Material level detector circuit

Abstract

Disclosed are apparatus and methods for detecting the presence, or absence, of material at a predetermined location. An oscillator generates a constant-frequency, constant-amplitude signal which is fed through a load resistor to an antenna probe positioned at the sensing location. The amplitude of the signal fed to the antenna probe varies as the impedance of the antenna probe is affected by material in its environment, or lack thereof. The signal amplitude is converted into a d-c voltage level, and is transmitted to a switching circuit which provides an output signal depending on a comparison between the d-c voltage level and a reference voltage level. The sensitivity of the switching circuit is adjustable to accommodate the degree to which the particular material, whose presence or absence is to be detected, affects the impedance of the antenna probe. The output from the switching circuit may be used to operate one or more devices indicative of the environment of the antenna probe and/or affecting the environment by adding to and/or removing therefrom material affecting the impedance of the antenna probe.