AS 3941-1990

Provides guidance for preparing and using number nonconforming control charts, for the purpose of reducing the amount of inspection needed to control process quality.

This Standard describes the simplest method of statistical quality control, i.e. charting the results of the number of nonconforming items in samples taken from a process that produces individual or discrete units of product rather than a bulk commodity or continuous material. This Standard also sets out accepted methods of charting which are easy to use, and which may safely and profitably replace 100 percent inspection or routine examination. They are applicable whenever the quality of work done can be assessed by classifying it as right or wrong. The guidance given in Sections 2 and 3 should be followed in preparing control charts. The purpose of Section 4 is to guide users in refinements to these methods. It also describes efficient methods, which may be used to reduce the sample sizes and the amount of inspection needed, and to control process quality so that nonconforming items are virtually eliminated. Clause 4.5 provides a fully worked example.NOTE: No attempt is made to deal at length with the statistical principles underlying these methods, the objective being to show how to use them. They may be employed far more widely than merely for the examination of dimensions. The methods have been used for such processes as making up packages at large mail-order stores, errors in bank statements, reservations and transfers in hotel accommodation, in addition to the more usual manufacturing processes.