A water-level sensor using a capacitance to frequency converter

A capacitive water-level sensor using PTFE-insulated wire and a capacitance to frequency converter is described. Construction is simple, yet overall linearity is 0.1%. Temperature drift of the sensor is -0.05%K-1 and that of the converter is <0.01%K-1. Long-term stability of the sensor appears excellent. The converter draws only 150 mu A from a 5 V supply and is insensitive to supply voltage variations.