1、Process InstrumentationTerminologyReaffirmed 26 May 1995ANSI/ISA51.11979 (R1993)FormerlyANSI/ISAS51.11979 (R1993)AMERICAN NATIONAL STANDARDISA The Instrumentation,Systems, andAutomation Society TMCopyright 1979 by the Instrument Society of America. All rights reserved. Printed in the UnitedStates of
2、 America. No part of this publication may be reproduced, stored in a retrieval system, ortransmitted in any form or by any means (electronic, mechanical, photocopying, recording, orotherwise), without the prior written permission of the publisher.ISA67 Alexander DriveP.O. Box 12277Research Triangle
3、Park, North Carolina 27709ANSI/ISA-51.1-1979 (R1993), Process Instrumentation TerminologyISBN 0-87664-390-4ANSI/ISA-S51.1-1979 (R 1993) 3PrefaceThis Preface is included for informational purposes and is not part of ANSI/ISA-51.1-1979 (R1993).This Standard has been prepared as a part of the service o
4、f ISA toward a goal of uniformity in the field of instrumentation. To be of real value this document should not be static, but should be subjected to periodic review. Toward this end the Society welcomes all comments and criticisms, and asks that they be addressed to the Standards and Practices Boar
5、d Secretary, ISA, 67 Alexander Drive, P.O. Box 12277, Research Triangle Park, NC 27709, Telephone 549-84111, e-mail: standardsisa.org.The ISA Standards and Practices Department is aware of the growing need for attention to the metric system of units in general, and the International System of Units
6、(SI) in particular, in the preparation of instrument standards. The Department is further aware of the benefits to USA users of ISA Standards of incorporating suitable references to the SI (and to the metric system) in their business and professional dealings with other countries. Towards this end t
7、his Department will endeavor to introduce SI and SI-acceptable metric units as optional alternatives to English units in all standards to the greatest extent possible.ISA COMMITTEE SP51NAME COMPANYN. Gollin (Chairman) Taylor Instrument Process Control Division,Sybron CorporationT. S. Imsland (Past C
8、hairman) Fisher Controls CompanyL. A. Dodge Bailey Meter CompanyD. S. Peikin United Engineers and Constructors, Inc.J. Stern National Bureau of StandardsR. K. Temple The Foxboro CompanyW. D. Wood Taylor Instrument Process Control Division,Sybron CorporationE. A. Capelle* Department of CommerceD. N.
9、Eggenberger* Argonne National LaboratoryG. J. Hagerty, Jr.* Stone including research, design, manufacture, sales, installation, test, use and maintenance.The Standard consists of terms selected primarily from Scientific Apparatus Makers Association (SAMA) Standard PMC20.1 and American National Stand
10、ards Institute (ANSI) Standard C85.1. Additional terms have been selected from other recognized standards. Selected terms and definitions have not been modified unless there was a sufficiently valid reason for doing so. New terms have been added and defined where necessary.This Standard is primarily
11、 intended to cover the field of analog measurement and control concepts, and makes no effort to develop terminology in the field of digital measurement and control.3 Introduction 3.1 Italicized termsDefined terms, where used as a part of other definitions, are set in italics to provide a ready cross
12、 reference.10 ANSI/ISA-S51.1-1979 (R 1993)3.2 Introductory notesIn defining certain performance terms, the context in which they are used has been considered. It is fitting, therefore, that the philosophy of performance evaluation on which these terms are based be explained.Ideally, instruments shou
13、ld be designed for realistic operating conditions, those they are likely to meet in service, and they should be evaluated under the same conditions. Unfortunately, it is not practical to evaluate performance under all possible combinations of operating conditions. A test procedure must be used which
14、 is practical under laboratory conditions and, at the same time, will make available with a reasonable amount of effort, sufficient data on which a judgment of field performance can be made.The method of evaluation envisioned is that of checking significant performance characteristics such as accura
15、cy rating, dead band, and hysteresis under a set of reference operating conditions, these having a narrow range of tolerances.Reference performance is, therefore, to be evaluated and stated in terms of reference operating conditions.Generally, reference performance under reference operating conditio
16、ns represents the “best“ performance that can be expected under ideal conditions.The effect of change in an individual operating condition, such as ambient temperature, atmospheric pressure, relative humidity, line voltage, and frequency will be determined individually throughout a range defined as
17、normal operating conditions. These can logically be expected to be encountered above and below the values of reference operating conditions during field operation.While this approach does not duplicate all actual conditions, where many operating variables may vary simultaneously in random fashion, i
