1、BRITISH STANDARD BS ISO 11631:1998 Measurement of fluid flow Methodsofspecifying flowmeter performance ICS 17.120.01BSISO11631:1998 This British Standard, having been prepared under the directionof the Sector Committeefor Materials and Chemicals, was published underthe authority of the Standards Com
2、mittee and comesinto effect on 15January1999 BSI 06-1999 ISBN 0 580 30767 0 National foreword This British Standard reproduces verbatim ISO11631:1998 and implements it as the UK national standard. This is a new standard, and no other standard is superseded. The UK participation in its preparation wa
3、s entrusted by Technical Committee CPI/30, Measurement of fluid flow in closed conduits, to Subcommittee CPI/30/9, General topics, which has the responsibility to: aid enquirers to understand the text; present to the responsible international/European committee any enquiries on the interpretation, o
4、r proposals for change, and keep the UK interests informed; monitor related international and European developments and promulgate them in the UK. A list of organizations represented on this subcommittee can be obtained on request to its secretary. Cross-references The British Standards which implem
5、ent international or European publications referred to in this document may be found in the BSI Standards Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Find” facility of the BSI Standards Electronic Catalogue. A British Standard does not purpor
6、t to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cov
7、er, pages i and ii, theISO title page, pages ii to iv, pages1 to9 and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Amendments issued since publication Amd. No. Date
8、 CommentsBSISO11631:1998 BSI 06-1999 i Contents Page National foreword Inside front cover Foreword iii Text of ISO 11631 1ii blankBSISO11631:1998 ii BSI 06-1999 Contents Page Foreword iii 1 Scope 1 2 Normative reference 1 3 Terms and definitions 1 4 General requirements 5 5 Traceability 5 6 Uncertai
9、nty of flow measurement 5 7 Conditions of use 5 8 Traceability group 6 Annex A (informative) Illustrations of linearity 7 Annex B (normative) Repeatability 8 Bibliography 9 Figure 1 Typical hysteresis loop 3 Figure A.1 Different expressions of linearity 7 Figure A.2 Typical application of independen
10、t linearity 8 Table B.1 Students t values (t 95 ) 9 Descriptors: Flow measurement, flowmeters, measurement characteristics, performance, description.BSISO11631:1998 BSI 06-1999 iii Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodie
11、s (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations,
12、 governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO
13、/IEC Directives, Part3. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least75% of the member bodies casting a vote. International Standard ISO11631 was prepared by Tec
14、hnical Committee TC30,Measurement of fluid flow in closed conduits, Subcommittee SC9, General topics. Annex B forms a normative part of this International Standard.Annex A is for information only.iv blankBSISO11631:1998 BSI 06-1999 1 1 Scope This International Standard applies to technical specifica
15、tions and descriptions issued by manufacturers of flowmeters. It specifies methods of describing the performance of any flowmeter, for use in either closed conduits or open channels. It indicates how flowmeters may be classified according to their traceability group, and specifies how manufacturers
16、statements on traceability, quality assurance and conditions of use should be expressed, although further statements may be required for other conditions of use. NOTEThe terms and definitions given in clause3 include a large number of associated terms to encourage common usage of these terms in tech
17、nical specifications. 2 Normative reference The following normative document contains provisions which, through reference in this text, constitute provisions of this International Standard. For dated references, subsequent amendments to, or revisions of, this publication do not apply. However, parti
18、es to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent edition of the normative document indicated below. For undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain
19、 registers of currently valid International Standards. ISO/TR5168, Measurement of fluid flow Estimation of uncertainty of a flowrate measurement. 3 Terms and definitions For the purposes of this International Standard, the terms and definitions given in ISO5168 apply, adapted where appropriate to re
