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ISO 2859-2

1st Edition, September 1, 1985

Complete Document

Sampling Procedures for Inspection by Attributes - Part 2: Sampling Plans Indexed by Limiting Quality (LQ) for Isolated Lot Inspection

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Description / Abstract:

This part of ISO 2859 establishes LQ sampling plans and procedures for inspection by attributes compatible with ISO 2859/1 that can be used when the switching rules given in ISO 2859/1 are not applied, for example, when lots are of an isolated nature.

The plans in this part of ISO 2859 are indexed by a preferred series of limiting qualities (LQ) with a consumer’s risk usually below 10 %, but always below 13 %. This method of indexing permits the “ad-hoc” procedure1) mentioned in sub-clause 12.6 of ISO 2859/1 to be implemented as a standard procedure.

NOTE - The plans in ISO 2859/1 are indexed by a preferred series of AQL values and inspection levels. During the inspection of a continuing 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) ISO 2859/1 sub-clause 12.6.2, states: “If the lot or batch is of an isolated nature, it may be desirable to limit the selection of sampling plans to those, associated with a designated AQL value, that provide not less than a specified limiting quality protection. Sampling plans for this purpose can be selected by choosing a limiting quality (LQ) and a consumer’s risk to be associated with it. Tables 6 and 7 give process levels for which the probabilities of lot acceptance under various sampling plans are 10 % and 5 %, respectively.” This part of ISO 2859 establishes preferred values for the LQ and allows the consumer’s risk to vary as indicated above.
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