Industrial Instrumentation: Principles and Design

657 Pages·2000·21.29 MB·English

by  Tattamangalam R. Padmanabhan PhD (auth.)

Industria l Instrumentatio n
Springer-Verla g London Ltd.
Tattamangalam R. Padmanabhan
Industrial
Instrumentation
Principles and Design
With 429 Figures
Springer
Tattamangalam R. Padmanabhan, PhD
Amrita Institute ofTechnology and Science, Ettimadai, Coimbatore 641105, India
ISBN 978-1-4471-1145-0
British Library CataIoguing in Publieation Data
Padmanabhan. Tattamanga1am R.
Industrial instrumentation : principles and design
1. Electronic instruments 2. Industrial electronics
1. Title
670.4'27
ISBN 978-1-4471-1145-0
Library of Congress CataIoging-in-Publication Data
Padmanabhan. TattamangalamR.. 1941-
Industrial instrumentation : principles and design I Tattamangalam
R. Padmanabhan.
p. cm.
ISBN 978-1-4471-1145-0 ISBN 978-1-4471-0451-3 (eBook)
DOI 10.1007/978-1-4471-0451-3
1. Process control-Instruments. 2. Electronic instruments.
3. Measuring instruments. L Title.
TSI56.8.PI8 1999 99-41995
629.8-dc21 CIP
Apart from any fair deaIing for the purposes oC research or private study. or criticism or review. as
permitted under the Copyright, Designs and Patents Act 1988. this publication may only be reproduced,
stored or transmitted, in any Corm or by any means, with the prior permission in writing of the publishers,
or in the case of reprographie reproduction in accordance with the terms of licences issued by the
Copyright Licensing Agency. Enquiries concerning reproduction outside those terms should be sent to the
publishers.
© Springer-Verlag London 2000
Originally published by Springer-Verlag London Berlin Heidelberg in 2000
Softeover reprint of the hardcover 1s t edition 2000
The use of registered names, trademarks, etc. in this publication does not imply. even in the absence of a
specific statement. that such names are exempt from the relevant laws and regulations and therefore free
for general use.
The publisher makes no representation. express or implied, with regard to the accuracy of the information
contained in this book and cannot accept any legal responsibility or liability for any errors or omissions
that may be made.
Typesetting: camera ready by author
69/3830-543210 Printedonacid-freepaper SPIN 10736297
To
MyUma
My Prop
Preface
Barely 10 years back, Instrumentation was considered a queer mix of technology
and practical skills. There were pneumatic schemes, hydraulic schemes, electro
pneumatic schemes, electro-hydraulic schemes and magnetic amplifier based
schemes; electronic schemes were essentially apologies. A lot of skill and technical
input went into the strip-chart recorder, the flapper-nozzle scheme and so on. The
copper tube lines that carried the pneumatic supply and signals were as common in
the industry as the electric power supply conduits. With the advent of electronic
schemes, all these have become things of the past. Microprocessors have a knack of
thrusting themselves everywhere - especially in instrumentation schemes.
Quantities, which were, ignored (gas concentration) and those perceived as 'not
measurable' (high temperature) have catapulted and fallen preys to sensors. On-line
correction and compensation have become common with electronic schemes.
Intensive calculations using sensor outputs - often on-line - have become the order
of the day. Though the principles remain the same, the trend for on-line correction,
compensation and information extraction is likely to continue unabated.
There is a clear-cut need for a book on industrial instrumentation, the stress
being on electronics based state-of-the-art schemes. This need is addressed to by
this book. In part I of the book the scope of an instrumentation scheme has been
brought out through specific examples and 'what one looks for in an
instrumentation scheme' identified. The functional modules that make up the
scheme are identified. The role of each such module is dealt with in succeeding
chapters. Despite the variety in the schemes and applications, there are certain
common threads running through many of the schemes. These lead to the 'Generic
Instrumentation schemes' which provide the basic framework for most of the
instrumentation schemes. The structure and scope of such generic schemes built
with the basic functional modules, are also discussed. Part II is devoted to schemes
and applications. Instrumentation of the most common industrial physical variables
is discussed in detail. Displacement, force and related quantities, temperature,
pressure and flow are the major ones here. Wherever possible attempts have been
made to identify the threshold level for sensing, full-scale accuracy and the like,
and quantify them.
