SANS 3951-2-2008 Sampling procedures for inspection by variables Part 2 General specification for single sampling plans indexed by acceptance quality limit (AQL) for lot-by-lot inss《计.pdf

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 978-0-626-21185-1 SANS 3951-2:2008 Edition 1 ISO 3951-2:2006 Edition 1SOUTH AFRICAN NATIONAL STANDARD Sampling procedures for inspection by variable

4、s Part 2: General specification for single sampling plans indexed by acceptance quality limit (AQL) for lot-by-lot inspection of independent quality characteristics This national standard is the identical implementation of ISO 3951-2:2006 and is adopted with the permission of the International Organ

5、ization for Standardization. Published by Standards South Africa 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

6、freemailing clients of the SABS.SANS 3951-2:2008 Edition 1 ISO 3951-2:2006 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

7、South Africa, in compliance with annex 3 of the WTO/TBT agreement. 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 3951-2:2006(E) ISO 2006INTERNATIONAL STANDARD ISO 3951-2 Fi

8、rst edition 2006-04-01 Sampling procedures for inspection by variables Part 2: General specification for single sampling plans indexed by acceptance quality limit (AQL) for lot-by-lot inspection of independent quality characteristics Rgles dchantillonnage pour les contrles par mesures Partie 2: Spci

9、fication gnrale pour les plans dchantillonnage simples, indexs daprs la limite dacceptation de qualit (LAQ), pour les contrles lot par lot des caractristiques de qualit indpendantes SANS 3951-2:2008This standard may only be used and printed by approved subscription and freemailing clients of the SAB

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13、s given below. ISO 2006 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, including photocopying and microfilm, without permission in writing from either ISO at the address below or ISOs m

14、ember 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 Published in Switzerland ii ISO 2006 All rights reservedSANS 3951-2:2008This standard may only be used and printed b

15、y approved subscription and freemailing clients of the SABS.ISO 3951-2:2006(E) ISO 2006 All rights reserved iii Contents Page Foreword. v Introduction vii 1 Scope . 1 2 Normative references . 1 3 Terms and definitions. 2 4 Symbols . 6 5 Acceptance quality limit (AQL) 8 6 Switching rules for normal,

16、tightened and reduced inspection 9 7 Relationship to ISO 2859-1 and ISO 3951-1 . 11 8 Consumer protection 12 9 Planning. 13 10 Choice between variables and attributes.13 11 Choice between the “s” and “ ” methods 14 12 Choice of inspection level and AQL . 14 13 Choice of sampling scheme 15 14 Prelimi

17、nary operations. 17 15 Standard univariate “s” method procedures. 17 16 Standard multivariate “s” method procedures for independent quality characteristics 26 17 Standard univariate “ ” method procedures 28 18 Standard multivariate “ ” method procedures for independent quality characteristics . 31 1

18、9 Standard multivariate combined “s” and “ ” method procedures for independent quality characteristics. 32 20 Procedure during continuing inspection . 34 21 Normality and outliers 34 22 Records 34 23 Operation of switching rules . 35 24 Discontinuation and resumption of inspection . 36 25 Switching

19、between the “s” and “ ” methods . 36 Annex A (normative) Tables for determining the appropriate sample size . 37 Annex B (normative) Form k single sampling plans for the “s” method . 39 Annex C (normative) Form k single sampling plans for the “ ” method. 43 Annex D (normative) Values of f sfor maxim

20、um sample standard deviation (MSSD) . 47 Annex E (normative) Values of f process standard deviation. 51 Annex F (normative) Estimating the process fraction nonconforming for sample size 3: “s” method . 54 SANS 3951-2:2008This standard may only be used and printed by approved subscription and freemai

21、ling clients of the SABS.ISO 3951-2:2006(E) iv ISO 2006 All rights reservedAnnex G (normative) Form p* single sample plans. 57 Annex H (normative) Values of c Ufor upper control limit on the sample standard deviation. 61 Annex I (normative) Supplementary acceptability constants for qualifying toward

22、s reduced inspection 62 Annex J (normative) Procedures for obtaining s or . 63 Annex K (normative) Estimating the process fraction nonconforming 65 Annex L (informative) Consumers risk qualities 69 Annex M (informative) Producers risks . 74 Annex N (informative) Operating characteristics for the “ ”

