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
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
  • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
  • G01S7/40—Means for monitoring or calibrating
  • G01S7/4004—Means for monitoring or calibrating of parts of a radar system
• • 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
• • 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
  • G01F23/296—Acoustic waves
  • G01F23/2962—Measuring transit time of reflected waves
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
  • G01S13/86—Combinations of radar systems with non-radar systems, e.g. sonar, direction finder
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
  • G01S13/86—Combinations of radar systems with non-radar systems, e.g. sonar, direction finder
  • G01S13/862—Combination of radar systems with sonar systems
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
  • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
  • G01S13/88—Radar or analogous systems specially adapted for specific applications
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S367/00—Communications, electrical: acoustic wave systems and devices
  • Y10S367/908—Material level detection, e.g. liquid level

Definitions

• the present invention relates to a device for gauging the level of a fluid in a container, above the surface of the fluid there being a gas, the device comprising a first transmitter for transmitting a microwave signal through said gas towards the surface of the fluid, a first receiver for receiving the microwave signal reflected against said surface, an electronic unit arranged to calculate from the propagation time of the emitted and reflected microwave signal a first distance from the first transmitter to the surface of the fluid and thereby its level in the container.
• Such devices have increasingly come in use, particularly for petroleum products such as crude oil and products made thereof.
• container in this context very large ones constituting parts of the total loading volume of a tanker as well as even larger, usually circular-cylindrical landbased tanks, with volumes of tens of thousands of cubic meters.
• Demands for accuracy of measurement have become increasingly greater. In some cases accuracy of measurement of 1 to 2 mm at a 20-meter distance from the transmitter to the surface of the fluid may be required. In order to achieve so high an accuracy of measurement special measures must be taken to eliminate disturbances.
• One problem frequently occurring in connection with level gauging of the kind mentioned in the introduction, particularly in what regards the containter containing the petroleum products or other chemical products, is the condition that the gas above the surface of the fluid, i.e.
• the "tank atmosphere” shows a partial pressure of vaporized fluid and also usually a partial pressure of air and possibly water vapour.
• a vaporized petroleum product i.e. a gaseous hydrocarbon, shows a somewhat lower velocity of translation for microwaves compared with air. This velocity of translation stands in a certain relation to the density of the gas.
• the velocity of translation of the microwave depends on the condition in the gas above the fluid in the container. If the container is essentially filled with a petroleum product, the corresponding partial pressure of the hydrocarbons will be essentially equal to the steam pressure when a steady condition has been obtained, i.e. the gas is saturated with gaseous hydrocarbon. The steam pressure varies substantially for different fluids such as hydrocarbon products, from practically zero to atmospherical pressure and thereabove. If, on the other hand, the container is emptied, air flows in from the atmosphere and mixes with the gaseous hydrocarbon so that a mixture of gaseous hydrocarbon and air takes place.
• the partial pressure of the air will be relatively high, but if the container is left unmoved, more hydrocarbon will evaporate from the surface and the partial pressure of the hydrocarbon will increase. It is evident that the microwave velocity will vary depending on the partial pessure of the hydrocarbon, which in turn means that the gauging result will show corresponding deviations from the correct values of level gauging.
• the object of the present invention is to provide a simple and reliable device of the kind mentioned in the introduction that admits correction of the level gauging result achieved therewith.
• the invention also admits that the correction becomes relatively independent of horizontal density gradient.
• such a device is characterized by a first means for gauging the sound velocity in said gas and a second means for correcting said first distance to a second distance with consideration to the microwave velocity in the gas through a known relation between the sound velocity and the microwave velocity.
• the relation between the sound velocity and the microwave velocity is known for a large number of gases and gas mixtures.
• the sound velocity in a mixture of gaseous hydrocarbon and air is affected about 500 times more by the partial pressure of the hydrocarbon, i.e. proportion of the gas mixture, than the microwave velocity.
• a level gauging effected above a fluid where there is a gas with a certain partial pressure of a gas corresponding to the fluid can be corrected with very great accuracy by gauging the sound velocity in the gas in question. If the same path is used for sound and microwaves the correction will be independent of the inhomogeneity.
• the sound velocity and the microwave velocity, respectively, in gases and gas mixtures can be described with more or less complex formulas, according to the need for accuracy. What regards the aforementioned relationship between the sound velocity and the microwave velocity the demands for accuracy should be relatively moderate, which means that approximate formulas can be used.
• ⁇ r relative permeability constant for the transmission medium
• ⁇ r relative dielectricity constant for the transmission medium ⁇ r can be assigned the value 1 for the gases here in question, and therefore only the variation of the relative dielectricity constant with the gas composition must be considered.
• ⁇ r can be calculated from the relationship :
• R can be calculated by adding certain data for atoms and bonds in a molecule. For a gas mixture the corresponding calculations can be effected. R can be approximated to being proportional to the molecular weight if there is a restriction to hydrocarbons. Some gases are polar which makes R seem bigger, and in that case R may have to be chosen according to the gas. For hydrocarbons it is not required to have detailed knowledge of the composition of the gas. ⁇ r - 1 can be considered proportional to the density of the gas as long as ⁇ r is close to 1 , which always is the case for gases close to atmospherical pressure (max. 1.01). For hydrocarbons an average of 0.0011 per 1 kg/m can be given.
• the microwave velocity decreases by 400 ppm (millionth parts) per kg hydrocarbon per m 3 , almost irrespective of what particular gaseous hydrocarbon.
• the given number is independent of the temperature within an interval of about 20 (i.e. usual storage temperature), but the increasing temperature will of course bring about an increased partial pressure of gaseous hydrocarbon above the surface of the fluid.
• gases such as water, ammonia etc., show a permanent moment of dipole which affects R in the relationship above.
• the density of air at 20 is about 1.2 kg/m while it is 3-3.5 kg/m for gaseous hydrocarbon of the kind in question.
• C ⁇ /C v for air is 1.40 and for gaseous hydrocarbon about 1.15.
• the inverted sound velocity i.e. the propagation time
• the partial pressure of the gaseous hydrocarbon increases essentially linearly with the density of the hydrocarbon.
• the density of the gas varies along the gauge length for the sound signal and the microwave signal.
• the sound signal it can be calculated approximately that the propagation time of sound is proportional to the average of the square root of the density, while regarding the microwave signal the propagation time is proportional to the density on the condition that the relative dielectricity constant is close to 1, which is true for the cases in question.
