1、BRITISH STANDARD BS 6001-4:2005 ISO 2859-5:2005 Sampling procedures for inspection by attributes Part 4: System of sequential sampling plans indexed by acceptance quality limit (AQL) for lot-by-lot inspection ICS 03.120.30 IncorporatingCorrigendum No.1BS 6001-4:2005 This British Standard was publish
2、ed under the authority of the Standards Policy and Strategy Committee on 4 August 2005 BSI 2006 ISBN 0 580 46463 6 National foreword This British Standard reproduces verbatim ISO 2859-5:2005 and implements it as the UK national standard. It supersedes BS 6001-4:1994 which is withdrawn. Readers shoul
3、d note that the 1994 edition of BS 6001-4 was identical to ISO 8422:1991. However, the responsible ISO committee have removed the acceptance procedures contained in Annex A of ISO 8422:1991 and published them separately as ISO 2859-5:2004. The revised edition of ISO 8422 will be published separately
4、 by BSI as BS ISO 8422. The UK participation in its preparation was entrusted to Technical Committee SS/5, Acceptance sampling systems, which has the responsibility to: A list of organizations represented on this committee can be obtained on request to its secretary. Cross-references The British Sta
5、ndards which implement international publications referred to in this document may be found in the BSI Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Search” facility of the BSI Electronic Catalogue or of British Standards Online. This publicati
6、on does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. aid enquirers to understand the text; present to the responsible international/E
7、uropean committee any enquiries on the interpretation, or proposals for change, and keep UK interests informed; monitor related international and European developments and promulgate them in the UK. Summary of pages This document comprises a front cover, an inside front cover, the ISO title page, pa
8、ges ii to vi, pages 1 to 43 and a back cover. The BSI copyright notice displayed in this document indicates when the document was last issued. Amendments issued since publication Amd. No. Date Comments 16506 June 2006 Correction to front cover. Corrigendum No. 1 Reference number ISO 2859-5:2005(E)IN
9、TERNATIONAL STANDARD ISO 2859-5 First edition 2005-06-15 Sampling procedures for inspection 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 dc
10、hantillonnage progressif pour le contrle lot par lot, indexs daprs la limite dacceptation de qualit (LAQ) ISO 2859-5:2005 ii ISO 2859-5:2005 iii Contents Page Foreword iv Introduction v 1 Scope . 1 2 Normative references . 2 3 Terms and definitions. 2 4 Symbols and abbreviated terms . 9 5 Expression
11、 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 inspection 12 11 Sampling plans . 14 12 Determination of acceptability 21 13 Further information. 21 14 Tables.
12、 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 D (informative) Average sample numbers for sequential sampling plans . 35 Bibliography . 43 ISO 2859-5:200
13、5 iv Foreword ISO (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 whic
14、h a technical committee 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 ma
15、tters of electrotechnical 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 circ
16、ulated to the member 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 respons
17、ible for identifying any or all such patent 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 i
18、mprove its compatibility with the sampling 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 in
19、dexed by limiting quality (LQ) for isolated 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 28
20、59 attribute sampling systems v Introduction In contemporary production processes quality is often expected to reach such high levels that the number of nonconforming items is reported in parts per million (10 6 ). Under such circumstances, popular acceptance sampling plans, such as those presented
21、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 extreme situations, abandon the use of acceptance sampling procedures altogether. However, in many situations there is still a
22、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 possible sample sizes. Sequential sampling plans are the only statistical procedures that satisfy that need as, among all possible
23、sampling plans having similar statistical properties, the sequential sampling plan has the smallest average sample number. Therefore, there is a strong need to present sequential sampling plans which are statistically equivalent to the commonly used acceptance sampling plans from ISO 2859-1, but whi
24、ch require significantly smaller average sample numbers. The principal advantage of sequential sampling plans is the reduction in the average sample number. The average sample number is the weighted average of all the sample sizes that may occur under a sampling plan for a given lot or process quali
25、ty 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 equivalent operating characteristics. However, the average savings are even greater when using a sequential sampling plan than when a
26、 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 sampling plans and 75 % for multiple sampling plans. On the other hand, when using a double, multiple or sequential sampling plan
27、, 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, there is an upper limit of 1,25 n 0to the actual number of items to be inspected. For classical sequential sampling plans the
28、re 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 sampling plans in this part of ISO 2859, a curtailment rule has been introduced involving an upper limit of 1,5 n 0on the actu
29、al 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 easily misunderstood by inspectors than the simple rules for a single sampling plan. b) Variability in the amount of inspection As
30、 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 example, scheduling of inspection operations may be difficult. c) Ease of drawing sample items If drawing sample items is exp
31、ensive 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 the test of a single item is of long duration and a number of items can be tested simultaneously, sequential sampling plans a
32、re much more time-consuming than the corresponding single sampling plans. ISO 2859-5:2005 vi e) 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, drawin
33、g of a representative sample 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 advant
34、age of a smaller average 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 s
35、ampling plan shall be made 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
36、acceptability criteria. 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 it
37、ems (or nonconformities) 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 qua
38、lity level (in terms of 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 th
39、e cumulative sample size 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
40、 use, curtailment usually 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 curta
41、ilment is an integral component of the provided plans. ISO 2859-5:2005 1 Sampling procedures for inspection by attributes Part 5: System of sequential sampling plans indexed by acceptance quality limit (AQL) for lot-by-lot inspection 1 Scope This part of ISO 2859 specifies sequential sampling scheme
42、s that supplement the ISO 2859-1 acceptance sampling system for inspection by attributes. The ISO 2859-1 acceptance sampling system is indexed in terms of the acceptance quality limit (AQL). Its purpose is to induce a supplier, through the economic and psychological pressure of lot non-acceptance, t
43、o 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 in
44、spection of: end items, components and raw materials, operations, materials in process, supplies in storage, maintenance operations, data or records, and administrative procedures. These schemes are designed to be applied to a continuing series of lots, that is, a series long enough to permit the sw
45、itching rules in 10.3 to be applied. These switching rules provide a) enhanced protection to the consumer (by means of tightened sampling inspection criteria or discontinuation of sampling inspection) should deterioration in quality occur, b) an incentive, at the discretion of the responsible author
46、ity, to reduce inspection costs (by means of reduced sampling inspection criteria) should consistently good quality be demonstrated over time. The individual sampling plans are not designed to be used outside of the schemes in which they are presented. Where lots are produced in isolation or in a se
47、ries too short for this part of ISO 2859 to apply, the user is advised to consult ISO 2859-2 for appropriate sampling plans. ISO 2859-5:2005 2 2 Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cite
48、d applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 2859-1:1999, Sampling procedures for inspection by attributes Part 1: Sampling schemes indexed by acceptance quality limit (AQL) for lot-by-lot inspection ISO 3534-2: 1) , Statist
49、ics Vocabulary and symbols Part 2: Applied statistics 3 Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 inspection conformity evaluation by observation and judgement accompanied as appropriate by measurement, testing or gauging ISO 3534-2 3.2 original inspection inspection of a lot, or other amount, not previously inspected NOTE This is in contrast, for example, to inspection of a lot which has pr