18、t does develop data from which performance may be inferred from any given set of operating conditions.The effect of changes in an individual operating condition, all other operating conditions being held within the reference range, is herein called operating influence. There may be an operating infl
19、uence corresponding to a change in each operating condition. In some cases the effect may be negligible, while in others it may have significant magnitude.Tabulations of operating influences will usually denote the performance quality level of a given design. Comparisons of reference performance and
20、 operating influences for instruments of a given design, or for different designs, will show clearly their relative merits and probable performance under actual operating conditions.3.3 Operating conditions vs. performanceOperating Conditions PerformanceReference Reference(narrow band) (Region withi
21、n which accuracy statements apply unless indicated otherwise.)Normal Conditional(wide band) (Region within which the influence ofenvironment on performance is stated.)Operative Limits Indefinite(extreme band) (Region within which influences are not statedand beyond which damage may occur.)ANSI/ISA-S
22、51.1-1979 (R 1993) 113.4 Sources and referencesIn the preparation of this Standard of Terminology, many standards and publications sponsored by technical organizations such as ASME, IEEE, and ISA were studied by the committee in addition to those listed as principal source documents. These are liste
23、d as References.Existing terms and definitions have been used wherever considered suitable. In many cases terms have been extracted from source documents with verbatim definitions and in such cases permission to quote from the respective source document has been obtained from the organization concer
24、ned, as indicated below. Terms defined verbatim are followed by the reference number in parenthesis. For example: (4) after a defined term indicates that this term is quoted verbatim from ANSI C85.1 “Terminology for Automatic Control.“In other cases definitions have been modified in varying degrees
25、in conformity with current practice in process instrumentation. These have been noted in parentheses as “Ref.“ followed by the reference number. For example: (Ref. 8) indicates that this term is a modified definition of the referenced term in SAMA-PMC 20.1-1973 “Process Measurement and Control Termi
26、nology.“An omission or alteration of a note following a definition is not considered a modification of the definition and is not identified by the prefix, “Ref.“Principal source documents used from the many reviewed are as follows:1) American National Standard C39.4-1966 “Specifications for Automati
27、c Null-Balancing Electrical Measuring Instruments,“ published by American National Standards Institute, Inc.; Copyright 1966 by ANSI.2) American National Standard C42.100-1972 “Dictionary of Electrical and Electronics Terms,“ published by the Institute of Electrical and Electronics Engineers, Inc.;
28、Copyright 1972 by IEEE.3) American National Standard C85.1-1963 “Terminology for Automatic Control,“ published by the American Society of Mechanical Engineers; Copyright 1963 by ASME.4) SAMA Standard PMC20.1-1973 “Process Measurement and Control Terminology,“ published by Scientific Apparatus Makers
29、 Association, Process Measurement and Control Section, Inc.; Copyright 1973 by SAMA-PMC.Copies of the American National Standards referred to above may be purchased from the American National Standards Institute, 1430 Broadway, New York, New York 10018. Copies of the SAMA Standard may be purchased f
30、rom Process Measurement and Control Section, Inc., SAMA, 1101 16th Street, N.W., Washington, D. C. 20036.4 Definition of termsaccuracy: In process instrumentation, degree of conformity of an indicated value to a recognized accepted standard value, or ideal value. (Ref. 4, Ref. 8)accuracy, measured:
31、The maximum positive and negative deviation observed in testing a device under specified conditions and by a specified procedure. See Figure 1.12 ANSI/ISA-S51.1-1979 (R 1993)NOTE 1: It is usually measured as an inaccuracy and expressed as accuracy.NOTE 2: It is typically expressed in terms of the me
32、asured variable, percent of span, percent of upper-range value, percent of scale length or percent of actual output reading.See test procedure, Section 5.Figure 1 Accuracyaccuracy rating: In process instrumentation, a number or quantity that defines a limit that errors will not exceed when a device
33、is used under specified operating conditions. See Figure 1.NOTE 1: When operating conditions are not specified, reference operating conditions shall be assumed.NOTE 2: As a performance specification, accuracy (or reference accuracy) shall be as-sumed to mean accuracy rating of the device, when used
