Monitoring of the Measurement Process Capability by Using Capability Indices

Requirements related to accuracy of measurement and other metrological properties are required for measurement. Expression of the quality of the measurement is generally solved by the uncertainty of measurement. For measurements in industry, in addition to uncertainty increasingly also used capability index. We take advantage of experiences when determining the capability of production processes. There are some specifics related to the probability of their validity and in particular due to the uncertainty of the check measurement standard used. With help of this standard, we determine capability of measurement process. This contribution is addressed mainly to the impact of the uncertainty of a check standard for the capability index calculation. In practice, it is generally assumed that the uncertainty of the check standard in the assessment of the capability indices of measurement process is negligible. However, there may be cases that it is not negligible. In this paper, we examine how uncertainty of the check standard affects capability indices. This may be particularly important for lower index values, when data from the uncertainty of the check standard indicate that the process is satisfactory and in fact it may not be. The contribution also includes correction factors that allow correct the empirical value of the capability index and thus avoiding a possible mistaken assessment of the measurement process capability.