Manufacturing Method of Dielectric Filling Member of Radar Level Gauge and Its Signal Propagation Device

Abstract

The present application discloses a method for manufacturing a dielectric filling member of a radar level gauge and its signal propagation device. The radar level gauge includes a signal propagation device, a dielectric filling member disposed in the signal propagation device, and a sealing device for preventing the contents of the storage tank from escaping into the external environment. The dielectric filling member includes a body formed of a polymer material and at least one structural reinforcement element formed of a modified polymer material, wherein the modified polymer material is obtained by modifying the polymer material with a filler material, and wherein the at least one structural reinforcement element is integrally formed with the body by sintering and forms a part of the sealing device. The present invention is based on the recognition that a structural reinforcement element made of a modified polymer material can be sintered and bonded to the body.

Description

Technical Field

[0001] The present invention relates to a radar level gauge having a waveguide structure with a sealed dielectric filling member, wherein the filling member comprises a mechanical strengthening element. The invention also relates to a method for manufacturing such a dielectric filling member. Background Art

[0002] A radar level gauge (RLG) is suitable for measuring the filling level of products such as process fluids, granular compounds, and other materials contained in a storage tank.

[0003] Examples of such a radar level gauge may include: a transceiver circuit for transmitting and receiving microwaves; a signal propagation device arranged to direct microwaves towards a surface and return the microwaves reflected by the surface to the transceiver; and a processing circuit adapted to determine the filling level based on the relationship between the microwaves transmitted and received by the transceiver.

[0004] The signal propagation device may include a hollow waveguide structure such as one or more hollow waveguides, and a directional antenna adapted to transmit free-propagating electromagnetic waves into the storage tank and receive the reflections of these waves. Such an RLG is sometimes referred to as a non-contact RLG (NCR). The antenna may be adapted to a specific frequency band. The currently most commonly used frequency bands have a center frequency of about 6 GHz or 26 GHz, although higher frequency bands are also conceivable.

[0005] Alternatively, the signal propagation device may include a microwave transmission line (commonly referred to as a probe) extending into the contents of the storage tank. In this case, the transmitted signal and the echo signal will propagate along the probe until they are reflected due to impedance discontinuities caused by the surface. The RLG with a probe is sometimes referred to as a guided wave radar (GWR) level gauge. Several types of probes may be used, such as single-wire (Goubau type) probes, coaxial probes, and twin-wire probes. The probes may be substantially rigid or flexible, and they may be made of metal such as stainless steel, plastic such as PTFE, or a combination thereof. The transmission line probe may be connected to a coaxial probe connector.

[0006] In the case of an NCR level gauge, a dielectric filling member may be arranged in the cavity of the antenna and / or waveguide in order to protect the waveguide / antenna from thermal and chemical effects from the storage tank atmosphere. In the case of a GWR level gauge, the coaxial probe connector includes a dielectric filling member between the coaxial conductors.

[0007] Such a dielectric filling member should be able to transmit microwaves, be chemically resistant, preferably hydrophobic (waterproof), and also need to withstand the temperature and pressure present within the storage tank. Some applications, referred to as high-pressure, high-temperature (HPHT) applications, present particularly challenging situations. One material commonly used for such filling members is PTFE, also known as

[0008] Dielectric filling members are also commonly used as process seals, i.e., to ensure that the contents of the storage tank do not release into the external environment. The process seal can be pressure-sealed. Here, the dielectric filling member, which is also used as a seal, is referred to as a "sealed dielectric filling member".

[0009] In some cases, one or several sealing elements such as O-rings, etc. are arranged between the dielectric filling member and the surrounding structure. Generally, grooves are formed in the dielectric filling member to secure the sealing element, thereby also providing mechanical fixation of the sealed dielectric filling member. As an example, see US 9,291,492. In other cases, a portion of the dielectric filling member itself serves as the sealing element. As an example, see US 6,401,532.

[0010] There are several challenges with such sealed dielectric filling members. One potential problem is that suitable materials such as PTFE have a large coefficient of thermal expansion and will expand at elevated temperatures. Thus, when the filling member contracts, the seal of the sealing element disposed between the filling member and the surrounding structure (e.g., metal) will deteriorate. Similarly, when the filling member contracts, the seal provided by the filling member itself will likely deteriorate.

[0011] Attempts have been made to address this problem. For example, unpublished US patent application 15 / 299,976 discloses a "barrel" type dielectric filling member, where the disk-shaped portion of the barrel serves as the seal. To compensate for any change in thickness, the disk is placed under pressure by means of a spring-loaded clamp. Summary of the Invention

[0012] The object of the present invention is to provide an improved method of combining a dielectric filling member with one or several structural reinforcement elements.