34、at reference operating conditions.NOTE 3: Accuracy rating includes the combined effects of conformity, hysteresis, dead band and repeatability errors. The units being used are to be stated explicitly. It is preferred that a sign precede the number or quantity. The absence of a sign indicates a + and
35、 a sign.Accuracy rating can be expressed in a number of forms. The following five examples are typical:a) accuracy rating expressed in terms of the measured variable. Typical expression: The accuracy rating is 1C, or 2F.b) accuracy rating expressed in percent of span. Typical expression: The accurac
36、y rating is 0.5% of span. (This percentage is calculated using scale units such as degrees F, psig, etc.)ANSI/ISA-S51.1-1979 (R 1993) 13c) accuracy rating expressed in percent of the upper-range value. Typical expression: The accuracy rating is 0.5% of upper-range value. (This percentage is calculat
37、ed using scale units such as kPa, degrees F, etc.)d) accuracy rating expressed in percent of scale length. Typical expression: The accuracy rating is 0.5% of scale length.e) accuracy rating expressed in percent of actual output reading. Typical expression: The accuracy rating is 1% of actual output
38、reading.accuracy, reference: see accuracy, rating. actuating error signal: see signal, actuating error. adaptive control: see control, adaptive.adjustment, span: Means provided in an instrument to change the slope of the input-output curve. See span shift.adjustment, zero: Means provided in an instr
39、ument to produce a parallel shift of the input-output curve. See zero shift.air conditioned area: see area, air conditioned.air consumption: The maximum rate at which air is consumed by a device within its operating range during steady-state signal conditions.NOTE: It is usually expressed in cubic f
40、eet per minute (ft3/min) or cubic meters per hour (m3/h) at a standard (or normal) specified temperature and pressure. (8)ambient pressure: see pressure, ambient. ambient temperature: see temperature, ambient.amplifier: In process instrumentation, a device that enables an input signal to control pow
41、er from a source independent of the signal and thus be capable of delivering an output that bears some relationship to, and is generally greater than, the input signal. (3)analog signal: see signal, analog.area, air conditioned: A location with temperature at a nominal value maintained constant with
42、in narrow tolerance at some point in a specified band of typical comfortable room temperature. Humidity is maintained within a narrow specified band.NOTE: Air conditioned areas are provided with clean air circulation and are typically used for instrumentation, such as computers or other equipment re
43、quiring a closely controlled environment. (Ref. 18)area, control room: A location with heat and/or cooling facilities. Conditions are maintained within specified limits. Provisions for automatically maintaining constant temperature and humidity may or may not be provided.NOTE: Control room areas are
44、 commonly provided for operation of those parts of a control system for which operator surveillance on a continuing basis is required. (18)area, environmental: A basic qualified location in a plant with specified environmental conditions dependent on severity.NOTE: Environmental areas include: air c
45、onditioned areas; control room areas, heated and/or cooled; sheltered areas (process facilities); outdoor areas (remote field sites). See specific definitions.area, outdoor: A location in which equipment is exposed to outdoor ambient conditions; including temperature, humidity, direct sunshine, wind
46、 and precipitation. (Ref. 18)14 ANSI/ISA-S51.1-1979 (R 1993)area, sheltered: An industrial process location, area, storage or transportation facility, with protection against direct exposure to the elements, such as direct sunlight, rain or other precipitation or full wind pressure. Minimum and maxi
47、mum temperatures and humidity may be the same as outdoors. Condensation can occur. Ventilation, if any, is by natural means.NOTE: Typical areas are: shelters for operating instruments, unheated warehouses for storage, and enclosed trucks for transportation. (18)attenuation: 1) A decrease in signal m
48、agnitude between two points, or between two frequencies. 2) The reciprocal of gain.NOTE: It may be expressed as a dimensionless ratio, scalar ratio, or in decibels as 20 times the log10of that ratio. (Ref. 4)auctioneering device: see signal selector.automatic control system: see control system, auto
49、matic.automatic/manual station: A device which enables an operator to select an automatic signal or a manual signal as the input to a controlling element. The automatic signal is normally the output of a controller while the manual signal is the output of a manually operated device.backlash: In process instrumentation, a relative movement between interacting mechanical parts, resulting from looseness, when motion is reversed. (Ref. 4)Bode diagram: In process instrumentation, a plot of log gain (magnitude ratio) and phase angle values on a log frequency base for a transfer
