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1、STD*ISO 141LL-ENGL 1777 q851703 Ub971Lili 37T I NTE RNATI ONAL STANDARD IS0 14111 First edition 1997-03-1 5 Natural gas - Guidelines to traceability in analysis Gaz naturel - Lignes directrices pour la traabilit en analyse This material is reproduced from IS0 documents under International Organizati
2、on for Standardization (EO) Copyright License number IHSIICCI1996. Not for resale. No part of these IS0 documents may be reproduced in any form, electronic retrieval system or otherwise, except as allowed in the copyright law of the country of use, or with the prior written consent of IS0 (Case post
3、ale 56,121 I Geneva 20, Switzerland, Fax +41 22 734 10 79), IHS or the IS0 Licensors members. Reference number IS0 14111:1997(E) STD*ISO 34333-ENGL 1997 E 4853903 Ob993Ll5 20b E IS0 14111:1997(E) Contents Page 1 2 3 4 5 6 7 8 9 10 11 12 Scope Normative references . .- Definit ions . . . . . . . . .
4、. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fundamental principles of metrological traceability . . . Elaboration of the traceability concept ._._ Chemical composition and the SI system Traceabi
5、lity in natural-gas analysis Hierarchy of reference gas mixtures Role of traceability in uncertainty assessment . Implementation of traceability in International Standards for natural-gas analysis . Examples . . . . . . . . . . . . ._. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
6、. . . . . . . . . Summary . . Annexes A Supplementary terms and definitions B Example of typical interlaboratory test results . C Bibliography 1 1 2 4 6 7 10 13 16 17 19 21 23 26 28 o IS0 1997 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized
7、in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the publisher. International Organization for Standardization Case postale 56 CH-1 21 1 Genve 20 Switzerland Internet: centraliso.ch X.400: c=ch; a=400net; p=iso; o=isocs;
8、s=central Printed in Switzerland II -,-,- STD-IS0 LLiLLL-ENGL 1777 4851703 Ob7714b 142 Q IS0 IS0 14111:1997(E) Foreword IS0 (the International Organization for Standardization) is a worldwide federation of national standards bodies (IS0 member bodies). The work of preparing International Standards i
9、s normally carried out through IS0 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, governmental and non-governmental, in liaison with ISO, also take par
10、t in the work. IS0 collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Stand
11、ard requires approval by at least 75 YO of the member bodies casting a vote. International Standard IS0 141 11 was prepared by Technical Committee lSO/TC 193, Natural gas, Subcommittee SC 1, Analysis of natural gas. Annexes A to C of this International Standard are for information only. t . . 111 -,
12、-,- Introduction At a time when assurances of measurement accuracy in natural-gas analyses are increasingly being sought, every analytical chemist responsible for the design and operation of systems used in such analyses needs to be aware of, and adopt, suitable means by which he or she will be able
13、 to provide these assurances. This implies that the analyst must employ validated methods in which each result is securely linked, through a series of reference materials (reference gas mixtures), to accepted metrological standards. The formal structure which the analyst creates in doing this consti
14、tutes what is called a traceability chain. Only by this means will the analyst be able to secure and support a proper estimate of measurement accuracy (uncertainty). This seemingly simple concept is elaborated in considerable detail in this International Standard. The practical considerations involv
15、ed in the establishment of a satisfactory traceability chain give rise to challenging problems, particularly in natural-gas analysis, but relevant and useful advice is provided. At present, traceability of measurement is universally defined through the existence of unbroken calibration chains ending
16、 at the level of international or national measurement standards realizing appropriate SI units. This concept originates from the field of physical metrology, where it has been implemented with apparent success. Transfer of the metrological scheme to chemical analysis and other domains in the field
17、of testing is, however, a highly difficult task, for which standard methods are not yet available. Therefore it is not possible, at present, to standardize the implementation of measurement traceability in natural-gas analysis, or in other areas of chemical analysis. For the reasons indicated above,