23、 method 79 Bibliography . 80 SANS 3951-2:2008This standard may only be used and printed by approved subscription and freemailing clients of the SABS.ISO 3951-2:2006(E) ISO 2006 All rights reserved v Foreword ISO (the International Organization for Standardization) is a worldwide federation of nation

24、al 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. Internatio

25、nal 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 rule

26、s 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 l

27、east 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 3951-2 was prepared by Technical Committee ISO/TC

28、69, Applications of statistical methods, Subcommittee SC 5, Acceptance sampling. This first edition of ISO 3951-2, together with ISO 3951, cancels and replaces ISO 3951:1989, of which it constitutes a technical revision. The most significant differences between ISO 3951-2:2006 and ISO 3951:1989 are

29、as follows: The acronym AQL now stands for Acceptance Quality Limit rather than Acceptable Quality Level, in order to reflect more accurately its function. ISO 3951-2:2006 not only covers the univariate procedures of ISO 3951:1989 but also includes separate and complex control of double specificatio

30、n limits and multivariate procedures for independent characteristics. The plans have been modified so that their operating characteristic curves match those of the plans in ISO 2859-1 more closely. The sample sizes for both the “s” method and the “ ” method are constant along rows of the master tabl

31、es. The acceptability constants of Annexes B and C have been recalculated and tabulated to three decimal places for an extended range of AQLs corresponding to ISO 2859-1:1999. A new master table of Form p* acceptability constants is provided as Annex G, tabulated to four significant figures. All tab

32、ulated values of operating characteristics have been recalculated and related directly to reduced inspection as well as to normal and tightened inspection. The annex containing statistical theory has been removed. It is planned ultimately to reintroduce this within a guidance document to sampling pr

33、ocedures for inspection by variables. Text and tables that are merely informative have been consigned to annexes wherever practicable. The annex dealing with the “R” method has been eliminated, now that the availability of calculators with a standard deviation function key is so widespread. Data for

34、 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 this data. SANS 3951-2:2008This standard may only be used and printed by approved subscription and freemailing clients of the SABS.I

35、SO 3951-2:2006(E) vi ISO 2006 All rights reservedISO 3951 currently 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 sing

36、le 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 5: Sequential sampling plans indexed by acceptance quality limit (AQL) for inspection by

37、variables (known standard deviation) The following part is under preparation: Part 3: Double sampling schemes indexed by acceptance quality limit (AQL) for lot-by-lot inspection SANS 3951-2:2008This standard may only be used and printed by approved subscription and freemailing clients of the SABS.IS

38、O 3951-2:2006(E) ISO 2006 All rights reserved vii Introduction This part of ISO 3951 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 alread

39、y familiar with sampling by variables or who have complicated requirements. (An 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 probabi

40、lity of not accepting inferior lots is as high as practicable. This is achieved by means of the switching rules, which provide 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 detecte

41、d; b) an incentive (at the discretion of the responsible authority) 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 implicitly or explicitly determined from an estimate of

42、 the percentage of nonconforming items in the process, based on 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

43、production processes, this part of ISO 3951 is applied to each one separately. This part of ISO 3951 is complementary to ISO 2859-1. When specified by the responsible authority, both ISO 3951-2 and ISO 2859-1 may be referenced in a product specification, contract, inspection instructions, or other d

44、ocuments, and the provisions set forth therein shall govern. The “responsible authority” shall be designated in one of the above documents. It is assumed in this part of ISO 3951 that measurement uncertainty is negligible (see ISO 10576-1:2003). For further information on allowing for measurement un

45、certainty in sampling by variables, see Reference 16 in the Bibliography. 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 the

46、present document, 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 limit, o

47、r double specification limits with combined, separate or complex control; univariate or multivariate cases; normal inspection, tightened inspection or reduced inspection. SANS 3951-2:2008This standard may only be used and printed by approved subscription and freemailing clients of the SABS.ISO 3951-

48、2:2006(E) viii ISO 2006 All rights reservedFourteen annexes are provided. Annexes A to I provide the tables needed to support the procedures. Annex J indicates how the sample standard deviation, s, and the presumed known value of the process standard deviation, , should be determined. Annex K provid

49、es 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 L provides the statistical theory underlying the calculation of the consumers risk qualities, together with tables showing these quality levels for normal, tightened and reduced inspection under the “s” and “ ” methods. Annex M provides similar information for the producers risks. Annex N giv