[0013] According to a first aspect of the present invention, this and other objects are achieved by a radar level gauge for determining a process variable of a product in a storage tank using electromagnetic measurement signals, the radar level gauge comprising: a signal propagation means adapted to direct a microwave transmission signal towards the product and return the reflection of the microwave transmission signal from the surface of the product; a dielectric filling member disposed in the signal propagation means to prevent the storage tank contents from entering the signal propagation means; and a sealing means for preventing the storage tank contents from escaping into the external environment. The dielectric filling member comprises a body formed of a polymeric material and at least one structural reinforcement element formed of a modified polymeric material, wherein the modified polymeric material is obtained by modifying the polymeric material with a filler material, and wherein the at least one structural reinforcement element is integrally formed with the body by sintering and forms part of the sealing means.

[0014] According to a second aspect of the present invention, this and other objects are achieved by a method for manufacturing a dielectric filling member for a signal propagation means of a radar level gauge, the method comprising the steps of: forming a body of polymeric material; obtaining a modified polymeric material by modifying the polymeric material with a filler material, the modified polymeric material providing at least 1 dB / cm of microwave attenuation at the operating frequency of the radar level gauge; forming at least one structural reinforcement element of the modified polymeric material; arranging the at least one structural reinforcement element in pressure contact with the body; and heating the body and the at least one structural reinforcement element to an extent that causes the at least one microwave absorbing element to sinter with the body; wherein the at least one structural reinforcement element is designed to act as a sealing means for preventing the storage tank contents from escaping into the external environment.

[0015] The present invention is based on the recognition that a structural reinforcement element made of a modified polymeric material can be sintered to the body. This results in a fully integrated dielectric filling member having a portion with improved mechanical properties. Advantageously, such a portion can be used to provide an improved seal for the storage tank, particularly under (cyclic) high pressure / high temperature conditions. For example, the present invention can be used to form a dielectric filling member having: a chemically resistant surface exposed to the storage tank contents and a structurally robust region for ensuring a satisfactory seal. In some embodiments, the structural reinforcement element is arranged around the outer periphery of the body and forms a groove for receiving a sealing element.

[0016] Thus, an element made of a modified polymer material is "structurally reinforced" compared to a body made of a polymer material. "Structural reinforcement" here means greater resistance to deformation when exposed to mechanical stress. An indicator of mechanical resistance is the Young's modulus, which specifies the elasticity of the material - i.e., the ability of the material to return to its original shape after deformation. The structurally reinforced element is preferably (almost) completely elastic at relevant temperatures and pressures, i.e., it will return to its original shape and form regardless of the duration of the deformation. This means that the structurally reinforced element is not susceptible to cold creeping - i.e., the process by which the element does not return to its original form after being deformed for a long time (but instead "creeps" into a different form).

[0017] The modified polymer material preferably has a Young's modulus that is significantly greater (e.g., at least 50% greater, or even 100% or more greater) than that of the (pure) polymer material. As an example, PTFE has a Young's modulus of about 0.5 GPa.

[0018] The "structurally reinforced" element can also exhibit greater hardness. Hardness can be expressed in Shore D as measured according to the ASTM D2240 standard, or in N / mm 2 as measured, for example, according to the DIN 53456 standard.

[0019] The "structurally reinforced" element can also exhibit higher temperature stability, i.e., less deformation with increasing temperature. An indication of such temperature stability can be a smaller coefficient of thermal expansion.

[0020] As used herein, the term "sintering" refers to the process of joining two elements by pressing them against each other and heating them without melting. Sintering of modified polymer materials such as modified PTFE is known per se. However, the present invention is based on the recognition that several advantages can be achieved in the specific field of dielectric filling members in horn antennas to be arranged in radar level gauges by using sintering to join a body of polymer material with one or several elements made of a modified polymer material.

[0021] More specifically, a very reliable bond is achieved by sintering a body of polymer material (e.g., PTFE) together with one or several structurally reinforced elements made of a modified polymer material (e.g., modified PTFE). Sintering also eliminates the need for adhesives and secures the microwave absorbing elements without the need for additional interfaces.

[0022] The dielectric filling member is made of a dielectric material with appropriate electromagnetic properties so as not to interfere with the operation of the RLG. Additionally, the material should generally be hydrophobic, i.e., waterproof, and preferably chemically resistant to the contents of the storage tank, which are typically petroleum products. It has been found that fluoropolymers have suitable properties, and examples of materials conventionally used as dielectric filling members in radar level gauges include PTFE (polytetrafluoroethylene), PFA (perfluoroalkoxy alkane), and FEP (fluorinated ethylene propylene). These materials have excellent chemical resistance and also have sanitary FDA approval, i.e., they can also be used in highly sanitary processes, such as in the food industry. Among these materials, PTFE is the only one that can withstand high temperatures (above 150 degrees Celsius) and is therefore usually the first choice.

