Filtered dielectric sensor apparatus

Filtered dielectric sensor apparatus

A sensor to measure dielectric constant of a medium may have a transmission line acting as a probe, and electronic circuit, and cable filter providing to reduce sensitivity of the sensor to cable parameters and influences. The sensor circuit may use 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 may be demodulated with an AM demodulator, such as a thermally compensated peak detector. This demodulated signal would be related to the characteristic impedance of the transmission line, and thus to the dielectric constant of the material surrounding the partially inserted transmission line probe. 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.