A study on the variable sampling interval EWMA X chart when the process parameters are unknown

L. V. Ong, Wei Lin Teoh, Michael Boon Chong Khoo, Z. L. Chong, W. C. Yeong

Research output: Contribution to journalConference article

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Abstract

The exponentially weighted moving average (EWMA) X chart is well known in statistical process control for detecting small and moderate process mean shift. A variablesampling-interval (VSI) control scheme of the EWMA X chart is able to enhance the speed of detection when the process is out-of-control as the intervals switch according to the value of the previous sample statistics. Generally, the performance of the VSI EWMA X chart is investigated under the assumption of known process parameters. However, in reality, these parameters are usually unknown and are estimated from a historical Phase-I dataset. Hence, the performance of the VSI EWMA X chart is significantly affected when the process parameters are unknown. This is due to estimation errors. In this paper, we investigate the effects of parameter estimation on the performance of the VSI EWMA X chart in terms of the average time to signal and standard deviation of the time to signal. Suggestions on the required number of Phase-I samples and sample sizes in designing the VSI EWMA X chart with unknown process parameters, are provided for practitioners' fast implementation.

Original languageEnglish
Article number012084
JournalJournal of Physics: Conference Series
Volume1132
Issue number1
DOIs
Publication statusPublished - 20 Dec 2018
Event3rd International Conference on Mathematical Sciences and Statistics 2018 - Putrajaya, Malaysia
Duration: 6 Feb 20188 Feb 2018

ASJC Scopus subject areas

  • Physics and Astronomy(all)

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