Monitoring Process Variability Using Double Moving Average Control Chart

Abstract

Enhancing the ability of control charts for detecting shifts of small magnitude in the process parameter is desirable. In this paper, a double moving average control chart based on the sample standard deviation is proposed for detecting shifts in the process variability. The performance of the proposed control chart is investigated in terms of average run length and compared with existing control charts. The results show that the proposed control chart performs better than the existing control charts. A numerical example based on simulated and real-life data is provided to demonstrate the application of the proposed chart.