SANS 3951-1-2008 Sampling procedures for inspection by variables Part 1 Specification for single sampling plans indexed by acceptance quality limit (AQL) for lot-by-lot inspection gle.pdf

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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 978-0-626-21188-2 SANS 3951-1:2008 Edition 1 ISO 3951-1:2005 Edition 1SOUTH AFRICAN NATIONAL STANDARD Sampling procedures for inspection by variable

4、s Part 1: Specification for single sampling plans indexed by acceptance quality limit (AQL) for lot-by-lot inspection for a single quality characteristic and a single AQL This national standard is the identical implementation of ISO 3951-1:2005 and is adopted with the permission of the International

5、 Organization 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 subscriptio

6、n and freemailing clients of the SABS.SANS 3951-1:2008 Edition 1 ISO 3951-1:2005 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 Stan

7、dards 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 3951-1:2005(E) ISO 2005INTERNATIONAL STANDARD ISO 395

8、1-1 First edition 2005-04-01 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 single quality characteristic and a single AQL Rgles dchantillonnage pour les contrles par mesures Pa

9、rtie 1: Spcifications pour les plans dchantillonnage simples indexs daprs le niveau de qualit acceptable (NQA) pour le contrle lot par lot pour une caractristique de qualit unique et un NQA unique SANS 3951-1:2008This standard may only be used and printed by approved subscription and freemailing cli

10、ents of the SABS.ISO 3951-1:2005(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 typefaces which are embedded are licensed to and installed on the computer performing the

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13、t at the address given below. ISO 2005 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

14、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 Published in Switzerland ii ISO 2005 All rights reservedSANS 3951-1:2008This standard may only be use

15、d and printed by approved subscription and freemailing clients of the SABS.ISO 3951-1:2005(E) ISO 2005 All rights reserved iiiContents Page Foreword. v Introduction vii 1 Scope 1 2 Normative references . 2 3 Terms and definitions. 2 4 Symbols . 5 5 Acceptance quality limit (AQL) 7 5.1 Principle . 7

16、5.2 Use 7 5.3 Specifying AQLs . 7 5.4 Preferred AQLs 7 5.5 Caution. 7 5.6 Limitation . 7 6 Switching rules for normal, tightened and reduced inspection. 7 7 Relation to ISO 2859-1 8 7.1 Similarities . 8 7.2 Differences. 8 8 Limiting quality protection. 9 8.1 Use of individual plans. 9 8.2 Consumers

17、risk quality tables 9 8.3 Producers risk tables. 9 8.4 Operating characteristic curves 9 9 Planning . 10 10 Choice between variables and attributes .10 11 Choice between the “s” and “ ” methods . 11 12 Choice of inspection level and AQL 11 13 Choice of sampling plan. 11 13.1 Standard plans 11 13.2 S

18、pecial plans . 12 14 Preliminary operations . 12 15 Standard procedure for the “s” method. 12 15.1 Obtaining a plan, sampling and preliminary calculations 12 15.2 Acceptability criteria for single specification limits 13 15.3 Graphical method for a single specification limit 14 15.4 Acceptability cr

19、iterion for combined control of double specification limits 15 16 Standard procedure for the “ ” method. 21 16.1 Obtaining a plan, sampling and preliminary calculations 21 16.2 Acceptability criteria for a single specification limit. 21 16.3 Acceptability criterion for combined control of double spe

20、cification limits 22 17 Procedure during continuing inspection23 18 Normality and outliers 24 18.1 Normality 24 18.2 Outliers. 24 SANS 3951-1:2008This standard may only be used and printed by approved subscription and freemailing clients of the SABS.ISO 3951-1:2005(E) iv ISO 2005 All rights reserved

21、19 Records 24 19.1 Control charts24 19.2 Lots that are not accepted24 20 Operation of switching rules24 21 Discontinuation and resumption of inspection25 22 Switching between the “s” and “ ” methods.25 22.1 Estimating the process standard deviation25 22.2 State of statistical control 26 22.3 Switchi

22、ng from the “s” method to the “ ” method26 22.4 Switching from the “ ” method to the “s” method26 23 Chart A Sample-size code letters of standard single sampling plans for specified quality levels 26 24 Charts B to R (Figures 5 to 19) Operating characteristic curves and tabulated values for sample-s

23、ize code letter B to R: “s” method .28 25 Charts s-D to s-R (Figures 20 to 32) Acceptance curves for combined control of double specification limits: “s” method56 Annex A (normative) Tables for determining the appropriate sample size69 Annex B (normative) Form k single sampling plans for the “s” met

