Radar level gauge system with improved feedthrough

Abstract

A radar level gauge system is provided, which includes: a transceiver; an antenna for radiating an electromagnetic emission signal from the transceiver towards the surface of the product and for returning an electromagnetic reflection signal towards the transceiver; a feedthrough connecting the transceiver and the antenna; and a processing circuit coupled to the transceiver for determining the fill level based on the relationship between the emission signal and the reflection signal, wherein the feedthrough includes a waveguide disposed between the transceiver and the antenna to receive the emission signal from the transceiver and guide the emission signal towards the antenna along a guiding direction, the waveguide including an elongated plug disposed in a hollow conductor extending along the guiding direction, wherein the plug includes a non-conductive sleeve member and a metal plug member, and the non-conductive sleeve member is sealingly engaged to a part of the hollow conductor and sealingly engaged to the metal plug member.

Description

Technical Field

[0001] The present invention relates to a radar level gauge system and a method of manufacturing a radar level gauge system. Background Art

[0002] Radar level gauge (RLG) systems are widely used to determine the fill level of a product in a storage tank. Radar level gauging is typically performed by non-contact measurement or by contact measurement, commonly known as guided wave radar (GWR), where, in non-contact measurement, an electromagnetic signal is radiated towards the product contained in the storage tank, and in contact measurement, the electromagnetic signal is guided towards and into the product through a probe acting as a waveguide. Typically, the probe is arranged to extend vertically from the top to the bottom of the storage tank.

[0003] An electromagnetic emission signal is generated by a transceiver and propagated towards the surface of the product in the storage tank, and an electromagnetic reflection signal resulting from the reflection of the emission signal at the surface is propagated back to the transceiver.

[0004] Based on the relationship between the emission signal and the reflection signal, the distance to the surface of the product can be determined.

[0005] In some applications, non-contact radar level gauge systems are used to measure the fill level in storage tanks having high pressure and / or high temperature conditions inside the storage tank. In such applications, there are special requirements for components of the radar level gauge system facing the inside of the storage tank, for example.

[0006] For example, US 2002 / 0053238 describes coupling a microwave signal from a control unit to an antenna via a waveguide. To provide a temperature and pressure resistant seal, US 2002 / 0053238 discloses welding a ceramic waveguide filler along a weld seam into a ferrite sleeve.

[0007] Level gauging using a high-frequency non-contact radar level gauge system has several advantages, such as simple installation, a narrow beam angle, and a longer measurement range. However, modifying the configuration described in US 2002 / 0053238 to high frequencies (e.g., >20 GHz) results in a very narrow waveguide. Using a typical ceramic waveguide filler, the diameter of the waveguide connecting the transceiver and the antenna can be as small as 3.5 mm or less.

[0008] Feeding an antenna with such a small-diameter waveguide increases the risk of the antenna being blocked by material (e.g., product or condensate). In addition, for example, narrow ceramic waveguide fillers are sensitive to handling, increasing production costs and / or making the operation and maintenance of the radar level gauge system more difficult and time-consuming. Summary of the Invention

[0009] In view of the above, a general object of the present invention is to provide an improved radar level gauge system, in particular an improved non-contact high-frequency radar level gauge system for applications with high temperature and / or high pressure inside a storage tank.

[0010] Accordingly, in a first aspect of the present invention, there is provided a radar level gauge system for determining the filling level of a product in a storage tank, the radar level gauge system comprising: a transceiver for generating, transmitting and receiving electromagnetic signals within a frequency range having a center frequency; an antenna for radiating an electromagnetic transmission signal from the transceiver towards the surface of the product for returning an electromagnetic reflection signal generated by the reflection of the electromagnetic transmission signal at the surface towards the transceiver; a feedthrough connecting the transceiver and the antenna; and a processing circuit coupled to the transceiver for determining the filling level based on the relationship between the transmission signal and the reflection signal, wherein the feedthrough comprises a waveguide arranged between the transceiver and the antenna to receive the transmission signal from the transceiver and guiding the transmission signal towards the antenna along a guiding direction, the waveguide comprising an elongated plug arranged in a hollow conductor extending along the guiding direction, wherein the plug comprises a non-conductive sleeve member and a metal plug member, the non-conductive sleeve member being sealingly joined to a part of the hollow conductor and sealingly joined to the metal plug member.

