SANS 2859-5-2008 Sampling procedures for inspection by attributes Part 5 System of sequential sampling plans indexed by acceptance quality limit (AQL) for lot-by-lot inspection《按属性.pdf

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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 978-0-626-21183-7 SANS 2859-5:2008 Edition 1 ISO 2859-5:2005 Edition 1SOUTH AFRICAN NATIONAL STANDARD Sampling procedures for inspection by attribut

4、es Part 5: System of sequential sampling plans indexed by acceptance quality limit (AQL) for lot-by-lot inspection This national standard is the identical implementation of ISO 2859-5:2005 and is adopted with the permission of the International Organization for Standardization. Published by Standard

5、s 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 freemailing clients of the SABS.SANS 2859-5:2008 E

6、dition 1 ISO 2859-5:2005 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 Standards South Africa, in compliance with annex 3 of the WT

7、O/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 2859-5:2005(E) ISO 2005INTERNATIONAL STANDARD ISO 2859-5 First edition 2005-06-15 Sampling procedures for ins

8、pection by attributes Part 5: System of sequential sampling plans indexed by acceptance quality limit (AQL) for lot-by-lot inspection Rgles dchantillonnage pour les contrles par attributs Partie 5: Systme de plans dchantillonnage progressif pour le contrle lot par lot, indexs daprs la limite daccept

9、ation de qualit (LAQ) SANS 2859-5:2008This standard may only be used and printed by approved subscription and freemailing clients of the SABS.ISO 2859-5:2005(E) PDF disclaimer This PDF file may contain embedded typefaces. In accordance with Adobes licensing policy, this file may be printed or viewed

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14、iso.org Web www.iso.org Published in Switzerland ii ISO 2005 All rights reservedSANS 2859-5:2008This standard may only be used and printed by approved subscription and freemailing clients of the SABS.ISO 2859-5:2005(E) ISO 2005 All rights reserved iii Contents Page Foreword iv Introduction v 1 Scope

15、 . 1 2 Normative references . 2 3 Terms and definitions. 2 4 Symbols and abbreviated terms . 9 5 Expression of nonconformity 10 6 Acceptance quality limit (AQL) 10 7 Submission of product for sampling 11 8 Acceptance and non-acceptance 11 9 Drawing of samples 12 10 Normal, tightened and reduced insp

16、ection 12 11 Sampling plans . 14 12 Determination of acceptability 21 13 Further information. 21 14 Tables. 22 Annex A (normative) Sampling plans for normal inspection 23 Annex B (normative) Sampling plans for tightened inspection 27 Annex C (normative) Sampling plans for reduced inspection 31 Annex

17、 D (informative) Average sample numbers for sequential sampling plans . 35 Bibliography . 43 SANS 2859-5:2008This standard may only be used and printed by approved subscription and freemailing clients of the SABS.ISO 2859-5:2005(E) iv ISO 2005 All rights reservedForeword ISO (the International Organ

18、ization 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 committee has been establish

19、ed 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 electrotechnical standardization.

20、 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 member bodies for voting. Pu

21、blication 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 identifying any or all such paten

22、t rights. ISO 2859-5 was prepared by Technical Committee ISO/TC 69, Applications of statistical methods, Subcommittee SC 5, Acceptance sampling. This first edition cancels and replaces Annex A of ISO 8422:1991, which has been technically revised to greatly improve its compatibility with the sampling

23、 systems in ISO 2859-1. ISO 2859 consists of the following parts, under the general title Sampling procedures for inspection by attributes: Part 1: Sampling schemes indexed by acceptance quality limit (AQL) for lot-by-lot inspection Part 2: Sampling plans indexed by limiting quality (LQ) for isolate

24、d lot inspection Part 3: Skip-lot sampling procedures Part 4: Procedures for assessment of declared quality levels Part 5: System of sequential sampling plans indexed by acceptance quality limit (AQL) for lot-by-lot inspection Part 10: Overview of the ISO 2859 attribute sampling systems SANS 2859-5:

25、2008This standard may only be used and printed by approved subscription and freemailing clients of the SABS.ISO 2859-5:2005(E) ISO 2005 All rights reserved v Introduction In contemporary production processes quality is often expected to reach such high levels that the number of nonconforming items i

26、s reported in parts per million (10 6 ). Under such circumstances, popular acceptance sampling plans, such as those presented in ISO 2859-1, require prohibitively large sample sizes. To overcome this problem, users apply acceptance sampling plans with higher probabilities of wrong decisions or, in e

27、xtreme situations, abandon the use of acceptance sampling procedures altogether. However, in many situations there is still a need to accept products of high quality using standardized statistical methods. In such cases, there is a need to apply statistical procedures that require the smallest possi

28、ble sample sizes. Sequential sampling plans are the only statistical procedures that satisfy that need as, among all possible sampling plans having similar statistical properties, the sequential sampling plan has the smallest average sample number. Therefore, there is a strong need to present sequen

29、tial sampling plans which are statistically equivalent to the commonly used acceptance sampling plans from ISO 2859-1, but which require significantly smaller average sample numbers. The principal advantage of sequential sampling plans is the reduction in the average sample number. The average sampl

