CA2629960A1 - Apparatus and method for improving the accuracy of measurements taken with a capacitance-type sensor - Google Patents

Apparatus and method for improving the accuracy of measurements taken with a capacitance-type sensor Download PDF

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Publication number
CA2629960A1
CA2629960A1 CA002629960A CA2629960A CA2629960A1 CA 2629960 A1 CA2629960 A1 CA 2629960A1 CA 002629960 A CA002629960 A CA 002629960A CA 2629960 A CA2629960 A CA 2629960A CA 2629960 A1 CA2629960 A1 CA 2629960A1
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CA
Canada
Prior art keywords
capacitance
calibration
sensor
measured
data
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
CA002629960A
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French (fr)
Other versions
CA2629960C (en
Inventor
Justin Duan
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Westport Fuel Systems Canada Inc
Original Assignee
Westport Power Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Westport Power Inc filed Critical Westport Power Inc
Priority to CA002629960A priority Critical patent/CA2629960C/en
Publication of CA2629960A1 publication Critical patent/CA2629960A1/en
Priority to PCT/CA2009/000562 priority patent/WO2009132437A1/en
Priority to AU2009242917A priority patent/AU2009242917B2/en
Priority to EP09737579.4A priority patent/EP2271949B1/en
Priority to CN200980113815.8A priority patent/CN102007424B/en
Application granted granted Critical
Publication of CA2629960C publication Critical patent/CA2629960C/en
Priority to US12/906,995 priority patent/US9255831B2/en
Active legal-status Critical Current
Anticipated expiration legal-status Critical

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D3/00—Indicating or recording apparatus with provision for the special purposes referred to in the subgroups
    • G01D3/02—Indicating or recording apparatus with provision for the special purposes referred to in the subgroups with provision for altering or correcting the law of variation
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
    • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
    • G01D5/12—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
    • G01D5/14—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage
    • G01D5/24—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage by varying capacitance
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F23/00—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm
    • G01F23/22—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water
    • G01F23/26—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of capacity or inductance of capacitors or inductors arising from the presence of liquid or fluent solid material in the electric or electromagnetic fields
    • G01F23/263—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of capacity or inductance of capacitors or inductors arising from the presence of liquid or fluent solid material in the electric or electromagnetic fields by measuring variations in capacitance of capacitors
    • G01F23/266—Indicating or measuring liquid level or level of fluent solid material, e.g. indicating in terms of volume or indicating by means of an alarm by measuring physical variables, other than linear dimensions, pressure or weight, dependent on the level to be measured, e.g. by difference of heat transfer of steam or water by measuring variations of capacity or inductance of capacitors or inductors arising from the presence of liquid or fluent solid material in the electric or electromagnetic fields by measuring variations in capacitance of capacitors measuring circuits therefor
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F25/00—Testing or calibration of apparatus for measuring volume, volume flow or liquid level or for metering by volume
    • G01F25/20—Testing or calibration of apparatus for measuring volume, volume flow or liquid level or for metering by volume of apparatus for measuring liquid level
    • G01F25/24—Testing proper functioning of electronic circuits

Abstract

An apparatus and method is disclosed for improving the accuracy of measurements taken with a capacitance-type sensor. In addition to the sensor the apparatus comprises a measurement circuit and a microprocessor. One of the sensor or a calibration capacitor with a known and fixed capacitance is connectable to the the measurement circuit by a switch that has its position controlled by the microprocessor. The microprocessor sends measurement signals to the measurement circuit and receives data therefrom. According to the disclosed method, the measurement circuit is programmed to determine an error between measured calibration data and the known capacitance and to use this error to calculate a correction value, which it applies to the measured sensor data to calculate corrected sensor measurements.

