ISA CONDSD HDBK MEAS CNTRL-2007 The Condensed Handbook of Measurement and Control (Third Edition).pdf

1、The CondensedHandbook of Measurement and Control3rd EditionThe CondensedHandbook of Measurement and Control3rd EditionN. E. BattikhaISA wishes to acknowledge the cooperation of those manufacturers, suppliers, and publishers who granted permission to reproduce material herein. The Society regrets any

2、 omission of credit that may have occurred and will make such corrections in future editions.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 information by the reader, bot

3、h 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 publisher have investigate

4、d 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 commercial products in the

5、 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 the availability of a

6、ny 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.Copyright 2007 ISAThe Instrumentation, Systems and Automation Society67 Alexander DriveP.O. Box 12

7、277Research Triangle Park, NC 27709All rights reserved. Printed in the United States of America.10987654ISBN-13: 978-1-55617-995-2ISBN-10: 1-55617-995-2No part of this work may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopyi

8、ng, recording or otherwise, without the prior written permission of the publisher.Library of Congress Cataloging-in-Publication DataBattikha, N. E. The condensed handbook of measurement and control / N. E. Battikha. 3rd ed. p. cm. Includes bibliographical references and index. ISBN 1-55617-995-2 (Pb

9、k.) 1. Process control-Instruments. 2. Measuring instruments. I. Title. TS156.8.B377 2007 629.8-dc22 2007024125DedicationThis book is dedicated to the pioneers of measurement and control. This technology took its firststeps along the Nile Valley about 2600 B.C., when Egyptian engineers began using p

10、recise yet sim-ple measuring devices to level the foundation for building the Great Pyramid and employing weirsto measure and distribute irrigation water across the fertile delta. Much more recently, hundreds ofdedicated people tinkering in their home and labs, working late at night, and overcoming

11、failuresand frustrations, created the powerful computer technology we now rely on. Without these pioneers, whose first tentative steps thousands of years ago have accelerated intotodays full-speed sprint toward on-going advances, the world of measurement and control wouldnot exist and this book woul

12、d never have been written. And instead of being an I one feeder for the UPS and theother for the bypass. Where raw power is used (i.e., bypassing the UPS), an isolation trans-former is required on the raw power side to reduce the transfer of electrical noise present in theelectrical supply system.Fo

13、r large time-retention capacity, a UPS with a diesel-driven generator is generally provided.This approach avoids having a large number of batteries.When electronic equipment is connected to a breaker panel (also know as a fuse panel), elec-tromagnetic interference (EMI) noise may travel to sensitive

14、 devices. EMI does not easilytravel through transformers, hence, isolating transformers are needed to isolate the electroniccontrol equipment from other EMI-generating devices. GroundingGrounding is an essential part of any modern control system. Good grounding requirementshelp ensure quality instal

15、lations and trouble-free operations. Users should implement ground-ing systems in compliance with the code and with the system vendors recommendations.Many electrical codes accept the use of a conductive rigid conduit to ground equipment. How-ever, electronic equipment necessitates the use of a copp

16、er wire conductor to ensure properoperation.Three grounds need to be considered; power, shield, and signal. Power ground is typicallyimplemented by Electrical Engineering and will not be covered in this book. Proper groundingis vital to the operation of computer-based control systems. Some organizat

17、ions will involvethe control equipment manufacturer in reviewing the detailed grounding drawings to ensurecorrectness.Chapter 1 - Introduction 9When grounding the shield that wraps around a pair of wires carrying the signal, only one endshould be grounded. The other end (typically on the field side)

18、 should be cut back and taped toprevent accidental grounding. Signal ground should also be grounded at one point only (typi-cally, the point closest to the signals power source). Multiple signal grounds generally result inground loops (i.e., grounds at different potentials). Such ground loops add to

19、 or subtract fromthe 4-20 mA signal, introducing an error to the measured signal (see figure 1-1). It may be dif-ficult to eliminate grounds for some devices such as analyzers, grounded thermocouples, andinstruments grounded for safety. For these devices, and in situations where more than oneground

20、exists, signal isolators should be used. Figure 1-1Ground loop errors. Installation and MaintenanceThe user should determine the capabilities of the plants in-house maintenance staff whenselecting measurement and control devices. Maintenance may need to be done by an outsidecontractor, in which case

21、 the user should determine whether that contractor has the necessaryexpertise and can reach the site in an acceptable time. Other considerations include the diffi-culty and frequency of calibration, as well as whether calibration should be done at the site orat the vendors facilities.Maintenance is

22、part of the cost of ownership, and the user should consider the cost of high-maintenance items that require specialized equipment and expertise. The frequency of requiredpreventive maintenance should be determined as well as the robustness of the instrument incomparison to its required performance.B

23、ecause some installation and maintenance activities require the process to be shut down, it isoften necessary to determine whether the measurement and control device can be removed online and how essential the device is to the ongoing process. In all cases, the measurement andcontrol devices should

24、be accessible from either grade or platform. Accuracy and RepeatabilityAccuracy and repeatability are essential terms in the world of measurement and control. Accu-racy (an indication of the measured error) displays the instruments capability to provide thecorrect value. Repeatability is the instrum

25、ents ability to give the same value every time.The composite accuracy of a measuring device includes the combined effects of repeatabilityand accuracy. Unfortunately, this concept is sometimes referred to simply as “accuracy.” Yet,without repeatability good accuracy cannot be obtained (see figure 1-

