Importance

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Abstract

The amount of liquid dielectric fuel in a tank is monitored with a capacitor including first and second electrodes immersed in the fuel. The fuel level determines the capacitance between the electrodes. Contaminants in the fuel are reflected as a shunt resistor for the capacitance between the electrodes. A periodic symmetrical triangle voltage is applied to the electrodes. The impedance between the electrodes responds to the voltage by deriving a composite current having a constant amplitude square wave component and a component that is a replica of the periodic voltage. The amplitude of the constant amplitude component is determined, in one embodiment, by sampling the amplitude of the composite current at the center of each square wave component to indicate the capacitance and the amount of fuel in the tank independently of effects of the shunt resistor on the electrodes. In a second embodiment, the amplitude of the composite current is sampled at two different times to indicate the slope of the replica and provide a measure of the resistor. By interpolating the two sampled amplitudes the capacitance is determined.

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First Claim