SEALING DIELECTRIC FILLING MEMBER WITH MECHANICALLY REINFORCED ELEMENT

Abstract

A radar level gauge comprising a signal propagation device, a dielectric filling member arranged in the signal propagation device, and a sealing arrangement for preventing tank content from escaping into the outside environment. The dielectric filling member includes a main body formed of a polymer material, and at least one structurally reinforced element formed of a modified polymer material providing, the modified polymer material being obtained by modifying the polymer material with a filler material, wherein the at least one structurally reinforced element is integrally formed with the main body by sintering, and forms part of the sealing arrangement.

The present invention is based on the realization that a structurally reinforced element, made of a modified polymer material, may be integrated into the main body by sintering.

Claims

1. A radar level gauge, for determining a process variable of a product in a tank using electromagnetic measuring signals, comprising: a signal propagation device adapted to direct a microwave transmit signal toward said product and return reflections thereof from a surface of said product; a dielectric filling member arranged in said signal propagation device to prevent entry of tank content into the signal propagation device; and a sealing arrangement for preventing tank content from escaping into the outside environment; said dielectric filling member including: a main body formed of a polymer material, and at least one structurally reinforced element formed of a modified polymer material providing, said modified polymer material being obtained by modifying said polymer material with a filler material, wherein said at least one structurally reinforced element is integrally formed with said main body by sintering, and forms part of said sealing arrangement.

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

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

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

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

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

8. The radar level gauge according to claim 1, wherein said at least one structurally reinforced element is arranged around a periphery of said main body and forms a groove for receiving a sealing element.

9. The radar level gauge according to claim 1, wherein said signal propagation device includes a hollow wave guiding structure and a cavity formed inside said wave guiding structure, and wherein said dielectric filling member is arranged at least partly within said cavity.

10. The radar level gauge according to claim 9, wherein said structurally reinforced element is located radially outside a microwave zone of said hollow waveguide structure.

11. The radar level gauge according to claim 9, wherein said hollow wave guiding structure includes a horn antenna having a waveguide section and a horn section, said cavity being formed inside said waveguide section and/or said horn section.

12. The radar level gauge according to claim 11, wherein said main body has a substantially conical portion filling said horn section, and an annular flange extending radially from a base portion of said conical portion, said annular flange forming part of said sealing arrangement, wherein said structurally reinforced element forms at least part of said annular flange.

13. The radar level gauge according to claim 11, wherein said main body has a center portion filling said waveguide section, and an annular collar portion extending radially from said center portion, said annular collar portion forming part of said sealing arrangement, wherein said structurally reinforced element forms at least part of said annular collar portion.

14. The radar level gauge according to claim 13, wherein said collar portion also has an axial extension along an axis of the center portion.

15. The radar level gauge according to claim 14, wherein the collar portion is bucket-shaped, with a disc-shaped portion extending radially out from the center portion, and a cylindrical portion coaxial with the center portion.

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

17. The radar level gauge according to claim 16, wherein said main body is a dielectric sleeve, and said at least one structurally reinforced element includes an inner sleeve arranged coaxially inside said dielectric sleeve, said inner sleeve forming a groove for receiving a sealing element.

18. The radar level gauge according to claim 16, wherein said main body is a dielectric sleeve, and said at least one structurally reinforced element includes an outer sleeve arranged coaxially outside said dielectric sleeve, said outer sleeve forming a groove for receiving a sealing element.

19. The radar level gauge according to claim 18, wherein said outer sleeve is axially displaced with respect to said main body.

20. The radar level gauge according to claim 16, wherein said main body and said at least one structurally reinforced element are formed by at least two first annular members made of said polymer material, and at least one second annular member made of said modified polymer material, at least one of said at least one first annular members being sandwiched between two of said at least two second annular members.

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

22. A method for manufacturing a dielectric filling member for a signal propagation device of a radar level gauge, including the steps: forming a main body of a polymer material, obtaining a modified polymer material by modifying said polymer material with a filler material, said modified polymer material providing a microwave attenuation of at least 1 dB/centimeter at an operating frequency of the radar level gauge, forming at least one structurally reinforced element of said modified polymer material, arranging said at least one structurally reinforced element in pressurized contact with said main body, and heating said main body and said at least one structurally reinforced element to such an extent that said at least one microwave absorbing element is sintered with said main body, wherein said at least one structurally reinforced element is designed to serve as sealing arrangement for preventing tank content from escaping into an outside environment.

