1、Essentials of Modern Measurements and Final Elements in the Process Industry A GUIDE TO DESIGN, CONFIGURATION, INSTALLATION, AND MAINTENANCEEssentials of Modern Measurements and Final Elements in the Process IndustryA GUIDE TO DESIGN, CONFIGURATION, INSTALLATION, AND MAINTENANCEBy Gregory K. McMilla
2、nNoticeThe information presented in this publication is for the general education of the reader. Because nei-ther 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 kind arising out of s
3、uch use. The reader is expected to exercise sound professional judgment in using any of the information presented in a particu-lar application.Additionally, neither the author nor the publisher have investigated or considered the affect of any patents on the ability of the reader to use any of the i
4、nformation in a particular application. The reader is responsible for reviewing any possible patents that may affect any particular use of the information pre-sented.Any references to commercial products in the work are cited as examples only. Neither the author nor the publisher endorse any referen
5、ced commercial product. Any trademarks or tradenames referenced belong to the respective owner of the mark or name. Neither the author nor the publisher make any repre-sentation regarding the availability of any referenced commercial product at any time. The manufac-turers instructions on use of any
6、 commercial product must be followed at all times, even if in conflict with the information in this publication.Copyright 2010 International Society of Automation (ISA)All rights reserved. Printed in the United States of America. 1098765432ISBN 978-1-936007-23-3No part of this work may be reproduced
7、, stored in a retrieval system, or transmitted in any form orby any means, electronic, mechanical, photocopying, recording or otherwise, without the prior writ-ten permission of the publisher.ISA67 Alexander Drive, P.O. Box 12277Research Triangle Park, NC 27709www.isa.orgLibrary of Congress Catalogi
8、ng-in-Publication Data in processDedicationThis book is dedicated to the automation engineers and technicianswho are responsible for the thousands of details in the specifica-tion, configuration, installation, and maintenance of measurementsand control valves. The performance and integrity of field
9、instru-mentation set by their dedication to excellence is the foundationthat is the basis for achievements at all levels of process control andoptimization.AcknowledgmentThe author wishes to thank Carol McMillan, Mark Nixon, Ron Pozarski, GalenWilke, Grant Wilson, and John Wright for their support i
10、n this endeavor; KenBrandt for the cover graphics; and the following individuals who wrote sectionsfor the chapters:Chapter 1 - Field Measurement Fundamentals - Mike Boudreau (safety systems)Chapter 2 - Temperature Measurement - Jim Cobb (thermocouples and resistancetemperature detectors) Chapter 3
11、- Pressure Measurement - Caitlin Thelemann (differential pressure andpressure) and Bill Zhou (diagnostics)Chapter 4 - Flow Measurement - Trever Ball (magnetic), Michael Bechthold (multi-variable), Kevin Green (differential head), John Herczeg (Coriolis), and MikeSchaefer (vortex) Chapter 5 - Level M
12、easurement - Christopher Chu and Michael Olivier (DP andremote seals), Lori Egbers (Radar) and Sarah Parker (Ultrasonic) Chapter 6 - pH Measurement - Jim Gray Chapter 7 - Final Element Fundamentals - Owen Campney (variable speed drives)Chapter 8 - Control Valves - Bert PetersonChapter 9 - Wireless -
13、 Mark NixonIn appreciation of the significant effort by Robert Montgomery and Frank Seibertin the use of wireless conductivity, flow, pH, pressure, and temperature measure-ments for carbon dioxide capture research in the Center for Energy and Environ-mental Resources at the University of Texas, the
14、royalties from this book aredonated to the University of Texas.viiTable of ContentsPreface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvChapter 1 Field Measurement Fundamentals . . . . . . . . . . . . . . . . . . . . .
15、. . . . . . . .11-1. Learning Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-2. Introduction and Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Advances in Measurements . . . . . . . . . . . .
