초록 ▼

A time varying excitation current (413) is provided to one side of a capacitive sensor (417), and two signal paths (420,430) are provided between the other side of the capacitive sensor (417) and signal conditioning circuitry (412), each signal path differing from the other according to its polarity

A time varying excitation current (413) is provided to one side of a capacitive sensor (417), and two signal paths (420,430) are provided between the other side of the capacitive sensor (417) and signal conditioning circuitry (412), each signal path differing from the other according to its polarity. The signal paths conduct monopolar signals from the capacitive sensor the magnitude of which are directly related to the capacitance of the sensor, and bi-polar signals the magnitude of which are directly related to the stray capacitance in the signal lines. The combined monopolar and bi-polar signal currents on each signal line are converted into voltage signals (422,433), and the voltage signals are thereafter differenced (460) to provide a null bi-polar output while providing a constant monopolar voltage level the magnitude of which is directly related to the probe capacitor current.

대표청구항 ▼

Circuitry for minimizing the effects of stray capacitance on the output of a capacitive liquid level measurement system, comprising: a capacitive sensor for mounting in a liquid storage container, the sensor having a capacitance the magnitude of which varies according to the liquid level in said sto

Circuitry for minimizing the effects of stray capacitance on the output of a capacitive liquid level measurement system, comprising: a capacitive sensor for mounting in a liquid storage container, the sensor having a capacitance the magnitude of which varies according to the liquid level in said storage container; voltage supply means for providing a time varying voltage to one side of said capacitive sensor; a pair of diodes connected to the other side of said capacitive sensor, said pair of diodes being oppositely directed from one another to thereby provide two signal paths from said other side of said capacitive sensor, each signal path differing from the other according to the polarity of signals conducted thereon; each of said signal paths conducting a current signal having a monopolar component corresponding to current flowing through said capacitive sensor and a bipolar component corresponding to current flowing through stray capacitance; said circuitry being characterized by: conversion means connected to each of said signal paths for providing a voltage signal the magnitude of which is related to the magnitude of said current signal being conducted by said signal path; and difference means connected to said conversion means for providing a difference signal indicative of the difference between said voltage signals, the magnitude of said difference signal being indicative of said liquid level.