JP2011141292A - Shielding mechanism for radar type liquid level measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mechanism which attains highly accurate measurement near the bottom surface of a tank. <P>SOLUTION: Concerning a shielding mechanism for liquid level radar measurement, the shielding mechanism 1 is positioned under a steel pipe on the bottom surface 10 of a container, and includes an electromagnetic wave shield 2 and a bottom surface part 3. The electromagnetic wave shield 2 through which liquid can be exchanged, forms a wall of the shielding mechanism 1, and the bottom surface part 3 has a grid pattern plate and an attenuation material layer. The grid pattern plate is arranged on an upper part of the bottom surface part, and the attenuation material layer has at least two zones positioned on places having each different interval from the grid pattern. A boundary between the two zones agrees with the axis of symmetry of a lobe of a radar beam. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a radar-type measuring instrument used for measuring the volume of liquid in a storage container, and more particularly, to a radar measuring instrument located at the top of a waveguide (stationary cylinder or stipipe) extending vertically downward of the container About. The waveguide may terminate at a slight distance above the bottom of the container for various reasons, thus leaving a small gap between the waveguide and the bottom. There is no protection provided by the waveguide on the liquid level below the waveguide, so that the liquid surface is subject to surface wave phenomena.

  Although the present invention will be described with reference to a storage tank-equipped marine vessel, it can be implemented in any type of container such as, for example, a ground LNG storage tank, a petroleum product tank, a chemical tank, and a liquid nutrient tank.

  In particular, for low-level liquids in storage tank-equipped marine vessels (eg, vessels carrying liquefied natural gas), on the other hand, radar echoes caused by the liquid level are subject to disturbances due to capillary waves (capillary surface waves) and turbulence, On the other hand, it is well known to be subjected to disturbance caused by echoes generated on the bottom surface of the tank. Both of these types of disturbances are generally recognized that radar level instruments should be minimized in order to measure the liquid level with the accuracy required for offshore vessels with trading flowmeters. Has been.

  In radar level measurement (for example, as described in Patent Document 1), steel pipes are used to avoid interference with equipment inside the tank, and so that liquid surface turbulence does not cause fluctuations in the reflected signal. To do. A steel pipe is a pipe that extends from the top of the tank to a certain distance above the bottom of the tank. An antenna is located in or just above the pipe and serves as a waveguide to direct radiation downward by pipe action. This configuration does not work well when the liquid level is low and the liquid level is below the opening of the steel pipe, because there is no steel zone provided by the pipe on the liquid level. In addition, high turbulence is seen in the lower zone of the tank because the pump mechanism has an opening in this zone.

  Furthermore, according to the prior art, in order to avoid interference due to the bottom reflection signal, a deflector or mechanism having a similar function, such as an attenuator, is directly installed under the antenna. The application of these types of techniques for level measurement in LNG tanks has already been described in 1996 (Non-Patent Document 1).

  Patent Document 2 is a device for obtaining a liquid level in a tank by a radar level measurement mechanism, in which a microwave absorber is disposed on a bottom surface of a tank below an opening of a pipe to absorb microwave energy. An apparatus is described that prevents echoes from the bottom of the tank. Such mechanisms, such as membrane tanks, are not suitable for use in major application areas, and in some designs all mechanisms are located at a distance from the bottom of the tank rather than directly to the bottom of the tank. I have to do it. Furthermore, this mechanism does not provide any protection against surface turbulence.

US Pat. No. 6,184,818 International Publication No. 01/29523 Pamphlet

committee drafts for ISO International Standard 13689: 2001 (1996)

  The object of the present invention is to obtain a controlled measurement state near the bottom of the tank in a state where the steel pipe cannot extend to the bottom of the tank for some reason. In the context of the application of the invention, the expression controlled measurement state refers in particular to a measurement state in which noise, surface turbulence and bottom reflections due to equipment in the tank are reduced. In the case of ship tanks, the source of such turbulence is due to wind-induced waves and swells, or in the tank formed by ship movement due to ship trim angle / lateral tilt angle due to loading / unloading of bottom cargo or cargo. It is a wave. Vibrations from machinery can also propagate through the tank walls and other mechanical structures inside the tank, forming small waves / capillary waves inside the tank. Inside the tank, the cargo pump will generate both vibrations and waves. Specifically, in LNG tanks, further sources of turbulence are spray pumps / stripping pumps and cargo drop lines, and for all types of cold cargo, turbulence is created on the surface by boiling.

