1、 Collection of SANS standards in electronic format (PDF) 1. Copyright This standard is available to staff members of companies that have subscribed to the complete collection of SANS standards in accordance with a formal copyright agreement. This document may reside on a CENTRAL FILE SERVER or INTRA
2、NET SYSTEM only. Unless specific permission has been granted, this document MAY NOT be sent or given to staff members from other companies or organizations. Doing so would constitute a VIOLATION of SABS copyright rules. 2. Indemnity The South African Bureau of Standards accepts no liability for any
3、damage whatsoever than may result from the use of this material or the information contain therein, irrespective of the cause and quantum thereof. ISBN 978-0-626-21186-8 SANS 3951-3:2008 Edition 1 ISO 3951-3:2007 Edition 1SOUTH AFRICAN NATIONAL STANDARD Sampling procedures for inspection by variable
4、s Part 3: Double sampling schemes indexed by acceptance quality limit (AQL) for lot-by-lot inspection This national standard is the identical implementation of ISO 3951-3:2007 and is adopted with the permission of the International Organization for Standardization. Published by Standards South Afric
5、a 1 dr lategan road groenkloof private bag x191 pretoria 0001 tel: 012 428 7911 fax: 012 344 1568 international code + 27 12 www.stansa.co.za Standards South Africa This standard may only be used and printed by approved subscription and freemailing clients of the SABS.SANS 3951-3:2008 Edition 1 ISO
6、3951-3:2007 Edition 1 Table of changes Change No. Date Scope National foreword This South African standard was approved by National Committee StanSA TC 169, Applications of statistical methods, in accordance with procedures of Standards South Africa, in compliance with annex 3 of the WTO/TBT agreeme
7、nt. This SANS document was published in April 2008. This standard may only be used and printed by approved subscription and freemailing clients of the SABS. Reference number ISO 3951-3:2007(E) ISO 2007INTERNATIONAL STANDARD ISO 3951-3 First edition 2007-05-01 Sampling procedures for inspection by va
8、riables Part 3: Double sampling schemes indexed by acceptance quality limit (AQL) for lot-by-lot inspection Rgles dchantillonnage pour les contrles par mesures Partie 3: Plans dchantillonnage doubles pour le contrle lot par lot, indexs daprs le niveau de qualit acceptable (NQA) SANS 3951-3:2008This
9、standard may only be used and printed by approved subscription and freemailing clients of the SABS.ISO 3951-3:2007(E) PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adobes licensing policy, this file may be printed or viewed but shall not be edited unless the typefac
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14、w.iso.org Published in Switzerland ii ISO 2007 All rights reservedSANS 3951-3:2008This standard may only be used and printed by approved subscription and freemailing clients of the SABS.ISO 3951-3:2007(E) ISO 2007 All rights reserved iii Contents Page Foreword. v Introduction . vi 1 Scope. 1 2 Norma
15、tive references. 2 3 Terms and definitions. 2 4 Symbols and abbreviations . 7 5 Acceptance quality limit (AQL) 9 6 Switching rules for normal, tightened and reduced inspection 10 7 Relation to ISO 2859-1 10 8 Limiting quality protection. 11 9 Planning. 12 10 Choice between variables and attributes.
16、12 11 Choice of method 13 12 Choice between single and double sampling plans . 13 13 Choice of inspection level and AQL . 14 14 Choice of sampling scheme 14 15 Preliminary operations. 15 16 Standard univariate “s” method procedures. 16 17 Standard univariate “ ” method procedures. 25 18 Procedure du
17、ring continuing inspection . 32 19 Normality and outliers 32 20 Records 32 21 Operation of switching rules . 33 22 Discontinuation and resumption of inspection . 33 23 Switching between the “s” and “ ” methods 34 Annex A (informative) Standard multivariate “s” method procedures for double sampling w
18、ith independent quality characteristics . 72 Annex B (informative) Standard multivariate “ ” method procedures for double sampling with independent quality characteristics . 74 Annex C (informative) Standard multivariate combined “s” and “” method procedures for double sampling with independent qual
19、ity characteristics 76 Annex D (informative) Location of text on key features. 78 Annex E (normative) Estimating the process fraction nonconforming 81 Annex F (informative) Form k “s” method single sampling plans matched to the corresponding single sampling plans by attributes 87 SANS 3951-3:2008Thi
20、s standard may only be used and printed by approved subscription and freemailing clients of the SABS.ISO 3951-3:2007(E) iv ISO 2007 All rights reservedAnnex G (informative) Form k “ ” method single sampling plans matched to the corresponding single sampling plans by attributes 91 Annex H (informativ
21、e) Average sample sizes for double sampling by variables: “s” method . 95 Annex I (informative) Producers risks for the “s” method 98 Annex J (informative) Tabulated operating characteristics for double sampling plans with known process standard deviation . 100 Annex K (informative) Ratios of ASSIs
22、of double sampling plans under normal inspection to the sample size of the corresponding single sampling plan by variables 107 Annex L (informative) Ratios of the ASSIs of double sampling plans by variables to the ASSIs of corresponding plans by attributes 109 Annex M (informative) Design methodolog
23、y . 112 Bibliography . 113 SANS 3951-3:2008This standard may only be used and printed by approved subscription and freemailing clients of the SABS.ISO 3951-3:2007(E) ISO 2007 All rights reserved v Foreword ISO (the International Organization for Standardization) is a worldwide federation of national
24、 standards bodies (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. Internationa
25、l organizations, 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
26、given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. 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 lea
27、st 75 % of the member bodies casting a vote. Attention 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 responsible for identifying any or all such patent rights. ISO 3951-3 was prepared by Technical Committee ISO/TC 69
