Relay failure detecting device
A relay failure detecting device able to detect reliably a fault in a relay circuit that provides alternating current power to a load through a relay that is a double-pole switch. Individual common terminals of first and second relays are connected individually to a pair of outputs terminals of an alternating current power supply, individual normally-open terminals of the first and second relays are connected to a pair of power supply input terminals, and a dummy load that is driven by the alternating current power supply through a diode between the individual normally-closed terminals of the first and second relays is provided. A fault in the first and second relays is evaluated from the state of operation of the dummy load when the first and second relays are not driven.
1. A relay failure detecting device in a relay output circuit that is provided with a plurality of relays that, when not driven, connected between a common terminal and a normally-closed terminal, and that when driven, connected between the common terminal and a normally-open terminal, where the individual common terminals of the relays are connected individually to the plurality of outputs terminals in an alternating current power supply, and the individual normally-open terminals in the relays are connected individually to a plurality of power supply input terminals; comprising:
a dummy load that is driven by the alternating current power supply through a diode, between the individual normally-closed terminals of the plurality of relays, and that is provided with an evaluating device evaluating, from the state of operation of the dummy load, whether or not there is a failure in the plurality of relays when the plurality of relays is not driven.
2. A relay failure detecting device as set forth in claim 1 , wherein:
the dummy load is a photocoupler made from a light-emitting element that is driven by the alternating current power supply, and a light-detecting element that is optically coupled to the light-emitting element; and
the evaluating device has a control device for controlling the operation of a driving circuit for each relay, and achieve a function for detecting the output of the light-detecting element.
3. A relay failure detecting device as set forth in claim 1 , further comprising:
a second dummy load device connected on one end to one of the power supply inputs of the load and connected on the other end through respective diodes to the individual common terminals of the plurality of relays; and
second evaluator evaluating whether or not there is a failure in the plurality of relays based on the operating status of the second dummy load when the plurality of relays is not driven.
4. A relay failure detecting device as set forth in claim 3 , wherein:
the second dummy load is a photocoupler made from a light-emitting element that is driven by the alternating current power supply and a light-detecting element that is optically coupled to the light-emitting element; and
the second evaluating device has a control device for controlling the operation of a driving circuit for each relay, and achieve a function for detecting the output of the light-detecting element.