A side-sensitive synthetic coefficient of variation chart

Yeong, Wai Chung and Lee, Ping Yin and Lim, Sok Li and Khaw, Khai Wah and Khoo, Michael Boon Chong (2021) A side-sensitive synthetic coefficient of variation chart. Quality and Reliability Engineering International, 37 (5). pp. 2014-2033. ISSN 0748-8017,

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Official URL: https://doi.org/10.1002/qre.2843


Control charts for monitoring the coefficient of variation (gamma) are useful for processes with an inconsistent mean (mu) and a standard deviation (sigma) which changes with mu, by monitoring the consistency in the ratio sigma over mu. The synthetic-gamma chart is one of the charts proposed to monitor gamma, and its attractiveness lie in waiting until a second point to fall outside the control limits before a decision is made. However, existing synthetic-gamma charts do not differentiate between the points falling outside the upper control limit (UCL) and lower control limit (LCL). Hence, this paper proposes a side-sensitive synthetic-gamma chart, where successive nonconforming samples must either fall above the UCL or below the LCL. Formulae to compute the average run length (ARL), the standard deviation of the run length (SDRL) and expected average run length (EARL) are derived using the Markov chain approach, and the algorithms to obtain the optimal charting parameters are proposed. Subsequently, the optimal charting parameters, ARL, SDRL and EARL values for various numerical examples are shown. Comparisons show that the side-sensitive synthetic-gamma chart consistently outperforms the existing synthetic-gamma chart, especially for small shifts. The proposed chart also consistently outperforms the Shewhart-gamma chart, while showing comparable or better performance than the Exponentially Weighted Moving Average (EWMA) chart for most shift sizes, except for very small shifts. Finally, this paper shows the implementation of the proposed chart on an industrial example.

Item Type: Article
Funders: Ministry of Education, Malaysia, Fundamental Research Grant Scheme (FP052-2018A ), Universiti Malaya (GPF030B-2018)
Uncontrolled Keywords: Average run length; Coefficient of variation; Control charts; Expected average run length; Process monitoring and control; Statistical quality control; Synthetic chart; Side-sensitive
Subjects: T Technology > TA Engineering (General). Civil engineering (General)
Divisions: Faculty of Science
Depositing User: Ms. Juhaida Abd Rahim
Date Deposited: 23 Feb 2022 04:58
Last Modified: 23 Feb 2022 04:58
URI: http://eprints.um.edu.my/id/eprint/26844

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