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1、 Reference number ISO 3951-3:2007(E) ISO 2007 INTERNATIONAL STANDARD ISO 3951-3 First edition 2007-05-01 Sampling procedures for inspection by variables Part 3: Double sampling schemes indexed by acceptance quality limit (AQL) for lot-by-lot inspection Rgles dchantillonnage pour les contrles par mes
2、ures Partie 3: Plans dchantillonnage doubles pour le contrle lot par lot, indexs daprs le niveau de qualit acceptable (NQA) Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 05/15/2007
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6、blem relating to it is found, please inform the Central Secretariat at the address given below. COPYRIGHT PROTECTED DOCUMENT ISO 2007 All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, incl
7、uding photocopying and microfilm, without permission in writing 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 www.iso.org Publis
8、hed in Switzerland ii ISO 2007 All rights reserved Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 05/15/2007 23:42:43 MDTNo reproduction or networking permitted without license from
9、IHS -,-,- ISO 3951-3:2007(E) ISO 2007 All rights reserved iii Contents Page Foreword. v Introduction. vi 1 Scope . 1 2 Normative 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 1
10、0 7 Relation to ISO 2859-1 10 8 Limiting quality protection. 11 9 Planning. 12 10 Choice between variables and attributes. 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 opera
11、tions. 15 16 Standard univariate “s” method procedures. 16 17 Standard univariate “” method procedures. 25 18 Procedure during 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 b
12、etween the “s” and “ ” methods 34 Annex A (informative) Standard multivariate “s” method procedures for double sampling with independent quality characteristics . 72 Annex B (informative) Standard multivariate “” method procedures for double sampling with independent quality characteristics . 74 Ann
13、ex C (informative) Standard multivariate combined “s” and “” method procedures for double sampling with independent quality 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
14、“s” method single sampling plans matched to the corresponding single sampling plans by attributes 87 Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 05/15/2007 23:42:43 MDTNo reproduc
15、tion or networking permitted without license from IHS -,-,- ISO 3951-3:2007(E) iv ISO 2007 All rights reserved Annex G (informative) Form k “” method single sampling plans matched to the corresponding single sampling plans by attributes91 Annex H (informative) Average sample sizes for double samplin
16、g 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 of double sampling plans under normal inspect
17、ion to the sample size of the corresponding single sampling plan by variables107 Annex L (informative) Ratios of the ASSIs of double sampling plans by variables to the ASSIs of corresponding plans by attributes109 Annex M (informative) Design methodology .112 Bibliography .113 Copyright Internationa
18、l Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 05/15/2007 23:42:43 MDTNo reproduction or networking permitted without license from IHS -,-,- ISO 3951-3:2007(E) ISO 2007 All rights reserved v Foreword ISO
19、(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 body interested in a subject for which a technical comm
20、ittee 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 Electrotechnical Commission (IEC) on all matters of electrote
21、chnical standardization. International Standards are drafted in accordance with the rules 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 memb
22、er bodies for voting. Publication as an International Standard requires approval by at least 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 identifyi
23、ng any or all such patent rights. ISO 3951-3 was prepared by Technical Committee ISO/TC 69, 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: Specific
24、ation for single sampling plans indexed by acceptance quality limit (AQL) for lot-by-lot inspection 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
25、 characteristics Part 3: Double sampling schemes indexed by acceptance quality limit (AQL) 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: Pro
26、cedures for assessment of declared quality levels Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 05/15/2007 23:42:43 MDTNo reproduction or networking permitted without license from I
27、HS -,-,- ISO 3951-3:2007(E) vi ISO 2007 All rights reserved Introduction Inspection by variables for percentage nonconforming items, as described in this part of ISO 3951, includes several possible modes, the combination of which leads to a presentation which may appear quite complicated to the user
28、: 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 “” method); b) a single specification limit, or double specification l
29、imits 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 unrelated quality characteristics (the multivariate independent case). The te
30、xt 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 independent cases are treated separately in Annex A for the “s” method
31、, 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 univariate situation with which he might be confronted; it only deals with Clau
32、ses 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 specified by the responsible authority, it would be valid to reference both IS
33、O 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 documents. In all parts of ISO 3951: the acronym AQL stands for “acceptan
34、ce 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 be presumed to be known (the “” method); the sampling plans have been cho
35、sen 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 guidance document to sampling procedures for inspection by variables); text, cha
36、rts 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 standard deviation function key is so widespread. Data for acceptance sa
37、mpling 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. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, Use
38、r=Wing, Bernie Not for Resale, 05/15/2007 23:42:43 MDTNo reproduction or networking permitted without license from IHS -,-,- 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 sing
39、le class of nonconformity, and includes the case of combined control 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 giv
40、en for multiple independent quality characteristics and/or multiple 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 selecti
41、ng from the lot and inspecting a random sample that is typically nearly 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 ins
42、pection results satisfy a non-acceptance criterion, an immediate decision 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 equi
43、vocal is a second random sample, of the same size as the first, selected; 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 ne
44、cessary provisions of a contract. Users are responsible for its correct application. Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 05/15/2007 23:42:43 MDTNo reproduction or networki
45、ng permitted without license from IHS -,-,- Copyright International Organization for Standardization Provided by IHS under license with ISO Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 05/15/2007 23:42:43 MDTNo reproduction or networking permitted without license from IHS -,-
46、,- INTERNATIONAL STANDARD ISO 3951-3:2007(E) 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 dou
47、ble 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 a high probability of acceptance and that the
48、probability of non-accepting inferior lots is as high as practicable. This is achieved by means of the switching rules, which provide 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, and an incentive (at the discretion of the responsible authority) to reduce inspection costs (by means of a switch to a smaller sample size) should consistent