WO1995005583A1 - Optic method for measuring of the level of the surface of a liquid - Google Patents

Optic method for measuring of the level of the surface of a liquid Download PDF

Info

Publication number
WO1995005583A1
WO1995005583A1 PCT/FI1994/000352 FI9400352W WO9505583A1 WO 1995005583 A1 WO1995005583 A1 WO 1995005583A1 FI 9400352 W FI9400352 W FI 9400352W WO 9505583 A1 WO9505583 A1 WO 9505583A1
Authority
WO
WIPO (PCT)
Prior art keywords
liquid
gauge
column
light
gauged
Prior art date
Application number
PCT/FI1994/000352
Other languages
French (fr)
Inventor
Pertti Puumalainen
Original Assignee
Petetronic T:Mi P. Kinnunen
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 Petetronic T:Mi P. Kinnunen filed Critical Petetronic T:Mi P. Kinnunen
Priority to AU74619/94A priority Critical patent/AU7461994A/en
Publication of WO1995005583A1 publication Critical patent/WO1995005583A1/en

Links

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
    • G01F23/28—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 the variations of parameters of electromagnetic or acoustic waves applied directly to the liquid or fluent solid material
    • G01F23/284—Electromagnetic waves
    • G01F23/292—Light, e.g. infrared or ultraviolet

Definitions

  • the present invention relates to an optical method of liquid level gauging.
  • liquid level gauging in, e.g., containers and similar vessels still is the insertion of a dipstick whose wetting line indicates the liquid level.
  • an electrode o pair placed in the container, whereby the capacitance between the electrodes is measured to gauge liquid level in the container.
  • ultrasonic methods have been used to gauge liquid level in containers.
  • the method according to the invention light is guided along an optical fiber to a gauge column of a secondary liquid contained in a transducer housing placed in the liquid, whereby the hydrostatic pressure of the primary s liquid to be gauged is allowed to inflict on the base of said secondary liquid gauge column, light is guided from the transducer along another optical fiber to a photo- diode, and the liquid level is gauged on the basis of the change in light intensity caused by the change of the secondary liquid gauge column height as compared to the light intensity of a reference fiber, said intensities being measured with the help of a selector, and the actual level of the primary liquid to be gauged is obtained by plotting the proportional ratio measurement result on a calibration curve.
  • the optical gauging method according to the invention overcomes the contamination problem, and the method is entirely optical with regard to the transducer structure.
  • the principal area of application for the present method is in the liquid level gauging of fuel tanks at, e.g., service stations. No electrical or mechanically moving elements or parts thereof need be introduced to the fuel tank, whereby the possibility of sparking is eliminated. Only light is guided to the .container and away therefrom. Further, the method performs continuous self-calibration.
  • the invention is also suited for other applications.
  • an opti ⁇ cal fiber or bunch of fibers is inserted in the gauge liquid column so as to be wetted by the liquid.
  • the wetting of the fiber surface causes a change in the light transmission property of the fiber detected as a change of the return intensity of light from the fiber, and the actual level of the outside liquid versus the detected intensity is logged in a calibration curve.
  • the light is guided close to the gauge liquid column and directed onto the end of the gauge liquid column so that the light propagating in the gauge liquid column is reflected from the column walls and the efficiency of the reflection is changed when the inner wall of the tube containing the gauge liquid column is wetted by the liquid, whereby changes in the liquid level outside the column can be detected by comparing the intensity of the light propagating in the gauge liquid column to light intensity received from a reference fiber and then reading the liquid level outside the column from a calibration curve in which the light intensity ratio is plotted against the actual level of the outside liquid. Also this method provides accurate and reliable gauging results.
  • the secondary liquid in the gauge column is complemented with additives which improve the detection of changes in the optical variables such as colour and refractive index.
  • the gauging system comprises a light source 1 from which light is launched to propagate in two optical fibers 2, 3.
  • the light ray is split between these two fibers: the light propagating in the fiber 3 is used to provide a reference channel and the light propagating in the fiber 2 is used as the gauging channel.
  • the gauging transducer communicates with a space having the same ambient press ⁇ ure as that prevailing above the liquid level to be gauged.
  • the transducer comprises a secondary liquid space 4 separated from the liquid 12 to be gauged by means of an flexible rubber diaphragm 5.
  • the rubber diaphragm is mounted is such a slack manner that its deformation under the gauging of the different heights of the outside liquid cause no significant elastic forces.
  • the rubber diaphragm transmits the outside liquid level via the hydrostatic pressure 11 to the height of the secondary liquid gauge column 8. As no force is required to move the rubber diaphragm and the densities of the liquids outside and inside the transducer typically are equal, the liquid level of the column is equilibrated with outside liquid level. However, this is not essential to the spirit of the invention, since the electrical output signal of the transducer is calibrated over the actual liquid level range to be gauged.
  • the light ray exiting from the fiber 2 is launched into a tubular light guide 6, where the light propagates in the fashion as in an optical fiber reflecting from the its inner walls.
  • the reflection pro ⁇ perties of the light guide change and the resulting reduction of light intensity is proportional to the height of the secondary liquid gauge column 8.
  • the tubular gauging space of the transducer is hermeti ⁇ cally sealed at its upper end by means of an elastic rubber pouch 9 to eliminate the evaporation of the secondary liquid.
  • the seal of the secondary liquid space is designed such that prevents the evaporation of the liquid contained in the space yet permitting changes in the height of the secondary liquid gauge column 8.
  • the light transmitted up to the upper end of the tubular light guide 6 is received by means of an optical fiber 10 and taken via a selector 13 to a photodiode 14 for intensity measurement.
  • the output signal of the photodiode is amplified and converted into a digital reading in a conventional manner by means of, e.g., a microcomputer.
  • the intensity measurement is always performed as a ratio measurement by alternately measuring the light transmitted via the fiber 3 of the reference channel and the light transmitted via the gauging channel element chain 2 ⁇ 6 ⁇ 10.
  • the actual liquid level outside the gauging transducer is then obtained by plotting the proportional intensity ratio value on the calibration curve. Owing to the proportional ratio measurement principle applied in the method, errors caused by drifts of the light source intensity and the amplifier are eliminated practically entirely. Also the contaminating effect of the outside liquid to be gauged is avoided by using a clean secondary liquid in the optical system contained in a hermetically sealed space.
  • the invention is not limited by the embodiment described above for liquid level gauging in a fuel tank, but rather, can be applied to any level gauging in which the pressure equalization port of the gauging transducer space can be arranged to communicate with the air or gas space of the gauged container.

