Variables inspection for production quarantined by statistical process control

When a control chart signals an out-of-control condition for a production process, it may be desirable to ‘quarantine’ all units produced since the last in-control SPC sample. This paper presents an efficient procedure for variables inspection of such ‘SPC quarantined’ product. A Bayesian sequential inspection procedure is developed which determines whether the out of control production is of acceptable quality. By inspecting the units in reverse of the order in which they were produced, the procedure is also capable of detecting the point at which the process went out of control, thus eliminating the need to inspect units produced prior to the onset of the out of control condition. Numerical examples are presented, and the performance characteristics of the procedure are demonstrated using Monte Carlo simulation.