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A New S 2 ‐EWMA Control Chart for Monitoring the Process Variance
Author(s) -
Castagliola Philippe
Publication year - 2005
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.686
Subject(s) - ewma chart , control chart , computer science , statistical process control , process (computing) , variance (accounting) , statistics , reliability engineering , engineering , mathematics , business , operating system , accounting
This article demonstrates how a three‐parameter logarithmic transformation combined with an exponentially weighted moving average (EWMA) approach can be used to monitor the sample variance of a process. The computation of the parameters of the logarithmic transformation and the control limits are explained. An easy‐to‐use table is provided and an illustrative example is given. The performance of the logarithmic transformation is evaluated under the assumption of normality. An optimal design strategy based on the ARL is presented and comparisons with other procedures are performed. Copyright © 2005 John Wiley & Sons, Ltd.