International Organization for Standardization

Sampling procedures for inspection by variables Part 1: Specification for single sampling plans indexed by acceptance quality limit (AQL) for lot-by-lot inspection for a single quality characteristic and a single AQL - First edition; Cancels and Replaces  3951:1989
 N 3951-1

Annotation

This part of ISO 3951 specifies an acceptance sampling system of single sampling plans for inspection by variables, in which the acceptability of a lot is implicitly determined from an estimate of the percentage of nonconforming items in the process, based on a random sample of items from the lot.

This part of ISO 3951 is primarily designed for application under the following conditions:

a) where the inspection procedure is to be applied to a continuing series of lots of discrete products all supplied by one producer using one production process;

b) where only a single quality characteristic x of these products is taken into consideration, which must be measurable on a continuous scale;

c) where the measurement error is negligible, i.e. with a standard deviation no more than 10 % of the process standard deviation;

d) where production is stable (under statistical control) and the quality characteristic x is distributed according to a normal distribution or a close approximation to the normal distribution;

e) 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 the appropriate one of the following inequalities:

1) x ? L (i.e. the lower specification limit is not violated);