[0023] Note that the polymeric material (such as PTFE) does not necessarily have to be completely pure (the so-called "virgin" grade), but can also be mixed with small amounts of other materials to provide the most suitable mechanical properties.

[0024] The filling materials mixed with the polymeric material to form a modified polymeric material can be glass (fibers or spheres), polymers (such as PEEK), carbon (fibers or coke), metals (such as bronze or stainless steel), or other suitable materials.

[0025] The amount of the filling material needs to be sufficient to provide the desired mechanical properties, such as an increased Young's modulus and / or hardness, but must be small enough to allow sintering of the modified material. As an example, the amount of the filling material is at least 5% by weight, or at least 10% by weight. As another example, the amount of the filling material does not exceed 45% by weight, or even does not exceed 30% by weight.

[0026] In some embodiments, the signal propagation device includes a hollow waveguide structure and a cavity formed within the waveguide structure, and the dielectric filling member is at least partially disposed within the cavity. The hollow waveguide structure can include a horn antenna having a waveguide portion and a horn portion, and the cavity is formed inside the waveguide portion and the horn portion.

[0027] The modified polymeric material may exhibit poor dielectric properties. For example, PTFE modified with PEEK has a significantly higher dielectric constant than "pure" PTFE. In applications where the dielectric filling member is disposed in a hollow waveguide and / or an antenna horn, the structural reinforcement element is therefore preferably placed outside the microwave region, i.e., outside the region where microwave propagation occurs.

[0028] In one example, the body has a generally conical portion that fills the horn section, and an annular flange that extends radially from the base portion of the conical portion. The annular flange forms part of the sealing device and can be clamped between the storage tank connection and the storage tank flange (sometimes called the storage tank nozzle). Then, a structural reinforcement element can form at least a part of the annular flange, making the annular flange more resistant to the applied pressure, thereby providing a more reliable seal.

[0029] In another example, the body has a central portion that fills the waveguide section, and an annular collar portion that extends radially from the central portion. The so-called "annular collar portion" means an impermeable portion that continuously extends from the center of the filling member at least beyond the inner peripheral edge of the annular abutment in the storage tank connection. When pressed against the annular abutment, the collar portion can thus provide a storage tank seal. Such a collar portion can also have an axial extension along the axis of the central portion, so as to have, for example, a conical shape, a bowl shape, or a barrel shape.

[0030] In this case, the annular collar portion forms part of the sealing device and can be clamped between the storage tank connection and one or more waveguide-forming members. Then, a structural reinforcement element can form at least a part of the annular collar portion, making it more resistant to the applied pressure, thereby providing a more reliable seal.

[0031] In other embodiments, the signal propagation device includes a coaxial coupling device having a central conductor, wherein a dielectric filling member surrounds the central conductor. Then, the signal propagation device can further include a transmission line probe electrically connected to the coaxial coupling device, and the transmission line probe is configured to hang in the storage tank and extend into the product.

[0032] In this case, the body can be a dielectric sleeve, and at least one structural reinforcement element can include an inner sleeve coaxially arranged within the body. The inner sleeve can also form a groove for receiving a sealing element, and the sealing element forms part of the sealing device by sealing the dielectric filling member to the central conductor.

[0033] In a similar manner, the body can be a dielectric sleeve, and the at least one structural reinforcement element can include an outer sleeve coaxially arranged outside the body. The outer sleeve can also form a groove for receiving a sealing element, and the sealing element forms part of the sealing device by sealing the dielectric filling member to a surrounding structure such as a storage tank connection.

[0034] By forming the inner sleeve and / or the outer sleeve of a structurally stronger material in which the groove is formed, the sealing effect of the sealing element received in the groove can be improved. Description of the Drawings

[0035] The present invention will be described in more detail with reference to the drawings showing the presently preferred embodiments of the invention.

[0036] Figure 1a Shown is a radar level gauge mounted on a storage tank according to an embodiment of the present invention.

[0037] Figure 1b Shown in more detail Figure 1a is a cross-section of the dielectric filling member in

[0038] Figure 2 is a flow chart of a method for manufacturing a dielectric filling member according to an embodiment of the present invention.

[0039] Figure 3a is a cross-sectional view of a storage tank connection of a non-contact radar level gauge according to an embodiment of the present invention.

[0040] Figure 3b is shown in more detail Figure 3a is a cross-sectional view of the dielectric filling member in

[0041] Figure 4a is a cross-sectional view of a storage tank connection of a guided wave radar (GWR) level gauge according to an embodiment of the present invention.