Landscapes

  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Thermal Sciences (AREA)
  • Fluid Mechanics (AREA)
  • General Physics & Mathematics (AREA)
  • Measurement Of Levels Of Liquids Or Fluent Solid Materials (AREA)

Abstract

The present invention relates to an optical method of liquid level gauging. Prior-art methods are not suited for use under all conditions. In the method according to the invention, light is guided along an optical fiber (2) to a gauge column of a secondary liquid (4) contained in a gauging transducer housing (7) placed in the liquid (12) to be gauged, whereby the hydrostatic pressure of the primary liquid to be gauged is allowed to inflict on the base of said secondary liquid gauge column, light is guided from the gauging transducer along another optical fiber (10) to a photodiode (14), and the liquid level is gauged on the basis of the change in light intensity caused by the change of the secondary liquid gauge column height so that the intensity change of the light exiting from said optical fiber (10) is compared to the light intensity measured exiting from a reference fiber (3), said intensities being measured with the help of a selector (13), and the actual level of the primary liquid to be gauged is obtained by plotting the proportional ratio measurement result on a calibration curve.

Description

OPTIC METHOD FOR MEASURING OF THE LEVEL OF THE SURFACE
OF A LIQUID.
The present invention relates to an optical method of liquid level gauging.
5
The method of widest use for liquid level gauging in, e.g., containers and similar vessels still is the insertion of a dipstick whose wetting line indicates the liquid level. To some degree is also used an electrode o pair placed in the container, whereby the capacitance between the electrodes is measured to gauge liquid level in the container. Further, ultrasonic methods have been used to gauge liquid level in containers. These gauging methods in fuel tanks are significantly limited by such s factors as explosion hazard, contamination of optical sensors particularly in liquid level gauging of lead- containing gasolines and changes of temperature and vapour pressure in the gauged volume.
o It is an object of the present invention to provide a method of liquid level gauging, said method being capable of overcoming the drawbacks of conventional methods. It is a particular object of the present invention to provide a method suited for liquid level gauging in fuel
5 tanks at a high reliability and safety level.
The goal of the invention is achieved by virtue of a method characterized by what is stated in the appended claims. o
In the method according to the invention, light is guided along an optical fiber to a gauge column of a secondary liquid contained in a transducer housing placed in the liquid, whereby the hydrostatic pressure of the primary s liquid to be gauged is allowed to inflict on the base of said secondary liquid gauge column, light is guided from the transducer along another optical fiber to a photo- diode, and the liquid level is gauged on the basis of the change in light intensity caused by the change of the secondary liquid gauge column height as compared to the light intensity of a reference fiber, said intensities being measured with the help of a selector, and the actual level of the primary liquid to be gauged is obtained by plotting the proportional ratio measurement result on a calibration curve.
The optical gauging method according to the invention overcomes the contamination problem, and the method is entirely optical with regard to the transducer structure. The principal area of application for the present method is in the liquid level gauging of fuel tanks at, e.g., service stations. No electrical or mechanically moving elements or parts thereof need be introduced to the fuel tank, whereby the possibility of sparking is eliminated. Only light is guided to the .container and away therefrom. Further, the method performs continuous self-calibration. The invention is also suited for other applications.
In an advantageous embodiment of the invention, an opti¬ cal fiber or bunch of fibers is inserted in the gauge liquid column so as to be wetted by the liquid. The wetting of the fiber surface causes a change in the light transmission property of the fiber detected as a change of the return intensity of light from the fiber, and the actual level of the outside liquid versus the detected intensity is logged in a calibration curve. This method provides accurate and reliable gauging results.