  The need for a controlled measurement condition near the bottom of the tank occurs, for example, in LNG membrane tanks, where in the case of some types of membranes (ie Invar metal sheet membranes) There should always be a safe distance between the bottom of the thin membrane tank. The limitations involved are that any structural component cannot be placed or supported directly on the bottom of the membrane tank, and the well of the tank floor can be placed in such a mechanism, or measured above the tank. Therefore, it may be impossible to measure the liquid level. Furthermore, pipes and pipe support structures (tripods or similar structures) can be subject to thermal shrinkage against the tank wall at low temperatures, so at least at low temperatures, between the lower end of the pipe and the tank bottom. There is a substantially free beam space, where the accuracy of the measure is reduced due to liquid level disturbances and bottom reflection interference.

  Therefore, an object of the present invention is to provide a mechanism capable of achieving high-precision measurement near the bottom surface of the tank.

  One object of the present invention is to provide a mechanism that is easy to manufacture and install, i.e., allows the brackets or other support mechanisms to be made compact with minimal separate parts and low weight. It is to be. The requirements for positioning the mechanism under the pipe should not be as critical as meeting the normal construction of such a tank (ie by bracket welding).

  Another object of the present invention is to prevent damage to the tank membrane and avoid the possibility of these parts breaking during operation as parts may be damaged by immersing them in the cargo pump. It is to provide a mechanism having a design to do.

  In one aspect, the present invention is a shielding mechanism for radar measurement at a low liquid level in a container, comprising an electromagnetic wave shielding member that is located near the bottom surface of the container and that is in fluid communication with the liquid. Is provided.

  In another aspect, the invention comprises an apparatus for determining a low level of liquid in a container, comprising a radar measurement mechanism having an antenna that sends a signal toward the liquid level and a waveguide. . The apparatus includes a shielding mechanism located near the bottom surface of the container, and the shielding mechanism is in fluid communication with a liquid.

  Accordingly, one aspect of the present invention provides a solution that shields a significant portion of the liquid level and gives the liquid surface the best possible state of producing good quality radar echo.

  In a second aspect, the present invention further comprises a mechanism adapted to minimize disturbances caused by radar signals reflected from the bottom of the tank. This can be achieved by various stealth techniques such as absorbers, deflection panels, and diffractive shapes, or combinations of these techniques (if possible).

  Both of these aspects of the present invention make it easier to increase signal fidelity with respect to echoes caused by the liquid level near the bottom of the container, thus providing accurate measurements of very low levels of liquid in the storage container to the radar instrument. The purpose is to make it happen.

  In one embodiment of the invention, the mechanism consists of a single type of material, such as a fiber mat or woven material containing fibers of carbon or similar material, and thus essentially meets the requirement of wave-dissipating the surface. It is flexible enough to fill and with no danger to the membrane. This embodiment is not appropriate if, for example, a high microwave absorption efficiency of the resonant damping structure is required, or if the danger that the fibers may come off and enter the cargo pump is not acceptable. I will. Accordingly, a variety of different designs of the mechanism are contemplated for a variety of different applications and requirements.

  In another embodiment, the mechanism is at least partially made from and / or covered by a radar absorbing material.

  In another embodiment, the mechanism comprises fastening means for fastening to the tripod guiding structure. In a special variant of this embodiment, the fastening means have at least articulations and / or are made of a heat insulating material and / or have extensible parts.

  In another embodiment of the invention, the shielding mechanism is adapted to minimize disturbances caused by radar signals reflected from the bottom of the tank. In another embodiment, the shielding mechanism includes a stealth mechanism such as an attenuator, a deflection panel, and a diffractive shape. In a special variant of the last-mentioned embodiment, the stealth mechanism is provided on the electromagnetic shield and / or on the bottom part.

  In another variant, the electromagnetic shielding is located in the main lobe of the radar beam. This particular embodiment of the invention applies to tanks with size limitations, such as Samsung 1442 (130 x 230 x 180 mm internal dimensions). In another variant, the mechanism is large in size with respect to the radiation lobe of the radar beam, and in this way the interaction with the electromagnetic shielding is negligible.

  In another embodiment, the electromagnetic shield is adapted to surround the steel pipe to provide a nested configuration.

  In one embodiment of the invention, the electromagnetic wave shield includes perforations. In another embodiment, the mechanism has a bottom surface that is adapted to minimize disturbances caused by radar signals reflected from the bottom surface of the tank.

  In another variant, the bottom part is rectangular or square.

  In another embodiment, the bottom surface includes a resonant absorber that attenuates most of the incident radar signal so that small radar echoes are detected at positions displaced downward to increase the virtual depth of the liquid. Have.

  In another embodiment, the bottom surface portion includes a lattice pattern plate that converts the input impedance so as to match the impedance of the LNG. In a variant of this embodiment, the bottom part comprises a damping material layer and preferably a screw for fastening the damping material layer to the backing metal. In another variation, the damping material layer is located below the lattice pattern. In another variant, the backing has at least two zones located at different distances (1/4 wavelength step) from the grating pattern. The attenuating material has a function of reflecting as weakly as possible from the bottom surface. A backing that provides a quarter wavelength step cancels reflections from the two zones back in the direction of the pipe. The attenuator is reverberant, ie the thickness of the attenuator adapts to the wavelength of the radar signal so that radar energy is captured and dissipated in the attenuator. Preferably, the boundary between the two zones corresponds to the symmetry axis of the radar beam lobe.

