ISA LOOP CHK-2005 Loop Checking - A Technician-s Guide.pdf
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1、LOOP CHECKING:A TECHNICIANS GUIDEJeffrey05.book Page i Thursday, March 3, 2005 2:56 PMJeffrey05.book Page ii Thursday, March 3, 2005 2:56 PMLOOP CHECKING:A TECHNICIANS GUIDEHarley JefferyISA TECHNICIAN SERIESJeffrey05.book Page iii Thursday, March 3, 2005 2:56 PMCopyright 2005 by ISA Instrumentation
2、, Systems, and Automation Society67 Alexander DriveP.O. Box 12277Research Triangle Park, NC 27709All rights reserved.Printed in the United States of America.1098765432ISBN 1-55617-910-3No part of this work may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, e
3、lectronic, mechanical, photocopying, recording or otherwise, without the prior written permission of the publisher.NoticeThe information presented in this publication is for the general education of the reader. Because neither the author nor the publisher has any control over the use of the informat
4、ion by the reader, both the author and the publisher disclaim any and all liability of any kind arising out of such use. The reader is expected to exercise sound professional judgment in using any of the information presented in a particular application. Additionally, neither the author nor the publ
5、isher have investigated or considered the effect of any patents on the ability of the reader to use any of the information in a particular application. The reader is responsible for reviewing any possible patents that may affect any particular use of the information presented. Any references to comm
6、ercial products in the work are cited as examples only. Neither the author nor the publisher endorses any referenced commercial product. Any trademarks or tradenames referenced belong to the respective owner of the mark or name. Neither the author nor the publisher makes any representation regarding
7、 the availability of any referenced commercial product at any time. The manufacturers instructions on use of any commercial product must be followed at all times, even if in conflict with the information in this publication.Library of Congress Cataloging-in-Publication DataJeffery, Harley.Loop check
8、ing :a technicians guide / Harley Jeffery.p. cm. - (ISA technician series)Includes bibliographical references.ISBN 1-55617-910-3 (pbk.)1. Process control-Automation. I. Title. II. Series. TS156.8.J44 2005629.83-dc222005001679Jeffrey05.book Page iv Thursday, March 3, 2005 2:56 PMTo Tamra, John, Chris
9、sy, Ashton, and SarahJeffrey05.book Page v Thursday, March 3, 2005 2:56 PMJeffrey05.book Page vi Thursday, March 3, 2005 2:56 PMACKNOWLEDGMENTSDuring the past several years, I have met many people who have shared their invaluable and memorable knowledge and insights. Loop Checking: A Technicians Gui
10、de combines this wisdom with the experiences of control loop device manufacturers, control system engineers, plant I the chapter takes a closer look at loop checking with and without smart instruments. A start-up scenario provides the process control example in Chapter 3.Chapter 4 Performance Benchm
11、arking reviews this tool which checks the loop and ensures performance is at the highest level possible, and which can set the benchmark for performance that is monitored over time (Chapter 5). Although performance testing occurs after start-up in this project sequence, the procedure can also be use
12、d with any loop/unit operation as a troubleshooting guide when process control problems arise, or as a general approach to improve existing operations. Again, planning is important; items to watch for are suggested and typical forms are included, along with some recommendations on how to perform the
13、 checks. The example process is then “benchmarked” using the techniques discussed in this chapter.Chapter 5 Sustaining the Performance makes sure you can maintain the high level of performance achieved and benchmarked in Chapter 4. Maintenance strategies show where the performance monitoring fits. S
14、uggestions on starting this program are included along with some in-depth considerations of how the program will address the elements of the loop. The implementation of a performance monitoring program is dependent on the particular control system architecture (single loop controllers, PLCs, DCSs, h
15、ybrid control, digital control systems, etc.) that your plant has installed (or is planning to install). Thus, several of these hardware architectures are examined with ideas and options for implementation. Jeffrey05.book Page xiv Thursday, March 3, 2005 2:56 PM1INTRODUCTION TO LOOPCHECKINGProcess c
16、ontrol loops have a major impact on the financial performance of todays manufacturing facilities. It is also recognized that a “good foundation” of the basic regulatory control loop is essential to the success of higher-level “Advanced Process Control (APC)” program (Ref. 6). Thus, it is critical th
17、at these facilities technicians focus on loop checking and performance. For this reason, this guide defines loop checking broadly to include control loop performance rather than merely in terms of plant start-up situations as in the traditional definition. Loop checking is also an important componen
18、t in any plants continuous improvement planning program insofar as it helps define and reduce the variability of key process parameters on an ongoing basis.The chapters of Loop Checking: A Technicians Guide are arranged to follow a typical automation project from design checkout at the factory accep
19、tance test (FAT) through to an ongoing sustaining loop performance program. The steps of such projects is as follows: loop checking basics the factory acceptance test (FAT)start-up performance benchmarking sustaining the performanceThis guide is intended to discuss general methods and practices that
20、 can be applied across many processes or industries. The technician will encounter different plans and programs in his or her own company for addressing loop performance. These will, of course, affect how loop checking is defined and accomplished for the technicians specific environment. However, th
21、e instrument technician typically has the best overall knowledge and skills for checking and maintaining control loop performance.Jeffrey05.book Page 1 Thursday, March 3, 2005 2:56 PM2 Introduction to Loop Checking1.1 THE OPPORTUNITYIn todays intensely competitive markets, manufacturers are striving
22、 to continually improve manufacturing performance to meet their business needs and goals. Typical business drivers are as follows: increased throughput increased yield increased quality minimized waste and off-specAs we noted, the control loop (and the continual checking of performance) plays a vita
23、l role in the plants financial performance. However, it has been observed that up to 80 percent of all loops are not performing their intended function of reducing the variability that results from the problems caused by the factors shown in Figure 1-1. Such issues as measurement placement and the d
24、ead time or process mixing it causes, undersized headers and valves, loop tuning, and control strategy, all affect the loops ability to accomplish the desired objectives.FIGURE 1-1Control Loop Performance IssuesIn addition, plant performance studies (such as those summarized in Figure 1-2) have show
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