[0011] The non-conductive sleeve member being "sealingly joined" to a part of the hollow conductor and "sealingly joined" to the metal plug member should be understood to mean that the connection between the non-conductive sleeve member and the part of the hollow conductor and the connection with the metal plug member are airtight. Advantageously, the connection can meet the requirements of applicable standards such as the international standard IEC 60079-1.

[0012] The "part" of the hollow conductor may constitute a part of the hollow conductor or the entire hollow conductor.

[0013] The "transceiver" can be a single functional unit capable of transmitting and receiving electromagnetic signals, or can be a system comprising separate transmitter and receiver units.

[0014] It should be noted that the processing circuit can be provided as a single device or several devices cooperating together.

[0015] The electromagnetic transmission signal can advantageously be a microwave signal. For example, the transmission signal can be frequency and / or amplitude modulated on a carrier within the microwave frequency range.

[0016] Examples of antennas include horn antennas and parabolic antennas, etc.

[0017] The present invention is based on the recognition that a composite plug including a metal plug member can be manufactured to have a cross-sectional area much larger than that of a conventional ceramic plug. For example, the lateral dimension (e.g., the diameter of a circular cross-section) can be manufactured to be approximately three times larger. This reduces the risk of blockage while retaining the desired characteristics of a conventional plug.

[0018] According to an embodiment, a non-conductive sleeve member can be arranged to electrically isolate the hollow conductor from the metal plug member.

[0019] Advantageously, the non-conductive sleeve member can be made of a ceramic material (e.g., Al 2 O 3 ). A particularly suitable ceramic material can be so-called ZTA (zirconia toughened alumina). This material and other suitable ceramic materials are well known per se to those skilled in the relevant art. Alternatively, the non-conductive sleeve member can be made of any other non-conductive material (e.g., glass) capable of withstanding the expected operating conditions of a particular application. However, from a production perspective, ceramic materials (e.g., the aforementioned ZTA) are advantageous.

[0020] Furthermore, according to various embodiments, the inner surface of the non-conductive sleeve member can be sealingly joined to the metal plug member; and, the outer surface of the non-conductive sleeve member can be sealingly joined to the portion of the hollow conductor. In an embodiment, the non-conductive sleeve member can be shaped such that its outer surface sealingly joins both the metal plug member and the portion of the hollow conductor.

[0021] To provide an increase in the desired lateral dimension (perpendicular to the guiding direction), the maximum dimension of the metal plug member in a direction perpendicular to the guiding direction can be at least half of the maximum dimension of the non-conductive sleeve member in a direction perpendicular to the guiding direction.

[0022] In various embodiments, the hollow conductor can have a substantially circular cross-section with respect to a plane perpendicular to the guiding direction. In such an embodiment, the non-conductive sleeve member can have an outer circular cross-section at least in a portion thereof, which is received by the hollow conductor to facilitate a sealing joint between the outer surface of the non-conductive sleeve member and the surface of the hollow conductor portion. In this case, the above-mentioned maximum lateral dimension can be the diameter.

[0023] According to an example, for a center frequency of the transmitted signal of about 26 GHz, the maximum diameter of the metal plug member can be about 8 mm, while the maximum diameter of the non-conductive sleeve member (in this case a ceramic sleeve member) can be about 11 mm. For comparison, for a center frequency of the transmitted signal of about 26 GHz, the maximum diameter of a conventional pure ceramic plug can be about 3.5 mm.

[0024] In an embodiment, the non-conductive sleeve member may be sealingly joined to the metal plug member in such a way that a physical or chemical bond is formed between the non-conductive sleeve member and the metal plug member.

[0025] The non-conductive sleeve member may advantageously be joined to the metal plug member by brazing, which is itself a well-known method of joining dielectrics (e.g., ceramics and metals).

[0026] Similarly, the non-conductive sleeve member may advantageously be joined to the said portion of the hollow conductor by brazing.

[0027] According to various embodiments, a radar level gauge system may include: a first metering component and a second metering component joined to the first metering component; and a metal sealing member, which includes: an inner peripheral portion that constitutes the said portion of the hollow conductor; and an outer peripheral portion that is sealingly joined to the first metering component.

[0028] In these embodiments, a sealed joint between the non-conductive sleeve member and the said portion of the hollow conductor may be achieved by sealingly joining the non-conductive sleeve member to the metal sealing member. Then, the metal sealing member may be sealingly joined to the first metering component.

