9.6 Ultrasound as a range sensor 13.9.7 Use of ultrasound in tracking 3D object motion 13.9.8 Effect of noise in ultrasonic measurement systems 13.9.9 Exploiting Doppler shift in ultrasound transmission 13.9.10 Ultrasonic imaging 13.10 Nuclear sensors 13.11 Microsensors References and further reading 14 TEMPERATURE MEASUREMENT 14.1 Principles of temperature measurement 14.2 Thermoelectric effect sensors (thermocouples) 14.2.1 Thermocouple tables 14.2.2 Non-zero reference junction temperature 14.2.3 Thermocouple types 14.2.4 Thermocouple protection 14.2.5 Thermocouple manufacture 14.2.6 The thermopile 14.2.7 Digital thermometer 14.2.8 The continuous thermocouple 14.3 Varying resistance devices 14.3.1 Resistance thermometers (resistance temperature devices) 14.3.2 Thermistors 14.4 Semiconductor devices 14.5 Radiation thermometers 14.5.1 Optical pyrometers 14.5.2 Radiation pyrometers 14.6 Thermography (thermal imaging) 14.7 Thermal expansion methods 14.7.1 Liquid-in-glass thermometers 14.7.2 Bimetallic thermometer 14.7.3 Pressure thermometers 14.8 Quartz thermometers 14.9 Fibre-optic temperature sensors 14.10 Acoustic thermometers 14.11 Colour indicators 14.12 Change of state of materials 14.13 Intelligent temperature-measuring instruments 14.14 Choice between temperature transducers

259 260 261 261 262 262 263 264 265 265 267 267 268 270 271 271 272 276 277 279 280 281 282 282 282 283 284 285 286 287 289 290 293 294 295 296 296 297 297 298 299 299 300 300

xii

Contents

14.15 Self-test questions References and further reading

302 303

15 PRESSURE MEASUREMENT 15.1 Diaphragms 15.2 Capacitive pressure sensor 15.3 Fibre-optic pressure sensors 15.4 Bellows 15.5 Bourdon tube 15.6 Manometers 15.7 Resonant-wire devices 15.8 Dead-weight gauge 15.9 Special measurement devices for low pressures 15.10 High-pressure measurement (greater than 7000 bar) 15.11 Intelligent pressure transducers 15.12 Selection of pressure sensors

304 305 306 306 307 308 310 311 312 312 315 316 316

16 FLOW MEASUREMENT 16.1 Mass flow rate 16.1.1 Conveyor-based methods 16.1.2 Coriolis flowmeter 16.1.3 Thermal mass flow measurement 16.1.4 Joint measurement of volume flow rate and fluid density 16.2 Volume flow rate 16.2.1 Differential pressure (obstruction-type) meters 16.2.2 Variable area flowmeters (Rotameters) 16.2.3 Positive displacement flowmeters 16.2.4 Turbine meters 16.2.5 Electromagnetic flowmeters 16.2.6 Vortex-shedding flowmeters 16.2.7 Ultrasonic flowmeters 16.2.8 Other types of flowmeter for measuring volume flow rate 16.3 Intelligent flowmeters 16.4 Choice between flowmeters for particular applications References and further reading

319 319 319 320 320

17 LEVEL MEASUREMENT 17.1 Dipsticks 17.2 Float systems 17.3 Pressure-measuring devices (hydrostatic systems) 17.4 Capacitive devices 17.5 Ultrasonic level gauge 17.6 Radar (microwave) methods

340 340 340 341 343 344 346

321 321 322 327 328 329 330 332 332 336 338 338 339

Contents xiii

17.7 17.8

Radiation methods Other techniques 17.8.1 Vibrating level sensor 17.8.2 Hot-wire elements/carbon resistor elements 17.8.3 Laser methods 17.8.4 Fibre-optic level sensors 17.8.5 Thermography 17.9 Intelligent level-measuring instruments 17.10 Choice between different level sensors References and further reading

346 348 348 348 349 349 349 351 351 351

18 MASS, FORCE AND TORQUE MEASUREMENT 18.1 Mass (weight) measurement 18.1.1 Electronic load cell (electronic balance) 18.1.2 Pneumatic/hydraulic load cells 18.1.3 Intelligent load cells 18.1.4 Mass-balance (weighing) instruments 18.1.5 Spring balance 18.2 Force measurement 18.2.1 Use of accelerometers 18.2.2 Vibrating wire sensor 18.3 Torque measurement 18.3.1 Reaction forces in shaft bearings 18.3.2 Prony brake 18.3.3 Measurement of induced strain 18.3.4 Optical torque measurement

