An improved variable sample size and sampling interval S control chart

Michael B. C. Khoo, May Yen See, Nger Ling Chong, Wei Lin Teoh

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

The standard deviation chart (S chart) is used to monitor process variability. This paper proposes an upper-sided improved variable sample size and sampling interval (VSSIt) S chart by improving the existing upper-sided variable sample size and sampling interval (VSSI) S chart through the inclusion of an additional sampling interval. The optimal designs of the VSSIt S chart together with the competing charts under consideration, such as the VSSI S and exponentially weighted moving average (EWMA) S charts, by minimizing the out-of-control average time to signal (ATS1) and expected average time to signal (EATS1) criteria, are performed using the MATLAB programs. The performances of the standard S, VSSI S, EWMA S, and VSSIt S charts are compared, in terms of the ATS1 and EATS1 criteria, where the results show that the VSSIt S chart surpasses the other charts in detecting moderate and large shifts, while the EWMA S is the best performing chart in detecting small shifts. An illustrative example is given to explain the implementation of the VSSIt S chart.

Original languageEnglish
Pages (from-to)392-404
Number of pages13
JournalQuality and Reliability Engineering International
Volume35
Issue number1
Early online date17 Oct 2018
DOIs
Publication statusPublished - Feb 2019

Keywords

  • average time to signal
  • control chart
  • expected average time to signal
  • process variability
  • variable sample size and sampling interval

ASJC Scopus subject areas

  • Safety, Risk, Reliability and Quality
  • Management Science and Operations Research

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