Field device with latching relay

Abstract

A field device (102) for industrial processes includes a digital isolator (124) that electrically isolates the field device (102) from the secondary side to the primary side for low-voltage electronic equipment. A device power supply (107) located on the secondary side is configured to supply power to a process control device (108) that monitors or controls process variables of the industrial process. A latching relay (128) located on the secondary side has a set input (S) for coupling to the process control device (108) and the device power supply (107) and for quickly responding to this by coupling the device power supply (107) to the process control device, and a reset input (R) for electrically opening the latching relay (128) and thereby disconnecting the device power supply (107) from the process control device (108). A controller (122) located on the primary side is configured to generate a switch signal. The digital isolator (124) extends between the primary and secondary sides, couples to the switch signal from the controller (122), and provides a digital output to the secondary side in response to the switch signal. The edge trigger circuit (160) is coupled to the digital output of the digital isolator (124) and provides a pulse output to the reset input (R) of the latching relay in response to the digital output of the digital isolator (124).

Claims

1. A field device for industrial processes, A digital isolator that electrically isolates the field device from the secondary side to the primary side for low-voltage electronic equipment. A device power supply located on the secondary side, configured to supply power to a process control device that monitors or controls process variables of the industrial process, A latching relay having a set input for rapidly reacting to couple the device power supply to the process control device, and a reset input for electrically opening the latching relay, thereby disconnecting the device power supply from the process control device, wherein the latching relay is located on the secondary side and coupled to the process control device and the device power supply. A controller located on the primary side, configured to generate a switch signal, wherein the digital isolator extends between the primary side and the secondary side and is coupled to the switch signal from the controller, which is configured to provide a digital output to the secondary side in response to the switch signal, and An edge trigger circuit coupled to the digital output of the digital isolator, configured to provide a pulse output to the reset input of the latching relay in response to the digital output of the digital isolator, A field device equipped with the following features.

2. The field device according to claim 1, wherein the process control device is selected from the group consisting of actuators, valves, and solenoids.

3. The field device according to claim 1, comprising a pulse duration circuit configured to control the duration of the pulse output provided to the reset input of the latching relay.

4. The field device according to claim 3, wherein the pulse duration circuit includes an RC circuit that charges in response to the digital output from the digital isolator.

5. The field device according to claim 3, wherein the pulse duration circuit includes a comparator that compares the rise voltage level with a threshold.

6. The field device according to claim 5, wherein the comparator rapidly responds by providing an output to a tristate buffer that lowers the pulse output supplied to the reset input.

7. The field device according to claim 1, wherein the edge trigger circuit includes a tristate buffer that provides the pulse output to the reset input of the latching relay.

8. The field device according to claim 7, wherein the pulse output is pulled low through a resistor connected to electrical ground.

9. The field device according to claim 7, wherein the tristate buffer is configured to enter a high-impedance output state after providing the pulse output to the new set input of the latching relay.

10. The field device according to claim 1, wherein the digital isolator has a default low output.

11. The field device according to claim 10, comprising an inverter coupled to the default low output of the digital isolator.

12. The field device according to claim 1, comprising a communication circuit coupled to a two-wire process control loop.

13. The field device according to claim 12, wherein the communication circuit receives power from the two-wire process control loop to supply power to the controller.

14. The field device according to claim 13, wherein the pulse output to the reset input of the latching relay is provided in the event of a loss of power from the two-wire process control loop.

15. The field device according to claim 14, wherein the switch signal from the controller is pulled high via a resistor coupled to the power supply.

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