[0042] Figure 4b is shown in more detail Figure 4a is a cross-sectional view of the dielectric filling member in

[0043] Figure 5a is a cross-sectional view of a storage tank connection of a guided wave radar (GWR) level gauge according to an embodiment of the present invention.

[0044] Figure 5b is shown in more detail Figure 5a is a cross-sectional view of the dielectric filling member in DETAILED DESCRIPTION

[0045] Figure 1a Schematically shown in

[0046] is a radar level gauge (RLG) 1 according to an embodiment of the present invention. The RLG 1 is mounted on a storage tank 2 and is arranged to perform a measurement of a process variable - such as the level L of an interface between two materials in the storage tank 2. Typically, the first material is a product 4 stored in the storage tank, such as a liquid like gasoline or a solid like a granular compound, the second material is air or other atmosphere 5 in the storage tank, and the interface is the surface 3 of the product 4. In some applications, the storage tank is a very large metal storage tank (on the order of 10 meters in diameter). Figure 1aThe transceiver circuit 6, the processing circuit 7, and the signal / power interface 8 are shown very schematically. The transceiver circuit 6, the processing circuit 7, and the interface 8 are arranged in the measurement unit (MU) 10, which is mounted to a storage tank connection piece 12 made of a metallic material, typically steel, and the storage tank connection piece 12 is adapted to be firmly assembled (e.g., bolted or welded) to the storage tank flange 13. The storage tank connection piece 12 is adapted to provide a passage (sometimes pressure-sealed) for electromagnetic signals through the storage tank wall, which passage connects the transceiver circuit 6 to the signal propagation means to allow signals to propagate into the storage tank.

[0047] The signal propagation means includes a waveguide structure, here a directional antenna 11 having a waveguide portion 15 and a horn portion 16. Here the horn portion 16 is formed by the storage tank connection piece 12, but may also be a separate part attached to the storage tank connection piece 12, for example by means of a threaded fitting.

[0048] The transceiver circuit 6 is configured to generate and transmit an electromagnetic (microwave) emission signal S T and to receive an electromagnetic (microwave) return signal S R . A coupling means such as a probe (not shown) is arranged to couple the emission signal from the transceiver circuit 6 into the waveguide portion 15.

[0049] The transceiver circuit 6 may be a single functional unit capable of transmitting and receiving electromagnetic signals, or may be a system comprising separate transmitter and receiver units. The elements of the transceiver circuit 6 are typically implemented in hardware and form part of an integrated unit commonly referred to as a microwave unit. For simplicity, the transceiver circuit will be referred to as the "transceiver" in the following description.

[0050] The processing circuit 7 is configured to determine the distance between a reference position (e.g., the passage between the outside and the inside of the storage tank) at the top of the storage tank and the surface 3 by analyzing the emission signal S T and the return signal S R . The processing typically includes generating a storage tank signal or "echo curve", which includes a plurality of peaks representing echoes from inside the storage tank. One of the peaks represents the echo from the surface 3. Based on the determined distance to the surface 3, which is typically referred to as the ullage, and the known dimensions of the storage tank 5, process variables such as the fill level L of the storage tank can be deduced.

[0051] The processing circuit 7 may include a combination of analog processing implemented in hardware and digital processing implemented by software modules stored in a memory and executed by an embedded processor. The present invention is not limited to a particular implementation, and any implementation found suitable for implementing the functions described herein may be envisaged.

[0052] The interface 8 is configured to allow the transfer of measurement values outside the RLG and is optionally used for the power supply of the RLG. For example, the interface 8 can be a two-wire control loop 9, such as a 4-20 mA loop. The interface 8 can also include a serial data bus to allow communication using digital communication protocols. Examples of available digital protocols include HART, Modbus, Profibus, and Foundation Fieldbus. The interface 8 can also be a wireless interface, such as WirelessHART, in which case the RLG is provided with some kind of internal energy storage, such as a battery 17 that may be solar-powered.

[0053] In use, the transmitted signal S generated by the transceiver T is coupled into the waveguide section 15, allowed to propagate into the horn section 16, and then transmitted into the storage tank. Here, the transmitted signal is a high-frequency signal having an operating frequency range greater than 1 GHz. Generally, the operating frequency range is centered around approximately 6 GHz or 26 GHz, where the bandwidth is 1 GHz or a few GHz. The transmitted signal S T propagates towards the surface 3 of the product 4 and generates an electromagnetic return signal S by reflection at the surface 3 R . The return signal is returned through the antenna 11, allowed to propagate through the waveguide section, and coupled back to the transceiver through the coupling means. In other words, the directional antenna 11 is arranged to act as an adapter to transmit a freely propagating electromagnetic wave into the storage tank 2 to be reflected by the interface, where the interface is the surface 3 of the product 4 in the storage tank 2. An RLG with a directional antenna is commonly referred to as a non-contact radar (NCR) level gauge.