• said first means is arranged to emit a sound signal parallelly to said microwave signal towards the surface of the fluid, and is arranged to receive the sound signal reflected against said surface. In this way both the sound signal and the microwave signal will pass through the same gas, i.e. the transmission medium, with the same composition, possibly showing a density gradient.
• the first means and the transmitter of a microwave signal to a unit, preferably arranged to transmit the sound signal and the microwave signal essentially the same way.
• this principle can be realized by letting said unit comprise a horn arranged to give directivity to both the sound signal and the microwave signal.
• the first means for gauging the sound velocity is formed with a second transmitter and a second receiver, both preferablylocated in the upper portion of the container.
• the device is suitably equipped with a third means, constituting a computer that comprises a memory unit for storing a first gauge value of the sound velocity for a relatively high level of the fluid an the container, further comprising a calculating unit for calculating the sound velocity in a gas showing a density gradient, starting out from the first stored gauge value and a recently gauged second gauge value for the sound velocity corresponding to a relatively lower level of the fluid in the container, and from an algorithm stored in the computer describing a probable density gradient in the gas.
• the device according to the invention can be formed in a number of ways, in addition to those mentioned above.
• the device can for instance comprise a vertical tube through which the microwave signal and possibly also the sound signal is led towards the reflecting surface of the fluid.
• the tube must naturally be provided with a number of openings along its longitudinal extension in order that the surface of the fluid will take the same level inside and outside the tube.
• Figure 1 shows schematically a vertical cross section through a device according to the invention in a first embodiment
• Figure 2 shows in the same manner a second embodiment of the device
• Figure 3-5 show different detail embodiments of the device
• Figure 6 shows schematically a vertical cross section through an alternative embodiment of the device according to the invention.
• Figure 7 shows a diagram of the gas density as a function of the distance, from a means for gauging the sound velocity according to Figure 6 to the surface of the fluid.
• 1 designates a container containing a fluid such as a petroleum product 2, with the surface 3.
• An electronic unit 7 comprises among other things equipment for calculating from the propagation time of a microwave signal transmitted and reflected against the surface 3 a first distance to the surface of the fluid.
• a first means 9 for transmitting and receiving a sound signal transmitted and reflected against the surface 3 of the fluid.
• L L M (L L -L M )/(k 1 -1) or when k 1 »1
• This correction is effected by a not shown second means included in the electronic unit 7.
• k 1 is independent of what hydrocarbon is in the container. This is important since the mixture is often unknown; e.g. petrol can contain about a thousand components. For other liquids, for instance polar liquid, k 1 can be chosen according to the content.
• the transmitter for the microwave signal 6 and the means for transmitting a sound signal are in this case placed at the same height above the level of the fluid, which of course is not necessary as the required conversions considering different heights
• FIG. 2 an embodiment of the device according to the invention is shown schematically, comprising a horn 11, which leads both the microwaves and the sound waves to being transmitted and reflected essentially coincidingly.
• the transmitter for the microwave signals shows a waveguide filled with a dielectric 12, a sound source and a receiver for reflected sound 13, with a lead-in 14 for sound signals and a horn with a wall 15.
• the variant in Figure 4 comprises a waveguide for microwaves 16 with dielectric filling.
• the waveguide is surrounded by a metal tube 17.
• a sound element 18 coaxial with the waveguide of piezoelectric or magnetostriction type surrounds the waveguide.
• Below the sound element 18 there is an acoustic resonator 19 arranged.
• a quarter-wave transformer 20 in the form of a ring slot which prevents the microwaves from ex- tending that way but limits them from leaving the waveguide.
• the wall in a horn is designated by 21.
• a variant with non-circular-symmetrical feeding of the sound waves is shown in Figures 5a and b.
• a waveguide 22 for microwaves is filled with dielectric and ends downwards with an edge 23 which is evident from the cross section according to the markings I-I, shown in Figure 5b.
• a sound source 24 is arranged at the side of one wall 25 of the waveguide, which limits the wedge- shaped lower portion of the waveguide on one side. The sound signal is reflected by the wall 25 downwards, and returns after the reflection against the surface of the fluid to be reflected by the opposite wall 26 of the waveguide to a receiver or microphone 27.
• the waveguide has one-mode propagation for both microwaves and sound waves there is relatively great freedom to form the transition unsymmetrically maintaining the propagationof the mode.
• FIG. 6 An alternative embodiment of the device according to the invention is shown in Figure 6.
• the designations in Figure 1 are repeated for the corresponding parts of the device, but the sound gauging is effected via a sound source 29 arranged in a bracket 28, the sound source being directed towards a receiver or microphone 30, also mounted on the bracket 28.
• the distance between the sound source and the microphone can be about 0.5 m.
• the drawback with this embodiment is that the sound signal does not go the same way as the microwave signal. This gives a satisfactory correction of the level gauging only if the gas 10 above the surface 3 of the fluid is homogeneous, i.e. does not show any density gradient. This is the case when the container has been filled with for instance a petroleum product, in which case the air has been displaced out of the container.
• the device can be supplemented with a third means constituting a computer comprising a memory for storing a first gauge value achieved when the container is more or less filled with fluid such as a petroleum product.
• This gauge value then constitutes a maximum density value for the gas in question, as it can be calculated that the space above the fluid is completely filled with homogeneous gas corresponding to the fluid.
• the third means also comprises a calculating unit which, starting out partly from the first
• FIG 7 the gauging method is described with a device according to Figure 6 in case the gas in the container shows a gradient.
• the shown diagram shows schematically the density of the gas as a function of the distance between the sound gauging means and the surface of the fluid.
• A the density value (i.e. corresponding to the sound velocity) A is gauged.
• this density value is maintained at the beginning until a point B, when air which is flowing in begins to decrease the density to a lowest value, at the point C. If then the container is left without any measure the fluid will evaporate gradually and the density gauged at this relatively large distance to the surface reaches a value D.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Radar, Positioning & Navigation (AREA)
• Remote Sensing (AREA)
• General Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Computer Networks & Wireless Communication (AREA)
• Fluid Mechanics (AREA)
• Thermal Sciences (AREA)
• Acoustics & Sound (AREA)
• Measurement Of Levels Of Liquids Or Fluent Solid Materials (AREA)
• Radar Systems Or Details Thereof (AREA)
• Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)
• Length-Measuring Devices Using Wave Or Particle Radiation (AREA)
• Control Of Motors That Do Not Use Commutators (AREA)
• Measurement Of Velocity Or Position Using Acoustic Or Ultrasonic Waves (AREA)

