Capacitance-type material level indicator.

摘要

A system and probe for indicating the level of material (28) in a vessel (22) as a function of material capacitance comprising a resonant circuit (14) including a capacitance probe (20) adapted to be disposed in a vessel so as to be responsive to variations in capacitance as a function of material level. An rf oscillator (10) has an output coupled to the resonant circuit (14) and to a phase detector (32) for detecting variations in phase angle as a function of probe capacitance. Level detection circuitry (36, 38) is responsive to an output of the phase detector and to a reference signal indicative of a predetermined level of material for indicating material level as a function of a difference between capacitance at the probe and the reference signal. In the preferred embodiments of the invention disclosed, an automatic calibration circuit (34) adjusts the resonance characteristics of the parallel resonant circuit of the reference signal indicative of a predetermined reference material level. Also disclosed is a capacitance probe (20) and method of probe manufacture for material level sensing systems and like applications.