Latching Relay Reset Circuit Across a Digital Isolation Barrier
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Solution Overview
Problem
Existing industrial process field devices with latching relays face challenges in resetting across isolation barriers due to the need for complex software and additional digital signals, which increase cost and complexity, and microcontrollers may not be able to generate specifically timed pulses.
Innovation Solution
A digital isolator with edge triggered circuitry generates a reset pulse across an isolation barrier using discrete components, triggered by a digital edge change, eliminating the need for microcontroller intervention and additional software complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a latching relay is used to conserve power, then power consumption is reduced, but the relay cannot reset automatically after power loss
Solution Approach 1:
The patent implements a reset circuit that is pre-configured with a capacitor and resistor network on the primary side of the isolator. When power is restored after a power loss event, the capacitor automatically charges through the resistor and generates a reset pulse without requiring any control action. This preliminary action ensures the relay resets automatically, resolving the contradiction between power conservation and reset capability.
2Reliability
If additional digital signals and software are used to reset the latching relay, then reset functionality is achieved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the reset functionality from the microcontroller software domain and implements it in the hardware domain using a dedicated reset circuit with capacitor and resistor components. This separation eliminates the need for additional digital signals and software complexity, achieving reset functionality through simple analog circuitry on the primary side of the isolator.
Solution Approach 2:
The patent introduces a capacitor as an intermediary energy storage element between the power supply and the latching relay reset input. The capacitor acts as a mediator that converts power restoration into a timed reset pulse, enabling reliable reset functionality without direct digital control signals or complex software intervention.
3Loss of time
If microcontrollers are used to generate reset pulses, then reset timing control is achieved, but the system requires additional power and complexity
Solution Approach 1:
The patent replaces the electronic control system (microcontroller) with a passive analog timing circuit using a capacitor and resistor. This substitution achieves reset timing control through the natural charge/discharge characteristics of the capacitor, eliminating the need for microcontroller-based timing control and reducing overall system complexity and power requirements.
Data Source
AI summary
A field device for an industrial process includes a digital isolator which electrically divides the field device into a primary side for low voltage electronics from a secondary side. A device power supply located in the secondary side is configured to provide power to a process control device which monitors or controls a process variable of the industrial process. A latching relay located in the secondary side couples to the process control device and the device power supply and has a set input to responsively couple the device power supply to the process control device and a reset input which causes the latching relay to enter an electrically open state to thereby disconnect the device power supply from the process control device. A controller located in the primary side is configured to generate a switch signal. The digital isolator extends between the primary side and the secondary side and couples to the switch signal from the controller and provides a digital output on the secondary side in response to the switch signal. Edge triggered circuitry couples to the digital output of the digital isolator and provides a pulse output to the reset input of the latching relay in response the digital output of the digital isolator.