The EWMA Run Length Distribution Analysis Tool (ERLDAT)

摘要

The run length distribution of a control chart completely characterizes the performance of a control chart. Quality practitioners usually do not have access to the run length distribution but rely on the average run length (ARL) to design and evaluate the peformance of an exponentially weighted moving average (EWMA) control charts. This paper will present a web-based tool that provides users access to the run length distribution for a EWMA control chart with known parameters. The web-based tool will calculate the run length distribution, percentiles of the run length distribution as well as the mean (ARL) and variance (VRL) of the run length distribution. Additional functionality of the web-based tool includes plotting the run length distribution functions, building tables of the quantiles of the run length distribution, finding the smoothing parameter (λ) for an EWMA control chart for fixed control limit that satisfies ARL, VRL or percentile performance, and finding the control chart limit (k) for an EWMA control chart that satisfies ARL, VRL or percentile performance. This tools and these techniques will enable quality practitioners to better design and evaluate EWMA control charts.