AN ECONOMIC DESIGN OF THE ZONE CONTROL CHART FOR JOINTLY MONITORING PROCESS CENTERING AND VARIATION

The Zone Control Chart is applied to joint monitoring of process centering and variation based on an economic criterion. The control chart design parameters are the subgroup size, sampling interval measured in hours, width of control limits for the mean, width of control limits for the range or ln(s2), and the four zone scores used on both charts. This study indicates that the joint Zone Control Chart is superior, from an economic viewpoint, to joint X-bar and R charts. Therefore, the joint Zone Control Chart is recommended for use in practice due to its performance, simplicity, efficiency, ease of use, and ease of understand.