Control charts with switching and sensitizing runs rules for monitoring process variation

摘要

In this work, we introduce and study one-sided variable sampling interval 5 control charts supplemented with signalling and switching rules based on runs. The proposed control schemes demonstrate an improved performance in the detection of small and moderate shifts (increasing or decreasing) in process standard deviation, retaining at the same time a relative low average number of switches. Comparison tables as well as practical guidelines that can assist practitioners in the selection of the parameters of the most suitable control scheme are also provided. The evaluation of the performance measures of the charts is carried out via a Markov chain approach.