[0029] Since the metal sealing member can be made much smaller and lighter than the first metering component, dedicated equipment can be used to reasonably and conveniently form a sealing assembly for forming a sealed joint between the non-conductive sleeve member and the metal sealing member. For example, the non-conductive sleeve member and the inner peripheral portion of the metal sealing member may advantageously be sealingly joined by brazing. During the assembly of the radar level gauge system, the plug assembly may be sealingly joined to the first metering component by sealingly joining the outer peripheral portion of the metal sealing member to the first metering component, advantageously by welding. The isolation between the inner peripheral portion and the outer peripheral portion of the metal sealing member can help reduce the risk of loss of the previously formed sealed joint between the non-conductive sleeve member and the inner peripheral portion of the metal sealing member due to heat from the process of joining the plug assembly to the first metering component. Additionally, during the operation of the radar level gauge system, using a separate metal sealing member instead of directly brazing a non-conductive (e.g., ceramic) sleeve member to a bulkier metering component reduces the stress induced on the relatively sensitive ceramic sleeve member due to the difference in the coefficients of thermal expansion between the metal part (usually made of stainless steel) and the ceramic sleeve member.

[0030] It should be noted that various configurations of the metal sealing member may advantageously depend on the application and other design considerations, provided that there is a gap between the inner peripheral portion and the outer peripheral portion. For example, the inner peripheral portion and the outer peripheral portion may be in the same plane, or the inner peripheral portion and the outer peripheral portion may be offset from each other in the guiding direction.

[0031] By offsetting the inner peripheral portion and the outer peripheral portion with respect to each other in the guiding direction, there is more space available for sealingly joining the outer peripheral portion of the metallic sealing member to the first metering member, which can facilitate the production of the radar level gauge system according to an embodiment of the present invention. The reduction of the above thermal stress can also be further reduced.

[0032] Furthermore, either or both of the inner peripheral portion and the outer peripheral portion of the metallic sealing member can advantageously extend in the guiding direction.

[0033] One of the first metering member and the second metering member can be configured to attach the radar level gauge system to the storage tank. To reduce the risk of leakage from the storage tank, the first metering member can advantageously be configured to attach the radar level gauge system to the storage tank such that the joining between the outer peripheral portion and the first metering member can be used to conveniently seal the storage tank when installing the radar level gauge system.

[0034] To conveniently provide a seal between the inside and the outside of the storage tank, the metallic sealing member can advantageously be joined to the first metering member by welding, and the welding can advantageously be a continuous weld. For example, the weld can be formed by laser welding to a depth of at least 1 mm.

[0035] Furthermore, according to various embodiments, the metallic plug member can include: a first pin member that is sealingly joined to the non-conductive sleeve member; and a second pin member that is attached to the first pin member in such a way that the second pin portion is conductively connected to the first pin member.

[0036] By providing the metallic plug member as two parts, there is more space available for sealingly joining the outer peripheral portion of the metallic sealing member to the first metering member, which can facilitate the production of the radar level gauge system according to an embodiment of the present invention.

[0037] The first part of the metallic plug member of the elongated plug can face the antenna, and the second part of the metallic plug member of the elongated plug can face the transceiver.

[0038] The center frequency of the transmitted signal can be higher than 20 GHz.

[0039] The antenna can be a horn-shaped antenna, and the non-conductive sleeve member and the metallic plug member can extend into the antenna.

[0040] According to a second aspect of the present invention, there is provided a method of manufacturing a radar level gauge system, the method comprising the steps of: providing a first metering member; providing a second metering member configured to engage with the first metering member; providing a sealing device comprising a metallic sealing member having an inner peripheral portion and an outer peripheral portion, and an elongate plug sealingly engaged to the inner peripheral portion of the metallic sealing member; attaching the sealing device to the first metering member by sealingly engaging the outer peripheral portion of the metallic sealing member to the first metering member; and engaging the first metering member and the second metering member.

[0041] It should be noted that the above steps need not be performed in any particular order.

[0042] According to an embodiment, the attaching step may include welding the outer peripheral portion of the metallic sealing member to the first metering member.

[0043] Welding between the non-conductive sleeve member and the metallic plug member and with the inner peripheral portion in combination with the dielectric-metal seal can provide area isolation by means of a so-called single seal. To this end, the welding step may provide a continuous weld meeting the requirements of applicable standards, such as the international standard IEC 60079-1 or similar standards.

