Gas Valve Control Circuit Fail-Safe Design
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Solution Overview
Problem
Existing control circuits for gas valves lack a reliable fail-safe mechanism to ensure the valve remains in a safe state in case of microprocessor failure, potentially leading to unsafe operation.
Innovation Solution
A control circuit design incorporating a drive circuit with at least two transistors, a fail-safe circuit, and specific diode and capacitor configurations to ensure the gas valve stops in a safe state even if the microprocessor fails, using distinct signal frequencies and duty cycles to control transistor operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If a microprocessor-based automatic control is used for gas valve control, then the control automation and functionality are improved, but the reliability and safety in case of microprocessor failure deteriorate
Solution Approach 1:
The control system is segmented into a microprocessor unit for normal operation and a separate fail-safe circuit for safety assurance. The fail-safe circuit includes independent components (transistors, diodes, capacitors, resistors) that can independently control the gas valve without relying on the microprocessor, thus resolving the contradiction between automation and reliability.
Solution Approach 2:
The fail-safe circuit acts as an intermediary between the microprocessor and the gas valve. It monitors the microprocessor's operation and can independently activate or deactivate the gas valve based on detected failures, ensuring safety even when the microprocessor fails. This intermediary layer resolves the trust issue between automated control and safety assurance.
2Reliability
If additional fail-safe watchdog circuits are added to ensure safety, then the reliability is improved, but the device complexity increases
Solution Approach 1:
The fail-safe circuit is merged with the existing microprocessor-based control system, sharing common components such as power supply connections and output contacts. The fail-safe circuit uses the same input contact as the microprocessor, and both control paths converge at the gas valve output contacts. This merging reduces overall complexity while maintaining dual control capability.
Solution Approach 2:
The fail-safe circuit is designed to perform multiple functions: it can detect microprocessor failures, independently control the gas valve opening/closing, and provide a backup control path. By making the fail-safe circuit multi-functional, the patent reduces the need for separate dedicated safety systems, thereby controlling complexity while improving reliability.
3Reliability
If the gas valve is designed to stop in safe status upon failure, then the safety is improved, but the loss of time for valve operation increases
Solution Approach 1:
The fail-safe circuit is pre-configured with capacitors charged during normal operation. Upon detecting a microprocessor failure, these pre-charged capacitors immediately provide the necessary energy to activate the fail-safe transistors and close the gas valve without waiting for external power or signal processing. This preliminary preparation eliminates time delays in the safety response.
Solution Approach 2:
The fail-safe circuit uses periodic signal monitoring from the microprocessor to detect failures. The circuit is designed to trigger immediately upon detecting abnormal signal patterns, ensuring rapid response. The periodic nature of microprocessor signaling allows the fail-safe circuit to continuously monitor and react promptly, minimizing operational interruption time while maintaining safety.
Data Source
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AI summary
Control circuit (10) for a gas valve, the control circuit (10) comprising in-put contacts (14, 21) by which the control circuit is connectable to a microprocessor, output contacts (31, 32) by which the control circuit is connectable to the gas valve to be operated, a drive circuit (11) and a fail-safe circuit (12), wherein the drive circuit (11) comprises a first transistor (19) and a second transistor (20) both being operated through the fail-safe circuit (12) on basis of a first signal provided by the microprocessor. The first signal is provided by the microprocessor at a first input contact (21) of the control circuit, namely at an input contact (21) of the fail-safe circuit (12). A first parallel connection of a resistor (33), a capacitor (34) and a first and a second diode (35, 36) being serially connected is connected between the gate and the source of the first transistor (19). A second parallel connection of a resistor (33), a capacitor (34) and a first and a second diode (35, 36) being serially connected is connected between the gate and the source of the second transistor (20). A first series connection (37) having a resistor (38) and a capacitor (39) is connected with a first contact point between the first diode (35) and the second diode (36) assigned to the first transistor (19) and with a second contact point to a first output contact (27) of the fail-safe circuit (12). A second series connection (40) having a resistor (38) and a capacitor (39) is connected with a first contact point between the first diode (35) and the second diode (36) assigned to the second transistor (20) and with a second contact point to the first output contact (27) of the fail-safe circuit (12). A series connection of the first transistor (19) and the second tran-sistor (20) is connected between a power supply contact (18) and a sec-ond output contact (28) of the fail-safe circuit (12).