A new exponentially weighted moving average control chart for monitoring the coefficient of variation

• We propose a new EWMA chart for monitoring the process coefficient of variation.
• Tables are provided for the statistical properties of the new scheme.
• The proposed scheme can be easily designed and constructed.
• The proposed scheme can effectively detect the changes in coefficient of variation.
• A real data example shows that the new scheme performs quite well in applications.

Monitoring coefficient of variation is one of the successful approaches to Statistical Process Control (SPC) when the process mean and standard deviation are not constants. This paper presents a modified Exponentially Weighted Moving Average (EWMA) chart in order to further enhance the sensitivity of the EWMA control chart proposed by Castagliola et al. (2011). Tables are provided for the statistical properties of the new chart. Some numerical results and comparisons are given and show that the new chart has an average run length performance that is superior to some other competing procedures. A real data example from manufacturing shows that it performs quite well in applications.