In a second advantageous embodiment of the invention, the light is guided close to the gauge liquid column and directed onto the end of the gauge liquid column so that the light propagating in the gauge liquid column is reflected from the column walls and the efficiency of the reflection is changed when the inner wall of the tube containing the gauge liquid column is wetted by the liquid, whereby changes in the liquid level outside the column can be detected by comparing the intensity of the light propagating in the gauge liquid column to light intensity received from a reference fiber and then reading the liquid level outside the column from a calibration curve in which the light intensity ratio is plotted against the actual level of the outside liquid. Also this method provides accurate and reliable gauging results.
In a further advantageous embodiment of the invention, the secondary liquid in the gauge column is complemented with additives which improve the detection of changes in the optical variables such as colour and refractive index.
The invention is next examined with reference to the attached drawing which illustrates in a schematic side view the principle of the gauging method according to the invention and its function in practice.
With reference to the embodiment shown in the drawing, the gauging system comprises a light source 1 from which light is launched to propagate in two optical fibers 2, 3. The light ray is split between these two fibers: the light propagating in the fiber 3 is used to provide a reference channel and the light propagating in the fiber 2 is used as the gauging channel. The gauging transducer communicates with a space having the same ambient press¬ ure as that prevailing above the liquid level to be gauged. The transducer comprises a secondary liquid space 4 separated from the liquid 12 to be gauged by means of an flexible rubber diaphragm 5. The rubber diaphragm is mounted is such a slack manner that its deformation under the gauging of the different heights of the outside liquid cause no significant elastic forces. The rubber diaphragm transmits the outside liquid level via the hydrostatic pressure 11 to the height of the secondary liquid gauge column 8. As no force is required to move the rubber diaphragm and the densities of the liquids outside and inside the transducer typically are equal, the liquid level of the column is equilibrated with outside liquid level. However, this is not essential to the spirit of the invention, since the electrical output signal of the transducer is calibrated over the actual liquid level range to be gauged.
The light ray exiting from the fiber 2 is launched into a tubular light guide 6, where the light propagates in the fashion as in an optical fiber reflecting from the its inner walls. As the secondary liquid enters the inside space of the tubular light guide, the reflection pro¬ perties of the light guide change and the resulting reduction of light intensity is proportional to the height of the secondary liquid gauge column 8.
The tubular gauging space of the transducer is hermeti¬ cally sealed at its upper end by means of an elastic rubber pouch 9 to eliminate the evaporation of the secondary liquid. The seal of the secondary liquid space is designed such that prevents the evaporation of the liquid contained in the space yet permitting changes in the height of the secondary liquid gauge column 8. The light transmitted up to the upper end of the tubular light guide 6 is received by means of an optical fiber 10 and taken via a selector 13 to a photodiode 14 for intensity measurement. The output signal of the photodiode is amplified and converted into a digital reading in a conventional manner by means of, e.g., a microcomputer. The intensity measurement is always performed as a ratio measurement by alternately measuring the light transmitted via the fiber 3 of the reference channel and the light transmitted via the gauging channel element chain 2 → 6 → 10. The actual liquid level outside the gauging transducer is then obtained by plotting the proportional intensity ratio value on the calibration curve. Owing to the proportional ratio measurement principle applied in the method, errors caused by drifts of the light source intensity and the amplifier are eliminated practically entirely. Also the contaminating effect of the outside liquid to be gauged is avoided by using a clean secondary liquid in the optical system contained in a hermetically sealed space.
The invention is not limited by the embodiment described above for liquid level gauging in a fuel tank, but rather, can be applied to any level gauging in which the pressure equalization port of the gauging transducer space can be arranged to communicate with the air or gas space of the gauged container.

