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.
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PJ Ross (1983) studied this question.
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