352 352 352 354 355 356 359 359 360 360 361 361 361 362 364

19 TRANSLATIONAL MOTION TRANSDUCERS 19.1 Displacement 19.1.1 The resistive potentiometer 19.1.2 Linear variable differential transformer (LVDT) 19.1.3 Variable capacitance transducers 19.1.4 Variable inductance transducers 19.1.5 Strain gauges 19.1.6 Piezoelectric transducers 19.1.7 Nozzle flapper 19.1.8 Other methods of measuring small displacements 19.1.9 Measurement of large displacements (range sensors) 19.1.10 Proximity sensors 19.1.11 Selection of translational measurement transducers 19.2 Velocity 19.2.1 Differentiation of displacement measurements 19.2.2 Integration of the output of an accelerometer 19.2.3 Conversion to rotational velocity 19.3 Acceleration 19.3.1 Selection of accelerometers

365 365 365 368 370 371 371 373 373 374 378 381 382 382 382 383 383 383 385

xiv

Contents

19.4

19.5

Vibration 19.4.1 Nature of vibration 19.4.2 Vibration measurement Shock

386 386 386 388

20 ROTATIONAL MOTION TRANSDUCERS 20.1 Rotational displacement 20.1.1 Circular and helical potentiometers 20.1.2 Rotational differential transformer 20.1.3 Incremental shaft encoders 20.1.4 Coded-disc shaft encoders 20.1.5 The resolver 20.1.6 The synchro 20.1.7 The induction potentiometer 20.1.8 The rotary inductosyn 20.1.9 Gyroscopes 20.1.10 Choice between rotational displacement transducers 20.2 Rotational velocity 20.2.1 Digital tachometers 20.2.2 Stroboscopic methods 20.2.3 Analogue tachometers 20.2.4 Mechanical flyball 20.2.5 The rate gyroscope 20.2.6 Fibre-optic gyroscope 20.2.7 Differentiation of angular displacement measurements 20.2.8 Integration of the output from an accelerometer 20.2.9 Choice between rotational velocity transducers 20.3 Measurement of rotational acceleration References and further reading

390 390 390 391 392 394 398 399 402 402 402 406 407 407 410 411 413 415 416 417 417 417 417 418

21 SUMMARY OF OTHER MEASUREMENTS 21.1 Dimension measurement 21.1.1 Rules and tapes 21.1.2 Callipers 21.1.3 Micrometers 21.1.4 Gauge blocks (slip gauges) and length bars 21.1.5 Height and depth measurement 21.2 Angle measurement 21.3 Flatness measurement 21.4 Volume measurement 21.5 Viscosity measurement 21.5.1 Capillary and tube viscometers 21.5.2 Falling body viscometer 21.5.3 Rotational viscometers 21.6 Moisture measurement 21.6.1 Industrial moisture measurement techniques 21.6.2 Laboratory techniques for moisture measurement

419 419 419 421 422 423 425 426 428 428 429 430 431 431 432 432 434

Contents xv

21.6.3 Humidity measurement Sound measurement pH measurement 21.8.1 The glass electrode 21.8.2 Other methods of pH measurement 21.9 Gas sensing and analysis 21.9.1 Catalytic (calorimetric) sensors 21.9.2 Paper tape sensors 21.9.3 Liquid electrolyte electrochemical cells 21.9.4 Solid-state electrochemical cells (zirconia sensor) 21.9.5 Catalytic gate FETs 21.9.6 Semiconductor (metal oxide) sensors 21.9.7 Organic sensors 21.9.8 Piezoelectric devices 21.9.9 Infra-red absorption 21.9.10 Mass spectrometers 21.9.11 Gas chromatography References and further reading 21.7 21.8

435 436 437 438 439 439 440 441 441 442 442 442 442 443 443 443 443 444

APPENDIX 1 Imperial–metric–SI conversion tables

445

APPENDIX 2 Th´evenin’s theorem

452

APPENDIX 3 Thermocouple tables

458

APPENDIX 4 Solutions to self-test questions

464

INDEX

469

Preface The foundations of this book lie in the highly successful text Principles of Measurement and Instrumentation by the same author. The first edition of this was published in 1988, and a second, revised and extended edition appeared in 1993. Since that time, a number of new developments have occurred in the field of measurement. In particular, there have been significant advances in smart sensors, intelligent instruments, microsensors, digital signal processing, digital recorders, digital fieldbuses and new methods of signal transmission. The rapid growth of digital components within measurement systems has also created a need to establish procedures for measuring and improving the reliability of the software that is used within such components. Formal standards governing instrument calibration procedures and measurement system performance have also extended beyond the traditional area of quality assurance systems (BS 5781, BS 5750 and more recently ISO 9000) into new areas such as environmental protection systems (BS 7750 and ISO 14000). Thus, an up-to-date book incorporating all of the latest developments in measurement is strongly needed. With so much new material to include, the opportunity has been taken to substantially revise the order and content of material presented previously in Principles of Measurement and Instrumentation, and several new chapters have been written to cover the many new developments in measurement and instrumentation that have occurred over the past few years. To emphasize the substantial revision that has taken place, a decision has been made to publish the book under ...