Patent ID: 8369060

Claim:
A monitoring circuit for monitoring at least one signal input, such as an emergency stop signal, comprising: at least first and second relays (K 1 , K 2 ) connected in series or in parallel to a DC-supply voltage (Vdc) and controlled into an active state by means of a start-up switch; wherein the relays are connected to the supply voltage (Vdc) by means of a self-maintaining contact of relay, and into a passive state in dependence on the signal applied at the least one signal input; wherein said first and second relays (K 1 , K 2 ) have different ohmic coil resistances (Rsp 1 , Rsp 2 ); and wherein the coil resistance (Rsp 1 ) of said first relay (K 1 ) is smaller than the coil resistance (Rsp 2 ) of said second relay (K 2 ), so that in the case of a short-term dip in the supply voltage (Vdc), said first relay (K 1 ) is dropped first, while said second relay (K 2 ) is still responding.