[0054] According to one measurement principle, the transmitted signal is a continuous signal with a varying frequency (frequency-modulated continuous wave, FMCW). The FMCW-based RLG will transmit a radar sweep with a gradually changing frequency and mix the received signal with the original signal (homodyne mixing) to form a frequency-domain tank signal.

[0055] According to another measurement principle, the transmitted signal is a series of different pulses with a duration on the order of ns and a repetition frequency on the order of MHz. In a process called time-domain reflectometry (TDR), the return signal is sampled using the original pulse sequence in a sample-and-hold circuit to form a time-domain tank signal. When time-domain reflectometry is used in an NCR level gauge, the pulses need to be frequency-modulated to allow transmission using a directional antenna.

[0056] The transmitted signal can also be some combination of FMCW and pulse signals. For example, a principle called multi-frequency pulse wave (MFPW) has been proposed.

[0057] In the case of a frequency-domain tank signal, the amplitude of the tank signal is represented as a function of frequency, where the frequency is related to the distance from a reference position. In the case of a time-domain tank signal, the amplitude of the tank signal is represented as a function of time, where the time is related to the distance from a reference position.

[0058] Figure 1b The microwave-transmissive dielectric filling member 20, shown more clearly in [reference], is disposed at least partially within the cavity 19 formed by the waveguide section 15 and the horn section 16. The filling member 20 serves to protect the antenna horn from the thermal and chemical effects of the tank atmosphere 5. The filling member 20 is preferably made of a chemically resistant and waterproof material, such as a fluoropolymer. In the present example, the polymeric material is PTFE selected for its temperature resistance.

[0059] Referring to Figure 1b , here the filling member 20 has a cylindrical portion 22 adapted to fit within the waveguide section 15 and a conical portion 23 adapted to fit within the horn section 16. The base 24 of the conical portion - i.e., the surface facing the interior of the tank - may have a convex shape so as to shape the radar beam of the transmitted wave in a beneficial manner and also to facilitate the dripping of condensate formed on the filling member.

[0060] The filling member 20 may also be provided with a groove 26 extending around the outer periphery of the conical portion 22. The groove is adapted to receive an annular sealing element 27, such as an O-ring. The O-ring may also be used to mechanically fix the filling member 20 within the cavity 19.

[0061] To seal the tank, the filling member 20 may be provided with an annular flange 25 (sometimes referred to as a gasket) that projects from the intersection of the convex base 24 and the conical portion 23. When the LRG 1 is mounted to the tank, the flange 25 is clamped between the tank connector 12 and the tank flange 13, thereby providing a seal between the tank 2 and the cavity 19. Such a seal is commonly referred to as a "tank seal" or a "process seal".

[0062] According to an embodiment of the present invention, the member 20 is formed by a body 21 and a structural reinforcement element 30. Here, the element 30 is an annular disc forming the flange 25.

[0063] Referring to Figure 2 , the dielectric filling member 20 is manufactured by the following process.

[0064] First, in step S1, the body 21 is formed from a first polymeric material having suitable properties - here PTFE. The first polymeric material may be substantially pure (virgin PTFE), but may alternatively be modified PTFE, i.e., PTFE mixed with a certain proportion of non-polymeric material such as glass in order to provide suitable mechanical properties.

[0065] When using PTFE, the body is typically formed by the following operations: First, a blank with an appropriate basic shape is formed by compression molding, and then the blank is machined into its final shape. The compression molding of PTFE involves filling a mold cavity with a relatively simple shape with PTFE resin (powder), and then using a hydraulic compression mold. As mentioned, in order to provide suitable mechanical properties, the PTFE resin can be mixed with a small amount of particles such as glass particles. The details of compression molding and other molding processes are known in the art. The molded (and possibly machined) blank is allowed to sit for up to several days to allow any air trapped in the molded blank to escape.

[0066] In step S2, a modified polymer material is obtained by mixing a polymer resin such as PTFE resin with a filler material, which is typically in powder form. The filler material is selected such that the modified polymer material has a greater structural strength than the first polymer material, i.e., is less prone to deformation, for example, has a greater hardness or elasticity. For example, the modified polymer material can have a Young's modulus that is at least 50% greater, or even 100% or more greater, than that of the first polymer. For reference, PTFE has a Young's modulus of approximately 0.5 GPa.

[0067] For example, the filler material can be a suitable polymer such as PEEK (polyetheretherketone), glass fiber, or carbon. Other materials including metal particles are also possible.

