Individual and Moving Ratio Charts for Weibull Processes
نویسنده
چکیده
This article proposes methods for monitoring Weibull processes when data collection is restricted to one observation per sampling period. Because the Weibull distribution is an asymmetric distribution, it is not appropriate to apply normal-based individuals-movingrange charts to Weibull data. A transformation of Weibull to approximate normality prior to applying normal-based methods has been suggested in the literature. This article studies the run length properties of and the difficulties encountered with this approach. As an alternative, this article proposes combined individual and moving range charts for monitoring changes in either the Weibull scale or shape parameter. A method for computing the average run length ARL is discussed, and control limits are presented for ARL-unbiased charts. The proposed method is applied to a Weibull data set.
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