PRINCIPLES OF ELECTRICAL MEASUREMENT Sensors Series Senior Series Editor: B E Jones Series Co-Editor: W B Spillman, Jr Novel Sensors and Sensing R G Jackson Hall Effect Devices, Second Edition R S Popovi´c Sensors and their Applications XII Edited by S J Prosser and E Lewis Sensors and their Applications XI Edited by K T V Grattan and S H Khan Thin Film Magnetoresistive Sensors S Tumanski Electronic Noses and Olfaction 2000 Edited by J W Gardner and K C Persaud Sensors and their Applications X Edited by N M White and A T Augousti Sensor Materials P T Moseley and J Crocker Biosensors: Microelectrochemical Devices M Lambrecht and W Sansen Current Advances in Sensors Edited by B E Jones Series in Sensors PRINCIPLES OF ELECTRICAL MEASUREMENT S Tumanski Warsaw University of Technology Warsaw, Poland New York London IP832_Discl.fm Page Wednesday, November 23, 2005 1:02 PM Published in 2006 by CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2006 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group No claim to original U.S Government works Printed in the United States of America on acid-free paper 10 International Standard Book Number-10: 0-7503-1038-3 (Hardcover) International Standard Book Number-13: 978-0-7503-1038-3 (Hardcover) Library of Congress Card Number 2005054928 This book contains information obtained from authentic and highly regarded sources Reprinted material is quoted with permission, and sources are indicated A wide variety of references are listed Reasonable efforts have been made to publish reliable data and information, but the author and the publisher cannot assume responsibility for the validity of all materials or for the consequences of their use No part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers For permission to photocopy or use material electronically from this work, please access www.copyright.com (http://www.copyright.com/) or contact the Copyright Clearance Center, Inc (CCC) 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400 CCC is a not-for-profit organization that provides licenses and registration for a variety of users For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe Library of Congress Cataloging-in-Publication Data Tumanski, Slawomir Principles of electrical measurement / by Slawomir Tumanski p cm. (Series in sensors) Includes bibliographical references and index ISBN 0-7503-1038-3 Electric measurements Electronic measurements Signal processing I Title II Sensors series TK275.T75 2005 621.37 dc22 2005054928 Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com Taylor & Francis Group is the Academic Division of Informa plc and the CRC Press Web site at http://www.crcpress.com Contents Preface ix Introduction to Measurements Fundamentals of Electrical Measurements 13 2.1 Main Terms and Definitions 2.1.1 Basic terms of measurement technique 2.1.2 The main methods of measurements 2.2 Uncertainty of Measurements 2.2.1 Errors, uncertainty, and reliability of signal processing 2.2.2 Basic statistical terms and concepts 2.2.3 Methods of evaluation and correction of the uncertainty related to limited accuracy of measuring devices 2.2.4 The estimation of uncertainty in measurements 2.3 Standards of Electrical Quantities 2.3.1 Standards, etalons, calibration and validation 2.3.2 The standards of electrical quantities referred to the physical phenomena and laws 2.3.3 Material standards of electrical quantities 2.3.4 The reference multimeters and calibrators References 13 13 18 26 26 34 58 63 69 71 Classic Electrical Measurements 73 3.1 Indicating Measuring Instruments 3.1.1 Electromechanical instruments versus digital measuring systems 3.1.2 The moving coil meters 3.1.3 The moving iron meters 3.1.4 Electrodynamic meters – wattmeters 3.1.5 Induction type watt-hour meters 3.2 Recording and Displaying Measuring Instruments 3.2.1 Fundamentals of oscilloscopes 3.2.2 Recorders and data storage devices 3.3 Bridge Circuits 3.3.1 Balanced and unbalanced bridge circuits 3.3.2 Null-type DC bridge circuits 73 V 40 52 57 57 73 74 81 82 86 88 88 93 94 94 96 VI PRINCIPLES OF ELECTRICAL MEASUREMENTS 3.3.3 The AC bridge circuits 3.3.4 The transformer bridge circuits 3.3.5 The unbalanced bridge circuits 3.3.6 The alternatives for bridge circuits – Anderson Loop 3.4 Potentiometers and Comparators References 99 104 107 112 114 118 Processing of the Analogue Measurement Signals 121 4.1 Signal Conditioning 4.1.1 Analogue measurement signals 4.1.2 Conditioning of resistance, capacitance and inductance 4.1.3 AC/DC conversion 4.1.4 Voltage to frequency conversion 4.2 Amplification of the Signals 4.2.1 Differential, operational and instrumentation amplifiers 4.2.2 Isolation amplifiers 4.2.3 Amplifiers of very small DC signals 4.2.4 Amplifiers of very small AC signals 4.2.5 Amplifiers of very large input resistance (electrometers) 4.2.6 The function amplifiers 4.3 Negative Feedback in the Measuring Technique 4.4 The Improvement of the Quality of the Analogue Signals 4.4.1 The noises and interferences of the analogue signals 4.4.2 The connection of the measuring signal to the amplifier 4.4.3 The analogue filtering of the signals References 121 121 126 131 141 143 143 147 150 154 159 161 169 179 179 184 191 201 Digital Processing of the Measurement Signals 205 5.1 Analogue-to-Digital Converters 5.1.1 Sampling, quantization and coding of signals 5.1.2 Analogue-to-digital converters ADC 5.1.3 The main specifications of analogue-to-digital converters 5.2 Digital-to-Analogue Converters 5.2.1 The reconstruction of the analogue signal 5.2.2 The digital-to-analogue converters DAC 5.2.3 The main specifications of digital-to-analogue converters 5.3 Methods and Tools of Digital Signal Processing 5.3.1 The main terms of digital signal processing 5.3.2 The Discrete Fourier Transform DFT and Fast Fourier Transform FFT 5.3.3 Short-time Fourier Transform and Wavelet transform 5.3.4 Digital filters 205 205 218 234 238 238 242 247 249 249 259 268 275 CONTENTS VII 5.4 Examples of Application of