Fill level sensor for detecting the fill level of a filling medium in a container

Abstract

The present invention shows and describes a fill level sensor for detecting the fill level of a filling medium. The fill level sensor comprises a generator with a feed line, an antenna, a feeder, and a controller. The generator is designed to generate electromagnetic waves having a resonant frequency and output the electromagnetic waves via the feed line, the feed line having a line impedance with a line impedance value, and the feeder is arranged between the feed line and the antenna. The present invention is based on the object of specifying a fill level sensor with increased sensitivity. This object is achieved in that the feeder comprises a resonant circuit; the resonant circuit and the antenna jointly have a resonant input impedance, and the resonant circuit converts the resonant input impedance at the resonant frequency into a real impedance with a predetermined resonant impedance value; and the antenna has an antenna resonant frequency that differs from the resonant frequency.

Description

Technical Field

[0001] The invention relates to a fill level sensor for detecting the fill level of a filling medium in a container.

[0002] The material level sensor comprises a generator with a feed line, an antenna, a feeder and a controller. The generator, antenna, feeder and controller are important components of the material level sensor.

[0003] The generator is designed not only to generate electromagnetic waves having a resonant frequency but also to output the electromagnetic waves via a feed line. In this case, the feed line has a line impedance having a line impedance value.

[0004] The feeder is arranged between the feeder line and the antenna and is configured to transmit electromagnetic waves from the feeder line to the antenna. The feeder is, for example, another feeder line.

[0005] The antenna is designed to radiate electromagnetic waves into a container containing a filling medium.

[0006] The electromagnetic waves are transmitted from the feed line via the feeder toward the antenna along a transmission direction. The electromagnetic waves radiated by the antenna have a propagation direction that substantially coincides with the transmission direction.

[0007] The controller is configured to detect changes in a near field around the antenna caused by changes in the filling level of the filling medium in the container and to detect the filling level of the filling medium in the container by analyzing the detected changes in the near field.

[0008] Here, the near field is formed by electromagnetic waves radiated by the antenna, and changes in the near field occur due to changes in the filling medium level in the container. Due to changes in the filling medium level, other media surrounding the antenna, such as air, is replaced by the filling medium, or vice versa. If the filling medium and the other medium have different dielectric constants, changes in the filling medium level surrounding the antenna cause changes in the antenna's near field. This is assumed in the following text.

[0009] Changes in the antenna's near field also cause changes in the antenna's adaptation, resulting in a change in the reflected power over frequency. Therefore, to detect the fill level of the filling medium in a container, either the absolute reflected power at a single frequency or the reflected power curve over frequency can be used. However, using the absolute reflected power at a single frequency is susceptible to tolerances and ambient conditions. This is not the case with the reflected power curve over frequency, and it also allows differentiation between different filling media when they have different dielectric constants. Background Art

[0010] From the prior art, for example, known material level sensors include a planar patch antenna as an antenna connected to a surface wave resonator. Here, the patch antenna is a half-wavelength resonator. Also known are material level sensors that use a quarter-wavelength resonator as an antenna. A disadvantage of these level sensors is their sensitivity to changes in the near field surrounding the antenna. This sensitivity only ensures the detection of the material level of filling media whose dielectric constant is greater than a certain dielectric constant value, making these level sensors unsuitable for filling media with smaller dielectric constants. Particularly in small containers, the patch antenna also produces parasitic resonances, making it difficult to detect the material level of the medium in the container. Furthermore, it is difficult to achieve a highly sensitive patch antenna that is separate from the medium in the container. Summary of the Invention

[0011] It is therefore an object of the present invention to specify a fill level sensor with increased sensitivity, such that it is also suitable for media with a low dielectric constant.

[0012] This object is achieved by the fill level sensor according to the invention.

[0013] In the fill level sensor according to the present invention, the feeder has a resonant circuit. The resonant circuit and the antenna share a resonant input impedance in the transmission direction. The resonant circuit converts the resonant input impedance at the resonant frequency into a real impedance with a predetermined resonant impedance value. The antenna has an antenna resonant frequency that differs from the resonant frequency. The near field of the antenna is not influenced by the fill medium, but is instead surrounded by another medium or a vacuum. The other medium is preferably air. It should be taken into account that the other medium and the fill medium have different dielectric constants. If the conversion previously performed was performed using air as the other medium and the fill medium has a greater dielectric constant than air, changes in the near field around the antenna caused by, for example, changes in the fill medium level toward the antenna, will result in a decrease in the resonant frequency.

