A conditional-reliability control-chart for the post-production extended reliability-test

This paper presents a new failure-percent control chart which is based on the conditional reliability of the sequential life tests. It provides a better reliability monitoring tool than the existing SPRT chart because: (1) the new control chart calculates and plots the failure percent batch by batch separately without mixing them and accumulating run hours and number of failures across batches, and therefore provides higher sensitivity of catching manufacturing aberration; (2) the new control chart does not assume a constant failure rate; (3) no assumption needs to be made on the population homogeneity; and (4) it is easier to trace back to the troublemaking batch, fix the problem and conduct more in-depth risk assessment. It is also found the proposed monitoring tool is not sensitive to the Weibull shape parameter selection in its actual feasible range