Claims (19)

1. An apparatus comprising:
a. ~a capacitance-type sensor for measuring a parameter;
b. ~a measurement circuit comprising:
i) ~a calibration capacitor with a known and fixed capacitance;
ii) ~a switch for selectively connecting the measurement circuit to one of the capacitance-type sensor or the calibration capacitor;
c. ~a microprocessor that is connected to the measurement circuit to send commands thereto and to receive data therefrom, wherein the microprocessor is programmed to:
i) ~command the position of the switch;
ii) ~determine an error between measured data that is collected by the measurement circuit when it is connected to the calibration capacitor, and predefined data associated with the known capacitance;
iii) ~calculate a correction value based on the error and measured data that is collected by the measurement circuit when it is connected to the capacitance-type sensor; and iv) ~determine a corrected data measurement by applying the correction value to measured data that is collected by the measurement circuit when it is connected to the capacitance-type sensor.
2. The apparatus of claim 1 wherein the calibration capacitor is one of at least two calibration capacitors.
3. The apparatus of claim 2 wherein one calibration capacitor has a fixed capacitance that is closer to a lower end of the capacitance-type sensor's measurable range of capacitance, and another calibration capacitor has a fixed capacitance that is closer to a higher end of the capacitance-type sensor's measurable range of capacitance.
4. The apparatus of claim 1 wherein the capacitance-type sensor is a capacitance-type liquid level sensor disposed within a storage vessel and a corrected liquid level measurement is determined from the corrected data measurement.
5. The apparatus of claim 4 wherein liquid stored in the storage vessel is a cryogenic liquid and the storage vessel is thermally insulated to reduce boiling and venting of vapor from the storage vessel.
6. The apparatus of claim 4 wherein the calibration capacitor is mounted with other components of the measurement circuit on a circuit board outside of the storage vessel.
7. The apparatus of claim 4 wherein the storage vessel is one of a plurality of storage vessels and each storage vessel has its own capacitance-type level sensor and the measurement circuit is connectable to each capacitance-type level sensor for measuring the capacitance thereof.
8. The apparatus of claim 1 wherein the measured data is voltage measured by the measurement circuit when the calibration capacitor or the capacitance-type sensor is charged.
9. The apparatus of claim 8 wherein the measurement circuit comprises an analog/digital reference voltage generator that adjusts the analog/digital reference voltage to provide a gain to a measured analog signal.
10. The apparatus of claim 1 wherein the microprocessor is a dedicated to the measurement circuit and the corrected data measurement is sent to a master electronic control unit that is programmed to use the corrected data measurement to control other devices associated with the apparatus.
11. A method for improving the accuracy of measurements taken with a capacitance-type sensor, the method comprising:
charging the capacitance-type sensor by connecting it to a measurement circuit and collecting measured sensor data correlating to the capacitance of the capacitance-type sensor when the capacitance-type sensor is charged;
charging a calibration capacitor, which has a known and fixed capacitance by connecting.it to the measurement circuit and collecting measured calibration data correlating to the capacitance of the calibration capacitor when the calibration capacitor is charged;
calculating an error between the measured calibration data and predefined calibration data that correlates to the known capacitance of the calibration capacitor;
calculating a correction value for the measured sensor data based on the calculated error alone or the calculated error in combination with and the measured sensor data; and calculating a corrected sensor measurement by applying the correction value to the measured sensor data.
12. The method of claim 11 wherein the measured sensor data and the measured calibration data are the respective voltages measured by the measurement circuit when the respective capacitance-type sensor and the calibration capacitor are charged.
13. The method of claim 11 wherein the calibration capacitor is one of a plurality of calibration capacitors, each with a different known and fixed capacitance, and the method further comprises for each sensor measurement, connecting at least two calibration capacitors to the measurement circuit one at a time, measuring the calibration voltage when the respective calibration capacitor is charged and for each of the connected calibration capacitors, calculating a voltage error as the difference between the measured calibration voltage and a predefined calibration voltage correlating to the known capacitance for each calibration capacitor, and extrapolating between measured calibration voltages and predefined calibration voltages to calculate the correction value for the sensor voltage, and then applying the correction value to the sensor voltage to calculate a corrected sensor voltage and the corrected sensor measurement.
14. The method of claim 13 wherein each time a sensor measurement is taken the method further comprises charging the capacitance-type sensor before any of the calibration capacitors and then charging, in tum, a predetermined number of calibration capacitors that have respective predefined calibration voltages that are closest to the measured sensor voltage.
15. The method of claim 11 wherein the capacitance-type sensor is a liquid level sensor and the method further comprises measuring the liquid level in a storage vessel for holding a liquid at cryogenic temperatures.
16. The method of claim 15 wherein the storage vessel is one of a plurality of storage vessels and the capacitance-type level sensor is one of a plurality of capacitance-type level sensors, each disposed in a different one of the storage vessels, and the method further comprises charging the calibration capacitor and correcting the measured sensor data when a liquid level measurement is taken.
17. The method of claim 11 wherein calibration steps comprising charging the calibration capacitor, calculating the error, calculating the correction value and calculating the corrected sensor measurement, are only done when a predetermined criteria is met.
18. The method of claim 17 wherein the predetermined criteria is the passing of a predetermined time since the previous time when the calibration steps were done.
19. The method of claim 17 wherein the predetermined criteria is met when the measured sensor data has changed from a previous value by more than a predetermined amount.
CA002629960A 2008-04-28 2008-04-28 Apparatus and method for improving the accuracy of measurements taken with a capacitance-type sensor Active CA2629960C (en)