Claims

Claims:
1. An optical method of liquid level gauging, c h a r ¬ a c t e r i z e d in that light is guided along an optical fiber (2) to a gauge column of a secondary liquid (4) contained in a gauging transducer housing (7) placed in the liquid (12) to be gauged, whereby the hydrostatic pressure of the primary liquid to be gauged is allowed to inflict on the base of said secondary liquid gauge column, light is guided from the gauging transducer along another optical fiber (10) to a photodiode (14), and the liquid level is gauged on the basis of the change in light intensity caused by the change of the secondary liquid gauge column height so that the intensity change of the light exiting from said optical fiber (10) is compared to the light intensity measured exiting from a reference fiber (3), said intensities being measured with the help of a selector (13), and the actual level of the primary liquid to be gauged is obtained by plotting the proportional ratio measurement result on a calibration curve.
2. A method as defined in claim 1, c h a r a c t e r ¬ i z e d in that an optical fiber or bunch of fibers is inserted in the gauge liquid column so as to be wetted by the liquid, whereby the wetting of the fiber surface causes a change in the light transmission property of the fiber detected as a change of the return intensity of light from the fiber, and the actual level of the primary liquid to be gauged versus the detected intensity is logged in a calibration curve.
3. A method as defined in claim 1, c h a r a c t e r ¬ i z e d in that the light is guided close to the gauge liquid column and directed onto the end of the gauge liquid column so that the light propagating in the gauge liquid column is reflected from the column walls and the efficiency of the reflection is changed when the inner wall of the tube (6) containing the gauge liquid column is wetted by the gauge liquid, whereby changes in the liquid level outside the column can be detected by comparing the intensity of the light propagating in the gauge liquid column to light intensity received from the reference fiber (3) and then reading the liquid level outside the column from a calibration curve in which the light intensity ratio is plotted against the actual level of the liquid to be gauged.
4. A method as defined in any of foregoing claims 1-3, c h a r a c t e r i z e d in that the secondary liquid (4) in the gauge column is complemented with additives which improve the detection of changes in the optical variables such as colour and refractive index.
5. A method as defined in any of foregoing claims 1-4, c h a r a c t e r i z e d in that the gauge space is hermetically sealed (9) at its upper end in a manner that prevents the evaporation of the gauge liquid (8) contained in the space yet permitting changes in the height of the secondary liquid gauge column (8).
6. A method as defined in any of foregoing claims 1-5, c h a r a c t e r i z e d in that the gauging transducer (7) communicates with a space having the same ambient pressure as that prevailing above the liquid level to be gauged.
7. A method as defined in any of foregoing claims 1-6, c h a r a c t e r i z e d in that the hydrostatic pressure of the outside liquid to be gauged is communi¬ cated via a rubber diaphragm (5) mounted is such a slack manner that its deformation under the gauging of the different heights of the outside liquid cause no signifi¬ cant elastic forces.
PCT/FI1994/000352 1993-08-17 1994-08-15 Optic method for measuring of the level of the surface of a liquid WO1995005583A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU74619/94A AU7461994A (en) 1993-08-17 1994-08-15 Optic method for measuring of the level of the surface of a liquid