28、 Applications of statistical methods, Subcommittee SC 5, Acceptance sampling. 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 i
29、nspection for a 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)
30、 for lot-by-lot inspection Part 5: Sequential sampling plans indexed by acceptance quality limit (AQL) for inspection by variables (known standard deviation) The following part is under preparation: Part 4: Procedures for assessment of declared quality levels SANS 3951-3:2008This standard may only b
31、e used and printed by approved subscription and freemailing clients of the SABS.ISO 3951-3:2007(E) vi ISO 2007 All rights reservedIntroduction Inspection by variables for percentage nonconforming items, as described in this part of ISO 3951, includes several possible modes, the combination of which
32、leads to a presentation which may appear quite complicated to the user: a) procedures for unknown process standard deviation (the “s” method), or procedures for where the process standard deviation is originally unknown then estimated with fair precision, or known since the start of inspection (the
33、 ” method); b) a single specification limit, or double specification limits with separate, combined or complex control; c) normal inspection, tightened inspection or reduced inspection; d) Form k plans and Form p* plans; e) a single quality characteristic (the univariate case) or a number of unrela
34、ted quality characteristics (the multivariate independent case). The text has been arranged so that the simpler procedures may be implemented without necessarily understanding the more complicated procedures. The main text of this part of ISO 3951 is confined to the univariate case. The multivariate
35、 independent cases are treated separately in Annex A for the “s” method, in Annex B for the “ ” method and in Annex C for combined “s” method and “ ” method procedures. Annex D facilitates the use of the main text of the standard by directing the user to the clauses and tables concerning any univari
36、ate situation with which he might be confronted; it only deals with Clauses 16, 17, 21, 22 and 23 and, in every case, it is necessary to have read Clauses 1 to 15 and Clauses 18 to 20 first. This part of ISO 3951 is complementary to the double sampling plans and procedures of ISO 2859-1. When specif
37、ied by the responsible authority, it would be valid to reference both ISO 3951-3 and ISO 2859-1 in a product specification, a contract, inspection instructions, or other documents, and the provisions set forth therein shall govern. The “responsible authority” can then be designated in one of these d
38、ocuments. In all parts of ISO 3951: the acronym AQL stands for “acceptance quality limit” rather than “acceptable quality level”, in order to more accurately reflect its function; procedures are given for the case where the process standard is unknown (the “s” method) and for the case where it may b
39、e presumed to be known (the “ ” method); the sampling plans have been chosen so that their operating characteristic curves closely match those of the corresponding single sampling plans in ISO 2859-1; minimal statistical theory has been given (it being planned ultimately to provide this in a guidanc
40、e document to sampling procedures for inspection by variables); text, charts and tables that are only informative have been consigned to annexes wherever practicable. In none of the parts have methods been given based on the sample range, now that the availability of computers and calculators with a
41、 standard deviation function key is so widespread. Data for acceptance sampling by variables is often substantially more expensive to acquire than data for sampling by attributes, and the “s” method makes more efficient use of these data. SANS 3951-3:2008This standard may only be used and printed by
42、 approved subscription and freemailing clients of the SABS.ISO 3951-3:2007(E) ISO 2007 All rights reserved vii The coverage of ISO 3951-1 is constrained to the case of a single, normally distributed, quality characteristic with a single class of nonconformity, and includes the case of combined contr
43、ol of double specification limits. ISO 3951-2 provides a more comprehensive treatment of single sampling plans by variables, including procedures for separate and complex control of double specification limits. Procedures are also given for multiple independent quality characteristics and/or multipl
44、e AQLs. ISO 3951-3 provides plans for double sampling by variables, which on average provide substantial savings of inspection effort in comparison with plans for single sampling by variables. The savings are achieved by first selecting from the lot and inspecting a random sample that is typically n
45、early 40 % smaller than that of the corresponding single sampling plan. If these inspection results satisfy an acceptance criterion, an immediate decision is made to accept the lot without further inspection. Alternatively, if the inspection results satisfy a non-acceptance criterion, an immediate d
46、ecision not to accept the lot is made without further inspection. Thus, when quality is very good or very poor, the saving in inspection effort can amount to nearly 40 %. Only when the inspection results from the first sample are equivocal is a second random sample, of the same size as the first, se
47、lected; the acceptability of the lot is then resolved by combining the results of the first and second samples and determining whether they satisfy a second acceptance criterion. This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its co
48、rrect application. SANS 3951-3:2008This standard may only be used and printed by approved subscription and freemailing clients of the SABS.SANS 3951-3:2008This standard may only be used and printed by approved subscription and freemailing clients of the SABS.INTERNATIONAL STANDARD ISO 3951-3:2007(E)
49、 ISO 2007 All rights reserved 1 Sampling procedures for inspection by variables Part 3: Double sampling schemes indexed by acceptance quality limit (AQL) for lot-by-lot inspection 1 Scope This part of ISO 3951 specifies an acceptance sampling system of double sampling schemes for inspection by variables for percent nonconforming. It is indexed in terms of the acceptance quality limit (AQL). The objectives of the methods laid down in this part of ISO 3951 are to ensure that lots of acceptable quality have
