Supervision of several electro-hydraulic actuators operating on a common output

Several electro-hydraulic actuators are supervised by means of comparators which compare respective two actuators whereby each actuator is connected to two comparators to obtain a closed comparison loop. The comparators are, for example, of the differential piston variety comparing the actuator chamber on one or both sides of the piston therein with the comparable chamber or chambers in another actuator. Alternatively, the outputs of pressure cells, individually connected to the actuators, are compared. The comparison signals in either case are paired in that the outputs of the comparators connected to the same actuator are combined to control or shut down the respective actuator. Additional comparators may be provided to permit each actuator to be compared with all others for establishing sub-loops which remain in-tact when one or more actuators have dropped out, so as to maintain the loop principle even when only three actuators remain operative.