A measurement circuit that has particular application for detecting a high impedance measurement signal from a liquid water sensor. The measurement circuit includes a high impedance resistance-to-frequency conversion circuit that is coupled to the sensor and receives a resistance signal therefrom. The resistance-to-frequency conversion circuit includes an oscillator that converts the resistance signal to a representative frequency. The measurement circuit also includes a frequency-to-voltage conversion circuit that receives the frequency signal from the resistance-to-frequency conversion circuit, and converts the frequency signal to a representative voltage that provides an indication of water on the sensor.