WO2002016888A1 - Detecteur de niveau - Google Patents

Detecteur de niveau Download PDF

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Publication number
WO2002016888A1
WO2002016888A1 PCT/GB2001/003678 GB0103678W WO0216888A1 WO 2002016888 A1 WO2002016888 A1 WO 2002016888A1 GB 0103678 W GB0103678 W GB 0103678W WO 0216888 A1 WO0216888 A1 WO 0216888A1
Authority
WO
WIPO (PCT)
Prior art keywords
fluid
fluid level
electrodes
level sensor
sensor
Prior art date
Application number
PCT/GB2001/003678
Other languages
English (en)
Inventor
Christopher John Collister
Original Assignee
Tandelta Limited
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 Tandelta Limited filed Critical Tandelta Limited
Priority to AU2001282285A priority Critical patent/AU2001282285A1/en
Publication of WO2002016888A1 publication Critical patent/WO2002016888A1/fr

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Classifications

    • 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
    • G01F23/268—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 mounting arrangements of probes
    • 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

Definitions

  • This invention relates to a fluid level sensor, especially a sensor for measuring the level of oil or fuel in a tank or sump.
  • a fluid level sensor comprising a pair of upright electrodes arranged so that the fluid rises between them and assumes a level to be measured, the fluid acting as a dielectric between the electrodes to form a capacitor, the capacitor being connected in series with an output resistor to form a potential divider, an alternating input signal being applied across the divider, and the output signal across the output resistor being monitored to give an indication of the fluid level.
  • the output voltage across the output resistor therefore produces a level function which can be converted by a microcontroller to a level measurement.
  • the level function will be approximately a parabola that could be generated entirely in hardware by a square law amplifier.
  • a higher degree of accuracy in measuring the fluid level can be achieved if required by also providing a fluid quality sensor that produces an error correction signal dependent on variation in the dielectric constant (pemiittivity) of the fluid, and which is applied to the level measurement.
  • Figure 1 shows an oil level sensor according to the invention for measuring oil level in an engine sump
  • Figure 2 shows a block schematic diagram of the electronics of the level sensor of Figure 1;
  • Figure 3 shows a basic circuit diagram with a potential divider including a capacitor representing the capacitance of the level sensor of Figure 1;
  • Figure 4 shows a graph of percentage error due to changes in oil permittivity with oil level in the level sensor of Figure 1;
  • Figure 5 shows a graph of the sensitivity of the level function to changes in permittivity with the level in the level sensor of Figure 1;
  • Figure 6 shows a typical complex plane plot for a liquid dielectric
  • Figure 7 is schematic diagram of an alternative form of oil level sensor comprising parallel plates.
  • the oil sensor shown in Figure 1 consists of a pair of concentric electrically conductive tubes (1, 2) arranged so as to act as a capacitor, whose capacitive value varies according to the level of fluid within the sump 9 and the annular space between the tubes 1 and 2.
  • the outer tube 1 is perforated and includes drain holes 20 at its base through which fluid is allowed to pass.
  • These tubes may be tapered for ease of manufacture, and may be injection moulded.
  • the fluid may be lubricating oil or fuel, whose permittivity (dielectric constant) will modify the capacitance according to the value of the permittivity and the level of the fluid. Relative permittivity is written as:
  • the capacitance C of the sensor will vary, so also will its impedance when excited by a high frequency sinusoidal voltage.
  • the capacitor C formed by the tubes (1, 2) is connected in a voltage divider circuit, the second arm of the voltage divider being a pure resistance R.
  • An oscillator 6 generates the sinusoidal voltage.
  • the permittivity of the oil is complex, that is, it has both real and an imaginary component, and that the value of the complex permittivity will change during the life of the oil. For a typical mineral oil, this value will be around 2.3 + 0.005J at a few MHz, rising to around 2.8 + O.lj for a seriously contaminated oil.
  • the curve also changes shape with temperature, which is therefore included in the general description of the changing characteristics of the fluid.
  • C 0 is a parameter which depends on the capacitor geometry
  • s is the non-dimensional oil level which varies between 0 and 1
  • ⁇ 0 is the permittivity of free space
  • L is the length of the capacitor
  • di and d 2 are the diameters of the conductive elements (1, 2).
  • the factor 1 in the term ⁇ ' - 1 represents the relative permittivity of air, which is assumed to be wholly real, and Tan ⁇ 5 is taken to be a linear function of ⁇ '.
  • Tan ⁇ 5 is taken to be a linear function of ⁇ '.
