Modified exponentially weighted moving average control chart for monitoring process dispersion

The exponentially weighted moving average ((Formula presented.)) charts are widely used memory-type charts for monitoring small to moderate shifts in process parameters. However, the performance of the (Formula presented.) chart has been improved over time due to various modifications and enhancements. This paper proposes two modified (Formula presented.) ((Formula presented.)) charts to monitor process dispersion. The upper-sided modified (Formula presented.) chart is denoted by (Formula presented.) while a lower-sided modified (Formula presented.) chart is symbolized as the (Formula presented.) chart. Monte Carlo simulations determine the proposed schemes’ run length (RL) properties in zero- and steady-state scenarios. The proposed upper- and lower-sided (Formula presented.) charts are compared to the upper- and lower-sided (Formula presented.) and SJ-EWMA charts. The comparisons reveal that the proposed M-EWMA charts have better detection ability than the upper- and lower-sided CH-EWMA, and SJ-EWMA charts, respectively. Finally, a real-life application is provided to illustrate the implementation of the upper-sided M-EWMA and CH-EWMA charts practically in both zero-state and steady-state cases.