[0068] The proportion of the filler material will depend on the filler material and the desired properties. Most importantly, the proportion must be large enough to obtain the required mechanical strength (e.g., Young's modulus) and small enough to allow the modified polymer material to sinter with the polymer material. As an example, for non-metallic materials, the proportion of the filler material can be in the range of 5 - 40% by weight. For metallic materials (heavier), the proportion of the filler material may be in the range of 40 - 60% by weight.

[0069] The following table shows examples of filler materials and suitable mixing ratios.

[0070]

[0071] In step S3, a structural reinforcement element 30 (here, an annular disk intended to form the flange 25) is formed from the modified polymer material. Techniques similar to those used to form the body 21 - for example, compression molding and appropriate machining - can be used to form the element 30. The element 30 can also be formed by sintering.

[0072] In step S4, pressure is applied by arranging the element 30 in pressing contact with the body 21, and in step S5, heat is applied to cause the structural reinforcement element 30 to sinter to the body. As mentioned above, sintering here refers to bonding without melting. Although the steps of applying pressure and temperature are shown here as separate steps, note that pressure can also be continued to be applied in step S5 such that pressure and temperature are applied simultaneously to effect bonding by sintering. The sintering cycle - i.e., the sequence of temperature and duration - can be up to 10 hours or longer, even up to or exceeding 50 hours, depending on the size of the element 30.

[0073] After the element 30 has been sintered to the body, additional machining may be required in step S5 to bring the dielectric filling member 20 to its final shape.

[0074] Figure 3a Another embodiment of the storage tank connection 112 for a non-contact RLG is shown. The storage tank connection 112 has a central channel 113 that forms part of a waveguide structure. The cylindrical portion 113a of the channel 113 forms the waveguide portion 115, while the lower outwardly tapered portion 113b of the channel 113 forms the upper portion 116a of the horn portion. Here, the lower portion 116b of the horn portion is formed by a separate conical portion of a fitting 114 attached to the storage tank connection 112. In some applications, a storage tank connection adapter 117 is used to adapt the inner diameter of the channel 113.

[0075] The dielectric filling member 120 is disposed in the waveguide portion 115. Figure 3b The filling member 120, shown in more detail herein, has a central cigar-shaped portion 122 and an annular collar portion 125. In the case shown, the collar portion 125 has a barrel shape including a disc-shaped portion 125a and a cylindrical portion 125b. Here, the barrel-shaped collar portion 125 has an opening facing away from the interior of the storage tank, but in other embodiments, it can face the interior of the storage tank. The central portion 122 has a tapered lower end 122a that extends into the tapered portion 113b of the channel 113. Details and benefits of such a "barrel" design of the filling member 120 are discussed in US 9,212,941, which is incorporated herein by reference.

[0076] The filling member 120 is held in place by an outer waveguide forming member 118, which is typically made of a conductive material the same as that of the storage tank connection 112. The member 118 has an opening 100 through which a connecting pin 119 extends. The pin 119 held in place by the metal element 118 is used to prevent the relatively soft dielectric waveguide filling member 120 from being pushed out of the channel 113 by the pressure inside the storage tank, particularly during periods of elevated temperature.

[0077] Refer toFigure 3b , the cylindrical portion 125b of the collar portion 125 forms a groove 126 for receiving a sealing element such as an O-ring 127. The sealing element provides a seal for the storage tank. To provide a more reliable seal, the cylindrical portion 125b is formed here by a structural reinforcement element 130 which has been attached to the central portion (body) 122 by sintering. The sintering process and the choice of materials are the same as those described above with reference to Figure 2 the content discussed.

[0078] It is important to note that the structural reinforcement element 130 (i.e., the cylindrical portion 125b here) can have waveguide characteristics different from those of the body of the filling member (i.e., the central portion 122). Therefore, preferably, the structural reinforcement element is located outside the microwave region, i.e., at a radial distance from the waveguide portion 115 where microwaves will not penetrate. Thus, the dielectric properties of the element 130 forming part of the collar portion 125 here have no adverse effect on the performance of the radar level gauge.

[0079] Figures 4a to 4b and Figures 5a to 5b shows two types of tank connectors for a radar level gauge in which the signal propagation device 10 includes a probe 12 - i.e., a transmission line extending into the tank contents. In this case, the transmitted signal and the echo signal will propagate along the probe until they are reflected by an impedance discontinuity caused by the surface 3. The RLG with a probe is sometimes called a guided wave radar (GWR) level gauge. Several types of probes can be used, such as single-wire (Goubau type) probes, coaxial probes, and two-wire probes. The probes can be substantially rigid or flexible, and they can be made of metal such as stainless steel, plastic such as PTFE, or a combination thereof.

[0080] The upper end of the probe is attached to the top of the tank and is connected to the transceiver via a sealed tank feedthrough. The tank feedthrough - which can also be considered to form part of the signal propagation device - is usually filled with a dielectric filling member that provides a seal for the tank.

