An Evaluation of Single-Featured EWMA-X (SFEWMA-X) Control Chart with Process Mean Shifts and Standard Deviation Changes

Quality control chart is an important tool for process monitoring and quality improvement. Several combined control charts have been proposed to enhance the detection ability in detecting small and large process parameter changes. However, two pairs of control limits and statistics on the control chart make the combined charts too complicated for the practitioners to use in practice. We have developed a single-featured EWMA-X (SFEWMA-X) control chart in previous study, which has the ability to monitor both large and small process shifts simultaneously using only one set of statistic and control limits. In this study, we presented an example to demonstrate the use of the SFEWMA-X chart, and performed the average run length (ARL) comparison between SFEWMA-X chart and the individual control charts to illustrate the detection ability of the SFEWMA-X chart. To facilitate the implementation of the proposed method in practice, we also introduced the algorithm for deriving optimal chart design tables.