18、 this International Standard does not give any specific traceability protocols. Instead, its purpose is to - clarify fundamental concepts involved in chemical traceability; - identify basic problems in the application of metrology in chemistry; - indicate feasible solutions on a reference material b
19、asis; - assist in the design of practical implementations using reference gas mixtures; - serve as a reference document for the application of the traceability concept in other International Standards for natural-gas analysis. iv STD-IS0 343L3-ENGL 1777 4853703 Ob97348 TL5 M INTERNATIONAL STANDARD O
20、 IS0 IS0 141 11:1997(E) Natural gas - Guidelines to traceability in analysis 1 Scope This International Standard provides general guidelines on the implementation and application of traceability concepts in the analysis of natural gas. Its purpose is to lay down the foundations for the development o
21、f specific traceability protocols in other International Standards for natural-gas analysis. NOTE - Besides the field of natural-gas analysis, this International Standard could also be useful as a guidance document in other areas of gas analysis and in related fields such as air quality measurement,
22、 vehicle emission monitoring and reference- gas mixture preparation. 2 Normative references The following standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the editions indicated were valid. All stand
23、ards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below. Members of IEC and IS0 maintain registers of currently valid International Standards. IS0
24、3534-1 :I 993, Statistics - Vocabulary and symbols - Part 1: Probability and general statistical terms. IS0 51 68:-1), Measurement of fluid flow - Evaluation of uncertainties. IS0 5725-1 :I 994, Accuracy (trueness and precision) of measurement methods and results - Part 1: General principles and def
25、initions. IS0 5725-2:1994, Accuracy (trueness and precision of measurement methods and results - fart 2: Basic method for the determination of repeatability and reproducibility of a standard measurement method. IS0 5725-3: 1994, Accuracy (trueness and precision) of measurement methods and results -
26、Part 3: Intermediate measures of the precision of a measurement method. IS0 5725-4: 1994, Accuracy (trueness and precision) of measurement methods and results - Part 4: Basic methods for the determination of the trueness of a standard measurement method. IS0 5725-6:1994, Accuracy (trueness and preci
27、sion) of measurement methods and results - Part 6: Use in practice of accuracy values. IS0 61 42:1981, Gas analysis - Preparation of calibration gas mixtures - Weighing methods (including addendum 1). 1) To be published. (Revision of IS0 51 68:1978) 1 STDmISO IiiLLL-ENGL 1797 i851703 Ob771LI9 951 IS
28、0 14111:1997(E) 0 IS0 IS0 6143:1981, Gas analysis - Determination of composition of calibration gas mixtures - Comparison methods. IS0 671 1 :I 981, Gas analysis - Checking of calibration gas mixtures by a comparison method. IS0 6974-1 :- 21, Natural gas - Determination of composition with defined u
29、ncertainty by gas chromatography - Part 7: Guidelines for tailored analysis. IS0 6974-2:- 2), Natural gas - Determination of composition with defined uncertainty by gas chromatography - Part 2: Measuring-system characteristics and statistics for data processing. IS0 6976:1995, Natural gas - Calculat
30、ion of calorific values, density, relative density and Wobbe index from composition. IS0 9001 : 1994, Quality systems - Model for quality assurance in design, development, production, installation and servicing. IS0 1 O 0 1 2-1 :I 992, Quality assurance requirements for measuring equipment - Part I:
31、 Metrological confirmation system for measuring equipment. IS0 10723: 1 995, Natural gas - Performance requirements for on-line analytical systems. IS0 Guide 30:1992, Terms and definitions used in connection with reference materials. IS0 Guide 33:1989, Uses of certified reference materials. IS0 Guid
32、e 35: 1989, Certification of reference materials - General and statistical principles. BIPM/IEC/ISO/OIML/IFCC/IUPAC. International vocabulary of basic and general terms in metrology (VIM), second edition, 1993. 3 Definitions For the purposes of this International Standard, the following definitions
33、apply. 3.1 traceability: A property of the result of a measurement or the value of a standard whereby it can be related to stated references, usually national or international standards, through an unbroken chain of comparisons all having stated uncertainties. NOTES 1 The concept is often expressed
34、by the adjective “traceable“. 2 The unbroken chain of comparisons is called a “traceability chain“. IVIMI 3.2 (measurement) standard, etalon: A material measure, measuring instrument, reference material or measuring system intended to define, realize, conserve or reproduce a unit or one or more valu