  • the sensing elements need not be concentric, and may instead consist for example of a central flat conductive plate sandwiched between two outer flat conductive plates as shown in Figure 7.
  • the inner plate is live, with the outer two plates connected to the ground.
  • the outer plates are wider than the inner plate to reduce the effect of field fringing, and the ratio of the width to the gap is preferably greater than 10.
  • the plates need not be parallel, but may vary in shape according to the variation in the cross section of the sump.
  • the gap may also vary with height.
  • f(s) is a geometric function incorporating variations in gap size and variations in width or cross section
  • ⁇ is the complex permittivity of the fluid
  • v v(s, ⁇ , R) is now a function of the angular frequency ⁇ , the non-dimensional height s, and the complex permittivity ⁇ . It is required ideally that v should be linear in s, or if not, that any departure from linearity should be small and/or capable of compensation by means, for example of a lookup table in software, or an additive polynomial function. Note that only the amplitude (magnitude) of the output signal, and not its phase, is of interest in this application.
  • the impedance will increase as the imaginary part increases, and it can be seen that the two effects act in opposition to one another. It is known from observation that the real part changes quite slowly with increasing contamination, while the imaginary part increases at a much faster rate, so it is easy to conclude that two oils at different stages of contamination may show the same magnitude of impedance. This is explained by noting that the fresher oil may have a low dielectric constant (giving rise to a high contribution to impedance), with a low loss factor, giving rise to a low contribution to impedance. The more contaminated oil will have a higher dielectric constant (giving rise to a low contribution to impedance), with a high loss factor, giving rise to a high contribution to impedance. If the capacitor containing the oil forms part of a potential divider circuit, the objective then is to find a value of the resistance in the potential divider which will make the difference in the voltage between the two oils as small as possible.
  • the maximum error using the above two representative values for complex permittivity and normalised with respect to the voltage range is typically 3%, and occurs at two points: the first when the sump (oilpan) is over three quarters empty, and the second when the sump has been overfilled. If the sensor is inverted so that it depends from the top of the sump, these maximum errors occur at three quarters full and empty, respectively. Zero error occurs when the sump is empty and about half full respectively.
  • An on-board microcontroller 3 shown in Figures 1 and 2 is used to linearise the level/voltage output curve; the same microcontroller may also be used to compensate for possible changes in the cross section of the sump by means of a suitable lookup table or polynomial function.
  • the dynamic range of the sensor is about 2% of the excitation voltage; reducing the resistance to three quarters of this value increases the maximum error to 5%, but increases the dynamic range to 4% of the input voltage.
  • an excitation voltage of 10V will provide a working range of 400mV from empty to full.
  • the output voltage contains a large non- varying offset which may be removed by, for example, subtracting a suitable reference voltage. This is preferably done after demodulating the sinusoidal voltage at 23 so that the reference voltage may be derived from a precision DC source.
  • an oil condition sensor 7 is provided which produces a correction signal that is fed to the microcontroller 3.
  • a suitable oil condition sensor would be that described in PCT/GB98/01321 " .
  • This particular condition sensor measures the loss factor of the oil, and shows a generally linear variation in output with contamination. It is found experimentally that as the loss factor increases, so also does the dielectric constant, and there is thus a good correlation between the real and the imaginary parts of the permittivity of the oil. This then provides a reliable means of compensating for the changes in dielectric constant which occur as the oil becomes contaminated with use, and offers the added advantage of both oil condition and level sensing within the same package.
  • the plastic body provides electrical insulation between the sensor electrical elements and connections to reduce problems associated with earth loop currents. It also provides a high thermal resistance to reduce the temperature differential across the active sensing components and the outside of the sump, which may be at -30°C, for example. Excessive temperature differentials can lead to inaccurate and inconsistent measurements.
  • the digital board 13 also comprises a number of filtering, regulating, and spike protection components 21 to prevent any damage from occurring to the electronics during normal automotive use. Brown-out protection may be included in the microcontroller coding to prevent processor core ock-up' during engine cranking, or when other power supply irregularities occur.

