Capacitive liquid level sensor

Abstract

A capacitive liquid level sensor is provided comprising a capacitive probe having a capacitance and comprising a sensing tip wherein the capacitive probe is configured such that the capacitance of the probe changes when the sensing tip is exposed to liquid. A signal generator operates to supply an electrical signal alternating between a high and low state to the capacitive probe, the electrical signal being configured such that the probe is alternately charged and discharged when the signal is high or low respectively. A comparator operates to detect the magnitude of an electrical signal across the capacitive probe and provides a first output signal value when the detected signal magnitude is greater than a predetermined threshold value and a second output signal value when the signal magnitude is less than the threshold value. A timer operates to receive an output signal from the comparator and measures a time period starting when the comparator output signal transitions to the first output signal value and ending when the comparator output signal transitions to the second output signal value. Liquid detection means also operate to utilize the time period measured by the timer to determine if the sensing tip is exposed to liquid.