  In another embodiment, the shielding mechanism according to the present invention is formed as a container, the electromagnetic wave shielding body consists of the wall of the container, and the bottom part consists of the bottom surface of the container.

  In one embodiment of the invention, the shielding mechanism comprises an attenuator at the bottom.

  The purpose of the container extends from the bottom of the tank to at least a few centimeters above the bottom of the steel pipe (but rarely exceeds 25 centimeters as a whole), thus surface waves and bottom reflections that corrupt the measurement signal Is to provide a steel zone.

  In one embodiment of the invention, the shielding mechanism wall is at least partially perforated for fluid communication with the outer liquid. The perforation has a maximum deviation of the inner surface of the shielding mechanism along the average surface outside the device, which is greater than the specified overall measurement accuracy at the highest pump speed specified for the installation. (Remarkably), it communicates with a small time delay. For current LNG applications, the delay typically must be less than 1-2 mm.

  However, another effect of wall drilling is that external disturbances enter the shielded area. For this reason, the perforated area is minimal in one embodiment of the present invention and is positioned around the bottom surface of the shielding mechanism to prevent capillary waves from entering until the tank level reaches the very bottom surface of the shielding mechanism. , It is configured in an irregular pattern so that constructive interference (strengthening due to interference) between the various openings is minimized. On the other hand, the perforations also have the effect of attenuating standing waves in the shielding mechanism, and for this reason, the perforation area in one embodiment of the invention is large and spreads in an irregular pattern across the side walls of the shielding mechanism, And / or may consist of vertical or diagonal slices. In order to obtain a desired hydrodynamic filter effect so as to prevent a suddenly changing disturbance from entering, while maintaining an average level with little abrupt fluctuation inside the shielding mechanism, A perforation consists of a number of small holes rather than a few large holes. Each hole edge is preferably sharp (90 degrees) to increase hydrodynamic losses, thereby obtaining sufficient attenuation of abrupt level fluctuations. From the above, the design of the shielding mechanism according to the present invention has three partially conflicting considerations: sufficiently rapid communication of the liquid level, prevention of wave entry into the shielding mechanism, and wave propagation within the shielding mechanism. It can be seen that the compromise between attenuation can be optimized for each type of equipment.

  As described above, the electromagnetic wave shield includes perforations in the first embodiment. These perforations allow the liquid level to be sufficiently quenched to obtain a stable measurement, yet still provide quick communication with the surrounding liquid, so that most rapid pumping in the bottom zone A sufficiently low time constant and reading delay are obtained. This is particularly important in embodiments of the invention where the electromagnetic shielding is closed.

  The shielding mechanism according to the present invention preferably comprises a perforated electromagnetic shield, preferably comprising a radar transparent material or covered on the inside with a radar absorbing material so that the minimal incident radar signal is reflected to the radar receiver (stealth function) It has such physical dimensions and shapes. This also achieves effective avoidance and suppression of resonant standing liquid level waves with capillary waves in the mechanism.

  The electromagnetic wave shielding body according to the embodiment of the present invention is narrow so as to surround the steel pipe, and can slide with respect to the steel pipe when contracted. In another embodiment of the invention, in use where the nesting may be restrained by thermal action or any other misalignment of moving parts of this configuration, the diameter of the electromagnetic shield is either In this case, the clearance is increased so that there is a clearance between the pipe and the shielding mechanism. The electromagnetic wave shielding body in one embodiment of the present invention does not form a closed shape in another embodiment, but has a tubular shape including a curved wall.

  In one embodiment of the present invention, the shielding mechanism includes a bottom surface portion. This bottom is designed not to damage the membrane during installation or if any damage to the system will occur during operation (double error). The shielding mechanism has a minimal sharp edge on the bottom side, and in one embodiment a non-metallic material such as Teflon (registered trademark) to minimize any risk of tank membrane fretting or wear. ) Several spacing pieces. This minimum spacing above the tank membrane is between the safe spacing applied by tank designers and shipyards in specific applications and the requirement to minimize the measurement level specified by the shipowner. Determined as a compromise. Typically, the safe spacing is 3-5 mm for an Invar sheet membrane tank.

  The bottom surface of the shielding mechanism can include an absorbent material, which essentially acts as an attenuator and in a preferred design encompasses the entire area of the bottom surface. However, this design allows the absorbing material to be distributed at different heights across the bottom surface of the shielding mechanism and is therefore well suited to deflect residual echo that occurs at the bottom surface outside the radar detection range (ie, Diffraction) structure.

