ECONOMIC DESIGN OF CONTROL CHARTS WITH 2 CONTROL LIMITS

The main difficulties in the use of economic designs are the computations involved, the difficulty in specifying process parameters, and the fact that the sampling interval h is rarely a natural quantity of time. In this paper, we derive an explicit equation for h in terms of n (sample size), k(1) (inner control limit factor) and k(2) (outer control limit factor). With the explicit equation for h, we can get an optimization procedure, which is implementable in real time on a personal computer, to get the optimal design of control charts with two control limits. The results and the execution times of all numerical examples show that our optimization procedure is accurate and efficient.