Premium
Monitoring the ratio of two normal variables using variable sampling interval exponentially weighted moving average control charts
Author(s) -
Nguyen Huu Du,
Tran Kim Phuc,
Heuchenne Cédric
Publication year - 2019
Publication title -
quality and reliability engineering international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.913
H-Index - 62
eISSN - 1099-1638
pISSN - 0748-8017
DOI - 10.1002/qre.2412
Subject(s) - ewma chart , control chart , statistics , x bar chart , interval (graph theory) , chart , control limits , mathematics , sampling interval , sampling (signal processing) , statistical process control , variable (mathematics) , computer science , process (computing) , mathematical analysis , combinatorics , filter (signal processing) , computer vision , operating system
We investigate in this paper a new type of control chart called VSI EWMA‐RZ by integrating the variable sampling interval feature (VSI) with the exponentially weighted moving average (EWMA) scheme to monitor the ratio of two normal random variables. Because the distribution of the ratio is skewed, we suggest designing two separated one‐sided charts instead of one two‐sided chart. A new coefficient is introduced allowing us to be free to choose a sampling interval provided that it optimizes the performance of the control chart. We also make a direct comparison between the VSI EWMA‐RZ charts and standard EWMA‐RZ control charts. The numerical simulations show that the proposed charts outperform the standard EWMA charts in detecting process shifts. An application is illustrated for the implementation of the VSI EWMA‐RZ control charts in the food industry.