An increasing number of applications in the chemical industry involve measuring nonconforming items, particularly in high-purity processes or high-yield processes. Dedicated monitoring tools such as the time-between-events (TBE) control charts have been developed for both discrete time (CCC-charts) and continuous time (tr-charts) for detecting any shifts in the process defect rate. However, most common performance metrics used in literature are not always appropriate and may not suffice to describe the efficiency of a monitoring system. The definition of conditional performance measures described in the literature is extended to TBE charts. These metrics are computed for Shewhart-type TBE charts with run rules and used to compare these charts at different aggregation levels.
- average length of inspection (ALI)
- conditional expected delay (CED)
- high-yield processes
- probability of successful detection (PSD)
- standard deviation of length of inspection (SDLI)
- statistical process control (SPC)