Patent ID: 6822460
Filing Date: 2004-11-23
Classification: G01F

Abstract:
A system for determining a level of a combustible fuel in an aircraft fuel tank with a thermistor bead comprising:an aircraft fuel tank containing said combustible fuel; means for disposing said thermistor bead at a height in said fuel tank; a temperature sensor disposed in said fuel tank for measuring a temperature in proximity to said thermistor bead; a first circuit disposed outside of said fuel tank and coupled to the thermistor bead for conducting a constant bias current into said fuel tank and through said thermistor bead, said first circuit operative to limit the constant bias current to less than thirty milliamps; a second circuit coupled to the temperature sensor for generating a reference voltage in proportion to the measured temperature of said sensor; a third circuit disposed outside of said fuel tank and coupled to the thermistor bead for measuring a voltage across said thermistor bead in response to said bias current, and also coupled to said second circuit for detecting said dry/wet state of said thermistor bead based on said measured and reference voltages and generating a signal indicative thereof; and a fourth circuit for determining the level of fuel in the fuel tank based on the bead height and dry/wet state signal.