Diagnostic Device And Method For Monitoring The Operation Of A Control Loop

A diagnostic device for monitoring operation of a control loop (R, P) of an automation system, the diagnostic device comprising a data memory (DS) for storing sequences of both setpoint data and actual-value data for the control loop and an evaluation device (AE) for determining a stochastic feature with reference to at least one segment of the sequences of setpoint data and actual-value data, wherein the stochastic feature determined for the actual-value data is a first dimension for scatter of the actual-value data, the diagnostic device being configured so that, for monitoring operation of a slave or ratio control loop in an meshed control structure, the evaluation device (AE) is operable for determining a second dimension for scatter of the setpoint data as a stochastic feature of the setpoint data and for determining a characteristic number (CPIVar, CPIKas) for evaluating the control quality as a function of a ratio of the first dimension to the second dimension.