An EWMA for Monitoring a Process Standard Deviation
作者:
CrowderStephen V.,
HamiltonMarc D.,
期刊:
Journal of Quality Technology
(Taylor Available online 1992)
卷期:
Volume 24,
issue 1
页码: 12-21
ISSN:0022-4065
年代: 1992
DOI:10.1080/00224065.1992.11979369
出版商: Taylor&Francis
关键词: Integral Equation;Location Parameter;Log-Gamma Distribution;Scale Parameter
数据来源: Taylor
摘要:
Most applications of the exponentially weighted moving average (EWMA) for process monitoring have concentrated on the problem of detecting shifts in the mean level of a process. Perhaps more important is the problem of detecting increases in process variability, which can also have a major impact on product quality. In this paper we propose using an EWMA based on the log transformation of the sample variance. Properties of this EWMA are given and an optimal design strategy is presented. It is shown that the EWMA is superior to the usual range chart or s2chart in terms of its ability to quickly detect small increases in the standard deviation of a normal process.
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