Basic closed-loop control circuits (such as position or pressure controls, for example) and technological closed-loop control circuits (such as gauge or flatness controls) are an impor-tant part of automation systems. There are, generally, a large number of such controls which have a varying influence on product quality and on the productivity of a system. A fundamen-tal prerequisite for optimum product quality and high productivity is that all the important closed-loop control circuits are, if possible, optimally adjusted. In practice, the controllers are adjusted at the time of initial start-up or when a modernisation takes place and, in most cases, are not adapted for years to the continually changing process characteristics and re-peatedly modified mix of products.
 
"Control Performance Monitoring“ methods and tools are being enlisted to monitor the per-formance of closed-loop control circuits. These make it possible to evaluate the performance of closed-loop control circuits sporadically or continuously. This is done by computing certain key figures or quality levels and comparing these data with those of optimally adjusted con-trollers. If a poor control performance is diagnosed, measures can be derived for modifying the controller setting or for designing a controller with a modified structure. The tools have already been used to evaluate the gauge control system at a tandem cold rolling mill.