[0014] Therefore, the resonant frequency is not a fixed frequency, but is within a resonant frequency range, and the generator is configured to generate electromagnetic waves within the resonant frequency range. In this case, the corresponding resonant frequency depends on the near field of the antenna.

[0015] The design of the controller for detecting changes in the near field around the antenna includes, for example, analyzing the resonant input impedance.

[0016] Compared to the fill level sensor known from the prior art, the fill level sensor according to the invention has the advantage that the sensitivity to changes in the near field around the antenna is increased, so that it also ensures detection of the fill level of filling media with a low dielectric constant.

[0017] One design of this level sensor provides that the feeder additionally includes a terminating circuit. The terminating circuit, the resonant circuit, and the antenna thus share a terminating input impedance in the transmission direction. The terminating circuit sets the terminating input impedance to the line impedance value. If the line impedance of the feeder line is, for example, 50 ohms, the terminating input impedance also has a value of 50 ohms. Consequently, no reflections occur at the transition between the feeder and the feeder line. The controller for detecting changes in the near-field around the antenna may, for example, include analyzing shifts in the resonant frequency. The reduction in resonant frequency described above represents such a shift.

[0018] In one embodiment of the above-mentioned configuration, it is provided that the terminating circuit has a quarter-wavelength line. The quarter-wavelength line is preferably implemented using an air gap. In a particularly preferred configuration, the terminating circuit consists of a quarter-wavelength line.

[0019] In another embodiment, the antenna resonant frequency is greater than the resonance frequency. This has the advantage that the antenna is smaller than when the antenna resonant frequency is less than the resonance frequency. Another advantage is that the resonant frequency range is larger. Otherwise, the resonant frequency range would be limited to the frequency range between the antenna resonant frequency and its first harmonic.

[0020] In principle, the generator is designed to generate electromagnetic waves with any resonant frequency. However, resonant frequencies in the microwave frequency range have proven particularly suitable for detecting the fill level of the medium in the container. The microwave frequency range is, for example, from 1 GHz to 300 GHz. Therefore, one embodiment of the fill level sensor provides that the generator is designed to generate electromagnetic waves with a resonant frequency in the microwave frequency range.

[0021] Another design provides for the antenna to be designed for direct contact with the filling medium. An alternative to direct contact is indirect contact between the antenna and the filling medium. Direct contact has the advantage over indirect contact in that it can detect even smaller changes in the near field surrounding the antenna, thereby further increasing sensitivity. This ensures the detection of the filling level of filling media with even lower dielectric constants.

[0022] In another embodiment, the controller is additionally configured to report the detected fill level of the filling medium. The controller, for example, has a bus interface, and this reporting is achieved by transmitting a corresponding bus message via the bus interface and the bus to a control room, where the bus message is then displayed to a user.

[0023] Another design provides for a feeder having a cylindrical inner conductor and a hollow cylindrical outer conductor for transmitting electromagnetic waves. Furthermore, the outer and inner conductors are arranged coaxially with one another. Thus, the outer conductor surrounds the inner conductor. This coaxial feeder has advantageous properties for transmitting electromagnetic waves.

[0024] Therefore, the portion of the inner conductor preferably also forms an antenna. Fill level sensors known from the prior art have a planar patch antenna as their antenna. Compared to a planar patch antenna, the portion of the inner conductor acting as an antenna is smaller, and thus the fill level sensor is also smaller. Due to its smaller size, the fill level sensor is also suitable for applications with only a small amount of installation space available. Furthermore, unlike a patch antenna, the portion of the inner conductor acting as an antenna only excites the near field, making it suitable for correspondingly smaller containers.

