RC Circuit Limits Sensor Energy in Fuel Tanks
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Solution Overview
Problem
Aircraft fuel tank sensors face challenges in limiting electrical energy to prevent spark-induced explosions, particularly under normal conditions and during failure modes or lightning events, with existing solutions either attenuating high-frequency sensor signals or lacking reliability in preventing high current levels.
Innovation Solution
A resistance-capacitance (RC) circuit is used to power a sensor driver, constraining output current and energy through a pulse generator, ensuring safe energy levels by charging a capacitor to a prescribed value between active pulses, and incorporating a high-frequency transformer for lightning protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a sensor driver is powered directly without energy limiting, then the sensor receives adequate current for operation, but the sensor may receive excessive current that could generate a spark and ignite fuel vapor in aircraft fuel tanks
Solution Approach 1:
The capacitor is pre-charged to a prescribed voltage level between pulses through the resistor from the voltage source. This preliminary charging action ensures that when a pulse is needed, the capacitor can immediately discharge to provide the required high current to the sensor driver without requiring the voltage source to directly supply that high current, thus limiting energy while maintaining operational adequacy.
Solution Approach 2:
The sensor driver operates in a pulsed manner rather than continuously. The pulse generator produces periodic pulses at a prescribed frequency, and the capacitor charges during the interval between pulses and discharges during each pulse. This periodic operation allows the sensor to receive adequate current during active periods while the average current remains limited by the resistor, resolving the contradiction between safety and operational adequacy.
2Reliability
If a resistor is used to limit current to the sensor driver, then average current is limited to safe levels, but the sensor driver may not receive adequate current during active pulses for proper operation
Solution Approach 1:
The capacitor maintains a charged state between pulses, ready to immediately discharge and provide high instantaneous power when needed. This continuous readiness ensures that the sensor driver receives adequate power during each active pulse period without interruption or delay, while the resistor continues to limit the average power drawn from the voltage source, thus resolving the contradiction between safety and operational power requirements.
3Power
If the RC circuit time constant is increased to allow capacitor charging between pulses, then adequate current can be supplied during pulses, but the response time of the circuit increases
Solution Approach 1:
The values of the resistor and capacitor are specifically selected to achieve an optimal time constant (RC) that balances two competing requirements: it must be long enough to allow the capacitor to charge to the prescribed voltage level between pulses, but short enough to allow the circuit to respond quickly when a pulse is generated. By adjusting these parameters, the system achieves both adequate current supply during pulses and acceptable response time, resolving the contradiction between power availability and speed.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The RC circuit effectively limits average current and energy supplied to sensors, ensuring safety while maintaining signal integrity and reliability, even under fault conditions or lightning threats, without the need for complex active circuits or built-in-test systems.
Implementation Method 1
a high current sensor driver is powered through a resistance-capacitance (RC) circuit
Implementation Method 2
The value of the resistor may be chosen to ensure that under short circuit conditions direct current (DC) is limited to a safe value
Implementation Method 3
incorporating a high-frequency transformer for lightning protection
Data Source
AI summary
A method and system for limiting energy to a sensor and/or an environment in which the sensor is located. A high current sensor driver is powered through a resistance-capacitance (RC) circuit. In a failure mode, the RC circuit constrains output of a sensor driver to the sensor in order to limit average current applied to the sensor. In one embodiment, the capacitor is chosen so that it can provide adequate current to the sensor driver for a short period of time. The value of the resistor may be chosen to ensure that under short circuit conditions direct current (DC) is limited to a safe value. The combined values of the resistor and capacitor may be adjusted such that the capacitor can charge to a prescribed level during the interval between active pulses.