20、fer specifically to flowmeters and to describe the characteristics of flowmeters. 3.1 accuracy (deprecated) gof a flowmeter ability of a flowmeter to give responses close to a true value NOTEAccuracy is a commonly used term and can include the effects of systematic and random errors, hysteresis, dea
21、dband,etc. Although it is convenient to combine all these errors under the heading of “accuracy”, it is a qualitative term: no numerical value is attached to it, and it is not used in the performance specification of a flowmeter. 3.2 accuracy class class of flowmeters which meets certain metrologica
22、l requirements that are intended to keep errors within specified limits NOTEAn accuracy class is usually denoted by a number or symbol which is adopted by convention and is called the class index. 3.3 bias gof a flowmeter systematic error of the indication of a flowmeter 3.4 calibration set of opera
23、tions which establish, under specified conditions, the relationship between values of quantities indicated by a flowmeter and the corresponding values indicated by a standard of reference NOTE 1The result of a calibration permits either the assignment of values of measurands to the indications or th
24、e determination of corrections with respect to indications. NOTE 2A calibration may also determine other metrological properties, such as the effect of influence quantities. NOTE 3The result of a calibration may be recorded in a document, sometimes called a calibration certificate or a calibration r
25、eport. NOTE 4The result of a calibration is often expressed as a calibration factor, or as a series of calibration factors, or as a calibration curve. NOTE 5Calibration does not include adjustment. 3.5 confidence limits lower and upper limits within which the true value is expected to lie with a spe
26、cified probability, assuming negligible systematic error 3.6 confidence level probability that the value will lie between the specified confidence limits, assuming negligible systematic error NOTEThis is generally expressed as a percentage, e.g.95%. 3.7 conformity gof a curve closeness to which a cu
27、rve approximates a specified curve (e.g.linear, logarithmic, parabolic, cubic, square root, etc.), expressed quantitatively NOTE 1Conformity is usually measured in terms of nonconformity and expressed as conformity; e.g.the maximum deviation between an average curve and a specific curve. The average
28、 curve is determined after making two or more full-measuring-range calibrations in each direction. The value of conformity is referred to the output span unless otherwise stated. NOTE 2As a performance specification, conformity may be expressed as independent conformity, terminal-based conformity, o
29、r zero-based conformity.BSISO11631:1998 2 BSI 06-1999 3.7.1 independent conformity maximum deviation of the actual characteristic (average of upscale and downscale readings) from a specified curve so positioned as to minimize the maximum deviation NOTEThe maximum deviation can be minimized by using
30、the method of least squares (see ISO7066-1 and ISO7066-2). 3.7.2 terminal-based conformity maximum deviation of the actual characteristic (average of upscale and downscale readings) from a specified curve coinciding with the actual characteristic at upper and lower range-values 3.7.3 zero-based conf
31、ormity maximum deviation of the actual characteristic (average of upscale and downscale readings) from a specified curve so positioned as to coincide with the actual characteristic at the lower range-value and to minimize the maximum deviation 3.7.4 linearity specific, but often used, case of confor
32、mity in which the specified curve is a straight line NOTEIllustrations of linearity are given inAnnex A. 3.8 deadband maximum interval through which a stimulus can be changed in both directions without producing a change in response of the flowmeter NOTESome flowmeters (turbines for example) may hav
33、e a “deadband” from zero flow to some flowrate but thereafter have a small discrimination threshold; i.e. they have a minimum starting flow. See minimum detectable flow (3.20). 3.9 discrimination ability of a flowmeter to respond to small changes in the value of the stimulus 3.10 discrimination thre
34、shold largest change in a stimulus that produces no detectable change in the response of a flowmeter, the change in the stimulus taking place slowly and monotonically NOTEThe discrimination (threshold) may not be constant through the flowrange. 3.11 drift slow change with time of a metrological char
35、acteristic of a flowmeter NOTEUnlike “stability”, “drift” is always considered with respect to time. 3.12 error result of a measurement minus a true value of the measurand NOTE 1Since a true value cannot be determined, in practice a conventional true value is used. NOTE 2When it is necessary to dist
