Evaluation of ATS for CRL control chart

The CRL (Conforming Run Length) control chart has attracted increasing inte rest in the last few years. Many researchers have claimed that the CRL char t is superior to the traditional attribute control charts (e.g. the np char t or p chart) in many aspects. In this paper, accurate formulae have been d erived for calculating the out-of-control ATS (Average Time to Signal) of t he CRL chart. These formulae take into account the random-shift model of p (fraction nonconforming), in which the p value may shift at any point durin g a conforming run length. Comparative studies reveal that the conventional approximate method for evaluating the ATS of the CRL chart may produce not able error. The new formulae provide the QA (Quality Assurance) engineers w ith a tool to accurately assess the performance of the CRL chart; and will therefore promote further application of the CRL chart.