  In order to minimize the probability of boiling inside the shielding mechanism, in one embodiment, the shielding mechanism is at least partially made of a material having a low specific heat capacity so that any temperature within the shielding mechanism can be To be equal to the ambient temperature.

  The material also meets other environmental requirements such as temperature range, aggressive chemicals, or applicability to corrosive liquids, and the shielding mechanism in one embodiment is supported by the use of thermal insulation parts of the support bracket. The structure is substantially insulated, thereby preventing the temperature of the liquid inside the shielding mechanism from rising due to the heat transferred from the top of the tank through the tripod structure and the steel pipe. Both the shielding mechanism and the insulating part of the bracket can be made of, for example, a plastic material in the case of an LNG tank, and Teflon of the plastic material could generally be used for low temperature applications.

  In order to minimize the probability of generating capillary waves within the shielding mechanism, the shielding mechanism support, in one embodiment of the present invention, is free from vibrations induced by the tank structure by the pump or other parts of the container. Means for vibration suppression to mechanically separate the shielding mechanism is provided.

  Damping dampers are made, for example, from metal springs or rubber blocks, but at low temperatures most materials become unstable or lose their flexibility, in which case polyester films and similar plastics, etc. Only a few materials are used.

  In some applications, the mechanism can be attached directly to the tank bottom by welding, screwing, or using a clamp bracket. In one embodiment of the present invention, the mechanism and the tank membrane are configured to allow free relative sliding when the mechanism and the tank membrane are not made of a material having equal thermal constants. With a thin Teflon sheet or the like.

  In an embodiment adapted when the mechanism cannot be directly attached to the tank bottom, the mechanism comprises fastening means, for example in the form of an arm or bracket connected to the support structure, which fastening means rest on the bottom. Or attached in any other way at a fixed vertical spacing to the bottom of the tank. In a preferred embodiment, the support structure is a tripod guiding structure, which is also used to support a stripping pump used when the tank is finally emptied. Thus, there will always be an associated selectable longitudinal spacing between the lowest measured level and the lowest liquid level reached by pumping.

  In one embodiment of the invention, the shielding mechanism comprises fastening means adapted to be mounted on a structural component that contracts relative to the longitudinal position of the tank bottom. This is achieved by an arm connected to the mechanism and the structural part of interest, which arm is contracted by using, for example, bimetal details in the structure or by active control of the longitudinal position of the mechanism. Adjust automatically.

  In one embodiment, the shielding mechanism is at least partially made from and / or covered by a radar absorbing material, which radar absorbing material is desired to attenuate standing hydrodynamic waves in the shielding mechanism. Woven or fabricated appropriately to provide the effect of Suitable materials are, for example, Kevlar® fibers or other carbon materials.

  As described above, in one embodiment, the shielding mechanism can be substantially made from a fiber mat or woven material containing fibers of a carbon material or similar material. This embodiment combines the desired effects of wall perforations to make the walls in fluid communication, attenuate hydrodynamic waves from the outside and from the inside, attenuate the microwaves by absorption by carbon, and Disperse from irregular surfaces. Such a flexible mechanism also essentially meets the requirement to avoid damage under the thin tank membrane. In order to increase the rigidity of the mechanism, in one embodiment of the invention, the mat is sprayed with an adhesive or plastic material to wet and harden the fibers. It is also possible that the mechanism comprises a support ring.

  In one embodiment of the invention, the internal wave pattern inside the shielding mechanism is broken up by making the shielding mechanism irregular and asymmetric in the horizontal plane using wedges or undulations on the side walls. Preferably, simple regular shapes are avoided due to strong half-wave resonance. The preferred overall shape is an odd polygon, and preferably also has an unequal side length.

  As can be seen, disturbances caused by capillary waves and turbulence are lowered to an acceptable level by using the shielding mechanism according to the present invention (with electromagnetic shielding), so that a significant portion of the liquid level is shielded, It can provide a fairly uniform surface that produces good quality radar echo. The electromagnetic wave shielding body can take various shapes and designs that give effective damping force to capillary waves and turbulent flow without impairing the quality of radar echo from the liquid. With respect to the latter feature, various stealth techniques can be used, such as absorbers, deflector panels, and diffractive shapes, or (where possible) combinations of these techniques.

  On the other hand, the disturbance caused by the radar signal reflected from the bottom of the tank can be minimized in many ways. One option is to use a material that absorbs radar energy to the extent that only an acceptable portion of energy is projected as a detectable echo from the bottom surface of the container to the mechanism or at least a component of the mechanism (eg, the bottom). It is. Another option is to use an angled metal plate that reflects the majority of the radar signal before reaching the bottom of the container, thus making the echo signal from the bottom of the container exclusively detectable to the radar. is there. The third method involves a grating or array of geometries and patterns designed to diffract most of the echo energy outside the radar's detection range. Those skilled in the art will appreciate that the solution of combining the concept of radar signal diffraction, deflection and absorption forms a considerable class of mechanisms that are well suited to minimize the disturbance caused by echo signals from the bottom of the container. You will easily understand what you get.

