Two-Controller Fault Protection Using XOR Feedback Isolation
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Solution Overview
Problem
Existing control systems for critical applications require three independent circuits to effectively detect and manage faults, as two circuits cannot determine which information is correct, leading to potential hazardous conditions when a 'Fail Passive' system is used with only two circuits.
Innovation Solution
A control system utilizing two redundant controllers with an Exclusive OR or Exclusive NOR logic gate, isolated by medium value resistors, allowing each controller to determine input matching and correct output states, while impedance protection prevents a faulted controller from influencing the other, enabling single fault detection and correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two independent circuits are used in a 'Fail Passive' system, then the system can lock out a failed circuit to prevent hazardous conditions, but the system cannot determine which controller's output is correct when faults occur
Solution Approach 1:
The patent introduces an intermediary logic gate (XOR or XNOR) that mediates between the two controllers. This logic gate receives inputs from both controllers and produces an output that indicates whether the controllers agree. The intermediary allows the system to detect discrepancies without requiring a third voting controller, thus resolving the information loss problem while maintaining reliability.
2Reliability
If three independent circuits are used for redundant control, then the system can vote to select the correct controller output, but the system complexity increases
Solution Approach 1:
The patent extracts the voting function from a traditional three-controller system and implements it using only two controllers plus a logic gate. By taking out the essential voting capability and implementing it with minimal components (two controllers and an XOR/XNOR gate), the system achieves fault detection and correction without the complexity of three full controllers.
Solution Approach 2:
The patent changes the system architecture from three controllers to two controllers plus a logic gate. This parameter change in the system configuration reduces complexity while maintaining the essential voting functionality through the logical operations of the XOR or XNOR gate, which can detect discrepancies between the two controllers.
3Productivity
If a faulted controller is allowed to output signals, then the system can maintain operation, but the faulted controller may force incorrect states creating hazardous conditions
Solution Approach 1:
The patent implements feedback through the logic gate that continuously monitors the outputs of both controllers. When a discrepancy is detected (indicating a fault), the feedback mechanism allows the system to identify the faulted controller and prevent its incorrect output from causing hazardous conditions, while maintaining system operation through the non-faulted controller.
Data Source
AI summary
A control system is provides that includes a logic gate generating an output state signal, and first and second redundant controllers, wherein the first controller is configured to output a first state signal to a first input of the logic gate, and the second controller is configured to output a second state signal to a second input of the logic gate, and wherein the first controller is configured to receive an impedance isolated feedback signal corresponding to the second state signal from the second controller, and the second controller is configured to receive an impedance isolated feedback signal corresponding to the first state signal from the first controller, so that each controller can determine whether both inputs to the logic gate match one another.