Advanced Diagnosis of Control Loops: Experimentation on Pilot Plant and Validation on Industrial Scale

The paper presents main features of a performance monitoring system, which, in addition to variables normally registered in industrial plants (controller output OP, controlled variable PV and set-point SP), makes use of additional variables made available by intelligent instrumentations and field bus communication systems. Experimental runs on a pilot plant scale have been carried out in order to introduce different types of valve malfunctions and to define suitable indices (KPI) able to diagnose them. Subsequently, threshold values for the indices have been calibrated and a logic has been developed to assign different performance grades. It is shown how the Travel Deviation allows specific evaluation of valve status and to detect different causes of malfunctioning. The same logic is implemented in an advanced release of an existing performance monitoring system and advantages in the accuracy of diagnosis are shown. Finally the system has been successfully validated by online implementation for control loops assessment of an industrial power plant.