New Interquartile Range EWMA Control Charts with Applications in Continuous Stirred Tank Rector Process

Monitoring of process parameters via control charts is exceptionally common exercise in statistical process control (SPC). The exponentially weighted moving average (EWMA) control chart is one of an outstanding powerful tool of the SPC for monitoring of process parameters. The performance of any process can be improved by the careful monitoring and removing of assignable causes of variation. The existence of outliers may influence the performance of traditional charts in the monitoring of a process. This study is planned for the monitoring of dispersion parameter through the interquartile range (IQR). We proposed EWMA-type IQR charts based on auxiliary information for the efficient monitoring of process dispersion for the process following bivariate normal distribution. The comparison of these charts is made with usual IQR chart as well as traditional R and S charts. We evaluate the efficiency of charts by some commonly used run length measures. Both contaminated and uncontaminated processes are considered in this study to examine the robustness of charts. The results revealed that our proposed control charts exhibit superior performance in the presence of outliers. A real application of our study is also provided based on non-iso-thermal continuous stirred tank chemical reactor process.