Title: Studies on EWMA Control Chart in Presence of Autocorrelation
Abstract: Control charts are used to monitor a production process. While using control charts, a standard assumption is that observations from the process at different time periods are independent random variable. However, the assumption of independency in observation is not always true rather they are dependent in many cases. For example, in many chemical process industries, the observation taken at different time points are often correlated due to the dynamic nature of the process. Sometimes, some process inherently produced data that are autocorrelated. The presence of autocorrelation in process observations can have a large impact on traditional control chart developed under independent assumptions. When there is significant autocorrelation in the process observation, it is not advisable to apply traditional control chart methodology without modification, as there is typical effect of the autocorrelation on the control limits. In this paper, an attempt has been made to study the effect of autocorrelation on EWMA chart which is used alternative to Shewhart Control Chart specially in detecting small shifts in the process. Both for positive and negative autocorrelation, the effect on EWMA control limits are studied and in order to account for the autocorrelation, control limits are adjusted with the modification of EWMA control chart parameters.
Publication Year: 2014
Publication Date: 2014-01-01
Language: en
Type: article
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Cited By Count: 1
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