초록 ▼

A system and probe for indicating the level of material in a vessel as a function of material capacitance comprising a resonant circuit including a capacitance probe adapted to be disposed in a vessel so as to be responsive to variations in capacitance as a function of material level. An rf oscillat

A system and probe for indicating the level of material in a vessel as a function of material capacitance comprising a resonant circuit including a capacitance probe 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 has an output coupled to the resonant circuit and to a phase detector for detecting variations in phase angle as a function of probe capacitance. Level detection circuitry 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 adjusts the resonance characteristics of the parallel resonant circuit of the reference signal indicative of a predetermined reference material level.

대표청구항 ▼

1. A system for indicating the level of material in a vessel as a function of material capacitance comprising a capacitance probe adapted to be disposed in a vessel so as to be responsive to variations in capacitance as a function of material level in said vessel, oscillator means for providing a pe

1. A system for indicating the level of material in a vessel as a function of material capacitance comprising a capacitance probe adapted to be disposed in a vessel so as to be responsive to variations in capacitance as a function of material level in said vessel, oscillator means for providing a periodic electrical signal, circuit means for coupling said periodic electrical signal to said capacitance probe such that operating characteristics of said circuit means responsive to said electrical signal vary as a function of capacitance at said probe, said circuit means including variable second capacitance means separate from said probe and connected in said circuit means such that said operating characteristics of said circuit means responsive to said electrical signal vary independently as functions of capacitance at said probe and at said second capacitance means, calibrating means including means for initiating a calibration operation, means for automatically varying said second capacitance means in a predetermined manner independently of said probe during said calibration operation and means responsive to operating characteristics of said circuit means during said calibration operation as a combined function of said electrical signal and said varying second capacitance means for terminating said calibration operation and variation of said second capacitance means when said circuit means obtains a predetermined operating characteristic, and means responsive to variations in operating characteristics of said circuit means from said predetermined operating characteristic for indicating material level in said vessel as a function of capacitance at said probe. 2. The system set forth in claim 1 wherein said predetermined operating characteristic corresponds to a low material level condition of said vessel. 3. The system set forth in claim 1 wherein said initiating means comprises electronic switch means. 4. The system set forth in claim 1 wherein said variable second capacitance means comprises a plurality of capacitors and a corresponding plurality of electronic switch means respectively connected in series with said capacitors and responsive to said automatically varying means for selectively connecting said capacitors into said circuit means. 5. The system set forth in claim 4 wherein said automatically varying means comprises counter means having outputs operatively connected selectively to control conductive conditions at said switch means, and means responsive to said initiating means and to said means for terminating said calibration operating for automatically varying the count in said counter means during said calibration operation. 6. A system for indicating the level of material in a vessel comprising probe means adapted to be coupled to a vessel so as to exhibit variations in electrical characteristics as a function of material level in said vessel; circuit means coupled to said probe means such that operating characteristics of said circuit means vary as a function of said electrical characteristics at said probe means, said circuit means including a plurality of separate impedance means separate from said probe means and switch means for selectively connecting each of said plurality of impedance means into said circuit means; calibration means including means for initiating a calibration operation, counter means having outputs operatively connected selectively to control a conductive condition at said switch means, means responsive to said initiating means for automatically varying the count in said counter means independently of said probe means in a predetermined manner during a said calibration operation, and means responsive to said circuit means during a said calibration operation for detecting a predetermined operating characteristic of said circuit means, corresponding to a predetermined material level condition in said vessel, and for terminating said calibration operation at said counter means when said predetermined operating characteristic is obtained; and means responsive to variations in operating characteristics of said circuit means including said probe means from said predetermined operating characteristic for indicating level of material in said vessel. 7. The system set forth in claim 6 for indicating level of material as a function of material capacitance wherein said probe means comprises a capacitance probe adapted to be disposed in a said vessel so as to be responsive to variations in capacitance as a function of material level in said vessel, and wherein said operating characteristics of said circuit means vary as a function of capacitance at said probe. 8. The system set forth in claim 7 wherein said predetermined operating characteristic corresponds to a low material level condition at said vessel.