ADAPTIVE SAMPLING ENHANCEMENTS FOR SHEWHART CONTROL CHARTS

Adaptive sampling is an enhancement to a classical statistical process control scheme in which the time between samples from the process is varied based on the available information. Unlike the classical Shewha rt control schemes, the performance of an adaptive sampling scheme for detecting a process which is off-target before the first observation is selected can differ from the steady-state performance, which is the performance of the scheme for detecting a process shift after the con trol scheme has been operating for some time. Often steady-state perfo rmance is the more important criterion for evaluating statistical proc ess control schemes. Previous work has considered initial performance and steady-state performance, but the charts examined were optimized f or initial performance. The development of charts optimized for steady -state performance and a comparison to previously developed schemes ar e the topics of this paper. Tables providing performance information o n adaptive schemes are included.