16、 . . . . . . . . . . . . . . . . . . . . . . . . . . 2Wireless Opportunities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Industrial R the material on control valves, dampers, guide vanes,and variable speed drives will be beneficial to students and new employe
17、es.Chapter 8 gets into the details of the types of control valves that are used in 95% ofthe applications in the chemical and petrochemical industry. The book concludeswith the latest details on WirelessHART automation systems in Chapter 9. Thequestions at the end of each chapter are designed to sti
18、mulate the thought pro-cesses needed for a successful application.The foundation of a process automation system is the measurements and final ele-ments. If you dont get this right, not much else matters. Measurements providethe only window into the process and final elements provide the only means o
19、fxviii Essentials of Modern Measurements and Final Elementsaffecting the process. The degree of process control improvement from increas-ingly advanced layers of process analysis and control depends upon the integrityand breadth of the foundation. The goal of this book is to create a foundationwhere
20、 imagination is the limit for automation. 11Field Measurement Fundamentals1-1. Learning ObjectivesA. Appreciate the importance of measurements in process monitoring, analysis, control, and risk prevention.B. Be introduced to the types of measurements and signals.C. Understand the role of measurement
21、s in batch and continuous processes.D. Learn how process dynamics and disturbances affect measurement requirements.E. See how industrial instruments can be used in research and development.F. Find out how the gap between universities and industry can be closed.G. Learn terminology and issues to inte
22、lligently discuss industrial applications.H. Recognize the advantages of wireless smart measurements.I. See how measurements are used in safety systems.J. Know the definition and relative importance of accuracy parameters.K. Find out how to reduce measurement errors.L. Distinguish the important aspe
23、cts of process and measurement dynamics.2 Essentials of Modern Measurements and Final ElementsM. Gain insight into the relative importance of measurement speed.N. Be able to set the transmitter damping to meet process requirements.O. Appreciate the advantage of the electronic device description lang
24、uage in the setup, calibration, and interrogation of measurement devices.P. Gain an overview of calibration methods and their effectiveness.Q. Learn the basic types and advantages of process connections.R. Understand the significance of sensor installation and location.1-2. Introduction and Overview
25、Field measurements provide the only window into what is reallyhappening in a process. Any technical job in the process industry dependsupon measurements. Jobs in research, process development, processdesign, process technology, automation, operations, or maintenancedepend upon the ability to see, tr
26、end, analyze, diagnose, and collect theinformation from measurements. Ultimately, what you want to know asan engineer or technician is “why.” Modern instruments have made greatprogress in not only answering “why” but also offering a higher level ofplant performance. The performance and integrity of
27、control systems and safety systemsdepend upon the accuracy, reliability, and speed of the measurements.You cannot control or protect something you cant measure. The most common measurements in the process industry are flow, pres-sure, temperature, level, and pH. The measurement of these process vari
28、-ables is important for a plant to run safely and efficiently and provideproducts that meet customer requirements for quantity, quality, and price. Advances in MeasurementsModern measurement instruments have made significant advances inaddressing an industrial plants requirements through:1. Technolo
29、gical advances in sensing element technology2. Indication and integration of multiple measurementsField Measurement Fundamentals 33. Compensation of application and installation effects4. Online device alerts and diagnostics5. Remote configuration and calibration6. Digital signals with extensive emb
30、edded user-selected information7. Wireless communicationTransmitters with features 1 through 6 are classified as “smart” or“intelligent.”There are 50 or more major types of instruments used to measure the mostcommon process variables. The most prevalent type of instrument to mea-sure flow, level, an
31、d pressure is the differential pressure transmitter, sim-ply referred to as the DP. This chapter will use the DP as an example to diginto the details of accuracy, configuration, calibration, and installation.(Note: accuracy is the maximum deviation error of the measured valuefrom the true value over
32、 a stated range of the measurement). Additionalinformation on the DP and details on the other instruments with the besttechnology will be covered in the succeeding chapters.Since the 1980s, the out-of-the-box accuracy of modern industrial instru-mentation has improved by an order of magnitude. Consi
33、der the differen-tial pressure transmitter. The 0.25% accuracy of an analog electronic DPhas improved to 0.025% accuracy for a smart microprocessor based DP.Furthermore, analog DP accuracy often deteriorated to 2% when it wasmoved from a nice bench-top setting to service outdoors in a nasty processw
