Control Charts for Processes with an Inherent Between-Sample Variation

Eva Jarošová

Control Charts for Processes with an Inherent Between-Sample Variation

Číslo: 2/2018
Periodikum: Statistika

Klíčová slova: Statistical process control, modified chart, acceptance chart, variance component chart, average run length

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Anotace: A number of processes to which statistical control is applied are subject to various effects that cause random

changes in the mean value. The removal of these fluctuations is either technologically impossible or economically
disadvantageous under current conditions. The frequent occurrence of signals in the Shewhart chart due to
these fluctuations is then undesirable and therefore the conventional control limits need to be extended. Several
approaches to the design of the control charts with extended limits are presented in the paper and applied
on the data from a real production process. The methods assume samples of size greater than 1. The performance
of the charts is examined using the operating characteristic and average run length. The study reveals that
in many cases, reducing the risk of false alarms is insufficient.