[0081] Figure 4a shows a first example of a tank connector 212 for a probe. The probe is not shown in Figure 4a but it is intended to be connected to the lower end 202a of the conductive probe connector 202. The probe connector 202 is suspended by a dielectric sleeve 203 which is installed in the central opening 204 of the tank connector 212. Here the sleeve 203 is formed by two separate parts - an inner (lower) sleeve 203a and an outer (upper) sleeve 203b. The inner dielectric sleeve 203a is in contact with the interior of the tank and is therefore usually made of a chemically resistant material such as PTFE.

[0082] Inner sleeve 203a is formed with groove 226a on its exterior and groove 226b on its interior for receiving sealing elements such as O-ring 227a and O-ring 227b respectively. The sealing elements provide a tank seal along both the probe connector 202 and the interior of the tank connector 212.

[0083] In order to provide a more reliable seal, the portion of the sleeve 203a forming the grooves 226a and 226b is formed by one or more structural reinforcement elements 230. Figure 4b In the example shown, the sleeve 203a is formed of five annular members 205a-205e. The innermost annular member 205a, the middle annular member 205c and the uppermost annular member 205e are all made of the first polymer material, while the middle annular members 205b and 205d are structural reinforcement elements 230 made of modified polymer material. The five annular members 205a-205e are sintered together to form the sleeve 203a. The sintering process and material selection are similar to those described above with reference to Figure 2 The content discussed.

[0084] Figure 5a A second example of a tank connection 312 for a probe is shown. Again, the probe is not Figure 5a 303a, but it is intended to be connected to the lower end 302a of the conductive probe connector 302. The probe connector 302 is suspended by a dielectric sleeve 303, which is mounted in the central opening 304 of the tank connection 312. The sleeve 303 is here formed of two separate parts - an inner (lower) part 303a and an outer (upper) part 303b. The inner dielectric part 303a is in contact with the inside of the tank and is therefore typically made of a chemically resistant material such as PTFE. The outer part 303b is typically made of a structurally stronger material so as to withstand pressure without deforming.

[0085] Here the inner part 303a is formed as two coaxial but axially displaced sleeves. The inner part 303a is formed with a groove 326a on its exterior and a groove 326b on its interior for receiving sealing elements such as O-rings 327a and 327b, respectively. The sealing elements provide sealing of the tank both along the probe connector 302 and along the interior of the tank connection 312.

[0086] In order to provide a more reliable seal, the portion of the part 303a forming the grooves 326a and 326b is formed by structural reinforcement elements 330a and 330b. Figure 5bIn the example shown, the inner part 303a is formed by a body in the form of a dielectric sleeve 305 and two structural reinforcement sleeves 330a and 330b. The first outer sleeve 330a forms a radially and axially extending collar portion. The second inner sleeve 330b forms a lining for the body dielectric sleeve 305. The three sleeves 305, 330a, and 330b are sintered together to form the inner part 303a of the filler member 303. The sintering process and the selection of materials are similar to those discussed above with reference to Figure 2 the content described.

[0087] In addition, the outer part 303b of the dielectric sleeve 303, which is typically formed as a separate component, is also formed here as another structural reinforcement element 330c, which can also be sintered together with the body 305 and the structural reinforcement elements 330a and 330b. Alternatively, two or even all three of the structural reinforcement elements 330a, 330b, and 330c can be integrally formed before being sintered to the body 305.

[0088] Note that the structural reinforcement element 330c does not form part of any sealing device, but rather forms a rigid part of the dielectric filler member, thus ensuring the fixed position of the filler member. This application is a separate application of the inventive concept, but is not covered by this claim. This application will not be transferred, but may be the subject of a future divisional application.

[0089] Those skilled in the art will recognize that the present invention is in no way limited to the preferred embodiments described above. On the contrary, within the scope of the appended claims, many modifications and variations are possible. For example, depending on the exact application, the shape and configuration of the filler member and the structural reinforcement element can be different from the example shown.

Claims

1. A radar level gauge for determining a process variable of a product in a storage tank using electromagnetic measurement signals, comprising: A signal propagation device adapted to direct a microwave emission signal towards the product and return a reflection of the microwave emission signal from the surface of the product; A dielectric filling member disposed in the signal propagation device to prevent the storage tank contents from entering the signal propagation device; And A sealing device for preventing the storage tank contents from escaping into the external environment; The dielectric filling member includes: A body formed of a polymer material, and At least one structural reinforcement element formed of a modified polymer material, wherein the modified polymer material is obtained by modifying the polymer material with a filler material, Wherein the at least one structural reinforcement element is integrally formed with the body by sintering and forms part of the sealing device; Wherein the signal propagation device includes a hollow waveguide structure and a cavity formed within the waveguide structure, and wherein the dielectric filling member is at least partially disposed within the cavity; Wherein the structural reinforcement element is located radially outside the microwave region of the hollow waveguide structure; Wherein the hollow waveguide structure includes a horn antenna having a waveguide portion and a horn portion, and the cavity is formed within the waveguide portion and / or the horn portion; Wherein the body has a central portion filling the waveguide portion and an annular collar portion radially extending from the central portion, and the annular collar portion forms part of the sealing device, Wherein the structural reinforcement element forms at least a part of the annular collar portion.

