Control system for a process that exhibits periodic disturbances

In a control system a characteristic quantity of a process (1) exhibits a periodic disturbance. A measuring system (2) generates a measuring signal (Vm) which represents the characteristic quantity. A control device controls the process in response to the measuring signal (Vm). To reduce the periodic disturbance, the control device (3) comprises a delay circuit (4) which delays an input signal (Vin) related to the measuring signal (Vm) by a time interval (T) having the length of a period (Tp) of the periodic disturbance. The control device (3) comprises an analysis circuit (6) for deriving an analysis signal (Va) which is indicative of a deviation between the period of the periodic disturbance and the delay time. By means of a control circuit (13) and an adapter circuit (7), the delay time (T) is set in dependence on the analysis signal (Va) to a value for which the analysis signal (Va) indicates that the delay time (T) is equal to the period (Tp). A correlation system can be used for deriving the analysis signal (Va).