[0044] According to various embodiments, the metallic plug member may include: a first pin member sealingly engaged to the non-conductive sleeve member; and a second pin member, and the method may further include the step of attaching the second pin member to the first pin member in such a way that the second pin member is conductively connected to the first pin member.

[0045] The step of attaching the second pin member to the first pin member may advantageously be carried out after the step of attaching the sealing device to the first metering member.

[0046] Additional effects and variations of the second aspect of the present invention are to a large extent similar to those described above with reference to the first aspect of the present invention.

[0047] Accordingly, in general, the present invention relates to a radar level gauge system, the radar level gauge system comprising: a transceiver; an antenna for radiating an electromagnetic emission signal from the transceiver towards the surface of the product and for returning an electromagnetic reflection signal towards the transceiver; a feedthrough connecting the transceiver and the antenna; and a processing circuit coupled to the transceiver for determining a fill level based on the relationship between the emission signal and the reflection signal, wherein the feedthrough comprises a waveguide arranged between the transceiver and the antenna to receive the emission signal from the transceiver and to guide the emission signal towards the antenna along a guiding direction, the waveguide comprising an elongated plug arranged in a hollow conductor extending along the guiding direction, wherein the plug comprises a non-conductive sleeve member and a metal plug member, the non-conductive sleeve member being sealingly engaged to a portion of the hollow conductor and being sealingly engaged to the metal plug member. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] These and other aspects of the invention will now be described in more detail with reference to the drawings showing currently preferred embodiments of the invention, in which:

[0049] Figure 1 A process monitoring system including a radar level gauge system according to an example embodiment of the invention is schematically shown;

[0050] Figure 2 is schematically shown Figure 1 a block diagram of the radar level gauge system in;

[0051] Figure 3 is Figure 1 a schematic side view of the radar level gauge system in;

[0052] Figure 4 is schematically shown Figure 3 a cross-sectional view of the feedthrough of the radar level gauge system in;

[0053] Figure 5 is included in Figure 4 a schematic cross-sectional view of a first example configuration of a sealing device in the feedthrough in;

[0054] Figures 6A to 6C Schematic views of other example configurations of the sealing device are shown;

[0055] Figure 7 is a flowchart schematically showing a manufacturing method according to an embodiment of the invention; and

[0056] Figures 8A to 8B is according to Figure 7 a schematic view of the method of. DETAILED DESCRIPTION

[0057] In this detailed description, various embodiments of the radar level gauge system according to the present invention are discussed mainly with reference to a battery-powered radar level gauge system having wireless communication capabilities.

[0058] It should be noted that this in no way limits the scope of the present invention. For example, the scope of the present invention also includes, among other things, radar level gauge systems not included in a process management system or radar level gauge systems powered by loop power or using dedicated power lines.

[0059] Figure 1 An example embodiment of a process monitoring system 1 including a plurality of field devices is schematically shown. The process monitoring system 1 includes a radar level gauge system 2 and a temperature sensing device 3 wirelessly connected to a host system 4. The radar level gauge system 2 includes a measurement electronics unit 10 arranged outside a storage tank 7, an antenna 5 arranged inside the storage tank 7, and a feedthrough 15 connecting the measurement electronics unit 10 and the antenna 5.

[0060] Both the radar level gauge system 2 and the temperature sensor 3 are arranged on a storage tank containing a product 8 to be measured.

[0061] To reduce the energy consumption of the radar level gauge system 2, at least a part of the radar level gauge system can be operated intermittently, and energy can be stored during inactive or idle periods for use during active periods.

[0062] For example, solutions for intermittent operation and energy storage are described in US 7,952,514, US 8,477,064, and US 8,688,279, and the entire content of each of these documents is incorporated herein by reference.

[0063] Referring to Figure 2 , Figure 1 the radar level gauge system 2 in Figure 2 includes a measurement unit (MU) 210, a wireless communication unit (WCU) 211, and a local energy storage device in the form of a battery 212. The wireless communication unit 211 can advantageously comply with WirelessHART (IEC 62591). As schematically shown in T and R , the MU 210 includes a transceiver 213 and a measurement processor 220. The transceiver 213 can be controlled by the measurement processor 220 to generate, transmit, and receive electromagnetic signals having a frequency within a defined frequency bandwidth (e.g., 24 GHz to 27 GHz). The measurement processor 220 is coupled to the transceiver 213 to determine the fill level in the storage tank 7 based on the relationship between the transmitted signal S