23. The method according to claim 22, wherein said polymer material is a fluoropolymer, preferably PTFE.

24. The method according to claim 22, wherein said filler material is selected from the group consisting of glass fiber, PEEK, carbon and metal particles.

25. The method according to claim 22, wherein said filler material constitutes at least 5% by weight of the modified polymer material.

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

27. The method according to claim 22, wherein said filler material constitutes less than 45% by weight of the modified polymer material.

28. The method according to claim 22, wherein said filler material constitutes less than 30% by weight of the modified polymer material.

29. The method according to claim 22, wherein said at least one structurally reinforced element is arranged around a periphery of said main body and forms a groove for receiving a sealing element.

30. The method according to claim 22, wherein said main body has a substantially conical portion intended to fill a horn section of a directional antenna, and an annular flange extending radially from a base portion of said conical portion, said annular flange forming part of said sealing arrangement, wherein said structurally reinforced element forms at least part of said annular flange.

31. The method according to claim 22, wherein said main body has a center portion filling a waveguide section of said signal propagation device, and an annular collar portion extending radially from said center portion, said annular collar portion forming part of said sealing arrangement, wherein said structurally reinforced element forms at least part of said annular collar portion.

32. The method according to claim 22, wherein said dielectric filling member is formed to surround a central conductor of a coupling arrangement forming part of the signal propagation device.

33. The method according to claim 32, wherein said main body is a dielectric sleeve, and said at least one structurally reinforced element includes an inner sleeve arranged coaxially inside said dielectric sleeve, said inner sleeve forming a groove for receiving a sealing element.

34. The method according to claim 32, wherein said main body is a dielectric sleeve, and said at least one structurally reinforced element includes an outer sleeve arranged coaxially outside said dielectric sleeve, said outer sleeve forming a groove for receiving a sealing element.

35. The method according to claim 34, wherein said outer sleeve is axially displaced with respect to said main body.

36. The method according to claim 32, wherein said main body and said at least one structurally reinforced element are formed by at least two first annular members made of said polymer material, and at least one second annular member made of said modified polymer material, at least one of said at least one first annular members being sandwiched between two of said at least two second annular members.

101-132. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

[0036] FIG. 1a shows a radar level gauge according to an embodiment of the present invention, mounted on a tank.

[0037] FIG. 1b shows a cross-section of the dielectric filling member in FIG. 1a in more detail.

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

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

[0040] FIG. 3b is a cross section view showing the dielectric filling member in FIG. 3a in more detail.

[0041] FIG. 4a is a cross section view of a tank connection of a guided wave radar (GWR) level gauge according to an embodiment of the invention.

[0042] FIG. 4b is a cross section view showing the dielectric filling member in FIG. 4a in more detail.

[0043] FIG. 5a is a cross section view of a tank connection of a guided wave radar (GWR) level gauge according to an embodiment of the invention.

[0044] FIG. 5b is a cross section view showing the dielectric filling member in FIG. 5a in more detail.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0045] A radar level gauge (RLG) 1 according to an embodiment of the present invention is illustrated schematically in FIG. 1a. The RLG 1 is mounted on a tank 2, and arranged to perform measurements of a process variable such as the level L of an interface between two materials in the tank 2. Typically, the first material is a product 4 stored in the tank, e.g. a liquid such as gasoline, or a solid such as a granular compound, the second material is air or other atmosphere 5 in the tank, while the interface is the surface 3 of the product 4. In some applications, the tank is a very large metal tank (diameter in the order of ten meters).

[0046] The radar level gauge 1 includes transceiver circuitry 6, processing circuitry 7 and a signal/power interface 8, illustrated very schematically in FIG. 1. The transceiver circuitry 6, processing circuitry 7 and interface 8 are arranged in a measurement unit (MU) 10 mounted to a tank connection 12 made of a metal material, typically steel, which is adapted to be securely fitted (e.g. bolted or welded) to a tank flange 13. The tank connection 12 is adapted to provide a passage (sometimes pressure sealed) for electromagnetic signals through the wall of the tank, which passage connects the transceiver circuitry 6 with a signal propagation device, for allowing signals to propagate into the tank.

[0047] The signal propagation device includes a wave guiding structure, here a directional antenna 11 with a waveguide section 15 and a horn section 16. The horn section 16 is here formed by the tank connection 12, but may also be a separate part attached to the tank connection 12, e.g. by means of a threaded fitting.

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

[0049] The transceiver circuitry 6 may be one 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 circuitry 6 are typically implemented in hardware, and form part of an integrated unit normally referred to as a microwave unit. For simplicity, the transceiver circuitry is referred to as the transceiver in the following description.

