TS ISO 3951-1

TS ISO 3951-1 addresses acceptance sampling by variables for lot-by-lot inspection when a single measurable quality characteristic is evaluated. This part defines single sampling plans indexed by acceptance quality limit (AQL) for one quality characteristic and one AQL, with particular relevance to continuing lots from a single producer operating a single production process.

What inspection by variables means

In variable inspection, the decision is based on the measured value itself rather than on counting conforming and nonconforming items. The quality characteristic is continuous, so values such as diameter, thickness, strength, or mass can be used to estimate conformance statistically. In general technical terms, this approach is most effective when the process is under statistical control and the characteristic is normally distributed, or closely approximates normality, which is the assumption named in the scope.

Specification limits and conformity logic

• Only one quality characteristic x is considered.
• The lots are discrete product lots from one producer using one production process.
• A lower specification limit L, an upper specification limit U, or both may be defined by contract or standard.
• Conformity is determined by whether x satisfies x ≥ L, x ≤ U, or both inequalities for double limits.
• For double specification limits, the document treats meeting both limits as equally important and uses a single AQL for the combined percentage outside the limits.

This standard provides the framework for single sampling plans and their AQL-based application; it does not replace the product specification itself. In practical use, such plans help align inspection effort with process consistency while preserving a statistically defined acceptance decision. TS ISO 3951-1 is the variables-based part of the broader ISO 3951 series for acceptance sampling.