[0064] As in Figure 2As schematically shown, the measurement unit 210 includes a first output 214, a second output 215, and a first input 216. The first output 214 is connected via a first dedicated line to the first input 217 of the wireless communication unit 211, the second output 215 is connected to the second input 218 of the wireless communication unit 211, and the first input 216 is connected via a second dedicated line to the first output 219 of the wireless communication unit 211. The second output 215 of the measurement unit 210 and the second input 218 of the wireless communication unit 211 may be configured to process bi-directional data communication according to a serial or parallel communication protocol to enable data exchange between the measurement unit 210 and the wireless communication unit 211. The communication between the measurement unit 210 and the wireless communication unit 211 using different inputs / outputs is described in more detail in US 8,970,395, the entire content of which is incorporated herein by reference.

[0065] The above examples of wireless and locally powered configurations are intended to provide a detailed example to those skilled in the art of how to implement various aspects and embodiments of the radar level gauge system according to the present invention. However, it should be noted that there are many other ways to power and interface with the radar level gauge system. Such other ways are generally acceptable to those of ordinary skill in the art and can be implemented without undue experimentation or excessive burden.

[0066] Figure 3 is Figure 1 a side view of the radar level gauge system 2 in Figure 3 Referring to Figure 3 as schematically shown, the radar level gauge system 2 includes a measurement and communication unit 13, a feedthrough 15, a process connection 17, and an antenna 5. The process connection 17 (here a flange) is provided for attaching the radar level gauge system to an opening provided in the storage tank 7, and the feedthrough 15 connects the transceiver in the measurement and communication unit 13 to the antenna 5. As

[0067] schematically shown in

[0068] Figure 4 is mainly showing the inclusion in Figure 3Partial cross-sectional view of the feedthrough 15 in an embodiment of the radar level gauge system 2 in []. Refer to Figure 4 , the feedthrough 15 includes a waveguide 19 arranged between a transceiver ( Figure 4 not shown in []) and the antenna 5 to receive the transmitted signal from the transceiver and guide the transmitted signal along the guiding direction r g (indicated by the arrow 21 in Figure 4 ) towards the antenna 5. As Figure 4 schematically shown in [], the waveguide 19 includes a sealing device 24, and the sealing device 24 includes an elongated plug 23 arranged in a hollow conductor 25 extending along the guiding direction r g .

[0069] Figure 5 is a schematic cross-sectional view of the sealing device 24 in the feedthrough 15 included in Figure 4 , refer to Figure 5 , the above part of the hollow conductor 25 is constituted by the inner peripheral part 31 of the metal sealing member 33, and the metal sealing member 33 further includes an outer peripheral part 35. Figure 4 The shown elongated plug 23 includes a non-conductive sleeve member 27 and a metal plug member 29 including a first part 29a and a second part 29b. The non-conductive sleeve member 27 provided in the form of a ceramic sleeve made of ZTA (zirconia toughened alumina) here is hermetically joined to the inner peripheral part 31 of the metal sealing member 33 by brazing, and is hermetically joined to the first part 29a of the metal plug member 29, thereby providing a storage tank seal resistant to high temperature and high pressure in the feedthrough 15. The second part 29b of the metal plug member 29 can be attached to the first part 29a of the metal plug member 29 to be in conductive contact with the first part 29a. As Figure 4 schematically shown in [], and as will be described in more detail below, the outer peripheral part 35 of the metal sealing member 33 is hermetically joined to the first metering member 16 by continuous welding.

[0070] Figures 6A to 6C Schematically shows other exemplary configurations of the sealing device 24, which may be included in various embodiments of the radar level gauge system 2 according to the present invention.

[0071] First refer to Figure 6A , the main difference between the sealing device 24 and the Figure 5 sealing device configuration in [] is that: the outer peripheral part 35 of the metal sealing member 33 and the inner peripheral part 31 are substantially in the same plane, and the metal plug member 29 is provided as a single piece instead of two separate pieces that can be joined together. Figure 6A The configuration of the sealing device in [] may facilitate welding the outer peripheral part 35 to the first metering member 16 (or the second metering member 18). The metering part may need to be adapted to metal sealing members 33 of different configurations.

[0072] Turn to Figure 6B , the metal sealing member 33 has been configured to implement an additional function of the antenna 5 (or the antenna adapter). This configuration of the metal sealing member can provide for a reduction in the number of components of the radar level gauge system 2 and can thus potentially provide for a reduction in production costs.