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Citations (7)

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• 1989
  • 1989-04-10 SE SE8901260A patent/SE466519B/sv not_active IP Right Cessation
• 1990
  • 1990-03-27 JP JP2506375A patent/JPH068741B2/ja not_active Expired - Fee Related
  • 1990-03-27 KR KR1019900702561A patent/KR940000144B1/ko not_active IP Right Cessation
  • 1990-03-27 DE DE90906420T patent/DE69005245T2/de not_active Expired - Fee Related
  • 1990-03-27 AU AU55288/90A patent/AU616357B2/en not_active Ceased
  • 1990-03-27 EP EP90906420A patent/EP0419636B1/en not_active Expired - Lifetime
  • 1990-03-27 CA CA002031453A patent/CA2031453C/en not_active Expired - Fee Related
  • 1990-03-27 ES ES90906420T patent/ES2048487T3/es not_active Expired - Lifetime
  • 1990-03-27 WO PCT/SE1990/000194 patent/WO1990012292A1/en active IP Right Grant
  • 1990-03-27 DK DK90906420.6T patent/DK0419636T3/da active
  • 1990-03-27 BR BR909006408A patent/BR9006408A/pt not_active IP Right Cessation
  • 1990-03-27 US US07/613,574 patent/US5070730A/en not_active Expired - Lifetime
  • 1990-07-23 SA SA90110002A patent/SA90110002B1/ar unknown
  • 1990-12-05 FI FI906016A patent/FI97999C/sv not_active IP Right Cessation
  • 1990-12-07 NO NO905314A patent/NO179385C/no unknown

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