34、ith all its non-ideal effects of installation, process, and ambient condi-tions 116. A smart DP with its integrated compensation for non-idealeffects will stay close to its inherent 0.025% accuracy. Additionally, asmart DP takes 10 years to drift as much as an analog DP did in one year.(Note: drift
35、is an error that increases with time). Smart instruments offer the ability to report additional process variables,such as the local ambient and process temperature, and alerts based on abroad spectrum of device diagnostics. These variables and alerts are com-municated digitally on the same signal as
36、 the primary process variablethat is being measured. The visibility of this wealth of additional informa-tion has been greatly improved in the modern distributed control system(DCS) and the associated asset management systems (AMS). The use of4 Essentials of Modern Measurements and Final Elementsthe
37、 Electronic Device Description Language (EDDL) standard technologyfor the interface to smart instrumentation enables easier and more effec-tive access to and visualization of the information. Instrument supplierscan readily provide an interface that optimizes the look and feel of thedata items in th
38、eir devices 2.Wireless OpportunitiesThe wireless transmission of the signals from smart devices eliminates thetime and cost of the design, installation, checkout, and troubleshooting ofwiring. Devices can be easily replaced and relocated. In plants, this facili-tates the movement of measurement inst
39、ruments for troubleshooting andfor finding optimum operating points; for example, the optimum locationfor temperature control in a fractionation column is the point where thegreatest and most symmetrical change in temperature occurs with achange in reflux or steam flow. Also, the temperature profile
40、s in certainsections of the column are more informative than those in others. Whilesome simulation models can provide an idea of the best locations for tem-perature measurements, the locations could change with load and feedcomposition. To facilitate the online identification and use of the best loc
41、a-tions, additional column connections for temperature sensors have longbeen provided. However, signal wiring and conduit runs have to bereplaced frequently whenever a measurement point is moved 3.Wireless smart instrument measurements create the opportunity toreadily relocate instruments for better
42、 analysis and control 3. Some of thepossibilities:Wireless temperatures and differential pressures for packedabsorber and distillation column hot spot and flow distributionanalysis and controlWireless temperatures and differential pressures for fluidizedbed reactor hot spot and flow distribution ana
43、lysis and controlWireless pressures to debottleneck piping systems, monitorprocess filter operation, and track down the direction andsource of pressure disturbancesWireless temperatures and flows to debottleneck coolantsystemsField Measurement Fundamentals 5Wireless instrumentation to increase the m
44、obility, flexibility,and maintainability of skids for process equipment service suchas cleaning and sterilizationWireless instrumentations to increase the mobility, flexibility,and maintainability of skids for lab and pilot plant unit opera-tions. (Note: skids are platforms of pre-assembled equipmen
45、t,piping, and automation to perform unit operations)The traditional concerns about using wireless devices in a plant for pro-cess control have been addressed in the WirelessHART network 3, 4. TheWirelessHART (Highway Addressable Remote Transducer) network has asophisticated inherent security mechani
46、sm design. Specific keys arerequired at both ends for a device to join the wireless mesh network. Arolling encryption of messaging protects devices as they communicate.The self-organizing and optimizing capability of the wireless networkmakes the setup and commissioning of a device fast, easy, and e
47、fficient.Simple modifications to the control algorithm in the DCS and exceptionreporting by the device remove concerns about battery life and controlsystem performance. Wireless smart devices will become the norm formost new plant installations 3. Smart instruments offer an improvement in installed
48、accuracy, a reductionin drift, an increase in reliability, and the integration of device diagnostics.The latest advances in intelligent features, such as electrode impedancediagnostics for pH, have been put into wireless transmitters. Wirelesstransmitters eliminate the installation and maintenance c
49、ost of wiring andoffer the mobility to optimize the measurement location. The significantlylower life-cycle cost and faster speed of installation, checkout, and com-missioning offers the opportunity to install more measurements to pro-vide additional process variables. Applications of smart transmitters canbe developed in labs, such as inferential measurement of concentrationsfrom conductivity and pH measurements, and readily connected to thecontrol system. When the application has been successfully demonstratedin the lab, the wireless transmitters can be directly moved