[0050] The processing circuitry 7 is configured to determine the distance between a reference position at the top of the tank (such as the passage between the outside and the inside of the tank) and the surface 3 by analyzing the transmit signal S.sub.T and the return signal S.sub.R. The processing typically includes generation of a tank signal or echo curve, including a plurality of peaks representing echoes from the interior of said tank. One of the peaks represent an echo from the surface 3. Based on the determined distance to the surface 3, generally referred to as ullage, and known dimensions of the tank 5, a process variable such as the filling level L of the tank can be deduced.

[0051] The processing circuitry 7 may include a combination of analogue processing realized in hardware, and digital processing realized embodied by software modules stored in a memory and executed by an embedded processor. The invention is not restricted to the particular realization, and any implementation found suitable to realize the herein described functionality may be contemplated.

[0052] The interface 8 is configured to allow communication of a measurement value externally of the RLG and optionally for power supply of the RLG. For example, the interface 8 may be a two-wire control loop 9, such as a 4-20 mA loop. The interface 8 may also include a serial data bus, allowing communication using a digital communication protocol. Examples of available digital protocols include HART, Modbus, Profibus and Foundation Fieldbus. The interface 8 may also be a wireless interface, employing e.g. wireless HART, in which case the RLG is provided with some sort of internal energy store, such as a battery 17, possibly solar powered.

[0053] In use, the transmit signal S.sub.T generated by the transceiver is coupled into the waveguide section 15, allowed to propagate to the horn section 16 and then emitted into the tank. The transmit signal is here a high frequency signal, with an operating frequency range greater than 1 GHz. Typically, the operating frequency range is centered around 6 GHz or 26 GHz, with a band-width of one or several GHz. The transmit signal S.sub.T is propagated towards the surface 3 of the product 4 and the electromagnetic return signal S.sub.R is caused by a reflection in the surface 3. The return signal is returned by the antenna 11, allowed to propagate through the waveguide section and is coupled back to the transceiver by the coupling arrangement. In other words, the directional antenna 11 is arranged to act as an adapter, transmitting free propagating electromagnetic waves into the tank 2 to be reflected by the interface, here the surface 3 of the product 4 in the tank 2. An RLG with a directional antenna is often referred to as a non-contact radar (NCR) level gauge.

[0054] According to one measuring principle, the transmit signal is a continuous signal with varying frequency (frequency modulated continuous wave, FMCW). An FMCW based RLG will emit a radar sweep with gradually varying 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 transmit signal is a train of distinct pulses with a duration in the order of ns and a repletion frequency in the order of MHz. The return signal is sampled with the original pulse train in a sample and hold circuit in a process known as time domain reflectometry (TDR), thereby forming a time domain tank signal. When time domain reflectometry is used in a NCR level gauge, the pulses need to be frequency modulated to allow emission with the directional antenna.

[0056] The transmit signal may also be some combination of FMCW and a pulsed signal. For example, a principle known as multiple frequency pulsed wave (MFPW) has been proposed.

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

[0058] A microwave transmissive dielectric filling member 20, shown more clearly in FIG. 1b, is arranged at least partly 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 against thermal and chemical impact of the tank atmosphere 5. The filling member 20 is preferably made of a chemically resistant and water repellant material, such as a fluoropolymer. In the present example, the polymer material is PTFE (Teflon), chosen for its temperature resistance.

[0059] With reference to FIG. 1b, the filling member 20 here has a cylindrical portion 22 adapted to fit in the waveguide section 15, and a conical portion 23 adapted to fit in 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 in order to shape the radar beam of emitted waves in a beneficial manner, and also promote dripping of condensate formed on the filling member.

[0060] The filling member 20 may further be provided with a groove 26 extending around the periphery of the conical portion 22. The groove is adapted to receive a ring-formed sealing element 27, such as an O-ring. An O-ring may also be employed to mechanically fixate the filling member 20 in the cavity 19.

[0061] In order to seal the tank, the filling member 20 may be provided with an annular flange 25 (sometimes referred to as a gasket), protruding from where the convex base 24 meets the conical portion 23. When the LRG 1 is mounted to the tank, the flange 25 is sandwiched between the tank connection 12 and the tank flange 13, thereby providing a sealing of tank 2 and cavity 19. Such sealing is often 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 main body 21 and a structurally reinforced element 30. Here, the element 30 is an annular disc which forms the flange 25.

[0063] With reference to FIG. 2, the dielectric filling member 20 is manufactured by the following process.

