US Patent 7503435 Elevator safety circuit monitoring system and method

The invention concerns a method and a system for monitoring the operation of the safety circuit of an elevator, said safety circuit containing safety switches connected in series with a contactor and a static circuit. In the method, the current flowing in the safety circuit is measured and the state of the safety circuit is determined on the basis of the measured current. The measurement of the safety circuit current is preferably performed without a galvanic connection to the safety circuit. The state of the safety circuit is determined on the basis of the magnitude of the measured current, from which the positions of the safety switches during the current measurement can be inferred.