EWMA Control Chart for Coefficient of Variation Using Log-Normal Transformation Under Ranked Set Sampling

The coefficient of variation is a variability measure used in manufacturing industries when the process mean fluctuates with time and process standard deviation is a linear function of process mean. In this paper, we proposed an exponential weighted moving coefficient of variation control chart by using three parametric log-normal transformations under ranked set sampling with different sample sizes. The average run length and standard deviation of run lengths are computed with an extensive Monte Carlo simulation study to measure the performance of the proposed chart. The comparison of the proposed control chart is made with considered CV control charts and concluded that the proposed control chart is efficient as compared to considered CV control charts to detect the small or moderate shifts in the process CV. An example is presented to demonstrate the implementation of the proposed control chart on the real data set.