Apparatus for generating an electrical signal indicative of liquid level

Abstract

Apparatus for generating an electrical signal indicative of the level of a liquid stored in a reservoir. The apparatus includes first and second probes spaced from one another and extending into the reservoir. Each of the probes includes a metal electrode surrounded by a preferably dielectric material. The liquid to be measured contacts the dielectric material, but does not directly contact the electrodes. A preferably alternating voltage is applied across the electrodes and the impedance therebetween is sensed. The impedance between the electrodes varies as a function of the level of the liquid in the reservoir and this impedance is substantially greater than the impedance between the probe areas of contact with the liquid. In effect, the liquid is treated as a conductor because its impedance is negligible as compared to the impedance between the probe electrodes, this impedance varying as a function of liquid level.