Reference signal differentiating capacitive fluid level gauge

Claim 2

A capacitance-type fluid level gauge comprising: a. a capacitor probe adapted to be inserted into a fluid containing vessel; b. reference oscillator means coupled to said capacitor probe for providing a triangular voltage of relatively constant frequency and amplitude, said reference oscillator means including: trigger means having input and output termiNals for providing a bi-directional trigger voltage; reference integrator means having input and output terminals for integrating said trigger voltage, said integrator output terminal being coupled to an input terminal of said trigger means and said integrator input terminal being coupled to the output terminal of said trigger means; and a pair of oppositely poled Zener diodes coupled to a common connection of the output terminal of said trigger means and the input terminal of said reference integrator means for maintaining said reference oscillator means at a relatively constant amplitude; c. circuit means coupled to and cooperating with said capacitor probe for differentiating said triangular voltage and further providing a DC operating voltage proportional to the capacitance of said probe; d. translating means coupled to said circuit means for amplifying the DC operating voltage to a DC output voltage directly proportional to the level of fluid contained in said vessel; and e. indicating means having said DC output voltage coupled thereto for indicating the level of fluid in said vessel.

Claim 3

A capacitance-type fluid level gauge comprising: a. a capacitor probe adapted to be inserted into a fluid containing vessel; b. reference oscillator means coupled to said capacitor probe for providing a triangular voltage of relatively constant frequency and amplitude; c. circuit means coupled to and cooperating with said capacitor probe for differentiating said triangular voltage and further providing a DC operating voltage proportional to the capacitance of said probe, the circuit means having a rectifier-amplifier including: a first operational amplifier having input and output terminals; a second operational amplifier having input and output terminals; a first resistor coupled from the output terminal to an input terminal of said second amplifier; a first diode having first and second electrodes, said first electrode being connected to the output terminal of said first amplifier and said second electrode being connected to an input terminal of said first amplifier; a second diode having first and second electrodes, said first electrode being connected to the output terminal of said first amplifier, and said second electrode being connected through a second resistor to the input terminal of said first amplifier; and means coupled to the input terminals of said first and second amplifiers for coupling said differentiated triangular voltage thereto, whereby the DC operating voltage is provided at the output terminal of said second amplifier that is equal to the peak value of said differentiated triangular voltage; d. translating means coupled to said circuit means for amplifying the DC operating voltage to a DC output voltage directly proportional to the level of fluid contained in said vessel; and e. indicating means having said DC output voltage coupled thereto for indicating the level of fluid in said vessel.

Claim 4

A capacitance-type fluid level gauge comprising: a. a capacitor probe adapted to be inserted into a fluid containing vessel; b. reference oscillator means coupled to said capacitor probe for providing a triangular voltage of relatively constant frequency and amplitude; c. circuit means coupled to and cooperating with said capacitor probe for differentiating said triangular voltage and further providing a DC operating voltage proportional to the capacitance of said probe, the circuit means having a rectifier-amplifier including: a first operational amplifier having input and output terminals; a second operational amplifier having input and output terminals; a first resistor coupled from the output terminal to an input terminal of said second amplifier; a first diode having first and second electrodes, said first electrode being connected to the output terminal of said first amplifier and said second electrode being connected to an input terminal of said first amplifier; a second diode having first and second electrodes, said first electrode being connected to the output terminal of said first amplifier, and said second electrode being connected through a second resistor to the input terminal of said first amplifier; and means coupled to the input terminals of said first and second amplifiers for coupling said differentiated triangular voltage thereto, whereby the DC operating voltage is provided at the output terminal of said second amplifier that is equal to the peak value of said differentiated triangular voltage; d. translating means coupled to said circuit means for amplifying the DC operating voltage to a DC output voltage directly proportional to the level of fluid contained in said vessel; and e. indicating means having said DC output voltage coupled thereto for indicating the level of fluid in said vessel.

Claim 5

A capacitance-type fluid level gauge comprising: a. a capacitor probe adapted to be inserted into a fluid containing vessel; b. reference oscillator means coupled to said capacitor probe for providing a triangular voltage of relatively constant frequency and amplitude; c. circuit means coupled to and cooperating with said capacitor probe for differentiating said triangular voltage and further providing a DC operating voltage proportional to the capacitance of said probe; d. translating means coupled to said circuit means for amplifying the DC operating voltage to a DC output voltage directly proportional to the level of fluid contained in said vessel, wherein said translating means includes: an operational amplifier having first and second input terminals and an output terminal, said first input terminal being resistance coupled to a reference terminal, said second input termInal being adapted to be coupled to a DC voltage; a transistor having emitter, base, and collector electrodes connected in an emitter follower configuration, said collector electrode being adapted to be connected to a source of operating voltage, said emitter electrode being resistance coupled to said reference terminal and said base electrode being coupled to the output terminal of said amplifier; and variable resistance means coupled between said first input terminal of said amplifier and the emitter electrode of said transistor for adjusting the amplitude of said DC output voltage; and e. indicating means having said DC output voltage coupled thereto for indicating the level of fluid in said vessel.

Claim 6

A capacitance-type fluid level gauge comprising: a. a capacitor probe adapted to be inserted into a fluid containing vessel; b. reference oscillator means coupled to said capacitor probe for providing a triangular voltage of relatively constant frequency and amplitude; c. circuit means coupled to and cooperating with said capacitor probe for differentiating said triangular voltage and further providing a DC operating voltage proportional to the capacitance of said probe; d. translating means coupled to said circuit means for amplifying the DC operating voltage to a DC output voltage directly proportional to the level of fluid contained in said vessel, wherein said translating means includes: an operational amplifier having first and second input terminals and an output terminal, said first input terminal being resistance coupled to a reference terminal, said second input termInal being adapted to be coupled to a DC voltage; a transistor having emitter, base, and collector electrodes connected in an emitter follower configuration, said collector electrode being adapted to be connected to a source of operating voltage, said emitter electrode being resistance coupled to said reference terminal and said base electrode being coupled to the output terminal of said amplifier; and variable resistance means coupled between said first input terminal of said amplifier and the emitter electrode of said transistor for adjusting the amplitude of said DC output voltage; and e. indicating means having said DC output voltage coupled thereto for indicating the level of fluid in said vessel.