Patent ID: 7845224

Claim:
A capacitive sensor for detecting a level of a liquid in a tank, comprising: a measurement capacitor configured to be placed in the tank; a reference capacitor configured to be placed in a bottom part of the tank; a calibration capacitor, having a capacitance higher than that of the measurement capacitor; a controller for delivering an estimation signal corresponding to the level of the liquid, the estimation signal being based on capacitance values of the measurement capacitor, the reference capacitor, and the calibration capacitor; an operational amplifier with an inverting input; an integrating capacitor connected between the inverting input of the amplifier and an output of the operational amplifier; a comparator configured to compare an output voltage of the amplifier with a threshold voltage and to deliver a comparison signal to the controller; and a complementary calibration capacitor having a capacitance higher than that of the reference capacitor and different from that of the calibration capacitor; wherein the controller is configured to implement, over successive accumulation periods and for a target capacitor and a discharge capacitor that are given for each period: charging the target capacitor by applying a given voltage to its terminals; transferring charge from the target capacitor to the integrating capacitor; deciding to skip a next discharging if the comparison signal is negative; discharging some of the charge of the integrating capacitor into the discharge capacitor and then completely discharging the discharge capacitor; and returning to the charging; and wherein the target and discharge capacitors given at each period are taken respectively from a group of pairs of capacitors, including: the measurement capacitor and the calibration capacitor; and the reference capacitor and the complementary calibration capacitor.