A combined upper-sided synthetic \(S^2\) chart for monitoring the process variance (Q779575)

Summary: In order to monitor the process variance, this paper proposes a combined upper-sided synthetic \(S^2\) chart for monitoring the process standard deviation of a normally distributed process. This combined upper-sided synthetic \(S^2\) chart comprises a synthetic chart and an upper-sided \(S^2\) chart. The design and performance of the proposed chart are presented, and the steady-state average run length comparisons show that the combined upper-sided synthetic \(S^2\) chart outperforms the standard synthetic \(S^2\) chart as well as several run rules \(S^2\) charts, especially for larger shifts in the process variance.