Digital Signal Processing in Measurements 5.4.1 The spectral analysis 5.4.2 Digital signal synthesis 5.4.3 Improvement of the signal quality and the signal recovery 5.5 Digital Measuring Instruments 5.5.1 Digital multimeters and frequency meters 5.5.2 Digital oscilloscopes 5.5.3 Digital measurement of power and energy 5.6 Intelligent Data Analysis 5.6.1 The artificial intelligence in measurements 5.6.2 The adaptive filters 5.6.3 Artificial neural networks 5.6.4 Fuzzy Logic References 287 287 297 303 312 312 318 323 326 326 327 331 340 344 Computer Measuring Systems 349 6.1 Introduction 6.2 Input Circuits of the Measuring Systems 6.2.1 Circuits for data conditioning and acquisition 6.2.2 The sensors with built-in interface – intelligent sensors 6.2.3 Analogue and digital transmitters 6.2.4 Data loggers 6.2.5 IEEE P1451 standard – smart sensors 6.3 Data Acquisition Circuits – DAQ 6.3.1 Plug-in data acquisition board 6.3.2 External data acquisition board 6.4 Data Communication in Computer Measuring Systems 6.4.1 Interfaces, buses and connectors 6.4.2 Serial interfaces: RS-232C and RS-485 6.4.3 Serial interfaces: USB and FireWire 6.4.4 Parallel GPIB interface (IEEE-488/IEC-625) 6.4.5 Wireless interfaces: IrDA, Bluetooth and WUSB 6.4.6 Mobile telephony systems GSM and UMTS as a tool for data transfer 6.4.7 Radio data acquisition and transfer 6.4.8 Computer systems using Ethernet and Internet 6.4.9 Dedicated interfaces: CAN, I2C, MicroLAN, SDI-12 6.4.10 HART interface and the – 20 mA standard 6.4.11 Industrial communication standards – Fieldbus, Profibus, SCADA 6.4.12 Modular systems – VXI, PXI 6.4.13 Standard command for measuring devices – SCPI 349 353 353 354 356 357 359 362 362 365 367 367 368 373 377 382 385 389 392 396 400 401 406 408 VIII PRINCIPLES OF ELECTRICAL MEASUREMENTS 6.5 Measuring Systems Basing on the Signal Processors 6.5.1 Microcontrollers and signal processors in measuring technique 6.5.2 Microinterfaces – SPI and UART 6.6 Virtual Measuring Systems 6.6.1 What is the virtual measuring device? 6.6.2 TestPoint 6.6.3 Agilent VEE Pro 6.6.4 LabVIEW of National Instruments 6.7 The Examples of Computer Measuring Systems 6.7.1 The measuring system for testing of magnetic materials 6.7.2 The arbitrary wave excitation systems 6.7.3 The scanning device for magnetic field imaging References 410 410 418 421 421 424 428 431 438 438 442 449 452 Symbols used in the Book Abbreviations used in the Book Index 455 457 461 Preface In libraries and bookshops we can find various books on electrical measurements Most of them describe various aspects of electrical measurements: digital or analogue techniques, sensors, data acquisition, data conversion, etc However, it can be difficult to find a book that includes a complete guide on the techniques used in taking electrical measurements The reason for this is rather obvious –modern measuring requires knowledge of many interdisciplinary topics such as computer techniques, electronics, signal processing, micro- and nanotechnology, artificial intelligence methods, etc It is practically impossible for one author to know and explain all these subjects Therefore, there are frequently available books called “Handbook of…” written by dozens of co-authors Unfortunately, such books are mainly more conglomerates of many encyclopaedia entries of unequal levels than comprehensive and compact knowledgeable books The other aspect of this problem is that the progress in measuring techniques is very fast, with every year bringing new developments It is really difficult to catch the state of the art in measurements It is much easier to gather knowledge on a particular subject in the form of a monograph focused on a special problem But on the other hand, students and industry engineers look for comprehensive books that are easy to understand and most of all include recent developments, such the computer measuring systems or virtual measuring methods I lecture on electrical measurements to students of electrical engineering, robotics and informatics To tell the truth I could not find a suitable book on the whole subject and therefore I decided to write one myself Last year I “tested” this book on students and the results were quite promising Most of the students understood the electrical measurements and what most importantly, they found that this subject was interesting, and even fascinating Let us look at modern measurement techniques, the present state and the future perspectives There is no doubt that the future is reserved for computer measuring systems It is no wonder that today, when a simple electric shaver is supported by a microcontroller that the measuring instruments are also A non-exhaustive list of market available books on measurements is included at the end of this preface IX x n >w n x n @ h n >w n h n @ >x n h n @ >w n x n h n @ (5.40) w n >x n h n @ The inverse operation to the convolution is deconvolution The deconvolution operation is the calculation of the x(n) signal from the convoluted result y(n) knowing the h(n) function (see equation 5.38) The deconvolution is much easier to perform in the frequency domain than in the time domain – this problem is described in more detail later (Section 5.4.3) Another important term is the correlation function, used for the comparison of two signals x1(n) and x2(n) The correlation function is described by following relation r12 k ... example of the structure of computer measuring system Figure 1.4 presents an example of the structure of a modern measuring system Properties of investigated object (electrical and non -electrical. .. parts: Principles of Electrical Measurements” and “Application of Electrical Measurements in Science, Industry and Everyday Life” This first part is presented in this book I understand the Principles. .. subjects: “Application of Electrical Measurements” – sensors, measurements of electrical and non -electrical quantities, non-destructive testing and material evaluation, design of measuring instruments,