05042299 is referenced by 38 patents and cites 33 patents.

A linear compensated capacitive fluid-level sensing device includes three capacitors. A measurement capacitor is positionable during use to receive a fluid. A compensation capacitor is submerged in the fluid so that the fluid fills the space between the electrodes. An offset capacitor has a capacitance equivalent to the capacitance of the measurement capacitor when only air exists between the measurement electrodes. Charge applied to each of the three capacitors is discharged to an associated differential amplifier through a respective switch when the capacitors are disconnected from a charging voltage supply. The offset amplifier generates an inverted output current that is applied to the discharge currents of the measurement and compensation amplifiers. The compensation amplifier output gates a frequency-controlled oscillator that in turn controls the switches.

Title
Capacitive fluid level sensor
Application Number
7/560870
Publication Number
5042299
Application Date
July 23, 1990
Publication Date
August 27, 1991
Inventor
Paul Wells
Newberg
OR, US
Agent
William A Birdwell
Assignee
IIMorrow
OR, US
IPC
G01F 23/26
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