Measurements with a periodicity are common in practice but there have been no specific monitoring control techniques for them. In this paper, we propose a type of control chart that plots measurements around a circle so that information from the same stage of different cycles can be readily compared. Some basic properties of such charts are investigated, and further developments are discussed. The basic circle chart can be applied under various kinds of control chart schemes, and there is potential for further development. Some application examples are also shown in this paper.

An important process characteristic is process maxima as it is often an important quality or performance parameter. Such measurements often play a vital role in process analysis and have to be monitored carefully. In this paper, we consider the problem of monitoring process maxima when the process exhibits a kind of periodicity. A circle chart for periodical process maxima with or without seasonal patterns monitoring is developed and studied, by modeling the process maxima using the extreme value distribution. Mean normalization is applied for periodic process monitoring with seasonal patterns to facilitate comparison between different sections and periods. The average cycle run length is proposed to measure charting efficiency. Copyright © 2014 John Wiley & Sons, Ltd.

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