36、inguish “error” from “relative error”, the former is sometimes called “absolute error of measurement”. This should not be confused with “absolute value of error”, which is the modulus of the error. 3.13 experimental standard deviation s quantity characterizing the dispersion of the results of a seri
37、es of n measurements of the same measurand where NOTE 1Considering the series of n values as a sample of a distribution, x is an unbiased estimate of the mean , and s 2is an unbiased estimate of the variance 2of that distribution. NOTE 2The expression is an estimate of the standard deviation of the
38、distribution ofand is called the experimental standard deviation of the mean. NOTE 3The term “experimental standard deviation of the mean” is sometimes incorrectly called “standard error of the mean”. 3.14 flowmeter flow-measuring device which indicates the measured flowrate 3.15 hysteresis property
39、 of a flowmeter whereby its response to a given stimulus depends on the sequence of the preceding stimuli NOTE 1Hysteresis may be expressed quantitatively as the maximum difference between the value of the measurand when the stimulus is increasing and the value of the measurand when the stimulus is
40、decreasing. An example is shown in Figure 1. NOTE 2Hysteresis may be quoted in terms of the measurand or, more usually, as a percentage given by the equation: where the terms H, Q imaxand Q iminare expressed in cubic metres per second and shown in Figure 1. NOTE 3Hysteresis does not include the effe
41、cts of deadband. x i is the result of the i th measurement; is the arithmetic mean of the n results considered. x sn x Hysteresis H Q imax Q imin -100%() =BSISO11631:1998 BSI 06-1999 3 3.16 K-factor output signal of a flowmeter, expressed in number of pulses per unit quantity NOTEWhere required, thi
42、s term may carry a subscript to show the unit quantity (e.g.K m -factor for pulses per unit mass, K v -factor for pulses per unit volume). 3.17 maximum scale value full scale full-scale deflection FSD full-scale reading FSR value of the quantity measured corresponding to the maximum limit of the sca
43、le 3.18 measuring range working range set of values of a measurand for which the performance of a flowmeter is intended to lie within specified limits 3.19 meter factor numerical factor by which the meter output is multiplied to obtain the measurand NOTEThis may vary with flowrate and is determined
44、by calibration. 3.20 minimum detectable flow flowrate at which, when increased from zero, the flowmeter first shows a response 3.21 operating range region, between the extreme lower and upper range-values, outside which irreversible change in the performance of the flowmeter will occur NOTEThe opera
45、ting range may be wider than the “specified measuring range”. 3.22 precision closeness of agreement between the results obtained by applying the experimental procedure several times under prescribed conditions NOTE 1The smaller the random part of the experimental errors which affect the results, the
46、 more precise the procedure. NOTE 2This term should not be used as a synonym for accuracy, and no numerical value should be attached to it. 3.23 rangeability ratio between the maximum and minimum upper range-values NOTEThis term applies to those flowmeters for which the upper range value may be set,
47、 by the user, to any value between upper and lower limits, nominated by the manufacturer, and still maintain the specified performance. Figure 1 Typical hysteresis loopBSISO11631:1998 4 BSI 06-1999 3.24 range of indication set of values bounded by the extreme indications NOTE 1For an analog display,
48、 this may be called the “scale range”. NOTE 2The range of indication is expressed in the units marked on the scale, regardless of the units of the measurand, and is normally stated in terms of its upper and lower limits, for example10 l/s to20 l/s. 3.25 lower range-value lowest value of the measuran
49、d that a flowmeter is adjusted to measure 3.26 upper range-value highest value of the measurand that a flowmeter is adjusted to measure 3.27 repeatability value below which the absolute difference between two single successive test results obtained with the same flowmeter on the same fluid under the same conditions (same operator, same test facility, and a short interval of time, but without disconnecting or dismounting the flowmeter) can be expected to lie with a probability of95% NOTEThe method for calc
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