Determination of Optimal Design Parameters of Moving Average Control Charts

The economic design of a control chart can reduce the cost of process control and promote the competitiveness of an enterprise. This type of design has been studied for over four decades since Duncan’s pioneering work in 1956. Few studies, however, have focused attention on the economic design of a moving average (MA) control chart. Montgomery pointed out that an MA control chart is more effective than a Shewhart control chart for detecting small process shifts and is considered by some to be simpler to implement than the CUSUM. This study proposes an economic model of an MA control chart with multiple assignable causes. This economic model is then applied to a realistic case from the chemical industry, and sensitivity analysis shows that the magnitude of shift, rate of occurrence of assignable causes and penalty cost, when the process is out of control, should be more carefully estimated when conducting an economic analysis..