26、2). Where repeatability10 The Condensed Handbook of Measurement and Control 3rd Editionchanges with time or where accuracy is an important factor, good performance will be a directresult of the frequency with which the equipment is calibrated.It is possible to have good repeatability without good ac

27、curacy. The term repeatability is anindication of the ability of a measuring device to reproduce a measurement each time a set ofconditions is obtained. It does not mean that the measurement is correct, only that the indica-tion is the same each time.Figure 1-2Measured error (accuracy) and repeatabi

28、lity.REPEATABILITY(CASE 1)BIAS ERROR(CASE 1)TOTAL MEASURED ERROR(CASE 1)TOTAL MEASURED ERROR(CASE 2)BIAS ERROR(CASE 2)REPEATABILITY(CASE 2)Chapter 2 - Identification and Symbols 11CHAPTER 2IDENTIFICATION AND SYMBOLSIdentificationUsers of instruments and control systems need some method for identifyi

29、ng equipment so theycan manage the engineering, purchasing, installation, and maintenance of such systems. There-fore, one of the key requirements of measurement and control systems is that every devicehave a unique tag number. An installations guidelines for these tag numbers should either con-form

30、 to a company standard or to ISA-5.1-1984 (R1992). Either way, these tag guidelinesshould be uniform throughout the plant.The practitioner is advised that, per ISA-5.1-1984 (R1992), identification of instruments isaccording to function and not construction. Thus, a differential pressure transmitter

31、across anorifice plate in a flow measuring application would be tagged as “FT,” not “PDT.”According to the ISA standards, the typical tag number consists of two parts (see figure 2-1):a functional identification and a loop number (e.g., TIC-103). The functional identificationconsists of a first lett

32、er (designating the measured or initiating variable; for example, F forFlow, T for Temperature, etc.) and one or more succeeding letters (identifying the functionsperformed; for example, I for Indicating, T for Transmitter, C for Controller, V for Valve,etc.). For example, a temperature indicating c

33、ontroller is identified as TIC, a flow transmitteras FT; a temperature recorder as TR, a level controller as LC, and so on.Figure 2-1Tag NumbersThe loop number is unique to each loop and is typically common to all instruments within aloop. For example, if in a loop, a transmitter FT is measuring flo

34、w, and a controller FC is con-trolling a valve FV, then they would all share the same loop number, that is, FT-123, FC-123,and FV-123. See figure 2-4 for further examples. The total number of letters in a tag number should not exceed four. Identification letters areshown in table 2-1; typical letter

35、 combinations are shown in table 2-2. Both tables are based onISA-5.1-1984 (R1992). For further information, the user should refer to the latest issue of thisISA standard.EXPANDED TAG NUMBER 10-PAH-5A - Tag Number 10 - Optional Prefix A - Optional Suffix Note: Hyphens are optional as separators TYPI

36、CAL TAG NUMBER TIC 103 - Instrument Identification or Tag Number T 103 - Loop Identification 103 - Loop Number TIC - Functional Identification T - First-letter IC - Succeeding-Letters 12 The Condensed Handbook of Measurement and Control 3rd EditionTable 2-1Identification letters.Notes: 1. To cover u

37、nlisted meanings that will be used repetitively. The meanings need be defined only once.2. To cover unlisted meanings that will be used only once (or used to a limited extent). The meanings must be defined outside the tagging bubble.3. The grammatical form may be modified as required. Example: “Indi

38、cate” may mean “indicator” or “indicating.”4. A first letter used with a modifier is treated as a first-letter entity. Example: “TDI” for dif-ferential temperature.NOTE: Numbers in parentheses refer to following explanatory notes.FIRST-LETTER (4) SUCCEEDING-LETTERS (3)MEASURED OR INITIATING VARIABLE

39、 MODIFIERREADOUT OR PASSIVE FUNCTION OUTPUT FUNCTION MODIFIERA Analysis (5,19) Alarm B Burner, Combustion Users Choice (1) Users Choice (1) Users Choice (1)C Users Choice (1) Control (13) D Users Choice (1) Differential (4) E Voltage Sensor (Primary Element)F Flow Rate Ratio (Fraction) (4) G Users C

40、hoice (1) Glass, Viewing Device (9)H Hand High (7, 15, 16)I Current (Electrical) Indicate (10, 3) J Power Scan (24) K Time, Time Schedule Time Rate of Change (4, 21)Control Station (22) L Level Light (11) Low (7, 15, 16)M Users Choice (1) Momentary (4, 25) Middle, Intermediate (7,15)N Users Choice (

41、1) Users Choice (1) Users Choice (1) Users Choice (1)O Users Choice (1) Orifice, Restriction (23) P Pressure, Vacuum Point (Test) Connection (26)Q Quantity Integrate, Totalize (4) R Radiation Record (17) S Speed, Frequency Safety (8) Switch (13) T Temperature Transmit (18)U Multivariable (6) Multifu

42、nction (12) Multifunction (12) Multifunction (12)V Vibration, Mechanical Analysis (19)Valve, Damper, Louver (13)W Weight, Force Well X Unclassified (2) X Axis Unclassified (2) Unclassified (2) Unclassified (2)Y Event, State or Presence (20)Y Axis Relay, Compute, Convert (13, 14)Z Position, Dimension Z Axis Driver, Actuator, Unclassified Final Control Element