Stability and Sensitivity of an EWMA Controller

Article

Ingolfsson, Armann; Sachs, Emanuel   (1993, ASQC)   Massachusetts Institute of Technology

Journal of Quality Technology    Vol. 25    No. 4
QICID: 11356    October 1993    pp. 271-287
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Article Abstract

The performance of a process control algorithm based on EWMA statistic is analyzed. A simple condition relating the EWMA weight and the estimated process gain is shown to ensure that the control strategy is stable for a first-order multiple-input, single-output process that may be drifting or wandering. A similar condition is shown to guarantee stability for a second-order, single-input process. An expression is derived for the output mean squared deviation from target as a function of the algorithm parameters, how quickly the process drifts or wanders, and the amount of noise. The results are illustrated in the context of an epitaxial growth process.

Keywords

Exponentially weighted moving average control charts (EWMA),Stability,Statistical process control (SPC),Feedback control


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