Adaptive Sampling for Process Control

Abstract

Statistical process control procedures typically entail monitoring the process by selecting rational subgroups of equal size at equal time intervals. A generalization of this standard paradigm removes the restriction of equal waiting times between subgroups. We consider process control procedures where the time until the next subgroup is shortened when there is evidence that the process is off target, with a compensating lengthening of the waiting time otherwise. This adapting of the waiting time significantly improves the performance of the process control procedure. Using the Shewhart X̄ procedure as an example, the adaptive sampling strategy is introduced. A simple, dual waiting time procedure is described and shown to be optimal and easy to implement in practice. Performance comparisons to classical procedures are provided.

• Average Run Length
• Control Charts
• Control Scheme
• Process Control
• Shewhart Control Charts
• Variable Sampling Frequency

Additional information

Notes on contributors

George C. Runger

Dr. Pignatiello is an Associate Professor with joint appointments in the Industrial Engineering and Statistics Departments. He is a Member of ASQC.

Joseph J. Pignatiello

Dr. Runger is an Assistant Professor in the Decision Sciences and Engineering Systems Department. He is a Member of ASQC.