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

[0065] When using PTFE, the main body is typically formed by first forming a blank having an appropriate basic shape by means of compression molding, and then machining this blank to its final shape. Compression molding of PTFE includes filling a PTFE resin (powder) into a die cavity of relatively simple shape, and then compressing the die using a hydraulic press. As mentioned, in order to provide appropriate mechanical properties, the PTFE resin may be mixed with small amounts of particles, such as glass particles. Details of compression molding, as well as other molding processes, are known in the art. The molded (and possibly machined) blank is allowed to rest for up to a few days, in order for any air trapped in the molded blank to escape.

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

[0067] As an example, the filler material may be a suitable polymer, such as PEEK (polyether ether ketone), glass fiber, or carbon. Also other materials, including metal particles, are possible.

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

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

TABLE-US-00001 Stainless Glass Bronze steel (fiber/ Polymer Soft Coke- Carbon (irregular (irregular Properties balls) (PEEK) carbon carbon fiber particles) particles) Mixing fraction 10% 10% 10% 10% 10% 40% 50% (min) (by weight) Mixing fraction 40% 25% 35% 35% 15% 60% 60% (max) (by weight)

[0070] In step S3, a structurally reinforced element 30 (here an annular disc intended to form the flange 25) is formed of the modified polymer material. The element 30 may be formed using a similar technique as that used for forming the main body 21, e.g. compression molding and appropriate machining. It may also be formed by sintering.

[0071] In step S4 pressure is applied by arranging the element 30 in pressurized contact with the main body 21, and in step S5 heat is applied such that the structurally reinforced element 30 is sintered with the main body. As mentioned above, sintering here refers to an integration without melting. Although the steps of applying pressure and temperature are here illustrated as separate steps, it is noted that pressure continues to be applied also in step S5, such that pressure and temperature are applied simultaneously in order to achieve integration by sintering. The sintering cyclei.e. the sequence of temperatures and durationsmay be as long as 10 hours or more, even up to or exceeding 50 hours, depending on the size of the element 30.

[0072] After the element 30 has been sintered with the main body, additional machining may be required in step S5 for the dielectric filling member 20 to take on its final shape.

[0073] FIG. 3a shows a further embodiment of a tank connection 112 for a non-contact RLG. The tank connection 112 has a central channel 113 forming part of a wave guiding structure. A cylindrical part 113a of the channel 113 forms a wave guide section 115, while a lower, outwardly tapered part 113b of the channel 113 forms an upper part 116a of the horn section. A lower part 116b of the horn section is here formed by a separate conical part attached to a fitting 114 of the tank connection 112. In some applications, the inner diameter of the channel 113 is adapted using a tank connection adaptor 117.

[0074] A dielectric filling member 120 is arranged in the waveguide section 115. The filling member 120, which is shown in more detail in FIG. 3b, has a central, cigar-shaped portion 122 and an annular collar portion 125. In the illustrated case, the collar portion 125 has a bucket-shape with a disc-shaped portion 125a and a cylindrical portion 125b. The bucket-shaped collar portion 125 here has an opening facing away from the tank interior, but in other embodiments it may face towards the tank interior. The central portion 122 has a tapered lower end 122a which extends into the tapered portion 113b of the channel 113. Details and benefits with such a bucket design of the filling member 120 are discussed in U.S. Pat. No. 9,212,941, hereby incorporated by reference.

[0075] The filling member 120 is held in place by an outer wave guide forming member 118, typically made of the same electrically conducting material as the tank connection 112. The member 118 has an opening 100 through which a connection pin 119 extends. The pin 119 held in place by the metal element 118 serves to prevent that a relatively soft dielectric wave guide filling member 120 is forced out of the channel 113 by the pressure inside the tank, in particular during conditions of elevated temperatures.

[0076] With reference to FIG. 3b, the cylindrical part 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 sealing of the tank. In order to provide a more reliable sealing, the cylindrical part 125b is here formed by a structurally reinforced element 130, which has been attached to the central portion (main body) 122 by sintering. The choice of materials and sintering process is the same as discussed above with reference to FIG. 2.

[0077] It is important to note that the structurally reinforced element 130 (i.e. here the cylindrical part 125b), may have different wave guiding properties than the main body of the filling member (i.e. the central portion 122). It is therefore preferred that the structurally reinforced element is located outside the microwave zone, i.e. at a radial distance from the waveguide section 115 where the microwaves will not penetrate. The dielectric properties of the element 130, here forming part of the collar portion 125, are therefore not detrimental to the performance of the radar level gauge.

