A Comparative Study of Exponential Time between Events Charts

Control charts based on time between events (TBE) data have been shown to be useful for monitoring production or failure processes where defect or failure occurrence can be recorded over time. One type of TBE chart is set up with probability control limits, e.g. the Cumulative Quantity Control (CQC) chart and its extension CQC-r chart, which monitors the quantity inspected until the occurrence of a fixed number of defects (r). Another type of TBE chart studied in the literature is to apply the CUSUM and EWMA methods to TBE data directly. In this paper, some exponential TBE charts are compared based on their Average Time to Signal (ATS) performance. Different in-control ATS values are used in order to evaluate its effect on the performance of the TBE charts. Based on the comparison analysis, some recommendations are made as guidelines for employing a proper chart under different situations.