Monitoring of time between events with a double generally weighted moving average control chart

Monitoring of time between events (TBE) instead of the number of events is used in high-quality processes where the events occur rarely. This article presents a double generally weighted moving average control chart with a lower time-varying control limit to monitor the TBE (regarded as DGWMA-TBE chart). The design parameters of the proposed chart are provided, and through a simulation study, it is shown that the DGWMA-TBE chart is more effective than the DEWMA and GWMA charts in detecting moderate to large shifts. Furthermore, the DGWMA-TBE chart is very robust for the same range of shifts when the TBE observations follow a Weibull or a lognormal distribution. Finally, examples are also presented to enhance the performance of the proposed chart.