1、BSI Standards Publication PD ISO GUIDE 33:2015 Reference materials Good practice in using reference materialsPD ISO GUIDE 33:2015 PUBLISHED DOCUMENT National foreword This Published Document is the UK implementation of ISO GUIDE 33:2015. It supersedes PD 6532-3:2000 which is withdrawn. The UK partic
2、ipation in its preparation was entrusted to Technical Committee RMI/1, Reference Materials. A list of organizations represented on this committee can be obtained on request to its secretary. This publication does not purport to include all the necessary provisions of a contract. Users are responsibl
3、e for its correct application. The British Standards Institution 2015. Published by BSI Standards Limited 2015 ISBN 978 0 580 59592 9 ICS 01.120; 71.040.30 This Published Document was published under the authority of the Standards Policy and Strategy Committee on 31 August 2015. Amendments issued si
4、nce publication Date Text affectedPD ISO GUIDE 33:2015 ISO 2015 Reference materials Good practice in using reference materials Matriaux de rfrence Bonne pratique dutilisation des matriaux de rfrence GUIDE 33 Third edition 2015-02-01 Reference number ISO GUIDE 33:2015(E)PD ISO GUIDE 33:2015ISO GUIDE
5、33:2015(E)ii ISO 2015 All rights reserved COPYRIGHT PROTECTED DOCUMENT ISO 2015 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on the intern
6、et or an intranet, without prior written permission. Permission can be requested from either ISO at the address below or ISOs member body in the country of the requester. ISO copyright office Case postale 56 CH-1211 Geneva 20 Tel. + 41 22 749 01 11 Fax + 41 22 749 09 47 E-mail copyrightiso.org Web w
7、ww.iso.org Published in SwitzerlandPD ISO GUIDE 33:2015ISO GUIDE 33:2015(E)Contents Page Foreword v Introduction vi 1 Scope . 1 2 Normative references 1 3 T erms and definitions . 2 4 Symbols 3 5 Conventions . 3 6 RMs and their role in measurement 4 6.1 Common applications of RMs . 4 6.2 Property va
8、lues . 6 6.2.1 General 6 6.2.2 Specification of the property . 6 6.3 Uncertainty statement 6 6.4 Traceability statement . . 8 7 Handling of RMs and CRMs 9 8 Assessment of precision . 9 8.1 General . 9 8.2 Number of replicate measurements . 9 8.3 Requirements with respect to the RM .10 8.4 Measuremen
9、t .11 8.5 Data treatment .11 8.6 Calculation and assessment of precision .12 9 Bias assessment 12 9.1 General 12 9.2 Approach to bias checking .13 9.3 Utilizing bias data 13 10 Calibration .14 10.1 General 14 10.2 Establishing metrological traceability .15 10.3 Calibration models 15 11 Assigning val
10、ues to other materials 15 11.1 General 15 11.2 Pure materials 16 11.3 Gravimetry and volumetry 17 12 Conventional scales 18 12.1 General 18 12.2 pH-scale 19 12.3 Octane number 19 13 Selection of CRMs and RMs .20 13.1 General 20 13.2 Selection of a CRM .20 13.3 Selection of RMs 23 13.4 Relevance to t
11、he measurement system.23 Annex A (informative) Key characteristics of a reference material with respect its common applications .25 Annex B (informative) Calibration models and associated uncertainty models .26 Annex C (informative) Decision errors .29 ISO 2015 All rights reserved iiiPD ISO GUIDE 33
12、:2015ISO GUIDE 33:2015(E)Bibliography .30 iv ISO 2015 All rights reservedPD ISO GUIDE 33:2015ISO GUIDE 33:2015(E) Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standard
13、s 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, governmental and non-governmental, in liaison with ISO, also take
14、part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. The procedures used to develop this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part 1. In part
15、icular the different approval criteria needed for the different types of ISO documents should be noted. This document was drafted in accordance with the editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives). Attention is drawn to the possibility that some of the elements of
16、this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any patent rights identified during the development of the document will be in the Introduction and/or on the ISO list of patent declarations received (see w
17、ww.iso.org/patents). Any trade name used in this document is information given for the convenience of users and does not constitute an endorsement. For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment, as well as information about ISOs adherence to
18、 the WTO principles in the Technical Barriers to Trade (TBT) see the following URL: Foreword - Supplementary information The committee responsible for this document is ISO/REMCO, Committee on reference materials. This third edition cancels and replaces the second edition (ISO Guide 33:2000), and ISO
