1、BSI Standards PublicationBS ISO 3951-2:2013Sampling procedures forinspection by variablesPart 2: General specification for singlesampling plans indexed by acceptancequality limit (AQL) for lot-by-lot inspectionof independent quality characteristicsBS ISO 3951-2:2013 BRITISH STANDARDNational foreword
2、This British Standard is the UK implementation of ISO 3951-2:2013. Itsupersedes BS 6002-2:2007 which is withdrawn.The UK participation in its preparation was entrusted to TechnicalCommittee SS/5, Acceptance sampling schemes.A list of organizations represented on this committee can beobtained on requ
3、est to its secretary.This publication does not purport to include all the necessaryprovisions of a contract. Users are responsible for its correctapplication. The British Standards Institution 2013. Published by BSI StandardsLimited 2013ISBN 978 0 580 75211 7ICS 03.120.30Compliance with a British St
4、andard cannot confer immunity fromlegal obligations.This British Standard was published under the authority of theStandards Policy and Strategy Committee on 30 September 2013.Amendments issued since publicationDate Text affectedBS ISO 3951-2:2013 ISO 2013Sampling procedures for inspection by variabl
5、es Part 2: General specification for single sampling plans indexed by acceptance quality limit (AQL) for lot-by-lot inspection of independent quality characteristicsRgles dchantillonnage pour les contrles par mesures Partie 2: Spcification gnrale pour les plans dchantillonnage simples indexs par une
6、 limite de qualit acceptable (LQA) pour le contrle lot par lot de caractristiques-qualit indpendantesINTERNATIONAL STANDARDISO3951-2Second edition2013-09-01Reference numberISO 3951-2:2013(E)BS ISO 3951-2:2013ISO 3951-2:2013(E)ii ISO 2013 All rights reservedCOPYRIGHT PROTECTED DOCUMENT ISO 2013All ri
7、ghts 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 internet or an intranet, without prior written permission. Permission can be requested from
8、either ISO at the address below or ISOs member body in the country of the requester.ISO copyright officeCase postale 56 CH-1211 Geneva 20Tel. + 41 22 749 01 11Fax + 41 22 749 09 47E-mail copyrightiso.orgWeb www.iso.orgPublished in SwitzerlandBS ISO 3951-2:2013ISO 3951-2:2013(E) ISO 2013 All rights r
9、eserved iiiContents PageForeword vIntroduction vi1 Scope . 12 Normative references 23 Terms and definitions . 24 Symbols 64.1 Univariate symbols 64.2 Multivariate symbols . 85 Acceptance quality limit (AQL) 85.1 Concept 85.2 Use . 85.3 Specifying AQLs 95.4 Preferred AQLs 95.5 Caution . 95.6 Limitati
10、on 96 Switching rules for normal, tightened, and reduced inspection . 97 Relation to ISO 2859-1 and ISO 3951-1 .107.1 Relation to ISO 2859-1 107.2 Relation to ISO 3951-1 118 Consumer protection 128.1 Use of individual plans 128.2 Consumers risk quality (CRQ) tables 128.3 Producers risk tables . 128.
11、4 Operating characteristic (OC) curves . 129 Accommodating measurement variability .1210 Planning 1311 Choice between variables and attributes 1312 Choice between the s-method and -method 1413 Choice of inspection level and AQL .1414 Choice of sampling scheme .1414.1 Standard plans 1414.2 Special pl
12、ans . 1515 Preliminary operations 1516 Standard procedures for the univariate s-method 1516.1 Obtaining a plan, sampling, and preliminary calculations .1516.2 Form k acceptability criterion for the s-method 1616.3 Form p* acceptability criterion for the s-method 1817 Standard multivariate s-method p
13、rocedures for independent quality characteristics 2517.1 General methodology . 2517.2 Example 2518 Standard univariate -method procedures .2718.1 Obtaining a plan, sampling, and preliminary calculations .2718.2 Acceptability criterion for a single specification limit or for double specification limi
14、ts with separate control . 2818.3 Acceptability criterion for double specification limits with combined or complex control . 29BS ISO 3951-2:2013ISO 3951-2:2013(E)iv ISO 2013 All rights reserved19 Standard multivariate -method procedures for independent quality characteristics .3119.1 General method
15、ology . 3119.2 Example 3120 Standard multivariate combined s-method and -method procedures for independent quality characteristics .3220.1 General methodology . 3220.2 Example 3321 Procedure during continuing inspection .3522 Normality and outliers 3522.1 Normality 3522.2 Outliers . 3523 Records 352
16、3.1 Control charts . 3523.2 Lots that are not accepted 3524 Operation of switching rules .3625 Discontinuation and resumption of inspection 3626 Switching between the s-method and -method 3726.1 Estimating the process standard deviation . 3726.2 State of statistical control . 3726.3 Switching from t