2. The radar level gauge according to claim 1, wherein, The polymer material is a fluoropolymer.

3. The radar level gauge according to claim 1, wherein, The filler material is selected from the group consisting of glass fiber, PEEK, carbon, and metal particles.

4. The radar level gauge according to claim 1, wherein, The filler material constitutes at least 5% by weight of the modified polymer material.

5. The radar level gauge according to claim 1, wherein, The filler material constitutes at least 10% by weight of the modified polymer material.

6. The radar level gauge according to claim 1, wherein, The filler material constitutes less than 45% by weight of the modified polymer material.

7. The radar level gauge according to claim 1, wherein, The filler material constitutes less than 30% by weight of the modified polymer material.

8. The radar level gauge according to any one of the preceding claims, wherein, The at least one structural reinforcement element is disposed around the outer periphery of the body and forms a groove for receiving a sealing element.

9. The radar level gauge according to claim 1, wherein, The annular collar portion further has an axial extension along the axis of the central portion.

10. The radar level gauge according to claim 9, wherein, The annular collar portion is barrel-shaped, having a disk-shaped portion radially extending outward from the central portion and a cylindrical portion coaxial with the central portion.

11. The radar level gauge according to claim 1, wherein, The signal propagation device includes a coaxial coupling device having a central conductor, and wherein the dielectric filling member surrounds the central conductor.

12. The radar level gauge according to claim 11, wherein, The body is a dielectric sleeve, and the at least one structural reinforcement element includes an inner sleeve coaxially disposed within the dielectric sleeve, and the inner sleeve forms a groove for receiving a sealing element.

13. The radar level gauge according to claim 11, wherein, The body is a dielectric sleeve, and the at least one structural reinforcement element includes an outer sleeve coaxially disposed outside the dielectric sleeve, and the outer sleeve forms a groove for receiving a sealing element.

14. The radar level gauge according to claim 13, wherein, The outer sleeve is axially displaced relative to the body.

15. The radar level gauge according to claim 11, wherein, The body and the at least one structural reinforcement element are formed by at least two first annular members made of the polymeric material and at least one second annular member made of the modified polymeric material, with at least one of the at least one second annular member sandwiched between two of the at least two first annular members.

16. The radar level gauge according to claim 11, wherein, The signal propagation device includes a transmission line probe electrically connected to the coaxial coupling device, the transmission line probe being configured to be suspended in the storage tank and extend into the product.

17. The radar level gauge according to claim 2, wherein, The polymeric material is PTFE.

18. A method for manufacturing a dielectric filling member of a signal propagation device for a radar level gauge, comprising the steps of: Forming a body of polymeric material; Obtaining a modified polymeric material by modifying the polymeric material with a filler material, the modified polymeric material providing at least 1 dB / cm of microwave attenuation at the operating frequency of the radar level gauge; Forming at least one structural reinforcement element of the modified polymeric material; Arranging the at least one structural reinforcement element in pressure contact with the body; And Heating the body and the at least one structural reinforcement element to an extent that causes the at least one structural reinforcement element to sinter with the body, wherein the at least one structural reinforcement element is designed to act as a sealing device for preventing the contents of the storage tank from escaping to the external environment; wherein the body has a central portion of a waveguide portion filling a hollow waveguide structure of the signal propagation device, and an annular collar portion radially extending from the central portion, the annular collar portion forming part of the sealing device, wherein the structural reinforcement element forms at least part of the annular collar portion and is located radially outside the microwave region of the hollow waveguide structure.

19. The method according to claim 18, wherein, The polymeric material is a fluoropolymer.

20. The method according to claim 18, wherein, The filler material is selected from the group consisting of glass fibers, PEEK, carbon, and metal particles.

21. The method according to claim 18, wherein, The filler material constitutes at least 5% by weight of the modified polymeric material.

22. The method according to claim 18, wherein, The filler material constitutes at least 10% by weight of the modified polymeric material.

23. The method according to claim 18, wherein The filler material constitutes less than 45% by weight of the modified polymeric material.

24. The method according to claim 18, wherein The filler material constitutes less than 30% by weight of the modified polymeric material.

25. The method according to claim 19, wherein, The polymeric material is PTFE.

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