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FI933616A FI93396C (en) 1993-08-17 1993-08-17 Optical method for measuring the level of a liquid
FI933616 1993-08-17

Publications (1)

Publication Number Publication Date
WO1995005583A1 true WO1995005583A1 (en) 1995-02-23

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AU (1) AU7461994A (en)
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WO (1) WO1995005583A1 (en)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6782122B1 (en) 2000-04-27 2004-08-24 Simmonds Precision Products, Inc. Apparatus for measuring height of a liquid in a container using area image pattern recognition techniques
US7244848B2 (en) 2000-11-21 2007-07-17 Janssen Pharmaceutica N.V. Biphenylcarboxamides useful as lipid lowering agents
CN100390507C (en) * 2004-05-20 2008-05-28 广州市敏通光电科技有限公司 Continuous fiber optic liquid level sensor
RU2503950C2 (en) * 2012-02-27 2014-01-10 Федеральное государственное бюджетное образовательное учреждение высшего профессионального образования "Башкирский государственный университет" System to control liquid parameters

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB905228A (en) * 1958-03-14 1962-09-05 Pynford Ltd Improvements in or relating to apparatus operable in accordance with a fluid pressure or head
EP0168842A2 (en) * 1980-11-20 1986-01-22 Atlantic Richfield Company Float apparatus and method for determining leaks using the apparatus
US5303586A (en) * 1993-01-22 1994-04-19 Wayne State University Pressure or fluid level sensor

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB905228A (en) * 1958-03-14 1962-09-05 Pynford Ltd Improvements in or relating to apparatus operable in accordance with a fluid pressure or head
EP0168842A2 (en) * 1980-11-20 1986-01-22 Atlantic Richfield Company Float apparatus and method for determining leaks using the apparatus
US5303586A (en) * 1993-01-22 1994-04-19 Wayne State University Pressure or fluid level sensor

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
DERWENT'S ABSTRACT, No. 87-226890/32, Week 8732; & SU,A,1 275 220 (KUSHTANIN K I), 7 December 1986. *

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6782122B1 (en) 2000-04-27 2004-08-24 Simmonds Precision Products, Inc. Apparatus for measuring height of a liquid in a container using area image pattern recognition techniques
US7244848B2 (en) 2000-11-21 2007-07-17 Janssen Pharmaceutica N.V. Biphenylcarboxamides useful as lipid lowering agents
CN100390507C (en) * 2004-05-20 2008-05-28 广州市敏通光电科技有限公司 Continuous fiber optic liquid level sensor
RU2503950C2 (en) * 2012-02-27 2014-01-10 Федеральное государственное бюджетное образовательное учреждение высшего профессионального образования "Башкирский государственный университет" System to control liquid parameters

Also Published As

Publication number Publication date
FI93396C (en) 1995-03-27
AU7461994A (en) 1995-03-14
FI933616A0 (en) 1993-08-17
FI93396B (en) 1994-12-15

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