[0073] In Figure 6C the example configuration, both the first sealing joint 37 between the ceramic sleeve member 27 and the inner peripheral portion 31 of the metal sealing member 33 and the second sealing joint 39 between the ceramic sleeve member 27 and the first metal pin portion 29a are on the outer surface of the ceramic sleeve member 27. This can provide a more reasonable process for forming the first sealing joint 37 and the second sealing joint 39, for example, by soldering.

[0074] Although various embodiments have now been described in which the elongated plug 23 is sealingly joined to the metal sealing member 33 and the inner peripheral portion 31 of the metal sealing member 33 forms part of the hollow conductor 25 in the feedthrough 15, it should be noted that alternatively, the elongated plug 23 can be sealingly directly joined to, for example, the first metering member 16 or the second metering member 18.

[0075] The following will refer to Figure 7 the flow chart in Figures 8A to 8B and the schematic diagram in

[0076] to describe an embodiment of a method for manufacturing a feedthrough according to the present invention. Figure 8A In a first step S1, with additional reference to

[0077] , the first metering member 16 is provided. In this example embodiment, the first metering member 16 includes a process connection in the form of a flange. The first metering member 16 also includes the upper part of the antenna 5. Figure 3 In a second step S2, the second metering member 18 is provided. The second metering member 18 is configured to be joined to the first metering member 16 by a nut 22 as shown in, for example, Figure 3 . The second metering member 18 includes a waveguide 19 for guiding microwave signals between the transceiver ( Figure 8A the measurement and communication unit 13 shown in) and the antenna 5. In

[0078] the example embodiment, the second metering member 18 is relatively long so as to keep the components in the measurement and communication unit 13 away from the heat inside the storage tank 7. Figure 5The partial seal device 24 is provided in the manner of the described example configuration. The first pin member 29a is brazed to the ceramic sleeve member 27, and then the ceramic sleeve member 27 is brazed to the inner peripheral portion 31 of the metal seal member 33.

[0079] In a subsequent step S4, the partial seal device 24 is inserted into the first metering member 16, and the outer peripheral portion 35 of the metal seal member 33 is welded to the first metering member 16. This is Figure 8B schematically shown in by a laser beam 41. As a result of the welding operation, a circumferential weld 43 is formed. The ceramic-metal connection between the ceramic sleeve member 27 and the inner peripheral portion 31 of the metal seal member 33, the ceramic-metal connection with the first pin member 29a, and this weld 43 form part of the gas-tight seal of the feedthrough 15.

[0080] In the next step S5, the second pin member 29b is attached to the first pin member 29a to achieve electrical contact between the first pin member 29a and the second pin member 29b.

[0081] Thereafter, in step S6, the first metering member 16 is joined to the second metering member 18, and finally, in step S7, the measurement and communication unit 13 is attached to the top of the second metering member 18 to form the final Figure 3 radar level gauge system 2 in.

[0082] Those skilled in the art should recognize that the present invention is in no way limited to the above preferred embodiments. On the contrary, many modifications and variations within the scope of the appended claims are possible.

Claims

1. A radar level gauge system for determining the filling level of a product in a storage tank, comprising: a transceiver configured to generate, transmit, and receive electromagnetic signals within a frequency range having a center frequency; an antenna configured to radiate an electromagnetic transmission signal from the transceiver towards the surface of the product and to return an electromagnetic reflection signal towards the transceiver, the electromagnetic reflection signal being generated by the reflection of the electromagnetic transmission signal at the surface; a feedthrough connecting the transceiver and the antenna; and a processing circuit coupled to the transceiver and configured to determine the filling level based on the relationship between the transmission signal and the reflection signal, wherein the feedthrough includes a waveguide disposed between the transceiver and the antenna to receive the transmission signal from the transceiver and to guide the transmission signal towards the antenna along a guiding direction, the waveguide including an elongate plug disposed within a hollow conductor extending along the guiding direction, wherein the elongate plug includes a non-conductive sleeve member and a metallic plug member, the non-conductive sleeve member being sealingly engaged to a portion of the hollow conductor and being sealingly engaged to the metallic plug member.

2. The radar level gauge system according to claim 1, wherein the non-conductive sleeve member is arranged to electrically isolate the hollow conductor from the metallic plug member.