17、he s-method to the -method .3726.4 Switching from the -method to the s-method .37Annex A (normative) Table for determining the sample size code letter .38Annex B (normative) Form k single sampling plans: s-method .39Annex C (normative) Form k single sampling plans: -method 42Annex D (normative) Form
18、 p* single sampling plans: s-method .45Annex E (normative) Form p* single sampling plans: -method .48Annex F (normative) Values of fsfor maximum sample standard deviation (MSSD) 51Annex G (normative) Values of ffor maximum process standard deviation (MPSD) 54Annex H (normative) Estimating the proces
19、s fraction nonconforming for sample size 3: s-method 57Annex I (normative) Values of cUfor upper control limit on the sample standard deviation .60Annex J (normative) Supplementary acceptability constants for qualifying towards reduced inspection 61Annex K (normative) Procedures for obtaining s and
20、62Annex L (normative) Estimating the process fraction nonconforming64Annex M (informative) Consumers risk qualities .70Annex N (informative) Producers risks .74Annex O (informative) Operating characteristics for the -method 78Annex P (informative) Accommodating measurement variability 79Bibliography
21、 .85BS ISO 3951-2:2013ISO 3951-2:2013(E)ForewordISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member bod
22、y 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 part in the work. ISO collaborates closely with the International Electrote
23、chnical 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 particular the different approval criteria needed for the different types of ISO
24、 documents should be noted. This document was drafted in accordance with the editorial rules of the ISO/IEC Directives, Part 2. www.iso.org/directivesAttention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsibl
25、e 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. www.iso.org/patentsAny trade name used in this document is information given for the con
26、venience of users and does not constitute an endorsement.The committee responsible for this document is ISO/TC 69, Application of statistical methods, Subcommittee SC 5, Acceptance sampling.For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment, as w
27、ell as information about ISOs adherence to the WTO principles in the Technical Barriers to Trade (TBT) see the following URL: http:/www.iso.org/iso/home/standards_development/resources-for-technical-work/foreword.htmThis second edition cancels and replaces the first edition (ISO 3951-2:2006), of whi
28、ch it constitutes a minor revision with the following changes: procedures have been introduced to accommodate measurement uncertainty; many of the sampling plans have been adjusted to improve the match between their operating characteristic curves and the operating characteristic curves of the corre
29、sponding plans for single sampling by attributes in ISO 2859-1.ISO 3951 consists of the following parts, under the general title Sampling procedures for inspection by variables: Part 1: Specification for single sampling plans indexed by acceptance quality limit (AQL) for lot-by-lot inspection for a
30、single quality characteristic and a single AQL Part 2: General specification for single sampling plans indexed by acceptance quality limit (AQL) for lot-by-lot inspection of independent quality characteristics Part 3: Double sampling schemes indexed by acceptance quality limit (AQL) for lot-by-lot i
31、nspection Part 4: Procedures for assessment of declared quality levels Part 5: Sequential sampling plans indexed by acceptance quality limit (AQL) for inspection by variables (known standard deviation) ISO 2013 All rights reserved vBS ISO 3951-2:2013ISO 3951-2:2013(E)IntroductionThis part of ISO 395
32、1 specifies an acceptance sampling system of single sampling plans for inspection by variables. It is indexed in terms of the acceptance quality limit (AQL) and is of a technical nature, aimed at users who are already familiar with sampling by variables or who have complicated requirements. (A more
33、introductory treatment is given in ISO 3951-1.)The objectives of the methods laid down in this part of ISO 3951 are to ensure that lots of an acceptable quality have a high probability of acceptance and that the probability of not accepting inferior lots is as high as practicable. This is achieved b
34、y means of the switching rules, which provide the following:a) automatic protection to the consumer (by means of a switch to tightened inspection or discontinuation of sampling inspection) should a deterioration in quality be detected;b) an incentive (at the discretion of the responsible authority)
