Temperature compensated transmission line based liquid level sensing apparatus and method

Abstract

A sensor having a transmission line acting as a probe and an electronic circuit measures liquid levels. The sensor circuit uses a periodic signal generator to produce a carrier wave, which stimulates the transmission line, through a complex network coupling element. The complex impedance network forms a voltage divider with the transmission line, wherein the output of the voltage divider, is demodulated with an AM demodulator, such as a thermally compensated peak detector. This demodulated signal is related to the dielectric constant, and thus the liquid level of the material surrounding the partially submerged transmission line probe. The liquid level and the demodulated signal may be offset, scaled and linearized with a microcontroller containing signal processing routines, linearizing equations, stored calibration constants and look up tables.

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