In the last chapter, an attempt has been made to identify an order and gradation
in the complexity levels of instrumentation schemes. Subsequently, typical practical
schemes of the more complex type are discussed.
Throughout, the stress has been on industrial instrumentation per se. As such
analysis instrumentation, biomedical instrumentation and laboratory instruments -
each a specialized area in its own right - have not been dealt with. To retain focus,
Displays, which has become a vast area of its own, has been left out consciously. I
viii
hope the book will be of use to the professionals in instrumentation as well as the
academic community.
T. R. Padmanabhan, Ph.D.
Amrita Institute of Technology and Science
Ettimadai
Coimbatore
October 1999
Acknowledgements
I have honed my skills through the discussions with my erstwhile teachers and
colleagues at the Electrical Engineering Department, Indian Institute of Technology
Kharagpur, India. My associates in the industry over the last two decades at the
Tata Iron & Steel Co. Ltd., Jamshedpur, Crompton Greaves Ltd., Mumbai and
Premier Polytronics Ltd., Coimbatore, too have been helpful in many ways in this
venture. lowe a lot to all of them. Ms Radhamani Pillai, Professor at Arnrita
Institute of Technology Coimbatore, has gone through the manuscript with
diligence and has been instrumental for many changes to improve the clarity of
expression, continuity and style. I thank her for her involvement. I am obliged to
my friend Mr K N Easwaran who stooped to conquer 'Word' and mastered it for
my sake; his eagle's eyes missed hardly any mistake in the edited text. Mr Oliver
Jackson of Springer Verlag has been informal, prompt and helpful in many ways
during this venture; I thank him for his involvement. I thank my family - my wife
Vma, kids Ravi and Chandra and my late mother - who have put up with my
apparent prolonged isolation on account of this effort.
Contents
Part I Principles and Components
1 Instrumentation Schemes Structure and Specifications .......................................... 3
1.1 Introduction ............................................................................................................ 3
1.2 Shop-Floor Compressor ......................................................................................... 3
1.3 Plastic Extrusion ..................................................................................................... 3
1.4 Reaction Vessel ...................................................................................................... 7
\.5 Characteristics of an Instrumentation Scheme ........................................................ 9
1.5.1 Accuracy ........................................................................................................ 9
1.5.2 Precision ...................................................................................................... 11
1.5.3 Errors and Correction .................................................................................. 12
1.5.4 Sensitivity .................................................................................................... 13
1.5.5 Hysteresis .................................................................................................... 14
1.5.6 Resolution .................................................................................................... 15
\.5.7 Threshold and Dead Zone ............................................................................ 15
1.5.8 Drift ............................................................................................................. 15
\.5.9 Repeatability and Zero Stability .................................................................. 17
1.5.10 Range ........................................................................................................... 17
1.5.11 Linearity ...................................................................................................... 18
1.5 .12 Input and Output Impedances ...................................................................... 19
\.6 Instrumentation Scheme -Block Diagram ............................................................ 21
1.6.1 Primary Sensor ............................................................................................ 22
1.6.2 Secondary Sensor ........................................................................................ 23
\.6.3 Stages of Analog Signal Processing ............................................................ 23
1.6.4 Output .......................................................................................................... 24
1.6.4.1 Display .................................................................................................... 24
1.6.4.2 Transmitter .............................................................................................. 24
1.7 Digital System ...................................................................................................... 25
2 Secondary Transducers .............................................................................................. 29
2.1 Introduction .......................................................................................................... 29
2.2 Unbalanced Wheatstone Bridge ........................................................................... 30
2.2.1 Assumptions ................................................................................................ 30
2.2.2 Bridge Near Balance .................................................................................... 30
2.2.3 Transducer Bridge Behaviour for Large E Values ....................................... 33
2.2.4 Transducer Bridge with Multiple Sensing Elements .................................... 36
2.2.4.1 Transducer Bridge with Diagonally Opposite Sensing Arms .................. 36
2.2.4.2 Transducer Bridge with Adjacent Sensing Arms .................................... 37
2.2.4.3 Transducer Bridges with Four Sensing Arms .......................................... 39
2.2.5 Unbalanced Bridges ..................................................................................... 39
2.3 AC Bridges ........................................................................................................... 40