3. The radar level gauge system according to claim 1 or 2, wherein the non-conductive sleeve member is made of a ceramic material.

4. The radar level gauge system according to claim 1 or 2, wherein: the inner surface of the non-conductive sleeve member is sealingly engaged to the metallic plug member; and the outer surface of the non-conductive sleeve member is sealingly engaged to the portion of the hollow conductor.

5. The radar level gauge system according to claim 1 or 2, wherein the maximum dimension of the metallic plug member in a direction perpendicular to the guiding direction is at least half of the maximum dimension of the non-conductive sleeve member in a direction perpendicular to the guiding direction.

6. The radar level gauge system according to claim 1 or 2, wherein the hollow conductor has a substantially circular cross-section with respect to a plane perpendicular to the guiding direction.

7. The radar level gauge system according to claim 1 or 2, wherein the non-conductive sleeve member is engaged to the metallic plug member in such a way that a physical or chemical bond is formed between the non-conductive sleeve member and the metallic plug member.

8. The radar level gauge system according to claim 1 or 2, wherein the non-conductive sleeve member is joined to the metallic plug member by soldering.

9. The radar level gauge system according to claim 1 or 2, wherein the non-conductive sleeve member is engaged to the portion of the hollow conductor in such a way that a physical or chemical bond is formed between the non-conductive sleeve member and the portion of the hollow conductor.

10. The radar level gauge system according to claim 1 or 2, wherein the non-conductive sleeve member is joined to the portion of the hollow conductor by soldering.

11. The radar level gauge system according to claim 1 or 2, wherein The radar level gauge system includes: A first metering member and a second metering member joined to the first metering member; and A metal sealing member, including: An inner peripheral portion that constitutes the portion of the hollow conductor; and An outer peripheral portion that is sealingly joined to the first metering member.

12. The radar level gauge system according to claim 11, wherein, The outer peripheral portion of the metal sealing member is sealingly joined to the first metering member by welding.

13. The radar level gauge system according to claim 11, wherein, The outer peripheral portion is spaced apart from the inner peripheral portion in the guiding direction.

14. The radar level gauge system according to claim 11, wherein, The outer peripheral portion extends in the guiding direction.

15. The radar level gauge system according to claim 1 or 2, wherein, The metal plug member includes: A first member that is sealingly joined to the non-conductive sleeve member; and A second member that is attached to the first member in such a way that the second member is conductively connected to the first member.

16. The radar level gauge system according to claim 15, wherein, The first member faces the antenna, and the second member faces the transceiver.

17. The radar level gauge system according to claim 1 or 2, wherein, The center frequency is higher than 20 GHz.

18. The radar level gauge system according to claim 1 or 2, wherein, The antenna is a horn antenna.

19. The radar level gauge system according to claim 1 or 2, wherein, The non-conductive sleeve member and the metal plug member extend into the antenna.

20. A method of manufacturing a radar level gauge system, including the following steps: Providing a first metering member; Providing a second metering member configured to be joined to the first metering member; Providing a sealing device, the sealing device including: A metal sealing member having an inner peripheral portion and an outer peripheral portion; and An elongated plug that is sealingly joined to the inner peripheral portion of the metal sealing member; Attaching the sealing device to the first metering member by sealingly joining the outer peripheral portion of the metal sealing member to the first metering member; and Joining the first metering member and the second metering member, wherein the plug includes a metal plug member and a non-conductive sleeve member, the non-conductive sleeve member being sealingly joined to the metal plug member and sealingly joined to the inner peripheral portion of the metal sealing member.

21. The method according to claim 20, wherein, The attaching step includes welding the outer peripheral portion of the metal sealing member to the first metering member.

22. The method according to claim 21, wherein: The metal plug member includes: A first pin member that is sealingly joined to the non-conductive sleeve member; and A second pin member, The method further includes the following steps: Attaching the second pin member to the first pin member in such a way that the second pin member is conductively connected to the first pin member.

23. The method according to claim 22, wherein, The step of attaching the second pin member to the first pin member is performed after the step of attaching the sealing device to the first metering member.

24. The method according to claim 20 or 21, wherein: the first metering member is one of a measurement electronic component including a transceiver for generating, transmitting, and receiving electromagnetic signals and a storage tank mounting member for attaching to a storage tank; and the second metering member is the other of a measurement electronic component including a transceiver for generating, transmitting, and receiving electromagnetic signals and a storage tank mounting member for attaching to the storage tank.

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