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Practitioner advice: ERLDAT–A web-based tool to design and analyze EWMA control charts

Summary: [This abstract is based on the authors' abstract.] The performance of a control chart is completely characterized by its run length distribution. Quality practitioners usually do not have access to the run length distribution but rely on the average run length (ARL) to design and evaluate the performance of an exponentially weighted moving average (EWMA) control chart. This article presents a web-based tool that provides users easy access to the Phase 2 (on line or monitoring phase) run length distribution for a two-sided EWMA control chart with known parameters. The web-based tool calculates the run length distribution, percentiles of the run length distribution, as well as the mean (ARL) and variance (VRL) of the run length distribution. Additional functionality of the web-based tool includes plotting the run length distribution functions, building tables of the quantiles of the run length distribution, finding the smoothing parameter (λ) for an EWMA control chart for fixed control limit that satisfies ARL, VRL or percentile performance, and finding the control chart limit (k) for an EWMA control chart that satisfies ARL, VRL, or percentile performance. This tool and these techniques enable quality practitioners to better design and evaluate EWMA control charts.

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  • Topics: Engineering, Statistics
  • Keywords: Exponentially weighted moving average (EWMA), Run length, Distribution, Analysis, Software, Tools, Average run length (ARL), Exponentially weighted moving average control charts
  • Author: Timmer, Douglas H.; Moya, Hiram;
  • Journal: Quality Engineering