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`

`Computer-Controlled
`Systems
`
`Theory and Design
`
`THIRD EDITION
`
`Karl J. Astrém
`
`Bjérn Wittenmark
`
`uuIll
`
`Prentice Hall, Upper Saddle River, New Jersey
`
`07458
`
`

`

`Library of Congress Cataloglng-ln-Publicalion Data
`
`Astrom, Karl I. (Karl Johan)
`Computer-Controlled systems : theory and design / Karl I. Astrom
`Bjorn Wittcnmark.
`-- 3rd ed.
`P.
`cm.
`Includes bibliographical references and index.
`ISBN 0-13-314899—8
`
`l. Automatic control--Data processing. 1. Wittenmark, Bjorn.
`11. Title.
`T1213.A78 1997
`629.8'9--dc20
`
`96-36745
`CIP
`
`Publisher: Tom Robbins
`Associate editor: Alice Dworkin
`
`Editorial production supervision: Joseph Scordato
`Editor-inwhief: Marcia Horton
`Managing editor: Bayani Mendoza Deleon
`Copyeditor: Peter I. Zurita
`Cover designer: Bruce Kenselaar
`Director of production and manufacturing: David W. Riccardi
`Manufacturing buyer: Donna Sullivan
`Editorial assistant: Nancy Garcia
`
`=
`5
`
`@1997 by Prentice-Hall. Inc.
`Simon & Schuster/A Viacom Company
`Upper Saddle River, NJ 07458
`
`All rights reserved. No part of this book may be
`reproduced. in any form or by any means.
`without permission irt writing from the publisher.
`
`The author and publisher of this book have used their best efforts in preparing this book. These efforts
`include the development. research. and testing of the theories and programs to determine their effectiveness.
`The author and publisher make no warranty of any kind, expressed or implied, with regard to these programs
`or the documentation contained in this book. The author and publisher shall not be liable in any event for
`incidental or consequential damages in connection with, or arising out of, the furnishing, performance, _or use
`of these programs.
`
`Printed in the United States of America
`
`‘0 9 8 7 6 5 “ 3 2
`
`ISBN D-lB-BLHB‘H-B
`
`Prentice-Hall International (UK) Limited. London
`Prentice-Hall of Australia Pty. Limited, Sydney
`Prentice-Hall Canada Inc.. Toronto
`Prentice-Hall Hispanoamen'cana, S.A., Mexico
`Prentice-Hall of India Private Limited, New Delhi
`Prentice-Hall of Japan, Inc.. Tokyo
`Simon & Schuster Asia Pte. L'.d., Singapore
`Editora Prentice-Hall do Brasil, Ltda., Rio de Ianeiro
`
`"Muir. HERMES
`
`MAY021997
`
`
`R 43%;, , .3
`“Rn.“‘c-VTP’V u-u—r
`
`

`

`6
`
`Computer Control
`
`Chap. 1
`
`an addition time of 2 ,us and a multiplication time of 7 ,us. The MTBF for a
`central processing unit was about 20,000 h.
`An important factor in the rapid increase of computer control in this period
`was that digital computer control now came in a smaller “unit.” It was thus
`possible to use computer control for smaller projects and for smaller problems.
`Because of minicomputers, the number of process computers grew from about
`5000 in 1970 to about 50.000 in 1975.
`
`Microcomputer Period and General Use of Computer Control
`
`The early use of computer control was restricted to large industrial systems
`because digital computing was only available in expensive, large, slow, and
`unreliable machines. The minicomputer was still a fairly large system. Even
`as performance continued to increase and prices to decrease, the price of a
`minicomputer mainframe in 1975 was still about $10,000. This meant that a
`small system rarely cost less than $100,000. Computer control was still out
`of reach for a large number of control problems. But with the development of
`the microcomputer in 1972, the price of a card computer with the performance
`of a 1975 minicomputer dropped to $500 in 1980. Another consequence was
`that digital computing power in 1980 came in quanta as small as $50. The
`development of microelectronics has continued with advances in very large-scale
`integration (VLSI) technology; in the 19903 microprocessors became available
`for a few dollars. This has had a profound impact on the use of computer control.
`As a result practically all controllers are now computer-based. Mass markets
`such as automotive electronics has also led to the development of special-purpose
`computers, called microcontrollers, in which a standard computer chip has been
`augmented with AD and DA converters, registers, and other features that
`make it easy to interface with physical equipment.
`Practically all control systems deve10ped today are based on computer
`control. Applications span all areas of control, generation, and distribution.
`of electricity; process control; manufacturing; transportation; and entertain-
`ment. Mass-market applications such as automotive electronics, CD players,
`and videos are particularly interesting because they have motivated computer
`manufacturers to make chips that can be used in a wide variety of applications.
`As an illustration Fig. 1.2 shows an example of a single-loop controller for
`process control. Such systems were traditionally implemented using pneumatic
`or electronic techniques, but they are now always computer-based. The con-
`troller has the traditional proportional, integral, and derivative actions (PID),
`which are implemented in a microprocessor. With digital control it is also pos-
`sible to obtain added functionality. In this particular case, the regulator is pro-
`vided with automatic tuning, gain scheduling, and continuous adaptation of
`feedforward and feedback gains. These functions are difficult to implement with
`analog techniques. The system is a typical case that shows how the function-
`ality of a traditional product can be improved substantially by use of computer
`control.
`
`