Table Of ContentControl Systems
Safety Evaluation
and Reliability
Third Edition
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Control Systems
Safety Evaluation
and Reliability
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Notice
The information presented in this publication is for the general education of the reader. Because
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The reader is expected to exercise sound professional judgment in using any of the information pre-
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Additionally, neither the author nor the publisher has investigated or considered the effect of
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Copyright © 2010 International Society of Automation
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P.O. Box 12277
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All rights reserved.
Printed in the United States of America.
10 9 8 7 6 5 4 3 2
ISBN 978-1-934394-80-9
No part of this work may be reproduced, stored in a retrieval system, or transmitted
in any form or by any means, electronic, mechanical, photocopying, recording or
otherwise, without the prior written permission of the publisher.
Library of Congress Cataloging-in-Publication Data
Goble, William M.
Control systems safety evaluation and reliability / William M. Goble.
-- 3rd ed.
p. cm. -- (ISA resources for measurement and control series)
Includes bibliographical references and index.
ISBN 978-1-934394-80-9 (pbk.)
1. Automatic control--Reliability. I. Title.
TJ213.95.G62 2010
629.8--dc22
2010015760
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ISA Resources for Measurement
and Control Series (RMC)
• Control System Documentation: Applying Symbols and Identification, 2nd
Edition
• Control System Safety Evaluation and Reliability, 3rd Edition
• Industrial Data Communications, 4th Edition
• Industrial Flow Measurement, 3rd Edition
• Industrial Level, Pressure, and Density Measurement, 2nd Edition
• Measurement and Control Basics, 4th Edition
• Programmable Controllers, 4th Edition
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Acknowledgments
This book has been made possible only with the help of many other persons.
Early in the process, J. V. Bukowski of Villanova taught a graduate course in
reliability engineering where I was introduced to the science. This course and
several subsequent tutorial sessions over the years provided the help necessary to
get started.
Many others have helped develop the issues important to control system safety
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Stavrianidis, Paul Gruhn, Aarnout Brombacher, Ad Hamer, Rolf Spiker, Dan
Sniezek and Steve Smith. I have learned from our debates.
Several persons made significant improvements to the document as part of the
review process. I wish to thank Tom Fisher, John Grebe, Griff Francis, Paul
Gruhn, Dan Sniezek, Rainer Faller and Rachel Amkreutz. The comments and
questions from these reviewers improved the book considerably. Julia Bukowski
from Villanova University and Jan Rouvroye of Eindhoven University deserve a
special thank you for their comprehensive and detail review. Iwan van Beurden
of Eindhoven University also deserves a special thank you for a detail review and
check of the examples and exercise answers. I also wish to thank Rick Allen, a
good friend, who reviewed the draft and tried to teach the rules of grammar and
punctuation.
Finally, I wish thank my wife Sandy and my daughters Tyree and Emily for their
patience and help. Everyone helped proofread, type, and check math. While the
specific help was greatly appreciated, it is the encouragement and support for
which I am truly thankful.
vii
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Contents
PREFACE xv
ABOUT THE AUTHOR xvii
Chapter 1 INTRODUCTION 1
Control System Safety and Reliability, 1
Standards, 4
Exercises, 6
Answers to Exercises, 7
References, 7
Chapter 2 UNDERSTANDING RANDOM EVENTS 9
Random Variables, 9
Mean, 18
Variance, 21
Common Distributions, 23
Exercises, 27
Answers to Exercises, 29
References, 31
Chapter 3 FAILURES: STRESS VERSUS STRENGTH 33
Failures, 33
Failure Categorization, 33
Categorization of Failure Stress Sources, 39
Stress and Strength, 46
Electrical Surge and Fast Transients, 55
Exercises, 56
Answers to Exercises, 56
References, 57
ix
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x Control Systems Safety Evaluation and Reliability
Chapter 4 RELIABILITY AND SAFETY 59
Reliability Definitions, 59
Time to Failure, 59
The Constant Failure Rate, 72
Steady-State Availability – Constant Failure Rate Components, 76
Safety Terminology, 78
Exercises, 85
Answers to Exercises, 86
References, 86
Chapter 5 FMEA / FMEDA 87
Failure Modes and Effects Analysis, 87
FMEA Procedure, 87
FMEA Limitations, 88
FMEA Format, 88
Failure Modes, Effects and Diagnostic Analysis (FMEDA), 94
Conventional PLC Input Circuit, 95
Critical Input (High Diagnostic) PLC Input Circuit, 97
FMEDA Limitations, 99
Exercises, 99
Answers to Exercises, 100
References, 100
Chapter 6 FAULT TREE ANALYSIS 103
Fault Tree Analysis, 103
Fault Tree Process, 104
Fault Tree Symbols, 105
Qualitative Fault Tree Analysis, 106
Quantitative Fault Tree Analysis, 108
Use of Fault Tree Analysis for PFDavg Calculations, 114
Using a Fault Tree for Documentation, 116
Exercises, 118
Answers to Exercises, 119
References, 119
Chapter 7 RELIABILITY BLOCK DIAGRAMS 121
Reliability Block Diagrams, 121
Series Systems, 123
Quantitative Block Diagram Evaluation, 137
Exercises, 146
Answers to Exercises, 147
References and Bibliography, 148
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