[0025] In another embodiment of the fill level sensor, the resonant circuit and / or the terminating circuit are arranged between the inner conductor and the outer conductor. This arrangement of the resonant circuit and / or the terminating circuit leads to a further reduction in the size of the fill level sensor and results in favorable electrical properties for electromagnetic waves.

[0026] It is often necessary to determine the fill level of a filling medium in a container, where the filling medium has a temperature, particularly a high temperature, that represents a thermal load on, for example, the generator and the controller and impairs their functionality. Since the terminal input impedance is set to the line impedance value, no reflections occur at the transition between the feeder and the feeder line. Therefore, the generator and the controller can be arranged spaced apart from the feeder, thereby thermally decoupling them from the filling medium and reducing their thermal load. To also reduce the thermal load on the feeder, one embodiment of the fill level sensor provides that the outer conductor has heat sinks. These heat sinks are designed to dissipate heat transferred from the filling medium to the feeder into the surroundings of the fill level sensor.

[0027] In another embodiment of the fill level sensor, the resonant circuit comprises a dielectric and a high-frequency absorber. The dielectric is preferably glass, in particular fused-metal glass. If the fill level sensor comprises the coaxial feeder described above, in a particularly preferred embodiment, the resonant circuit comprises the dielectric, the high-frequency absorber, and the inner conductor.

[0028] A container having an interior space for a filling medium, in which the filling level of the filling medium is to be detected, has a wall on which the filling level sensor is arranged. If the antenna of the filling level sensor is to come into direct contact with the filling medium at a specific filling level, a hole in the container wall is necessary. Therefore, in another embodiment, the filling level sensor has a process window that closes the hole in the container wall and arranges the antenna in the container interior.

[0029] In a development of the above-mentioned embodiment in combination with a resonant circuit having a dielectric, it is provided that the dielectric also additionally serves as the process window. The dielectric ensures an effective, robust, and chemically stable separation of the residual fill level sensor from the medium.

[0030] In another refinement, it is provided that the resonant impedance value is in the range of 150 ohm to 300 ohm.

[0031] In the case of fill level sensors arranged on containers known from the prior art, it often happens that the near field around the antenna is impaired due to the excitation of higher modes of electromagnetic waves in the container, which are excited into the container by the radiated electromagnetic waves, especially in the transition area of ​​the feeder and / or the antenna. This excitation is carried out by the discontinuity of the electromagnetic field of the electromagnetic wave at the transition. Higher modes are modes that are higher than the fundamental mode of the electromagnetic wave. The container itself is usually also a waveguide for transmitting electromagnetic waves. If the waveguide mode is now excited into the container by electromagnetic waves, standing waves can be formed in the container, which lead to multi-valued properties when detecting changes in the near field. If the container is a hollow cylinder, the fundamental mode is calculated according to the following formula:

[0032]

[0033] In order to avoid waveguide modes in the container, a further embodiment therefore provides that the fill level sensor has a modal filter on the antenna; and that the modal filter is designed to avoid excitation of higher modes of electromagnetic waves in the container.

[0034] In another embodiment, the modal filter comprises a horn having a horn interior; the antenna projects into the horn interior; and the horn interior widens continuously in the transmission direction. The electromagnetic waves radiated by the antenna are guided by the horn into the horn interior, thereby at least reducing or even avoiding discontinuities in the electromagnetic waves at the transition from the antenna into the container.

[0035] The cross-section of the horn interior relative to the transmission direction is preferably circular, and the radius of this cross-section is determined, taking into account the geometry of the container's interior and the assumed maximum dielectric constant of the filling medium, so that only propagating higher modes of electromagnetic waves in the container, higher than the fundamental mode, with frequencies above the resonant frequency, are excited. This radius is preferably the minimum radius of the horn interior. Because the horn interior continuously widens in the transmission direction, the minimum radius of the horn interior is at the end where the antenna of the horn protrudes.

