Abstract

In the literature the Exponentially Weighted Moving Average EWMA and Exponentially Weighted Moving Variance EMWV control schemes have been used separately to monitor the process average and process variability respectively Here the two are combined and applied on simulated process with different level of variation The control limit interval CLI and the average run length ARL were evaluated for the combined chart The combined chart performed better than the two independently Furthermore an algorithm was developed for the two control charts and implemented on visual basic VB6 0 The obtained results show that the combined EWMA and EWMV control chart is very sensitive in detecting shift in production process and every shift in the process mean is always preceded by shift in the process variability