The economic assessment of process control quality using a Taguchi-based method

This paper derives a measure of dynamic control quality within the Taguchi framework (G. Taguchi, E.A. Elsayed, T. Hsiang, Quality Engineering in Prod uction Systems, McGraw-Hill, New York, 1989) which estimates product qualit y (in economic terms) by the losses incurred when specified product charact eristics depart from their nominal values. In this sense, a control system may be viewed as a "product" with stability and performance properties as i ts required characteristics. The degree to which system inputs and outputs depart from their nominal values is used to give an estimate of stability a nd performance quality, respectively. Displaying control quality graphicall y with stability and performance qualities as the two axes can be used to h ighlight the trade-off between these two characteristics. This technique wa s used to evaluate the quality offered by four model-based controllers on a distillation column model responding to a typical disturbance, and how the presence of measurement and valve dynamics affected control quality. It is anticipated that the measures derived in this paper (being both time-based and economic) may prove useful in conveying control quality in a common la nguage understood by engineers, operators and management. (C) 2000 Elsevier Science Ltd. All rights reserved.