# ISO 3951-1:2005

**Ausgabedatum:** 2005 04 07

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

ISO 3951-1:2005 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.

ISO 3951-1:2005 is primarily designed for application under the following conditions:

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;

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

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

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;

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:

*x* greater than or equal to *L* (i.e. the lower specification limit is not violated);

*x* less than or equal to *U* (i.e. the upper specification limit is not violated);

*x* greater than or equal to *L* and *x* less than or equal to *U* (i.e. neither the lower nor the upper specification limit is violated).

The first two inequalities are called cases with a single specification limit, and the third a case with double specification limits.

If double specification limits apply, it is assumed in ISO 3951-1:2005 that conformance to both specification limits is equally important to the integrity of the product; in such cases it is appropriate to apply a single AQL to the combined percentage of product outside the two specification limits. This is referred to as combined control.

**Ausgabedatum :**2013 08 27