The process capability chart is a frequency histogramA bar graph that shows frequency of occurrence versus value. Quite often the data is fitted to a distribution such as a normal distribution. . and distribution of the sample data currently displayed (on the Mean chart). Citect SCADA automatically takes the data being trended, builds a distribution, adds the LSL and USL. It also calculates the Cp, Cpk, kurtosisAn index indicating the degree of peakedness of a frequency distribution (usually in relation to a normal distribution). Kurtosis < 3 indicates a thin distribution with a relatively high peak. Kurtosis > 3 indicates a distribution that is wide and flat topped., and skewness indices.
The process capability is defined in relation to the upper and lower specification limits (USL and LSL) for a given SPC Tag. These values are defined in SPC Tags and accurately represent the users requirements.
To configure a capability chart:
Published June 2018