ISO-2859-2-1985.pdf
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1、International Standard 285912 INTERNATIONAL ORGANIZATION FOR STANDARDIZATlON.MEXAYHAPOAHAR OPTAHI43AMR f-l0 CTAHAAPTM3AMM.ORGANlSATlON INTERNATIONALE DE NORMALISATION Sampling procedures for inspection by attributes - Part 2: Sampling plans indexed by limiting quality (La) for isolated lot inspectio
2、n Rigles d b) “our industry . product is special so IS0 2859/l stan- dard plans need not apply to us”; c) production is intermittent (not continuous); d) production is from several different sources in varying quantities, i.e. “job lots”; e) purchases are from stock-holders - no source data availabl
3、e; f) lots are “small” (use of hypergeometric distribution re- quired); g) lots are “isolated”; h) lots are re-submitted after initial rejection. Consequently, in certain of the above cases consumer protec- tion may need to be attained or measured by other methods. This part of IS0 2859 uses the lim
4、iting quality to measure con- sumer protection. It should be remembered, however, that prior information on the supplier s quality assurance system and its effectiveness may play a major part in deciding whether or not to accept a single lot. 0.2 Objectives In an attempt to reconcile the somewhat di
5、verse requests for assistance made over the past few years by committees of international standardizing bodies representing various product sectors, this part of IS0 2859 was drawn up in accordance with the following principles: a) the new LO plans can be easily integrated with the existing AQL plan
6、s in IS0 2859/l; b) the LQ indexing uses a preferred series of values that cannot be confused with the preferred series of AQL values; c) the five basic numbers associated with a single sampl- ing plan, i.e. lot size, sample size, acceptance number, AQL (or quality accepted with probability 0,951 an
7、d LQ, appear in the same table, whenever possible. 0.3 Summary The problems associated with acceptance sampling inspection involve defining unambiguously the criteria used to judge discrete individual items supplied in quantity, the quality level expected from the manufacturing process, the discrimi
8、nation offered by the plans and the procedure to be followed when a lot is not accepted. Above all, however, it is necessary to design the sampling scheme so that it may easily be invoked in a purchasing contract. The plans in this part of IS0 2859 make maximum use of the established plans given in
9、IS0 2859/l, so that sub-clause 12.6 of IS0 2859/l (see 1 .l) can be made directly operational, by providing a rationalized series of plans indexed in terms of limiting quality (La). 1s0 2859/2-1985 E) 1 Scope and field of application 1.1 Scope This part of IS0 2859 establishes LO sampling plans and
10、pro- cedures for inspection by attributes compatible with IS0 2859/l that can be used when the switching rules given in IS0 2859/1are not applied, for example, when lots are of an isolated nature. The plans in this part of IS0 2859 are indexed by a preferred series of limiting qualities (LQ) with a
11、consumer s risk usually below 10 %, but always below 13 %. This method of indexing permits the “ad-hoc” procedure 1) mentioned in sub-clause 12.6 of IS0 2859/l to be implemented as a standard procedure. NOTE - The plans in IS0 2859/l are indexed by a preferred series of AQL values and inspection lev
12、els. During the inspection of a continu- ing series of lots the application of switching rules helps to ensure that the process average in that series of lots is kept below the specified AQL. Limiting quality does not have the same direct relationship with the process average (see 3.5.1). 1.2 Field
13、of application Alternative procedures are provided in this part of IS0 2859 to cater for two situations often met in practice: a) Procedure A, to be used when the supplier and con- sumer both wish to regard the lot in isolation. The tables are based on random sampling from finite lots for both con-
14、sumer and producer risks. This procedure shall be used unless there is a specific instruction to use procedure B. b) Procedure B, to be used when the supplier regards the lot as one of continuing series but the consumer considers the lot received in isolation. The tables are based on random sampling
15、 from a finite lot for consumer s risk at the limiting quality, but random sampling from a process for the pro- ducer s risk and the tabulated values of the operating characteristic (OC) curves. The plans used are a selection of the plans available in IS0 2859/l so that a producer can maintain consi
16、stent procedures for customers whether or not they receive individual lots or a continuing series of lots. This procedure is suitable for inclusion in product standards or specifications that contain sampling clauses. The manufacturer will be concerned with all of his production, but the individual
17、consumer only with the particular lot received. 2 Definitions The definitions given in IS0 2859/l shall apply. 3 Choice of sampling plan 3.1 Specifying a sampling plan When reference is made to this part of IS0 2859 in a contract or specification, it is necessary to specify the procedure to be used
18、(i.e. either A or B). In the absence of any reference to either procedure, then procedure A shall be used. 32 . Choice of sampling procedure Although procedure A is based on the hypergeometric distribu- tion for sampling results, this distribution is well approximated by the binomial distribution fo
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