Distributed control systems : their evaluation and design

302 Pages·1986·15.328 MB·English

by  Michael P. Lukas

DISTRIBUTED
CONTROL SYSTEMS
Their Evaluation and Design
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DISTRIBUTED
CONTROL SYSTEMS
Their Evaluation and Design
Michael P. Lukas
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Copyright © 1986 by Van Nostrand Reinhold Company Inc.
Library of Congress Catalog Card Number: 85-22691
ISBN 0-442-26020-2
All rights reserved. No part of this work covered by the copyright hereon may
be reproduced or used in any form or by any means—graphic, electronic or
mechanical, including photocopying, recording, taping, or information storage
and retrieval systems—without permission of the publisher.
Manufactured in the United States of America.
Published by Van Nostrand Reinhold Company Inc.
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Van Nostrand Reinhold
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Macmillan of Canada
Division of Gage Publishing Limited
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Library of Congress Cataloging-in-Publication Data
Lukas, Michael P.
Distributed control systems.
Includes index.
1.Process control—Data processing. 2. Electronic
data processing—Distributed processing. I. Title.
TS156.8.L85 1986 629.8'95 85-22691
ISBN 0-422-26020-2
To Marj-
who inspired me
to get this done
and kept things going
while I was doing it.

PREFACE
In less than a decade, microprocessor-based distributed control systems
have grown from a technical novelty to a dominant force in the marketplace
for industrial automation equipment. The markets involved include the
chemical, petroleum, metals processing, pulp and paper, power generation,
and similar production industries. Every month, the trade press announces
new systems or enhancements to existing systems. These announcements
are usually accompanied by glowing claims of technical superiority or
cost advantages over competing equipment.
The main purpose of this text is to help the reader navigate through
this maze of claims and counterclaims by providing a sound base of tech-
nical information for use in evaluating or designing such systems. In one
sense, the book is a tutorial on distributed control systems, in that it de-
scribes their basic structure and summarizes the functions of each of their
elements. However, it goes beyond the level of a tutorial in that it also
reviews and compares alternative approaches that have been used to im-
plement each of these functions.
A text of this size cannot provide an exhaustive analysis of each technical
area in the distributed control field. My purpose is more modest—to ad-
dress the needs of several classes of readers:
1. For a potential user of a distributed control system, the book provides
insight into the major issues to consider when evaluating such systems
for purchase and application.
2. For a designer of a distributed control system, it reviews typical
approaches used in the design of each system element and sum-
marizes issues beyond the designer’s immediate area of technical
expertise (such as communications or software design).
3. For managers and for students interested in distributed process con-
trol, the book provides an introduction to and survey of industrial
practice in the field.
vii
viii PREFACE
This text is written for people who are not necessarily computer experts
but who are familiar with and interested in the field of industrial process
control. I have intentionally avoided technical jargon and mathematical
derivations, placing emphasis instead on defining and discussing the key
concepts of distributed control. Extensive references are provided at the
end of each chapter for the reader interested in additional details.
The book is divided into five topical areas:
1. Chapter 1—An introduction and background on distributed control
systems;
2. Chapters 2, 3, and 4—A discussion of the subsystems used to control
and gather data from the process;
3. Chapter 5—A discussion of the issues dealing with the shared com-
munications facility in a distributed control system;
4. Chapters 6 and 7—A description and analysis of the human interfaces
in a distributed system;
5. Chapter 8—A review of several other key technical issues and a
survey of future trends in the distributed control field.
The structure of the discussion in each subject area follows a standard
format. First, the subject area is introduced and the distributed control
element being discussed is put into the context of the total system. Then,
the key requirements on the design of that element are summarized. After
reviewing several of the alternative design approaches one can take, the
discussion provides some comments on the pros and cons of each alter-
native. In most cases, I have made no attempt to recommend a best al-
ternative, since that choice usually depends heavily on the intended ap-
plication of the system. The reader must make that informed decision
based on his or her knowledge of the process to be controlled.
This book is based on a working background of fifteen years in the field
of distributed control systems. I acquired a good deal of this background
at a time when there were no books or papers on the subject. During this
period, I learned the basics from several people who were ahead of their
time in conceiving distributed control systems: Bud Keyes, John Werme,
and Dick Boyd. I also am indebted to several others who, like me, learned
the subject on the job from each other: Jim Hoffmaster, Tom Scheib, Chet
Slabinski, Tom Bean, and Dave Hankinson; I want to thank these people
for their help over the years. There are many others that I would like to
thank by name but am unable to do so in a limited amount of space.
Michael P. Lukas
Eastlake, Ohio
CONTENTS
Preface / vii
1. EVOLUTION OF DISTRIBUTED CONTROL SYSTEMS / 1
1.1 Introduction and Historical Background / |
1.1.1 Traditional Control System Developments / 3
1.1.2 Computer-based Control System Developments / 5
1.1.3 Resulting System Architectures / 6
1.2 Emergence of the Distributed Control System Architecture / 8
1.3 Comparison with Previous Architectures / 12
References / 16
2. LOCAL CONTROL UNIT ARCHITECTURE / 19
2.1 Introduction/ 19
2.2 Basic Elements of a Microprocessor-based Controller / 19
2.3 Function Blocks—An Intoduction / 21
2.4 A Comparison of Architectures / 23
2.4.1. Architectural Parameters / 24
2.4.2 Impact of Architecture on Cost-Effectiveness / 30
2.9 Hardware Design Issues / 37
2.5.1 Accommodating Technological Change / 37
2.5.2 Selecting a Microprocessor / 38
2.5.3 Effects of Developments in Memory / 39
References / 44
3. LOCAL CONTROL UNIT LANGUAGES / 46
3.1 Introduction /‘46
3.2 Language Requirements / 46
3.3 Language Alternatives / 48