Method and apparatus for detecting a dry/wet state of a thermistor bead using temperature compensation

摘要

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