MINIMUM-VARIANCE AS A BENCHMARK FOR FEEDBACK-CONTROL

Minimum variance is a better benchmark than zero variance for evaluati ng controller performance. Control systems cannot reduce the variance in product quality below the variance inherent in the process. On the basis of minimum variance, an investment in controller maintenance can be evaluated realistically. Minimum variance control does not have to be implemented, and controller tuning parameters have no effect on th e evaluation. A performance index based on minimum variance can also b e calculated.