A new control chart using the process loss index function

Abstract

A control chart is a powerful tool used to monitor the variation of a proccss. In tliis paper, a new viewpoint of control chart based on process loss index is proposed. The control limits for chart are constructed. The operating characteristics function of chart is derived, which is used to describe how well the control chart can detect assignable causes. Also an average run length is computed to show how many samples are needed for the control chart to discover a change of proccss. In addition, comparisons are made with the existing control chart based on Cpm (Spiring, 1995) in terms of the operating characteristic curve and average run length. Finally. a real world example is given to illustrate the proposed methodology. Through the proposed method, practitioners can determine the corresponding sample size based on a desired value of the average run length to make the chart for monitoring the process capability.