CUSUM control charts with Variable Sampling Interval for monitoring the ratio of two normal variables

Overview & Synopsis

In many industrial manufacturing processes, the ratio of two normal random variables plays a key role in ensuring product quality. Monitoring this ratio then becomes an important task that is well worth considering. In this paper, we combine variable sampling (VSI) feature with the cumulative sum (CUSUM) scheme to create new type of control chart for purpose of tracking the ratio of two normal variables. The average time to sign (AT S) is used as a measure to evaluate the performance of VSI CUSUM charts. The sensitive of the charts for different deterministics process shifts as well as random process shifts is displayed in several tables. The results show that our proposed control charts have much more attractive power in comparison with the standard CUSUM charts.