Variable sampling interval one-sided CUSUM control charts for monitoring the multivariate coefficient of variation

In recent years, monitoring techniques based on the multivariate coefficients of variation (MCV) have received a great deal of attention for their ability to monitor multivariate processes with a fixed functional relationship between the mean and variance. To improve the performance of existing MCV control charts, two one-sided cumulative sum (CUSUM) charts are proposed to monitor the MCV and a variable sampling interval (VSI) strategy is incorporated into these charts in this paper. The average time to signal (ATS) measure of the proposed control charts is derived based on the Markov chain method and the corresponding optimization procedure is designed to obtain and evaluate the optimal performance of the control charts. The superiority of the proposed control charts is confirmed by comparing their performance with two existing MCV charts.