2.3.1 Possible Configurations .............................................................................. .40
2.3.2 Sensitivity of Unbalanced AC bridges ......................................................... 43
xii
2.3.3 Transducer with Off-Balance AC Bridge .................................................... 46
2.3.4 Wein Bridge ............................................................................................... .47
2.3.5 Mutual Inductance Bridges .......................................................................... 49
2.4 Oscillator Type of Transducers ............................................................................ 51
2.4.1 Sensitivity of Oscillator Type Transducers .................................................. 54
2.5 Feedback Type Transducers ................................................................................. 54
3 Operational Amplifiers •••••.•..•••••••.•....•••....•......••••.......••......•..••...••.•••..••...•••••.••••..•••.••• 56
3.1 Introduction .......................................................................................................... 56
3.2 Ideal Opamp ......................................................................................................... 56
3.3 Specifications of Opamps ..................................................................................... 57
3.3.1 Open Loop Gain .......................................................................................... 57
3.3.2 Gain Bandwidth Product ............................................................................. 58
3.3.3 Phase Lag .................................................................................................... 58
3.3.4 Range of Output Voltage ............................................................................. 59
3.3.5 Linearity ...................................................................................................... 59
3.3.6 Input Currents .............................................................................................. 60
3.3.7 Offset Voltage (Vos) ..................................................................................... 61
3.3.8 Input Offset Voltage Drift ........................................................................... 61
3.3.9 Input Offset Current and its Drift ................................................................ 62
3.3.10 Common Mode Rejection ............................................................................ 62
3.3.11 Output Impedance ....................................................................................... 62
3.3.12 Slew Rate ..................................................................................................... 63
3.3.13 Noise in Opamps ......................................................................................... 63
3.3.13.1 Schottky Noise (Shot Noise) ............................................................... 64
3.3.13.2 Flicker Noise ( IIf Noise) .................................................................. 64
3.3.13.3 Popcorn Noise ..................................................................................... 65
3.3.13.4 Total Opamp Noise ............................................................................. 65
3.4 Opamp Characteristics - Trade-offs ..................................................................... 66
3.5 Characteristics of Typical Commercial Opamps .................................................. 66
3.6 Opamp Selection .................................................................................................. 68
4 Linear Signal Processing ............................................................................................ 74
4.1 Introduction .......................................................................................................... 74
4.2 General Considerations ........................................................................................ 74
4.3 Inverting Amplifiers ............................................................................................. 76
4.3.1 Analysis of the Non-ideal Amplifier. ........................................................... 78
4.3.2 Noise in the Amplifier ................................................................................. 82
4.3.3 Minimisation of Leakage Errors .................................................................. 85
4.4 Summing Amplifier .............................................................................................. 86
4.5 Current to Voltage Convertor ............................................................................... 87
4.6 Integrator .............................................................................................................. 87
4.7 Non-Inverting Amplifier ...................................................................................... 89
4.8 Buffers .................................................................................................................. 90
4.9 Differentiator ........................................................................................................9 1
4.10 Difference Amplifier ............................................................................................ 92
4.11 Adaptations of the Difference Amplifier .............................................................. 94
4.12 Instrumentation Amplifier .................................................................................... 96
4.13 Isolation Amplifier ............................................................................................. 102
4.13.1 Schematic Arrangement... .......................................................................... 102
4.13.2 Transformer Type ...................................................................................... 10 3
4.13.3 Capacitance Coupled Type ........................................................................ 104
4.13.4 Opto-coupled Type .................................................................................... 105
4.13.5 Comparison ............................................................................................... 106