1、Fieldbuses forProcess Control:Engineering, Operation and MaintenanceFieldbus-Front.fm Page i Thursday, March 31, 2011 1:54 PMFieldbus-Front.fm Page ii Thursday, March 31, 2011 1:54 PMFieldbuses forProcess Control:Engineering, Operation and MaintenanceJonas BergeFieldbus-Front.fm Page iii Thursday, M
2、arch 31, 2011 1:54 PMNoticeThe information presented in this publication is for the general education of the reader. Because neither the author nor the publisher have any control over the use of the information by the reader, both the author and the publisher disclaim any and all liability of any ki
3、nd 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 publisher have investigated or considered the affect of any patents on the ability of the reader t
4、o 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 commercial products in the work are cited as examples only. Neither the author nor the publisher en
5、dorse any referenced commercial product. Neither the author nor the publisher make any representation regarding 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 t
6、he information in this publication.Any trademarks or tradenames reference belong to the respective owners of the mark or name. FOUNDATION Fieldbus is a registered trademark of the Fieldbus Foundation, HART is a registered trademark of the HART Communication Foundation, SERIPLEX is a registered trade
7、mark of Square D Company, Interbus-S is a trademark of the Interbus Club, DeviceNet is a trademark of the Open DeviceNet Vendor Association and ControlNet is a trademark of ControlNet International.Copyright 2002 ISA - The Instrumentation, Systems, and Automation SocietyAll rights reserved. Printed
8、in the United States of America. 10 9 8 7 6 5 4 3 2ISBN 1-55617-760-7No 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 writ-ten permission of the publisher.
9、ISA67 Alexander DriveP.O. Box 12277Research Triangle Park, NC 27709Library of Congress Cataloging-in-Publication DataBerge, Jonas.Fieldbuses for process control:engineering, operation, andmaintenance / Jonas Berge.p. cm.Includes bibliographical references and index.ISBN 1-55617-760-71. Intelligent c
10、ontrol systems. 2. Process control. 3. Industrialelectronics. I. Title.TJ217.5 .B47 2001629.8-dc212001003483Fieldbus-Front.fm Page iv Thursday, March 31, 2011 1:54 PMDedicationTill min pappa och till minne av min mammaFieldbus-Front.fm Page v Thursday, March 31, 2011 1:54 PMFieldbus-Front.fm Page vi
11、 Thursday, March 31, 2011 1:54 PMviiContentsChapter 1 INTRODUCTION 1Digital Communication Networks, 1Automation Networking Application Areas, 7History of Fieldbus, 14Evolution of Control System Architecture, 18Basic Network Differences, 23Chapter 2 BENEFITS, SAVINGS, AND DOUBTS 27Realizing Fieldbus
12、Benefits, 27Achieving Fieldbus Savings, 40Fieldbus Doubts Addressed, 60Chapter 3 INSTALLATION AND COMMISSIONING 67HART, 67IEC 61158-2 (FOUNDATION Fieldbus H1 and PROFIBUS PA), 79Ethernet and IP (FOUNDATION HSE and PROFInet), 114Chapter 4 CONFIGURATION 149Network Configuration, 151Device Configuratio
13、n, 154Control Strategy Configuration, 199Chapter 5 INTEGRATE AND MIGRATE 279Hybrid I/O, 279Migration, 283Integration, 287Fieldbus2001.book Page vii Thursday, March 31, 2011 2:17 PMviii Table of ContentsChapter 6 TROUBLESHOOTING 295Device, 295Communication, 301Control Strategy, 309Chapter 7 OPERATION
14、 315Getting the Most Out of Fieldbus, 316Configuring the Process Visualization, 318Performance Considerations, 329Operating a Fieldbus Control Loop, 330Chapter 8 ENGINEERING AND DESIGN 335Conceptual Design and Functional Specification, 336Engineering, 337Factory Acceptance Test (FAT), 354Site Accept
15、ance Test (SAT), 357Chapter 9 MAINTENANCE AND ASSET MANAGEMENT 359Asset Management-enabled Systems, 361Calibrating Fieldbus Devices, 362Diagnosing Fieldbus Devices, 367Predicting Failures in Fieldbus Devices, 369Information from Fieldbus Devices, 372Replacing Fieldbus Devices, 373Chapter 10 AVAILABI
16、LITY AND SAFETY 377Fault-tolerant versus Safe Systems, 377Improving Availability, 380Improving Safety, 393Balancing Availability and Safety, 401Chapter 11 HOW FIELDBUSES WORK 407Primer, 407Physical Layer, 409Data Link Layer, 414Application Layer, 421System Management and Network Management, 432User
17、Layer, 433Fieldbus on Ethernet and IP, 441Appendix A SOLUTIONS TO EXERCISES 445Appendix B PARAMETERS INDEX 453INDEX 457Fieldbus2001.book Page viii Thursday, March 31, 2011 2:17 PM1IntroductionThe first process control systems were understandably analog, simple devices with signal formats that were e
18、ssentially deter-mined by the need for an architecture with a minimum number of costly CPUs. Networking was introduced into industrial automa-tion in the 1970s and first utilized in direct digital control (DDC) systems between computer and I/O (input/output). Later, it was used in distributed contro