  While the various features of the present invention have been described as different embodiments of the present invention, it will be apparent to those skilled in the art that they can be combined to provide a mechanism adapted to a particular use.

It is a figure which shows the mechanism by this invention in 1st Embodiment. FIG. 6 shows a second embodiment of the mechanism according to the invention. FIG. 6 shows a second embodiment of the mechanism according to the invention. It is a figure which shows a diffraction shape and a different wave shielding shape. It is a figure which shows a diffraction shape and a different wave shielding shape. It is a figure which shows a diffraction shape and a different wave shielding shape. It is a figure which shows a diffraction shape and a different wave shielding shape. It is a figure which shows a diffraction shape and a different wave shielding shape. It is a figure which shows a diffraction shape and a different wave shielding shape. It is a figure which shows a diffraction shape and a different wave shielding shape. It is a figure which shows a diffraction shape and a different wave shielding shape. It is a figure which shows a diffraction shape and a different wave shielding shape. It is a figure which shows a diffraction shape and a different wave shielding shape. It is a figure which shows a diffraction shape and a different wave shielding shape. It is a figure which shows a diffraction shape and a different wave shielding shape. It is a figure which shows a diffraction shape and a different wave shielding shape. It is a figure which shows a diffraction shape and a different wave shielding shape. It is a figure which shows a diffraction shape and a different wave shielding shape. It is a figure which shows a diffraction shape and a different wave shielding shape. It is a detailed view of the bottom part structure in one embodiment of the device according to the present invention. It is a figure which shows the 3rd Embodiment of this invention. It is a figure which shows one method of attaching this mechanism to a tank. It is a figure which shows one method of attaching this mechanism to a tank. It is a figure which shows one method of attaching this mechanism to a tank. It is a figure which shows the shielding mechanism by this invention, and its attachment. It is a figure which shows the shielding mechanism by this invention, and its attachment. It is a figure which shows the shielding mechanism by this invention, and its attachment. It is a figure which shows the shielding mechanism by this invention, and its attachment. It is a figure which shows the shielding mechanism by this invention, and its attachment. FIG. 5 shows a shielding mechanism according to the present invention including a grid pattern. FIG. 5 shows a shielding mechanism according to the present invention including a grid pattern. FIG. 6 shows several tests and analysis of those tests. FIG. 6 shows several tests and analysis of those tests. FIG. 6 shows several tests and analysis of those tests. FIG. 6 shows several tests and analysis of those tests. FIG. 6 shows several tests and analysis of those tests. FIG. 6 shows several tests and analysis of those tests. FIG. 6 shows several tests and analysis of those tests. FIG. 6 shows several tests and analysis of those tests.

  Next, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 shows a shielding mechanism 1 for liquid level radar measurement, which includes an electromagnetic wave shielding body 2 and a bottom surface portion 3, and the electromagnetic wave shielding body 2 is in fluid communication with a liquid 4 (means for fluid communication are not shown). ), Shows the shielding mechanism for liquid level radar measurement. This figure also shows the steel pipe 5 and the support arm or fastening means 6. In this embodiment, the shielding mechanism 1 is formed as a container, the electromagnetic wave shielding body 2 is composed of a container wall, and the bottom surface portion 3 is composed of a bottom surface of the container. The bottom 10 of the tank is shown in the figure along with the bottom structure 11.

  FIG. 2 shows an embodiment of the present invention in which the electromagnetic wave shielding body 2 extends only to the outer peripheral portion of the bottom surface portion 3. This figure also shows the perforations 12 of the electromagnetic wave shield 2.

  3A and 3B show the diffraction shape of the bottom surface portion 3. These diffractive shapes can also be located on the electromagnetic wave shield 2, and a combination of the diffractive shape on the electromagnetic wave shield 2 and the diffractive shape on the bottom surface portion 3 is also possible. These figures show several different parts of the bottom part 3: 20, 21, 24, 25, 26, which are in several different levels (spacings d1 and d2). Accordingly, it is possible to form a diffraction pattern that reduces bottom noise, preferably in combination with the overlapping of the edges of the portions (for example, edges 22 and 23). The spacing d2 may be the same for all parts or may be different, i.e. there may be one spacing between part 24 and part 27 and another spacing between part 24 and part 25. . One skilled in the art will understand that the distances d1 and d2 are closely related to both the refractive index of the liquid medium and the operating frequency of the radar. However, the intentional change of the spacing will give a diffractive back-confusion that adapts well to the geometry of the electromagnetic shielding. Therefore, the amount of energy (although there is residual) that echoes the radar instrument is kept to a minimum. As an example, the operating frequency is 10 GHz, the fluid is liquefied natural gas (LNG), and the interval is in the range of 3 to 10 millimeters (the lower the frequency, the longer the interval is, and vice versa). It is done.