24、hod 71 Annex C (normative) Form k single sampling plans for the “” method .75 Annex D (normative) Values of f sfor maximum sample standard deviation (MSSD) .79 Annex E (normative) Values of f for maximum process standard deviation (MPSD) .83 Annex F (normative) Estimating the process fraction noncon

25、forming for sample size 3: “s” method84 Annex G (normative) Type p* single sampling plans87 Annex H (normative) Values of c ufor upper control limit on the sample standard deviation .88 Annex I (normative) Supplementary acceptability constants for qualifying towards reduced inspection.89 Annex J (no

26、rmative) Procedures for obtaining s and 90 Annex K (informative) Consumers risk qualities92 Annex L (informative) Producers risks 96 Annex M (informative) Operating characteristics for the “” method100 Annex N (informative) Estimating the process fraction nonconforming for sample sizes 3 and 4 “s” m

27、ethod101 Bibliography103 SANS 3951-1:2008This standard may only be used and printed by approved subscription and freemailing clients of the SABS.ISO 3951-1:2005(E) ISO 2005 All rights reserved vForeword ISO (the International Organization for Standardization) is a worldwide federation of national st

28、andards 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. International o

29、rganizations, 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 giv

30、en 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 least

31、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 3951-1 was prepared by Technical Committee ISO/TC 69, A

32、pplications of statistical methods, Subcommittee SC 5, Acceptance sampling. This first edition of ISO 3951-1 cancels and replaces ISO 3951:1989, of which it constitutes a technical revision. The most significant differences between ISO 3951-1:2003 and ISO 3951:1989 are as follows. The acronym AQL no

33、w stands for Acceptance Quality Limit rather than Acceptable Quality Level, in order to reflect more accurately its function. The coverage of this part of ISO 3951 is constrained to a single, normally distributed variable with a single class of nonconformity. This part of ISO 3951 includes the case

34、of combined control of double specification limits, but procedures for separate or complex control of double specification limits are deferred to ISO 3951-2. More general procedures that can be used for multiple characteristics and/or multiple AQLs are also given in ISO 3951-2. The plans have been m

35、odified so that their operating characteristic curves more closely match those of the plans in ISO 2859-1. The sample sizes for both the “s” method and the “ ” method are constant along rows of the master tables. All acceptability constants (see Annexes B, C, G and I) have been revised and tabulated

36、 to three decimal places for an extended range of AQLs corresponding to ISO 2859-1:1999. All tabulated values of operating characteristics have been recalculated and related directly to reduced inspection as well as to normal and tightened inspection. The annex containing the general statistical the

37、ory has been removed. It is planned ultimately to reintroduce this within a guidance document to sampling procedures for inspection by variables. Tables that are required for implementing the procedures have been relocated into annexes. The annex dealing with the “R” method has been eliminated, now

38、that the availability of calculators with a 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 this data. SANS 3951-1:2008Thi

39、s standard may only be used and printed by approved subscription and freemailing clients of the SABS.ISO 3951-1:2005(E) vi ISO 2005 All rights reservedISO 3951 currently consists of the following parts, under the general title Sampling procedures for inspection by variables: Part 1: Specification fo

40、r 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 charact

41、eristics The following parts are under preparation: 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 SANS 3951-1:2008This standard may only be us

42、ed and printed by approved subscription and freemailing clients of the SABS.ISO 3951-1:2005(E) ISO 2005 All rights reserved viiIntroduction 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 Qua

43、lity Limit (AQL), and is designed for users who have simple requirements. A more comprehensive and technical treatment is given in ISO 3951-2. This part of ISO 3951 is complementary to ISO 2859-1. The objectives of the methods laid down in this part of ISO 3951 are to ensure that lots of an acceptab

44、le quality have a high probability of acceptance, and that the probability 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 discontinuati

45、on of sampling inspection) should a deterioration in quality be detected; b) an incentive (at the discretion of the responsible authority) to reduce inspection costs (by means of a switch to a smaller sample size) if consistently good quality is achieved. In this part of ISO 3951, the acceptability

46、of a lot is implicitly determined from an estimate of 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 pro

47、duction process. If there are different producers or production processes, this part of ISO 3951 is applied to each one separately. This part of ISO 3951 is intended for application to a single quality characteristic that is measurable on a continuous scale. For two or more such quality characterist

48、ics, see ISO 3951-2. It is assumed in this part of ISO 3951 that measurement error is negligible. For information on allowing for measurement error, see Reference 17 in the Bibliography. For double specification limits, this part of ISO 3951 treats combined control. For other types of control, see I

49、SO 3951-2. Inspection by variables for percent nonconforming items, as described in the 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, or combined control of double specification limits; normal inspection, tight