19、 Guide 32:1997 which have been technically revised. ISO 2015 All rights reserved vPD ISO GUIDE 33:2015ISO GUIDE 33:2015(E) Introduction The aim of this Guide is to provide general recommendations on the use of RMs. These recommendations are exemplified by real-world examples, which to some degree al
20、so reflect the level of complexity associated with RMs. This level of detail is deemed to be useful for anyone who has a responsibility in the quality management in laboratories, such as drafters, reviewers, managers, and assessors of procedures, working instructions, standard operating procedures a
21、nd the like. The main applications of reference materials are calibration, establishing traceability, method validation, assigning values to other materials, and quality control.vi ISO 2015 All rights reservedPD ISO GUIDE 33:2015Reference materials Good practice in using reference materials 1 Scope
22、1.1 This Guide describes good practice in using reference materials (RMs), and certified reference materials (CRMs) in particular, in measurement processes. These uses include the assessment of precision and trueness of measurement methods, quality control, assigning values to materials, calibration
23、, and the establishment of conventional scales. This Guide also relates key characteristics of various types of RMs to the different applications. 1.2 For CRMs, the metrological traceability of the property values to international scales or other measurement standards has been established. For RMs n
24、ot being CRMs, this kind of traceability of property values has often not been established. Nevertheless, these RMs can still be used for assessing parts of measurement procedures, including evaluating various levels of precision 1.3 Mainstream applications of RM include precision control (Clause 8)
25、, bias assessment (Clause 9), calibration (Clause 10), preparation of calibration RMs (Clause 11) and maintaining conventional scales (Clause 12). NOTE Not all types of RMs can be used for all indicated purposes. 1.4 The preparation of RMs for calibration is also part of the scope of ISO Guides 34 1
26、and 35 2 . The treatment in this Guide is limited to the fundamentals of small-scale preparation of RMs and the value assignment, as used by laboratories to calibrate their equipment. Larger scale production of such RMs, with the possible aim of distribution is beyond the scope of this Guide. This t
27、ype of activity is covered in ISO Guides 34 1and 35 2 . 1.5 The development of working standards, as used in, e.g. natural gas analysis, clinical chemistry, and the pharmaceutical industry is not covered in this Guide. This type of activity is covered in ISO Guides 34 1and 35 2 . 2 Normative referen
28、ces ISO 3534-1, Statistics Vocabulary and symbols Part 1: General statistical terms and terms used in probability ISO Guide 30, Terms and definitions used in connection with reference materials ISO/IEC Guide 98-3, Uncertainty of measurement Part 3: Guide to the expression of uncertainty in measureme
29、nt (GUM:1995) ISO/IEC Guide 99:2007, International vocabulary of metrology Basic and general concepts and associated terms (VIM) NOTE The “Guide to the expression of uncertainty in measurement” is referred to as “GUM”, whereas the “International vocabulary of basic and general terms in metrology” is
30、 referred to as “VIM”. GUIDE ISO GUIDE 33:2015(E) ISO 2015 All rights reserved 1PD ISO GUIDE 33:2015ISO GUIDE 33:2015(E) 3 T erms a nd definiti ons For the purposes of this document, the terms and definitions in ISO/IEC Guide 98-3, ISO/IEC Guide 99 and ISO Guide 30 and the following apply. NOTE Furt
31、her definitions can be found in the ISO online browsing platform, accessible through h t t p s :/ www.iso.org/OBP/ui/ 3.1 reference material RM material, sufficiently homogeneous and stable with respect to one or more specified properties, which has been established to be fit for its intended use in
32、 a measurement process Note 1 to entry: RM is a generic term. Note 2 to entry: Properties can be quantitative or qualitative, e.g. identity of substances or species. Note 3 to entry: Uses may include the calibration of a measurement system, assessment of a measurement procedure, assigning values to
33、other materials, and quality control. Note 4 to entry: ISO/IEC Guide 99:2007, has an analogous definition (5.13), but restricts the term “measurement” to apply to quantitative values. However, Note 3 of ISO/IEC Guide 99:2007, 5.13 (VIM), specifically includes qualitative properties, called “nominal
34、properties”. SOURCE: ISO Guide 30 3.2 c er t i f i e d r ef er en c e m a t er i a l CRM reference material characterized by a metrologically valid procedure for one or more specified properties, accompanied by an RM certificate that provides the value of the specified property, its associated uncer