  FIG. 3 shows a different embodiment of the mechanism according to the invention. Some of the figures are a bottom surface 34, which is an attenuator in a preferred embodiment of the present invention, rings 300, 301 that fasten the bottom surface and provide a stealth effect, and an electromagnetic shield 2. FIG.

  3C and 3D and 3E show a variety of different shapes of the bottom portion 3 (cylindrical odd polygons and irregular shapes (with few or no parallel sides, respectively)).

  FIG. 3F shows one embodiment of a bottom surface 3 that includes a woven fabric structure and support ring 100 for rigidity.

  FIG. 3G shows an embodiment of the present invention in which the electromagnetic wave shielding body 2 has a waveform (undulation shape). This embodiment has the advantage that the internal standing waves in the shielding mechanism are more quickly dispersed and dissipated by the corner structure.

  In FIGS. 3H-3K, the electromagnetic shield comprises a thin sheet metal or plastic material, i.e., stainless steel, aluminum, Teflon or the like. In the embodiment shown in FIGS. 3L-3N, the electromagnetic shield comprises a woven material. The various shapes, types, and microwave attenuator designs and shapes of the wall structures described above are combined in some embodiments of the invention to provide a wave quencher optimized for various applications and requirements. It is done.

  FIG. 3O shows one embodiment of a mechanism according to the invention comprising a plate 501 adapted to be fitted between undulations at the bottom of the tank. The plate 501 shows a relatively large area where the shielding mechanism can be placed, and the shielding mechanism can be moved on the plate to achieve an optimum placement of the mechanism in view of the radar tube / radar footprint. . The plate 501 includes a wall that provides the electromagnetic shielding body 2. The mechanism also includes a perforation shield or wave absorber 500. FIG. 3O also shows a steel chamber 502.

  FIG. 3P shows an alternative embodiment of the present invention, in which a cylindrical shielding mechanism including the electromagnetic wave shield 2, the perforated membrane 500, and the attenuation plate 34 is located on the plate member 501.

  FIG. 4 shows details relating to the basic structural features of the bottom surface portion 3 which in one embodiment of the invention includes an attenuator. From below the structure includes a metal support 31, which in a preferred design is placed as close as possible to the base 10 of the storage container (tank) without contacting the base. The latter design feature requires a support whose lower surface 32 extends substantially parallel to the bottom surface of the container (tank), while the upper surface 33 or lower portion of the support is inclined with respect to the bottom surface of the container. It will also include panels and facets set at the corners. The second structural feature of the attenuator 3 is an absorbent material 34 that is attached to the upper surface of the support so as to absorb most of the energy penetrating from the steel pipe 5 through the intermediate liquid level 4 downward. Those skilled in the art will readily appreciate that the upper and lower surfaces of the absorbent material 34 are mismatched with respect to the propagation of radar signal waves, and thus both surfaces are prone to radar echo. This double echo feature is commercially used in a product commonly referred to as a resonant absorber (Derenback layer) and is well suited for use as the absorbent material 34 of the attenuator 3. Additional structural features of the attenuator 3 include an additional layer of plastic material 35. The layer is primarily intended to provide protection of the absorbent material. If so required, some degree of design freedom is also provided for optimizing the radar signal performance of the attenuator 3 for its intended use. To illustrate this design freedom, in one embodiment of the present invention, as an alternative, the device can include an absorbent material 34 having a high attenuation factor, which is too thick to provide resonance due to the Derenbuck design. Therefore, only the upper surface of the absorbing material for generating a detectable echo remains. However, this echo can be significantly reduced by providing an embodiment of the present invention with a layer of plastic material 35 having a suitable thickness and refractive index, and thus a possible alternative to the Derenbuck design. Provide a productive solution.

  Besides this, through careful testing of the Derenbeck design, we assume new features and inventive concepts regarding the measurable position of the echo generated by the bottom attenuator 3, which This is a beneficial mode for the purpose of use. The resonance of the Deren back layer can be designed to eliminate back-up confusion or to create some sort of back-up confusion. The latter feature inevitably displaces the detectable position of the echo produced by the attenuator 3. The displacement is pushed out by careful selection of the absorbent material to provide a detectable position under the support 31, thus also providing a virtual liquid depth deeper than the actual depth. This beneficial feature increases the margin for a software-based algorithm that can be used to resolve the liquid echo from the echo produced by the attenuator 3. Useful features increase margins. This proper attenuator 3 property is equally well applied when applying a layer of plastic material 35 having a suitable thickness and reflectivity to provide the above-described alternative to the Derenbuck design.