19、l systems (DCS) and programmable logic controller (PLC) systems to connect the controllers and operator consoles. However, digital communications in smaller devices such as transmitters on the plant floor was not seen until the 1980s, and true communication bus networking of field instruments did no
20、t gain wide acceptance until the 1990s. At the other extreme, corporations network their plants across the globe to the corporate headquarters via the Internet. The coordina-tion of production and other business functions has become an integral part of the corporate information technology (IT) struc
21、-ture. Networking has made it possible to collect more information from the plant and to disseminate it far and wide throughout the enterprise. Geographically distributed components with lots of “intelligence” are now expected to work together. Networking has become essential for automation and is c
22、hanging the way plants and factories work.Digital Communication NetworksMany networks, such as telephone, radio, and television, are pri-marily analog, but the trend is definitely toward all-digital com-munication. So too, the networking used in automation is Fieldbus2001.book Page 1 Thursday, March
23、 31, 2011 2:17 PM2 Fieldbuses for Process Controlpredominantly digital, that is, data is transmitted serially between devices as a stream of ones and zeroes. Digital communications now makes possible data transfer between devices such as trans-mitters, valve positioners, controllers, workstations, a
24、nd servers.More InformationA major advantage of digital communications is that a great deal of information can be communicated on a single cable. Instead of one hardwired cable for each variable, thousands and even millions of pieces of information can be communicated along just one network cable. T
25、his makes it possible to extract much more information from each device than was realistically possible using analog sig-nals. For example, before digital communications was introduced it was impossible to remotely transmit anything other than simple I/O. Tuning and controller settings had to be don
26、e locally (figure 1-1). Therefore all controllers had to be placed in large panels lin-ing the walls of the control room to enable operation directly from the controller faceplate. Sensors and actuators were hardwired to their controllers using an individual dedicated pair of wires and transmitting
27、nothing more than a single process or manipulated variable. The analog signal only traveled in one direction, from the transmitter to the controller or from the controller to the posi-tioner.Figure 1-1. In the past, controllers had to be located in the control room panel.AnnunciatorRecordersIndicato
28、rsControllersXTXTFieldbus2001.book Page 2 Thursday, March 31, 2011 2:17 PMChapter 1 Introduction 3The advent of digital communications made it possible for the DCS and PLC controllers to be placed away from the control room in an auxiliary rack room. All the supervisory information for hundreds of l
29、oops and monitoring points could be transmitted to the opera-tor console in the control room over a single network. Digital com-munications carry not only I/O like process and manipulated variables but also operational information such as setpoint and mode, alarms, and tuning in both directions to a
30、nd from the con-trol room. Communications thus enabled distributed processing, and diagnostic, configuration, range, identification, and other information could now be added, initially in controllers but then also in field instruments such as transmitters and valve position-ers. Thanks to communicat
31、ions, field instruments now perform not only a basic measurement or actuation but also have features and functions for control and asset management.MultidropA second major benefit of digital communications is the capacity to connect several devices to the same single pair of wires to form a multidro
32、p network that shares a common communications media (figure 1-2). Compared to running a separate wire for each device, this reduces the wiring requirement, especially for field-mounted instrumentation involving large distances and many devices. Even by putting just a few devices on each pair of wire
33、, the amount of cable required is greatly reduced, translating into hardware and installation savings.Figure 1-2. Network nodes sharing a common media.Fieldbus2001.book Page 3 Thursday, March 31, 2011 2:17 PM4 Fieldbuses for Process ControlThe communicating devices on the network are called nodes, a
34、nd each node is given a different address that distinguishes it from the other devices. This makes it possible to interrogate and send mes-sages to any one specific device.In the simplest form of communication, a device such as a host workstation or PLC is the master that sends requests to read or w