30、e number is the weighted average of all the sample sizes that may occur under a sampling plan for a given lot or process quality level. Like double and multiple sampling plans, the use of sequential sampling plans leads to a smaller average sample number than single sampling plans having the equival

31、ent operating characteristics. However, the average savings are even greater when using a sequential sampling plan than when a double or multiple sampling plan is used. For lots of very good quality, the maximum savings for sequential sampling plans may reach 85 %, as compared to 37 % for double sam

32、pling plans and 75 % for multiple sampling plans. On the other hand, when using a double, multiple or sequential sampling plan, the actual number of items inspected for a particular lot may exceed the sample size of the corresponding single sampling plan n 0 . For double and multiple sampling plans,

33、 there is an upper limit of 1,25 n 0to the actual number of items to be inspected. For classical sequential sampling plans there is no such limit, and the actual number of inspected items may considerably exceed the corresponding single sample size, n 0 , or even the lot size, N. For the sequential

34、sampling plans in this part of ISO 2859, a curtailment rule has been introduced involving an upper limit of 1,5 n 0on the actual number of items to be inspected. Other factors that should be taken into account include the following. a) Simplicity The rules of a sequential sampling plan are more easi

35、ly misunderstood by inspectors than the simple rules for a single sampling plan. b) Variability in the amount of inspection As the actual number of items inspected for a particular lot is not known in advance, the use of sequential sampling plans brings about various organisational difficulties. For

36、 example, scheduling of inspection operations may be difficult. c) Ease of drawing sample items If drawing sample items is expensive at different times, the reduction in the average sample number by sequential sampling plans may be cancelled out by the increased sampling cost. d) Duration of test If

37、 the test of a single item is of long duration and a number of items can be tested simultaneously, sequential sampling plans are much more time-consuming than the corresponding single sampling plans. SANS 2859-5:2008This standard may only be used and printed by approved subscription and freemailing

38、clients of the SABS.ISO 2859-5:2005(E) vi ISO 2005 All rights reservede) Variability of quality within the lot If the lot consists of two or more sublots from different sources and if there is likely to be any substantial difference between the qualities of the sublots, drawing of a representative s

39、ample under a sequential sampling plan is far more awkward than under the corresponding single sampling plan. The advantages and disadvantages of double and multiple sampling plans always lie between those of single and sequential sampling plans. The balance between the advantage of a smaller averag

40、e sample number and the above disadvantages leads to the conclusion that sequential sampling plans are suitable only when inspection of individual items is costly in comparison with inspection overheads. The choice between the use of a single, double, multiple, or sequential sampling plan shall be m

41、ade before the inspection of a lot is started. During the inspection of a lot, it is not permitted to switch from one type of plan to another, because the operating characteristics of the plan may be drastically changed if the actual inspection results influence the choice of acceptability criteria.

42、 Although use of sequential sampling plans is on average much more economical than the use of corresponding single sampling plans, during inspection of a particular lot, acceptance or non-acceptance may occur at a very late stage due to the cumulative count of nonconforming items (or nonconformities

43、) remaining between the acceptance number and the rejection number for a long time. When using the graphical method, this corresponds to the random progress of the step curve remaining in the indecision zone. Such a situation is most likely to occur when the lot or process quality level (in terms of

44、 percent nonconforming or in nonconformities per 100 items) is close to (100g), where g is the parameter giving the slope of the acceptance and rejection lines. To improve upon this situation the sample size curtailment value is set before the inspection of a lot begins. If the cumulative sample siz

45、e reaches the curtailment value n twithout determination of lot acceptability, inspection terminates and the acceptance or non-acceptance of the lot is then determined using the curtailment values of the acceptance and rejection numbers. For sequential sampling plans in common use, curtailment usual

46、ly represents a deviation from their intended usage, leading to a distortion of their operating characteristics. In this part of ISO 2859; however, the operating characteristics of the sequential sampling plans have been determined with curtailment taken into account, so curtailment is an integral c

47、omponent of the provided plans. SANS 2859-5:2008This standard may only be used and printed by approved subscription and freemailing clients of the SABS.INTERNATIONAL STANDARD ISO 2859-5:2005(E) ISO 2005 All rights reserved 1 Sampling procedures for inspection by attributes Part 5: System of sequenti

48、al sampling plans indexed by acceptance quality limit (AQL) for lot-by-lot inspection 1 Scope This part of ISO 2859 specifies sequential sampling schemes that supplement the ISO 2859-1 acceptance sampling system for inspection by attributes. The ISO 2859-1 acceptance sampling system is indexed in te

49、rms of the acceptance quality limit (AQL). Its purpose is to induce a supplier, through the economic and psychological pressure of lot non-acceptance, to maintain a process average at least as good as the specified acceptance quality limit, while at the same time providing an upper limit for the risk to the consumer of accepting the occasional poor lot. The sampling schemes defined in this part of ISO 2859 are applicable, but not limited, to the inspection of: end items, components and raw materials, operations, mate