35、es of a quantity to serve as a reference. EXAMPLES a) 1 kg mass standard; b) 1 O0 i2 standard resistor; c) standard ammeter; d) caesium frequency standard; e) standard hydrogen electrode; f) reference solution of cortisol in human serum having a certified concentration. VIMI 2) To be published. (Rev
36、ision. in parts, of IS0 6974:1984) 2 -,-,- STDmISO LLiLLL-ENGL 1777 4853903 Ob9735O b73 IS0 141 11:1997(E) 0 IS0 3.3 reference material: A material or substance one or more of whose property values are sufficiently homogeneous and well established to be used for the Calibration of an apparatus, the
37、assessment of a measurement method or for assigning values to materials. NOTE - A reference material may be in the form of a pure or mixed gas, liquid or solid. Examples are water for the calibration of viscometers, sapphire as a heat-capacity calibrant in calorimetry, and solutions used for calibra
38、tion in chemical analysis. IS0 Guide 3 0 1 3.4 Terms related to accuracy and uncertainty NOTE - Since traceability essentially serves the purpose of assessment and control of accuracy, viz the uncertainty of measurement, the following terms relating to accuracy and uncertainty are also key terms of
39、this document. The definitions, taken from IS0 3534-1, have been adapted to usage in the field of measurement instead of testing, by substitution of corresponding terms (”measurement result” instead of “test result”, and ”true value” instead of ”accepted reference value”). In some cases, the notes t
40、o the definitions have also been modified. 3.4.1 accuracy: The closeness of agreement between a measurement result and the true value of the measurand. NOTE - The term accuracy, when applied to a set of measurement results, describes a combination of random components and a common systematic error o
41、r bias component. Adapted from IS0 3534-1 1 3.4.2 trueness: The closeness of agreement between the average value obtained from a large series of measurement results and the true value of the measurand. NOTES 1 The measure of trueness is usually expressed in terms of bias. 2 Until recently, ”accuracy
42、” was used with the meaning of ”trueness”. This usage no longer conforms with international standardization. Adapted from IS0 3534-1 I 3.4.3 precision: The closeness of agreement between independent measurement results obtained under prescribed conditions. NOTES 1 Precision depends only on the distr
43、ibution of random errors and does not relate to the true value. 2 Precision is a qualitative term relating to the dispersion between the results of measurements of the same measurand, carried out under specified conditions of measurement. Quantitative measures of precision such as variance or standa
44、rd deviation critically depend on the variation implied by the specified measurement conditions Repeatability and reproducibility are two particular concepts of precision, relating to the endpoints on the scale of variability in measurement conditions. Adapted from IS0 3534-1 1 3.4.4 uncertainty: An
45、 estimate attached to a measurement result which characterizes the range of values within which the true value is asserted to lie. NOTES 1 Uncertainty of measurements comprises, in general, many components. Some of these components may be estimated on the basis of the statistical distribution of the
46、 results of series of measurements and can be characterized by experimental standard deviations. Estimates of other components can only be based on experience or other information. 2 Uncertainty should be distinguished from an estimate attached to a measurement result which characterizes the range o
47、f values within which the expectation is asserted to lie. This latter estimate is a measure of precision rather than of accuracy and should be used only when the true value is not defined. When the expectation is used instead of the true value, the expression ”random component of uncertainty” must b
48、e used. Adapted from IS0 3534-1 1 For suggested further reading see annex C, reference 17l. 3.4.5 Further comment on main terms Since the terminology relating to accuracy/uncertainty of measurement has recently undergone substantial changes, a short comment on the meaning of the main terms will be g
49、iven. 3 STD*ISO LLiLLL-ENGL 1777 Li851703 Ob97151 50T 0 IS0 IS0 14111:1997(E) “Accuracy“, “trueness“ and “precision“ are qualitative terms used to express the smallness of expected measurement errors. Hereby accuracy as the more general term refers to the total measurement error, trueness to the systematic component(s) of the measurement error and precision to the random component(s) of the mea su re me nt er ror. “Uncertainty“, “s