The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Aug. 27, 1991
Filed:
Jul. 23, 1990
Paul Wells, Newberg, OR (US);
IIMorrow, Inc., Portland, OR (US);
Abstract
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.