35、to reduce inspection costs (by means of a switch to a smaller sample size) should consistently good quality be achieved.In this part of ISO 3951, the acceptability of a lot is either implicitly or explicitly determined from an estimate of the percentage of nonconforming items in the process, based o
36、n a random sample of items from the lot.This part of ISO 3951 is intended for application to a continuing series of lots of discrete products all supplied by one producer using one production process. If there are different producers or production processes, this part of ISO 3951 is applied to each
37、one separately.This part of ISO 3951 is complementary to ISO 2859-1. When specified by the responsible authority, both this part of ISO 3951 and ISO 2859-1 may be referenced in a product specification, contract, inspection instructions, or other documents, and the provisions set forth therein govern
38、. The responsible authority shall be designated in one of the above documents.Caution The procedures in this part of ISO 3951 are not suitable for application to lots that have been screened previously for nonconforming items.Inspection by variables for percent nonconforming items, as described in t
39、his part of ISO 3951, includes several possible modes, the combination of which leads to a presentation that may appear quite complex to the user: unknown standard deviation, or originally unknown then estimated with fair precision, or known since the start of inspection; a single specification limi
40、t, or double specification limits with combined, separate, or complex control; univariate or multivariate cases; three inspection severities, namely normal inspection, tightened inspection, or reduced inspection.Table 1 is intended to facilitate the use of this part of ISO 3951 by directing the user
41、 to the paragraphs and tables concerning any situation with which he may be confronted. Table 1 only deals with Clauses 15, 16, 17, 18, 19, 23, 24, and 25; in every case, it is necessary first of all to have read all the preceding clauses.vi ISO 2013 All rights reservedBS ISO 3951-2:2013ISO 3951-2:2
42、013(E)Table 1 Summary tableSingle specification limit Double specification limits with combined con-trols-method -method s-method -methodClauses or sub-clausesTables/AnnexesClauses or sub-clausesTables/AnnexesClauses or sub-clausesTables Clauses or sub-clausesTables/AnnexesNormal inspection16.1, 16.
43、2,16.3, 17,1, 17.2, 2024.1A.1,B.118.1, 18.2,19, 20, 24.1A.1,G.316.1, 16.3,17.1,17.2,20, 24.1Annex LA.1, D.1,Annex F (for n = 3), G.118.1, 18.3,19, 20, 24.1A.1, C.1, E.1Switching between normal and tightened inspection24.2, 24.3 B.1, B.2 24.2, 24.3 C.1, C.2 24.2, 24.3D.1, D.2F.1, F.224.2, 24.3E.1G.1,
44、 G.2Switching between normal and reduced inspection24.4, 24.5B.1, B.3J.124.4, 24.5C.1,J.124.4, 24.5D.1, D.3F.1, F.3J.124.4, 24.5E.1G.1, G.3J.1Switching between tightened and dis- continued inspection22, 25 B.2 25 C.2 22, 25D.2F.225E.1G.2Switching between the s-method and -method26 I.1 26 K.2, I.126L
45、.2.1L.3, L.4, L.5I.126L.2.2K.2, I.1 ISO 2013 All rights reserved viiBS ISO 3951-2:2013ISO 3951-2:2013(E)Table 1 (continued)Double specification limits with separate control Double specification limits with complex controls-method -method s-method -methodClauses or sub-clausesTables/AnnexesClauses or
46、 sub-clausesTables/AnnexesClauses or sub-clausesTables/AnnexesClauses or sub-clausesTables/AnnexesNormal inspection16.1,17.1, 17.2,20, 24.1,Annex LA.1, D.1,Annex F (for n = 3), G.118.1, 18.2, 18.3, 19,20, 24.1Annex A, C.1, E.116.1, 16.3.4,17.1, 17.2, 20, 24.1,Annex LA.1, D.1,Annex F (for n = 3), G.1
47、18.1, 18.3,19, 20, 24.1A.1, C.1, E.1Switching between normal and tightened inspection24.2, 24.3 D.1, D.2,F.1, F.224.2, 24.3 E.1, E.2,G.224.2, 24.3 D.1, D.2,F.1, F.224.2, 24.3 E.1, E.2,G.3Switching between normal and reduced inspection24.4, 24.5 D.1, D.3F.1, F.3J.124.4, 24.5 E.1, E.3,G.2, J.124.4, 24
48、.5 D.1, D.3F.1, F.3J.124.4, 24.5 E.1, E.3,G.3, J.1Switching between tightened and dis-continued inspection22, 25 D.2F.225 E.2G.222, 25 D.2F.225 E.2G.3Switching between the s-method and -method26L.2.1L.3, L.4, L.5I.1 26L.2.2I.1, K.2 26L.2.1L.3, L.4, L.5I.1 26L.2.2I.1, K.216 annexes are provided. Anne
49、xes A to J provide the tables needed to support the procedures. Annex K indicates how the sample standard deviation, s, and the presumed known value of the process standard deviation, , should be determined. Annex L provides formulae for the estimation of the process fraction nonconforming, together with a highly accurate approximation for use when the process standard deviation is unknown. Annex M provides formulae for the consumers risk qualities, together with tables showing these quality levels for nor