  FIG. 5 shows a third embodiment of the present invention, in which the shielding mechanism includes only the electromagnetic wave shielding body 2, and the electromagnetic wave shielding body 2 is not completely tubular but partially open.

  FIG. 6 shows a different way of attaching the mechanism 1 to the tank. In FIG. 6A, the shielding mechanism is fastened by a tripod guidance 701 or a bracket to a similar structure. This figure shows the mechanism attached to the tank bottom surface 10 but at some distance (no contact). FIG. 6B shows the mechanism mounted on the tank bottom 10 with a separate backing. In this case, the mechanism can be fastened by bolting, welding or gluing and is in contact with the tank bottom. FIG. 6C shows the mechanism mounted on the tank bottom, using a metal membrane as the backing. This mechanism can be fastened by bolting, welding, or gluing, and the figure also shows a clamp ring 700.

  FIG. 7A illustrates the positioning of one embodiment of the present invention. This embodiment of the bottom surface portion 3 of the shielding mechanism 1 includes a microwave attenuator and further includes a discharge hole 600. This figure shows the spacing between the bottom surface of the bottom surface 3 and the bottom surface of the tank, with a minimum complete scale that requires a gauge height of 26 mm, in this case 4 mm, the top surface of the bottom surface 3 and the tank The distance from the bottom is 8 mm. This figure also shows a plate joint 610 and a tank membrane 10 that are 15 mm high in the illustrated case (Inver tank).

  FIG. 7B shows one embodiment of a shielding mechanism 1 according to the present invention comprising fastening means 800, whereby the mechanism is secured to a tripod guiding structure or any other support mounted on the tank bottom 10. be able to.

  FIG. 7C shows an alternative positioning of the shielding mechanism 1 according to the invention, in which the bracket of the mechanism is fixed to another bracket protruding from the tripod guide structure and again the cargo stripping pump is Fixed.

  FIG. 7D shows another possibility for the positioning of the shielding mechanism 1.

  FIG. 7E shows the mounting details of the dimensions.

  FIG. 8A shows a shielding mechanism having a lattice pattern. The shielding mechanism 1 includes an electromagnetic wave shielding body 2 and a bottom surface portion 3. According to this embodiment of the present invention, the bottom surface portion 3 includes a lattice pattern layer 902. The lower surface of the grating pattern and the corresponding lower layer 900 have zones of different thickness and provide a quarter wavelength step 901. The attenuation material layer 34 is located between the lattice pattern layer 902 and the lower layer 900. A test object was generated corresponding to FIG. 8A for testing. This test object comprises a plastic material with an impedance equal to that of kerosene, making the slab immersed in both LNG and kerosene invisible. On the other hand, the slab is visible in the air. The quarter wavelength step 901 and the attenuating material 34 are adapted to remove the effects of reflection on the back side of the slab material in this embodiment of the invention.

  As described above, in one embodiment of the present invention, the shielding mechanism is provided with fastening means for fastening the slab to the damping material. A special variant of this embodiment is that the fastening device is a screw that pushes the slab firmly into the damping material, the bottom part is rectangular, and the screw is targeted to each short wall.

  FIG. 8B shows a shielding mechanism formed as a container and including a grid pattern.

  8C-8G show the results of testing an apparatus immersed in kerosene. Kerosene has a dielectric constant approximating that of LNG. In the measurement, the distance to the slab is 147 mm (72 mm in the previous test). Although mainly shown in FIG. 8B, a device provided with a fastening screw is used, and a hole in the wall and a leaky corner are taped with duct tape so as to avoid leakage of kerosene. .

  FIG. 8C shows the first measurement of the slab air (gamma = 1.98). This results in an almost perfect pulse (gamma = 2.00 equals a perfect Hanning pulse) and is easy to detect (45 dB) (0 ullage pulses originate from the test tube and can be ignored. Please note.)

  FIG. 8D shows the first measurement in the measurement state with no liquid in the shielding mechanism, ie with a flat metal reflector (bottom of the mechanism) and the air (gamma = 2.12).

  FIG. 8E shows the results of testing with kerosene 20 mm above the slab. A very fine pulse has a gamma = 2.08. FIG. 8F shows the results with kerosene 60 mm above the slab (gamma = 2.15). FIG. 8G shows the results for kerosene 140 mm above the slab (gamma = 2.07). The centroids of these measurement points and similar centroids at different levels of kerosene are compared to the ruler results in FIG. 9A.

  The results shown above show that the shielding mechanism is effective with no interference echo and can move the focus accurately. To test this part, the reference (ruler) reading was compared to the radar reading. The deviation between the radar measurement and the nominal kerosene level measured by the ruler can be seen in FIG. 9A. FIG. 9A shows that the reference deviation for this data set is 4.2 mm, which is within the required accuracy of +/− 5 mm.

