Auto-compensating capacitive level sensor
First Claim
1. A capacitive level sensor for measuring the level of fluid or material contained within a reservoir comprising:
- a capacitive sensor array adapted to be disposed in the reservoir along an axis of measurement of the material or fluid contained within the reservoir, the sensor array comprising a plurality of reference electrodes wherein the capacitance of each of the electrodes varies in accordance both with the extent of the array'"'"'s immersion in the fluid or material and the dielectric constant of the fluid or material, the plurality of reference electrodes comprising;
a lower electrode adapted to be positioned near the bottom of the reservoir and whose capacitance provides an estimate of the dielectric constant of the fluid or material contained within the reservoir; and
a middle electrode that extends along the length of the array and whose capacitance varies from a calibrated initial value to a value that is dependent on the level of and the dielectric constant of the fluid or material contained within the reservoir as determined from the capacitance of the lower electrode;
a circuit capable of measuring the capacitance of each reference electrode and generating a digitized sensor voltage representing the capacitance of each electrode; and
a microprocessor for receiving and processing the digitized sensor voltages to determine the fluid or material level, wherein the level is determined as a linear function of the capacitance of the middle electrode and is compensated by the amount and rate of change of the capacitance of the lower electrode, and wherein the microprocessor determines the level of the fluid or material in accordance with;
VMcorrected(l)=VM(l)−
VMcal
1 Assignment
0 Petitions
Accused Products
Abstract
A capacitive sensor array is adapted to be disposed in a reservoir containing fluid or material along an axis of measurement of the fluid or material to determine the level of fluid or material contained within the reservoir. The sensor array includes a plurality of reference electrodes, wherein the capacitance of each of the electrodes varies in accordance both with the extent of the array'"'"'s immersion in the fluid or material and the dielectric constant of the fluid or material. The plurality of reference electrodes preferably includes a lower electrode adapted to be immersed within the fluid or material in the reservoir and whose capacitance provides an estimate of the dielectric constant of the fluid or material contained within the reservoir. The reference electrodes also include an upper electrode adapted to be positioned above the fluid or material level that provides an estimate of the dielectric constant above the level of the fluid or material in the reservoir, and a middle electrode whose capacitance varies from a calibrated initial value to a value that is dependent on the level of and the dielectric constant of the fluid or material contained within the reservoir as determined from the capacitance of the lower electrode.
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Citations
18 Claims
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1. A capacitive level sensor for measuring the level of fluid or material contained within a reservoir comprising:
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a capacitive sensor array adapted to be disposed in the reservoir along an axis of measurement of the material or fluid contained within the reservoir, the sensor array comprising a plurality of reference electrodes wherein the capacitance of each of the electrodes varies in accordance both with the extent of the array'"'"'s immersion in the fluid or material and the dielectric constant of the fluid or material, the plurality of reference electrodes comprising;
a lower electrode adapted to be positioned near the bottom of the reservoir and whose capacitance provides an estimate of the dielectric constant of the fluid or material contained within the reservoir; and
a middle electrode that extends along the length of the array and whose capacitance varies from a calibrated initial value to a value that is dependent on the level of and the dielectric constant of the fluid or material contained within the reservoir as determined from the capacitance of the lower electrode;
a circuit capable of measuring the capacitance of each reference electrode and generating a digitized sensor voltage representing the capacitance of each electrode; and
a microprocessor for receiving and processing the digitized sensor voltages to determine the fluid or material level, wherein the level is determined as a linear function of the capacitance of the middle electrode and is compensated by the amount and rate of change of the capacitance of the lower electrode, and wherein the microprocessor determines the level of the fluid or material in accordance with;
VMcorrected(l)=VM(l)−
VMcal - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A capacitive level sensor for measuring the level of fluid or material contained within a reservoir comprising:
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an elongate capacitive sensor array having a first and second end and adapted to be disposed in the reservoir along an axis of measurement of the material or fluid contained within the reservoir, the sensor array comprising;
a compensation electrode formed from an electrode positioned at each end of the sensor array, wherein the electrodes are electrically coupled together such that the sensor array may be disposed in the reservoir regardless of its orientation, the compensation electrode having a capacitance that provides an estimate of the dielectric constant of the fluid or material contained within the reservoir; and