35、rite a value to other devices such as field instruments, which are called slaves (figure 1-3). The slave that was addressed then responds to the request. An example of this is a HART or PROFI-BUS master configuration tool or handheld terminal writing a parameter in a slave positioner from time to ti
36、me, acyclically. In networks with no specific master or slaves such as FOUNDATION Fieldbus this method is called “client/server”: a device acting as a client requests, and the device acting as server responds. Another example of the master/slave configuration is a master PLC reading a process value
37、from a slave transmitter and then after executing a control algorithm writing the output to a slave positioner. For PROFIBUS closed-loop control this reading and writing is repeated cyclically. Another mode of communications that is ideal for cyclic communi-cation is where a device acting as a “publ
38、isher” broadcasts a value that is then used by all interested devices, which act as “subscrib-ers” (figure 1-4). This is very efficient because the value is transmit-ted directly from one field device to another in one single communication, reaching several subscribers at once. This method Figure 1-
39、3. Client-server (master-slave) relationship.Server(Slave)Server(Slave)Server(Slave)Server(Slave)Client(Master)Client(Master)Fieldbus2001.book Page 4 Thursday, March 31, 2011 2:17 PMChapter 1 Introduction 5is used by FOUNDATION Fieldbus for closed-loop control. Commu-nicating from one device to anot
40、her without going through a cen-tral master is called peer-to-peer communication.A third mode of communication is when a device acting as a “source” transmits a message to a device acting as a “sink” without the sink having to solicit the data (figure 1-5). While the state remains the same it is not
41、 communicated. The transmission is only made when there is a change of state sometimes called “report by exception”, e.g. when an alarm occurs. This configuration is ideal for environments where operators want devices to report process alarms or fault events as they occur, while otherwise remaining
42、silent.Rather elaborate schemes are used by all protocols to ensure that no two devices communicate at the same time. This and other aspects of digital communications networks are explained in chap-ter 11.RobustIn a 4-20 mA analog system value is transmitted by the infinite variation of a current. A
43、 signal error just changes a valid signal into another valid signal. The signal from even the most accurate ana-log transmitter may be totally inaccurate by the time it reaches the controller. Digital communications has the advantage of being a very robust signal with only two valid states (one and
44、zero). It is transmitted directly or encoded in some form and is therefore less Figure 1-4. Publisher-subscriber relationship.PublisherSubscriber SubscriberSubscriberSubscriberFieldbus2001.book Page 5 Thursday, March 31, 2011 2:17 PM6 Fieldbuses for Process Controlsensitive to distortion than an ana
45、log signal. Even more impor-tantly, by using error-checking techniques it is possible to detect if the digital signal has been distorted, and if it has, to discard the message and possibly ask to have it retransmitted. Signal distor-tion cannot be detected in an analog system because a distorted sig
46、nal still looks like a valid process signal. An analog signal that should be 19 mA may jump between 18.97 and 19.03 mA because of electrical interference or be limited to 18 mA because of insuffi-cient supply voltage. There is no way to tell this, however, because it is still a valid signal. Operato
47、rs may suspect a noisy or limited signal, but there is no way to tell what is distortion and what is the real process change. However, a received digital signal is true to what was originally transmitted. The superior fidelity of digital signals over analog signals is why they are used in compact di
48、sks as well as in automation; it results not only in higher accuracy but also in greater confidence level.InteroperabilityA potential problem with digital communications is that there are many different ways to do it. The method of representing, encod-ing, and transmitting the data is called the pro
49、tocol. Manufacturers have devised many different protocols, and products designed for one protocol cannot work with those designed for another. One of the goals of standardization committees is to define a standard protocol that all devices can follow, thus making it possible for products from different manufacturers to interoperate, that is, work with each other. A key point is that a systems power is not defined by the capability of each of its individual devices but by the ability of these devices to communicate with each other. Two Figure 1-5. Source-sink relatio
