標準號：BS 6002-4-2006
中文標準名稱：用變量檢驗抽樣程序.變量檢驗用按接收質量限(AQL)檢索的連續抽樣計劃(知道標準偏差)
英文標準名稱：Sampling procedures for inspection by variables - Sequential sampling plans indexed by acceptance quality limit (AQL) for inspection by variables (known standard deviation)
標準類型：A41
發布日期：2006/5/31 12:00:00
實施日期：2006/5/31 12:00:00
中國標準分類號：A41
國際標準分類號：03.120.30
引用標準：ISO 2859-1-1999;ISO 3534-1;ISO 3534-2;ISO 3951-1-2005
適用范圍：This part of ISO 3951 specifies a system of sequential sampling plans (schemes) for lot-by-lot inspection byvariables. The schemes are indexed in terms of a preferred series of acceptance quality limit (AQL) values,ranging from 0,01 to 10, which are defined in terms of percent nonconforming items.The schemes of ISO 3951 are intended to induce a supplier through the economic and psychological pressureof lot non-acceptance to maintain a process average at least as good as the specified AQL value, while at thesame time providing an upper limit for the risk to the consumer of accepting the occasional poor lot.The schemes are designed to be applied to a continuing series of lots, that is, a series long enough to allowthe switching rules (Clause 6) to be applied. These switching rules provide:- automatic protection to the consumer (by means of a switch to tightened inspection or discontinuation ofsampling inspection) should a deterioration in quality be detected;- an incentive (at the discretion of the responsible authority) to reduce inspection costs (by means of aswitch to reduced inspection) should consistently good quality be achieved.This part of ISO 3951 is designed for use under the following conditions:a) where the inspection procedure is to be applied to a continuing series of lots of discrete products allsupplied by one producer using one production process. If there are different producers or productionprocesses, apply this part of ISO 3951 to each one separately;b) where only a single quality characteristic, x, of these products is taken into consideration, which must bemeasurable on a continuous scale;c) where the uncertainty of the measurement system is negligible with respect to the production processstandard deviation;d) where production is stable (under statistical control) and the quality characteristic, x, is distributedaccording to a normal distribution (or a close approximation to the normal distribution) or a distributionwhich may be mathematically transformed to a normal distribution;e) where the standard deviation of the quality characteristic, x, is known;f) where a contract or standard defines an upper specification limit, U, a lower specification limit, L, or both;an item is qualified as conforming if and only if its measured quality characteristic, x, satisfies theappropriate one of the following inequalities:1) x u U (i.e. the single upper specification limit is not violated);2) x W L (i.e. the single lower specification limit is not violated);3) L u x u U (i.e. the upper and lower double specification limits are not violated).In this part of ISO 3951, it is assumed that, where double specification limits apply, conformance to bothspecification limits is either equally important to the integrity of the product or is considered separately for bothspecification limits. In the first case, it is appropriate to apply a single AQL to the combined percentage ofproduct outside the two specification limits. This is referred to as a combined AQL requirement. In the secondcase, separate AQLs apply to nonconformity beyond each of the limits, and this is referred to as a separateAQL requirement.In this part of ISO 3951, the acceptability of a lot is implicitly determined from an estimate of the percentage ofnonconforming items in the process, based on a random sample of items from the lot. As such, it is notapplicable for judging the acceptability of isolated lots or short series of lots. Refer to ISO 2859-2 forapplicable sampling plans in this case.