Comparison of the traditional exponential weighted moving average chart (EWMA) and modified EWMA chart (MEWMA)

Abstract

Any production process that needs statistical control to exit the production process as required, whether from the consumer or producer point of view, and in this research a comparison was made between the two control charts of the modified and traditional exponential weighted moving average chart. The modified chart takes into consideration the autocorrelation that arises between the observations, unlike the traditional chart, which is affected by the autocorrelation between the values of the observations, which leads to giving inaccurate results on the progress of the production process. To clarify the work of the modified chart and compare it with the traditional chart, data representing the temperature of a chemical industrial process was relied on, because such data are autocorrelation, meaning that small or sudden transformations may occur. The two charts were also applied to data taken from the Quality Control Department in the General Facility for Vegetable Oils in Baghdad Governorate affiliated to the Ministry of Industry. The modified chart showed its efficiency and accuracy in detecting deviations in the production process better than the traditional chart.