Field device latching relay reset

An industrial process control system comprising:

• a field device configured to control an active component comprising a control device configured to control a process of the industrial process;
• an external device electrically coupled to a latching relay;
• a device power supply electrically coupled to the latching relay and configured to power the external device through the latching relay;
• the latching relay is configured to connect the external device to the device power supply through the latching relay based upon a set state and a reset state of the latching unit;
• a controller configured to generate a switch signal;
• a relay drive configured to set the latching relay in one of the set state and the reset state based on the switch signal;
• a reset circuit;
• and
• a relay power supply configured to provide electrical power to the relay drive;
• wherein the reset circuit is configured to set the latching relay to the reset state in response to an interruption of the electrical power supplied by the relay power supply by applying power to the latching relay stored in a charge reservoir;
• wherein the relay drive is powered by a relay voltage supplied by the relay power supply;
• and
• the reset circuit comprises:
• a comparator configured to detect the interruption of electrical power from the relay power supply;
• wherein the reset circuit sets the latching relay in the reset state when the comparator detects the interruption of electrical power from the relay power supply using an electrical charge from the charge reservoir.

A method of controlling a latching relay of a field device for an industrial process comprising:

• controlling a process parameter of the industrial process using a control device of an active component of the field device;
• powering a relay drive of the latching relay using a relay power supply;
• controlling power to an external device comprising setting the latching relay of the field device in one of a set state and a reset state in which the latching relay is configured to connect the external device, electrically coupled to the latching relay, to a device power supply, electrically coupled to the latching relay and configured to power the external device, through the latching based on a switch signal from a controller of the field device;
• comparing a voltage supplied by the relay power supply to a threshold voltage using a comparator of a reset circuit of the field device;
• and
• setting the latching relay in the reset state with the switch signal using an electrical charge stored in a charge reservoir of the reset circuit when the voltage reaches a predetermined relationship to the threshold voltage.