An Improved Variable Sample Size And Sampling Interval S Control Chart

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dc.contributor.authorSee, May Yen
dc.date.accessioned2019-03-07T07:18:58Z
dc.date.available2019-03-07T07:18:58Z
dc.date.issued2018-05
dc.description.abstractThe standard deviation chart or S chart is used to monitor the process standard deviation. In this thesis, some of the features of the S chart are altered to increase the chart’s sensitivity towards small and moderate shifts in the process standard deviation. This new chart for monitoring the process standard deviation is known as the improved variable sample size and sampling interval ( t VSSI ) S chart. The design and construction of the t VSSI S chart is based on the idea of the improved variable sample size and sampling interval ( t VSSI ) X chart proposed by Noorossana et al. in 2016. The t VSSI X chart improves the efficiency of the X-type charts in detecting small and moderate shifts in the process mean. The t VSSI S chart uses two sample sizes and three sampling intervals. The Markov chain approach is employed in the design of the t VSSI S chart for evaluating the chart’s average time to signal (ATS) and expected average time to signal (EATS) performances. The ATS and EATS performances of the optimal t VSSI S chart are compared with that of the optimal exponentially weighted moving average (EWMA) S, optimal modified variable sample size and sampling interval (VSSI) S and standard S charts. The ATS and EATS values of all the charts are computed using the MATLAB programs. The simulation programs in the Statistical Analysis System (SAS) software are also used to verify the accuracy of the ATS and EATS values computed via MATLAB. It is found that the t VSSI S chart is superior to the standard S, modified VSSI S and EWMA S charts, in detecting moderate and large shifts in the process standard deviation, in terms of the ATS and EATS criteria. An illustrative example is given to show the construction of the t VSSI S chart.en_US
dc.identifier.urihttp://hdl.handle.net/123456789/7858
dc.language.isoenen_US
dc.publisherUniversiti Sains Malaysiaen_US
dc.subjectThe standard deviation chart or S charten_US
dc.subjectmonitor the process standard deviationen_US
dc.titleAn Improved Variable Sample Size And Sampling Interval S Control Charten_US
dc.typeThesisen_US
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