Abstract

La présente invention concerne un détecteur servant à mesurer le niveau de liquides non polaires tels que des huiles minérales lubrifiantes ou des combustibles, les propriétés diélectriques du liquide et le niveau du liquide provoquant la variation de la capacité entre des électrodes verticales (1, 2). La capacité est considérée comme complexe, les parties réelle et imaginaire variant avec la température et le degré de contamination du liquide. La résistance (R) d'un séparateur de potentiel appartenant au circuit de mesure, est choisie de sorte que les effets de variation de la permittivité complexe du liquide sont minimisés, ce qui rend inutile la mise en place d'un circuit de compensation supplémentaire. Une compensation supplémentaire peut être appliquée grâce à l'utilisation d'un détecteur d'état d'huile (7, 8) qui mesure les propriétés diélectriques du liquide.
PCT/GB2001/003678 2000-08-18 2001-08-17 Detecteur de niveau WO2002016888A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2001282285A AU2001282285A1 (en) 2000-08-18 2001-08-17 Level sensor

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB0020506.2 2000-08-18
GB0020506A GB0020506D0 (en) 2000-08-18 2000-08-18 Level sensor

Publications (1)

Publication Number Publication Date
WO2002016888A1 true WO2002016888A1 (fr) 2002-02-28

Family

ID=9897961

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB2001/003678 WO2002016888A1 (fr) 2000-08-18 2001-08-17 Detecteur de niveau

Country Status (3)

Country Link
AU (1) AU2001282285A1 (fr)
GB (1) GB0020506D0 (fr)
WO (1) WO2002016888A1 (fr)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2386688A (en) * 2002-03-21 2003-09-24 Fozmula Ltd A solid state sensor for liquid level measurement
CN106225876A (zh) * 2016-08-18 2016-12-14 四川泛华航空仪表电器有限公司 电容式温度补偿油位测量传感器
EP3130896A1 (fr) 2015-08-13 2017-02-15 AIRBUS HELICOPTERS DEUTSCHLAND GmbH Capteur de niveau de liquide avec région isolante sur le pied de sonde
US10203238B2 (en) 2014-03-07 2019-02-12 Barrelogix, Llc Liquid detection apparatus
US20210129549A1 (en) * 2017-10-18 2021-05-06 Hewlett-Packard Development Company, L.P. Fluid property sensor

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP3612491A4 (fr) * 2017-05-03 2020-05-13 NYPRO Inc. Appareil, système et procédé de fourniture d'un moniteur de niveau de liquide

Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1359799A (en) * 1973-02-16 1974-07-10 Polischuk K E Volokhov V N Enclosed liquid quantity sensor
US4418569A (en) * 1979-11-14 1983-12-06 Vdo Adolf Schindling Ag Device for the capacitive measurement of the filling level of fluid to a container
US4674329A (en) * 1983-12-01 1987-06-23 Richard Mulder Gauge for measuring the level or the conductance of a liquid present between two electrodes
US5001596A (en) * 1990-05-07 1991-03-19 Therm-O-Disc, Incorporated Capacitive fluid level sensor
US5097703A (en) * 1984-11-30 1992-03-24 Aisin Seiki Kabushiki Kaisha Capacitive probe for use in a system for remotely measuring the level of fluids
US5611240A (en) * 1992-04-03 1997-03-18 Toyota Tsusho Corporation Level detector
US5726908A (en) * 1995-03-20 1998-03-10 Figgie International Inc. Liquid quantity sensor and method
WO1999010714A1 (fr) * 1997-08-25 1999-03-04 Millennium Sensors Ltd. Detecteur de niveau de liquide a effet capacitif compense

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB1359799A (en) * 1973-02-16 1974-07-10 Polischuk K E Volokhov V N Enclosed liquid quantity sensor
US4418569A (en) * 1979-11-14 1983-12-06 Vdo Adolf Schindling Ag Device for the capacitive measurement of the filling level of fluid to a container
US4674329A (en) * 1983-12-01 1987-06-23 Richard Mulder Gauge for measuring the level or the conductance of a liquid present between two electrodes
US5097703A (en) * 1984-11-30 1992-03-24 Aisin Seiki Kabushiki Kaisha Capacitive probe for use in a system for remotely measuring the level of fluids
US5001596A (en) * 1990-05-07 1991-03-19 Therm-O-Disc, Incorporated Capacitive fluid level sensor
US5611240A (en) * 1992-04-03 1997-03-18 Toyota Tsusho Corporation Level detector
US5726908A (en) * 1995-03-20 1998-03-10 Figgie International Inc. Liquid quantity sensor and method
WO1999010714A1 (fr) * 1997-08-25 1999-03-04 Millennium Sensors Ltd. Detecteur de niveau de liquide a effet capacitif compense

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2386688A (en) * 2002-03-21 2003-09-24 Fozmula Ltd A solid state sensor for liquid level measurement
US10203238B2 (en) 2014-03-07 2019-02-12 Barrelogix, Llc Liquid detection apparatus
EP3130896A1 (fr) 2015-08-13 2017-02-15 AIRBUS HELICOPTERS DEUTSCHLAND GmbH Capteur de niveau de liquide avec région isolante sur le pied de sonde
US10107669B2 (en) 2015-08-13 2018-10-23 Airbus Helicopters Deutschland GmbH Liquid level sensor with insulating region over the probe foot
CN106225876A (zh) * 2016-08-18 2016-12-14 四川泛华航空仪表电器有限公司 电容式温度补偿油位测量传感器
CN106225876B (zh) * 2016-08-18 2023-05-09 四川泛华航空仪表电器有限公司 电容式温度补偿油位测量传感器
US20210129549A1 (en) * 2017-10-18 2021-05-06 Hewlett-Packard Development Company, L.P. Fluid property sensor

Also Published As

Publication number Publication date
AU2001282285A1 (en) 2002-03-04
GB0020506D0 (en) 2000-10-11

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