  FIG. 9B shows a comparison of level measurements with radar versus ruler. The standard deviation of the measured value is 4.2 mm, ie the accuracy is within +/− 5 mm. The estimation accuracy of the ruler measurement value (reference) is +/− 2 mm in error bars.

  FIG. 9C shows kerosene amplitude as a function of level, and the results in this figure are constant.

  The above measurements show that the rectangular shielding mechanism does not produce significantly unwanted reflections.

  In experiments, it has also been confirmed that it is possible to obtain an accuracy higher than +/− 5 mm by lowering the level by 10 to 15 mm above the slab.

  Although different features of the invention have been described as belonging to different embodiments, it is within the scope of the invention to combine some or all of the above features in one embodiment. Therefore, in one embodiment of the present invention, the mechanism has a stealth mechanism on the bottom surface and a perforation in the electromagnetic wave shield. In another embodiment, the mechanism includes perforations in the bottom surface and the electromagnetic shield to surround the steel pipe. In yet another embodiment, the mechanism comprises only an electromagnetic shield substantially made from a fiber mat.

  The shielding mechanism for the radar-type liquid level measuring device according to the present invention is an arbitrary type such as a container mounted on a storage tank-equipped marine ship, a ground LNG storage tank, a petroleum product tank, a chemical tank, and a liquid nutrient tank. It is applied to the liquid level measuring device of the container.

Claims (18)

  A shielding mechanism for liquid level radar measurement, wherein the shielding mechanism is located below the still pipe and on the bottom surface of the container, and includes an electromagnetic wave shielding body and a bottom surface portion, and the electromagnetic wave shielding body passes through it. The liquid is exchangeable and forms a wall of the shielding mechanism, the bottom portion includes a lattice pattern plate and an attenuation material layer, and the lattice pattern plate is disposed on the bottom portion, and the attenuation material The layer has at least two zones located at different distances from the grating pattern, the boundary between the two zones being coincident with the symmetry axis of the radar beam lobe.   The shielding mechanism according to claim 1, wherein the electromagnetic wave shielding body includes a perforation.   3. The shielding mechanism according to claim 2, wherein the bottom surface portion uses a stealth mechanism provided on the bottom surface portion to minimize disturbance caused by a radar signal reflected from the bottom surface of the tank. A shielding mechanism characterized by   2. The shielding mechanism according to claim 1, wherein the bottom surface portion uses a stealth mechanism provided on the electromagnetic wave shield or the bottom surface portion to cause disturbance caused by a radar signal reflected from the bottom surface of the tank. A shielding mechanism characterized by being designed to be minimal.   5. The shielding mechanism according to claim 4, wherein the stealth mechanism is included as one of an attenuator, a deflection panel, and a diffractive shape.   6. The shielding mechanism according to claim 5, wherein the bottom surface portion has a resonance absorber that attenuates most of the incident radar signal, and the resonance absorber has a small radar echo that increases the virtual depth of the liquid. A small radar echo detected at a position displaced downward as described above.   The shielding mechanism according to claim 1, further comprising a screw that fastens the lattice pattern plate to the damping material layer.   The shielding mechanism according to claim 1, wherein the attenuation material layer is located under the lattice pattern.   The shielding mechanism according to claim 1, wherein the bottom surface portion is rectangular or square.   9. The shielding mechanism according to claim 8, wherein the electromagnetic wave shielding body is located in a main lobe of a radar beam.   The shielding mechanism according to claim 1, wherein the shielding mechanism includes fastening means for fastening the shielding mechanism to the tripod guiding structure.   12. The shielding mechanism according to claim 11, wherein the fastening means includes at least articulations, or are made of a heat insulating material or include extensible parts. Shielding mechanism.   4. The shielding mechanism according to claim 3, wherein the shielding mechanism is formed as a container, wherein the electromagnetic wave shielding body has a wall of the container, and the bottom surface portion has a bottom surface of the container.   2. The shielding mechanism according to claim 1, wherein the electromagnetic wave shielding body surrounds the still pipe so as to give a multistage structure.   2. The shielding mechanism according to claim 1, wherein the shielding mechanism is made at least partially from a radar absorbing material or covered by the radar absorbing material.   2. The shielding mechanism according to claim 1, wherein the shielding mechanism is substantially made of a fiber mat or woven material containing carbon fibers.   The shielding mechanism according to claim 1, wherein the attenuation material layer has at least two zones located at a distance of ¼ wavelength step from the grating pattern.   An apparatus for determining a liquid level, comprising: a radar measurement mechanism having an antenna and a waveguide for sending a signal toward the liquid surface; and an electromagnetic wave shielding body, wherein the apparatus further comprises: An apparatus comprising the shielding mechanism according to any one of items 1 to 17.

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