Economic stoplight control design

Abstract

The choice of stoplight control parameters - sample size, sampling interval, and control limits - is considered from an economic point of view. The hourly cost function is derived to allow the optimal choice of the width of the green region of the stoplight control rule also. The average number of samples to signal and the average number of sample units to signal by using the modified stoplight rules are determined, under the assumption that the measured characteristic is normally distributed. An example illustrates the potential savings of this technique of designing stoplight control charts.