Capacitive Fuel Gaging System with Contamination Compensation
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Solution Overview
Problem
Conventional capacitive fuel gaging systems face challenges in accurately measuring fuel quantity in aircraft fuel tanks due to the introduction of high-resistance elements to minimize electrical conduction, which can lead to system inaccuracy and contamination-related errors.
Innovation Solution
The enhanced capacitive fuel gaging system incorporates a high-resistance wire measurement mode and a gaging mode with contamination compensation, utilizing a static DC voltage source, analog switches, and a probe-mounted diode to isolate contamination resistance and compensate for slope errors in the output waveform.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If high-resistance elements are used to minimize electrical conduction into fuel tanks, then electrical safety is improved, but measurement precision deteriorates due to contamination-related errors
Solution Approach 1:
The patent introduces a contamination resistance measurement mode that acts as an intermediary measurement path. By measuring the total resistance (wire resistance + contamination resistance) and separating it from the pure wire resistance measurement, the system isolates the contamination effect without requiring direct electrical conduction into the fuel tank, thus maintaining safety while enabling compensation
Solution Approach 2:
The system implements feedback by continuously measuring contamination resistance and using this information to compensate for errors in the fuel gaging measurement. The contamination resistance value is fed back to the measurement circuit to adjust and correct the fuel level indication, thereby maintaining precision despite the presence of high-resistance elements
2Object-affected harmful factors
If high-resistance wires are used in capacitive gaging, then electrical safety is improved, but system accuracy deteriorates due to contamination affecting the square wave output
Solution Approach 1:
The patent uses contamination resistance measurement as an intermediary to understand and compensate for the contamination effect on the square wave output. By measuring the contamination resistance separately, the system can calculate the expected error in the fuel gaging measurement and apply compensation, thereby maintaining accuracy despite using high-resistance wires
Solution Approach 2:
The system changes the measurement parameter by introducing a resistance measurement mode that measures contamination resistance. This additional parameter allows the system to characterize the contamination effect and use it to correct the fuel level measurement, thereby maintaining precision while using high-resistance wires for safety
3Device complexity
If contamination resistance is not compensated, then system complexity is reduced, but measurement precision deteriorates due to slope errors in the output waveform
Solution Approach 1:
The patent segments the measurement process into distinct modes: a wire resistance measurement mode and a contamination resistance measurement mode, followed by a fuel gaging mode. This segmentation allows the system to separately characterize and compensate for contamination effects without requiring complete redesign of the entire measurement system, thus balancing complexity and precision
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
This system effectively minimizes electrical conduction into fuel tanks while accurately compensating for fuel contamination, ensuring precise fuel quantity measurement by isolating contamination resistance and flattening the slope of the output waveform.
Implementation Method 1
concentric probes to produce a variable capacitor probe dependent on a change of the dielectric coverage within the tube formed by the concentric probes
Implementation Method 2
The probe capacitor dielectric is a combination of air space and the fuel level
Implementation Method 3
high resistance wires or standard wires using high resistance safety resistors in the gaging system
Implementation Method 4
a probe-mounted diode to isolate contamination resistance from wire resistance
Data Source
AI summary
A fuel gaging system, such as may be used in determining an amount of fuel in an aircraft fuel system, includes a capacitance probe and a capacitance measurement circuit component including high resistance elements. The capacitance measurement circuit component includes a first excitation generator, an excitation wire connected between the first excitation generator and the capacitance probe, and a signal wire connected to the capacitance probe with the capacitance probe being connected between the excitation wire and the signal wire, wherein the first excitation generator generates an input signal applied to the excitation wire and an output signal is read from the signal wire to determine a capacitance at the capacitance probe. The system further includes a wire resistance measurement circuit component configured to isolate a contamination resistance to account for variations in wire resistance of the system wires in determining the capacitance at the capacitance probe; and a contamination compensation circuit component configured to compensate for fuel contamination in determining the capacitance at the capacitance probe by compensating for a slope error in the output signal.