Exponentially weighted moving average control charts for three-level products

In this paper, exponentially weighted moving average (EWMA) control charts for multinomial data are developed with a three-level classification scheme. The lower and upper control limits of the proposed EWMA control chart are evaluated using Markov chain approximation. Compared with the three-level Shewhart control chart, numerical results indicate that the proposed EWMA control chart is relatively sensitive to small shifts in a three-level multinomial process. A figure and a table are provided for practitioners to select the value of chart limit coefficient that gives the desired in-control average run length.