a measurement electrode that extends along the length of the array and whose capacitance varies from a calibrated initial value to a value that is dependent on the level of and the dielectric constant of the fluid or material contained within the reservoir as determined from the capacitance of the compensation electrode;
a circuit capable of measuring the capacitance of each electrode and generating a digitized sensor voltage representing the capacitance of each electrode; and
a microprocessor for receiving and processing the digitized sensor voltages to determine the fluid or material level, wherein the level is determined as a linear function of the capacitance of the measurement electrode and is compensated by the amount and rate of change of the capacitance of the compensation electrode, and wherein the microprocessor determines the level of the fluid or material in accordance with;
VMcorrected(l)=VM(l)−
VMcal - View Dependent Claims (10, 11, 12, 13, 14, 15)
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16. A method for calculating the level of fluid or material contained within a reservoir comprising the steps of:
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providing a capacitive sensor array adapted to be disposed in the reservoir along an axis of measurement of the fluid or material contained within the reservoir, the sensor array comprising a middle and a lower reference electrode wherein the capacitance of each of the electrodes varies in accordance both with the extent of the electrode'"'"'s immersion in the fluid or material and the dielectric constant of the fluid or material;
determining the calibrated capacitance of each of the electrodes in air;
determining the capacitance of each of the electrodes when the reference electrodes are fully immersed in the fluid or material;
positioning the sensor array within the reservoir such that the lower electrode is submersed in the fluid or material with the fluid or material surface being in contact with the middle electrode;
measuring the capacitance of each reference electrode and generating a digitized sensor voltage representing the capacitance of each electrode; and
calculating the level of the fluid or material within the reservoir as a linear function of the capacitance of the middle electrode compensated by the amount and rate of change of the capacitance of the lower electrode, and wherein the microprocessor determines the level of the fluid or material in accordance with;
VMcorrected(l)=VM(l)−
VMcal - View Dependent Claims (17)
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18. A method for calculating the level of fluid or material contained within a reservoir comprising the steps of:
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providing a capacitive sensor array adapted to be disposed in the reservoir along an axis of measurement of the fluid or material contained within the reservoir, the sensor array comprising a plurality of reference electrodes wherein the capacitance of each of the electrodes varies in accordance both with the extent of the electrode'"'"'s immersion in the fluid or material and the dielectric constant of the fluid or material;
determining the calibrated capacitance of each of the electrodes in air;
determining the capacitance of each of the electrodes when the reference electrodes are fully immersed in the fluid or material;
positioning the sensor array within the reservoir such that at least one of the electrodes is submersed in the fluid or material;
another of the electrodes is in contact with the fluid or material surface; and
at least one of the electrodes is positioned above the fluid or material level;
dynamically selecting a lower electrode as the electrode positioned directly below the fluid or material level;
dynamically selecting a middle electrode as the electrode positioned at or near the fluid or material surface;
dynamically selecting an upper electrode as the electrode positioned directly above the fluid or material level;
measuring the capacitance of each of the lower, middle and lower electrodes and generating a digitized sensor voltage representing the capacitance of each electrode; and
calculating the level of the fluid or material within the reservoir as a linear function of the capacitance of the middle electrode compensated by the amount and rate of change of the capacitance of the lower electrode, wherein the capacitance of the upper electrode provides an estimate of any offset drift in the measurement of the current required to repetitively charge each of the lower, middle and lower electrodes to the predetermined voltage, wherein the level of the fluid or materials is calculated in accordance with;
Lmax represents the fluid or material level when the fluid or material is at the top of the middle reference electrode;
levelmax represents a calibrated full fluid level;
VLΔ
0, VMΔ
0, VUΔ
0 represent the change in the digitized sensor voltages from the lower, middle and upper reference electrodes from the calibrated values to values obtained when the level of the fluid or material is at the bottom of each electrode;
VLΔ
max, VMΔ
max, VUΔ
max represent the change in digitized sensor voltages from the lower, middle and upper reference electrodes from the calibrated values to values obtained when the electrodes are each fully immersed in the fluid or material;
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Specification