35、tainty, and a statement of metrological traceability Note 1 to entry: The concept of value includes a nominal property or qualitative attribute such as identity or sequence. Uncertainties for such attributes may be expressed as probabilities or levels of confidence Note 2 to entry: Metrologically va
36、lid procedures for the production and certification of RMs are given in, among others, ISO Guides 34 and 35. Note 3 to entry: ISO Guide 31 17gives guidance on the contents of RM certificates. Note 4 to entry: ISO/IEC Guide 99:2007 has an analogous definition (5.14). SOURCE: ISO Guide 30 3.3 property
37、 valuevalue corresponding to a quantity representing a physical, chemical or biological property of a reference material SOURCE: ISO Guide 30 3.4 c er t i f ie d v a l ue value, assigned to a property of a reference material (RM) that is accompanied by an uncertainty statement and a statement of met
38、rological traceability, identified as such in the RM certificate SOURCE: ISO Guide 302 ISO 2015 All rights reservedPD ISO GUIDE 33:2015ISO GUIDE 33:2015(E) 3.5 indicative value information value informative value value of a quantity or property of a reference material, which is provided for informat
39、ion only Note 1 to entry: An indicative value cannot be used as a reference in a traceability chain SOURCE: ISO Guide 30 3.6 calibrant reference material used for calibration of equipment or a measurement procedure SOURCE: ISO Guide 30 2.7 quality control material reference material used for quality
40、 control of a measurement SOURCE: ISO Guide 30 4 Symbols risk of error of the first type (type I error) risk of error of the second type (type II error) 2 Chi-squared d measurement bias k coverage factor s w standard deviation computed from repeat observations wo required within-laboratory standard
41、deviation u() standard uncertainty of the parameter in parenthesis U() expanded uncertainty of the parameter in parenthesis u CRM standard uncertainty associated with property value of the CRM u meas standard uncertainty associated with value obtained by measuring the CRM u prep uncertainty associat
42、ed with the value obtained from preparation of a calibrant x CRM value of a specified property of the CRM x meas value obtained by measuring the CRM x prep value obtained from preparation of a calibrant x average of repeat observations 5 Conventions In this Guide, the following conventions are used.
43、 ISO 2015 All rights reserved 3PD ISO GUIDE 33:2015ISO GUIDE 33:2015(E) 5.1 A measurand is specified in such a way that there exists a unique, but unknowable, true value. 5.2 All statistical methods used in this Guide are based on the following assumptions. a) The certified value is the best estimat
44、e of the true value of the property of the CRM. b) All variation, be it associated with the material (i.e. homogeneity) or the measurement process, is random and follows a normal probability distribution. The values of probabilities stated in this Guide assume normality. The probability may be diffe
45、rent if there is deviation from normality. 5.3 The concept of “certified reference material” (CRM) as used in this Guide also includes RMs with property values that are accompanied by the statements of metrological traceability or measurement uncertainty. These property values are assumed to be obta
46、ined through characterization as described in ISO Guides 34 1and 35 2 . 5.4 Where the term RM is used in this Guide, it means that any RM can be used for the purpose described. The use of a CRM is an option, but usually not the most economical one. In practice, in most cases an RM will be used that
47、comes without property values, uncertainties and a traceability statement. 5.5 Values, given as “indicative”, “informative”, “for information” or otherwise identified as not being covered by the statements of metrological traceability or measurement uncertainty, are considered to be unfit for use in
48、 metrological applications requiring a value assigned to the measurand, such as, calibration, or the assignment of values to other materials. These values are however useful to verify whether an RM is suitable for precision control, or other applications that do not require a property value. 5.6 Thr
49、oughout this Guide, the law of propagation of uncertainty is used. Other methods of propagating uncertainties can be applied as well, and in some cases such alternative methods are required by the circumstances of the application. Further guidance on these matters is given in the GUM and its supplements. 6 RMs and their role in measurement 6.1 Common applications of RMs 6.1.1 RMs, and CRMs in particular, are widely used for the following purposes: Calibration of equipment or a measureme
