Performance assessment: a requisite for maintaining your APC assets

This paper discusses the practical application of continuous performance assessment as a requisite for maintaining the advanced process control (APC) assets in the process industry. The commissioning of elaborate control system platforms, advanced control applications, and information management systems e.g. historians and databases etc., have become commonplace in the process industry. Incidentally, these investments have led to the accumulation of tremendous process data with few data-mining tools and control-relevant techniques for extracting information. In this paper, the theory of performance assessment is presented as a technique for continuously assessing the performance of the basic control loops in a plant, as a means towards maintaining APC assets. Continuous performance assessment allows detection of performance degradation in the basic control loops in a plant by monitoring the variance in the process variable and comparing it to that of a minimum variance controller. The resulting index gives an indication of the level of performance of the controller and an indication of the action required to improve its performance, e.g., re-tune the controller or consider process re-engineering. A process application of this technique will be demonstrated with the use of a software tool-ProcessDoc/sup TM/-which computes loop performance indices from archived routine operating data from an industrial process.