The economic design of Shewhart control chart : a sensitivity study of X-bar control chart under Weibull shock model and variable control limits
One of the most typically used economic designs of control chart models is the standard Shewhart control chart model. Understanding the policies of the Shewhart control chart model is necessary before a sensitivity analysis of control chart cost model can be made. This thesis compares the performance of the standard Shewhart control chart model with that of a modified Shewhart control chart model with non-fixed control limits. In both cases, the occurrence time of the assignable cause is assumed to have a Weibull distribution. The formulation and the procedure for the design of the two models is examined. Following the theoretical development, both mathematical and numerical analyses are performed to validate the modified model. Finally, numerical results generated from experimental tests show the relative performance of the two models. The results of the numerical study indicate that a modified model can be more efficient in loss-cost reduction than standard model, based on a certain cost criterion.