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.

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• 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)

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Publications (1)

Family

ID=8538424

Family Applications (1)

Country Status (3)

Cited By (4)

Families Citing this family (1)

Citations (3)

• 1993
  • 1993-08-17 FI FI933616A patent/FI93396C/sv active
• 1994
  • 1994-08-15 WO PCT/FI1994/000352 patent/WO1995005583A1/en active Application Filing
  • 1994-08-15 AU AU74619/94A patent/AU7461994A/en not_active Abandoned

Patent Citations (3)

Non-Patent Citations (1)

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