Use

In a variable inspection , you must specify at least one tolerance limit in the inspection plan for the quantitative characteristic in question. ISO 3951 serves as a standard for a variable inspection. The Quality Management application component has two valuation procedures for variable inspections:

When you perform a variable inspection according to the s-method for normally distributed characteristic values, the sample size, mean value (x-bar), and standard deviation (s) of the characteristic values are required as inspection results. Depending on the recording form used, you either enter the statistics, or the system calculates them from the single values.

Depending on whether there is an upper specification value ( USL ) or a lower specification value (LSL) for the characteristic values, the inspection characteristic is rejected if the following conditions are met:

Mean > USL - k * s

or

Mean < LSL + k * s

The value k is the acceptance factor defined in the sampling plan. The mean value and standard deviation must be known.

If the tolerance range is limited on both sides (double-sided) , there are two variants for conducting the s-method valuation. You define which variant is used in the function module for the valuation rule. The variants differ in their acceptance range.

When the s-method uses the double-sided tolerance range, both limits of the tolerance range are treated together . The share above the tolerance range and the share below are estimated and compared with a critical value that is calculated from the sample size and acceptance factor. This form of variable inspection leads to the same decision as the graphical procedure described in the ISO 3951 standard (see the figure below). Given the same sampling plan, the acceptance range is smaller than for the variant of the s-method in which the two limit values are handled separately. In this case, the upper and lower specification values are checked separately . The characteristic is rejected when one of the two rejection conditions is met.

Acceptance Areas for a Variable Inspection