[0078] FIGS. 4a-b and 5a-b illustrate two types of tank connections for radar level gauges where the signal propagation device 10 includes a probe 12, i.e. a transmission line extending into the content of the tank. In this case the transmit signal and echo signal will propagate along the probe until they are reflected by the impedance discontinuity caused by the surface 3. An RLG with a probe is sometimes referred to as guided wave radar (GWR) level gauge. Several types of probes, for example single-line (Goubau-type), coaxial, and twin-line probes may be used. The probes may be essentially rigid or flexible and they may be made from metal, such as stainless steel, plastic, such as PTFE, or a combination thereof.

[0079] The upper end of the probe is attached to the roof of the tank, and connected to the transceiver via a sealed tank feed through. This tank feed through, which also can be considered to form part of the signal propagation device, is typically filled by a dielectric filling member which provides a tank seal.

[0080] FIG. 4a shows a first example of a tank connection 212 for a probe. The probe is not shown in FIG. 4a, but is intended to be connected to the lower end 202a of an electrically conducting probe connector 202. The probe connector 202 is suspended by a dielectric sleeve 203, which is fitted in the central opening 204 of the tank connection 212. The sleeve 203 is here formed by two separate pieces, an inner (lower) sleeve 203a and an outer (upper) sleeve 203b. The inner dielectric sleeve 203a is in contact with the tank interior, and is therefore typically made of a chemically resistant material such as PTFE.

[0081] The inner sleeve 203a is formed with grooves 226a on its outside and 226b on its inside for receiving sealing elements such as O-rings 227a and 227b respectively. The sealing elements provide sealing of the tank, both along the probe connector 202 and along the inside of the tank connection 212.

[0082] In order to provide a more reliable sealing, the parts of the sleeve 203a forming the grooves 226a and 226b is here formed by one or several structurally reinforced elements 230. In the example illustrated in FIG. 4b, the sleeve 203a is formed by five annular members 205a-e. The innermost annular member 205a, the middle annular member 205c, and the uppermost annular member 205e are all made of a first polymer material, while the intermediate annular members 205b and 205d are the structurally reinforced elements 230 made of a modified polymer material. The five annular members 205a-e are sintered together to form the sleeve 203a. The choice of materials and sintering process is analogous to that discussed above with reference to FIG. 2.

[0083] FIG. 5a shows a second example of a tank connection 312 for a probe. Again, the probe is not shown in FIG. 5a, but is intended to be connected to the lower end 302a of an electrically conducting probe connector 302. The probe connector 302 is suspended by a dielectric sleeve 303, which is fitted in a central opening 304 of the tank connection 312. The sleeve 303 is here formed by two separate pieces, an inner (lower) piece 303a and an outer (upper) piece 303b. The inner dielectric piece 303a is in contact with the tank interior, and is therefore typically made of a chemically resistant material such as PTFE. The outer piece 303b is typically made of a structurally stronger material, in order to withstand pressure without being deformed.

[0084] The inner piece 303a is here formed as two coaxial but axially displaced sleeves. The inner piece 303a is formed with grooves 326a on its outside and 326b on its inside 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 inside of the tank connection 312.

[0085] In order to provide a more reliable sealing, the parts of the piece 303a forming the grooves 326a and 326b are here formed by structurally reinforced elements 330a and 330b. In the example illustrated in FIG. 5b, the inner piece 303a is formed by a main body in the form of a dielectric sleeve 305, and two structurally reinforced sleeves 330a and 330b. The first, outer sleeve 330a forms a radially and axially extending collar portion. The second, inner sleeve 330b forms an inner lining of the main body dielectric sleeve 305. The three sleeves 305, 330a and 330b are sintered together to form the inner piece 303a of the filling member 303. The choice of materials and sintering process is analogous to that discussed above with reference to FIG. 2.

[0086] Additionally, also the outer piece 303b of the dielectric sleeve 303, which is conventionally formed as a separate part, is here formed as another structurally reinforced element 330c, which also may be sintered together with the main body 305 and the structurally reinforced elements 330a and 330b. Alternatively, two of the structurally reinforced elements 330a, 330b and 330c, or even all three, may be integrally formed before being sintered to the main body 305.

[0087] It is noted that the structurally reinforced element 330c does not form part of any sealing arrangement, but rather forms a rigid part of the dielectric filling member, ensuring a fixed position of the filling member. This application is a separate application of the inventive concept, although not covered by the present claims. This application is not surrendered, but may be made the subject of a future divisional application.

[0088] The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For example, the shape and form of the filling member and the structurally reinforced elements may be different than the illustrated examples, depending on the exact application.