Priority Applications (6)

Application Number Priority Date Filing Date Title
CA002629960A CA2629960C (en) 2008-04-28 2008-04-28 Apparatus and method for improving the accuracy of measurements taken with a capacitance-type sensor
PCT/CA2009/000562 WO2009132437A1 (en) 2008-04-28 2009-04-27 Apparatus and method for improving the accuracy of measurements taken with a capacitance- type sensor
AU2009242917A AU2009242917B2 (en) 2008-04-28 2009-04-27 Apparatus and method for improving the accuracy of measurements taken with a capacitance- type sensor
EP09737579.4A EP2271949B1 (en) 2008-04-28 2009-04-27 Apparatus and method for improving the accuracy of measurements taken with a capacitance- type sensor
CN200980113815.8A CN102007424B (en) 2008-04-28 2009-04-27 Apparatus and method for improving the accuracy of measurements taken with a capacitance-type sensor
US12/906,995 US9255831B2 (en) 2008-04-28 2010-10-18 Apparatus and method for improving the accuracy of measurements taken with a capacitance-type sensor

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CA002629960A CA2629960C (en) 2008-04-28 2008-04-28 Apparatus and method for improving the accuracy of measurements taken with a capacitance-type sensor

Publications (2)

Publication Number Publication Date
CA2629960A1 true CA2629960A1 (en) 2008-08-06
CA2629960C CA2629960C (en) 2009-12-08

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Family Applications (1)

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CA002629960A Active CA2629960C (en) 2008-04-28 2008-04-28 Apparatus and method for improving the accuracy of measurements taken with a capacitance-type sensor

Country Status (6)

Country Link
US (1) US9255831B2 (en)
EP (1) EP2271949B1 (en)
CN (1) CN102007424B (en)
AU (1) AU2009242917B2 (en)
CA (1) CA2629960C (en)
WO (1) WO2009132437A1 (en)

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Also Published As

Publication number Publication date
CA2629960C (en) 2009-12-08
US9255831B2 (en) 2016-02-09
WO2009132437A4 (en) 2010-01-21
AU2009242917A1 (en) 2009-11-05
EP2271949B1 (en) 2017-08-09
EP2271949A1 (en) 2011-01-12
AU2009242917B2 (en) 2013-08-29
CN102007424B (en) 2015-04-08
WO2009132437A1 (en) 2009-11-05
EP2271949A4 (en) 2016-03-30
US20110071777A1 (en) 2011-03-24
CN102007424A (en) 2011-04-06

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