[0036] In another embodiment, the horn has a recess for allowing the filling medium to enter the horn interior. This ensures that when the filling medium level in the region of the horn changes, no air bubbles form in the horn interior, but rather the horn interior is filled with the filling medium in a manner corresponding to the filling medium level. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Various possibilities for designing and expanding the fill level sensor are given in detail. For this purpose, reference is made to the following description of preferred embodiments in conjunction with the accompanying drawings. In the drawings:

[0038] Figure 1 An embodiment of a fill level sensor is shown, which is arranged in the wall of a container;

[0039] Figure 2 An embodiment of a level sensor is shown in cross-section;

[0040] Figure 3a An embodiment of a modal filter is shown in cross-section; and

[0041] Figure 3b An embodiment of a modal filter is shown in perspective view. DETAILED DESCRIPTION

[0042] Figure 1 An embodiment of a fill level sensor 1 for detecting the fill level of a filling medium in a container is shown in an abstract manner. The fill level sensor 1 is arranged on a wall 2 of a container 3. The container 3 has an interior 4. The interior 4 has a fill level 5 of a filling medium 6. Air is located above the filling medium 6 as a further medium. The filling medium 6 and the air have different dielectric constants. An opening 7 is formed in the wall 2 of the container 3, through which the fill level sensor 1 reaches the interior 4 of the container 3.

[0043] Figure 2 Abstractly shows Figure 1 A longitudinal section of a fill level sensor 1 is shown in FIG. The fill level sensor 1 comprises a generator 8 with a feed line 9, an antenna 10, a feeder 11, a controller 12, and a modal filter 13. The generator 8 is configured to generate electromagnetic waves having a resonant frequency and to output these electromagnetic waves via the feed line 9. The resonant frequency is 6 GHz, thus within the microwave frequency range. The feed line 9 has a line impedance with a line impedance value of 50 ohms.

[0044] The feeder 11 is arranged between the feeder line 9 and the antenna 10 and is configured to transmit electromagnetic waves from the feeder line 9 toward the antenna 10 .

[0045] Feeder 11 has a cylindrical inner conductor 14 and a hollow cylindrical outer conductor 15 for transmitting electromagnetic waves. Outer conductor 15 and inner conductor 14 are arranged coaxially with each other and have a circular cross-sectional profile. Outer conductor 15 also has heat sinks 16. Heat sinks 16 are configured to dissipate heat transferred to feeder 11 by filler medium 6 to the surrounding environment. Feeder 11 also has a dielectric 17 in the form of a metallic molten glass and a high-frequency absorber 18. Dielectric 17 also serves as a process window. Together with outer conductor 15, dielectric 17 closes hole 7 in wall 2 of container 3. Therefore, dielectric 17 is also designed to be stable relative to filler medium 6 and the pressure and temperature within container 3. Both dielectric 17 and high-frequency absorber 18 are annular in shape and are arranged between cylindrical inner conductor 14 and hollow cylindrical outer conductor 15.

[0046] Feeder 11 has a resonant circuit 19 and a terminal circuit 20. Resonant circuit 19 includes a dielectric 17 and a high-frequency absorber 18. Terminal circuit 20 includes a quarter-wavelength line, implemented using an air gap. Therefore, both resonant circuit 19 and terminal circuit 20 are arranged between inner conductor 14 and outer conductor 15. In the present embodiment, feeder line 9 includes the same inner conductor 14 and outer conductor 15 as feeder 11, and a feed dielectric 21 between inner conductor 14 and outer conductor 15. Feeder line 9 is also shown as a single line in the area of ​​generator 8 and controller 12.

[0047] Electromagnetic waves are transmitted from the feed line 9 via the feeder 11 toward the antenna 10 along a transmission direction 22. The antenna 10 is configured to radiate electromagnetic waves into the interior 4 of the container 3 containing the filling medium 6. A portion 23 of the inner conductor 14 forms the antenna 10 by extending beyond the dielectric 17 in the transmission direction 22. The antenna 10 is configured for direct contact with the filling medium 6. When the fill level 5 of the medium 6 is sufficiently high, the antenna 10 is in direct contact with the filling medium 6.

[0048] In the transmission direction 22, the resonant circuit 19 and the antenna 10 have a common resonant input impedance Z R The antenna has a resonant input impedance Z R In particular, a capacitive contribution is provided. The resonant input impedance Z of the resonant circuit 19 will be at the resonant frequency and when the filling medium 6 does not affect the near field of the antenna 10. R is converted into a real impedance with a predetermined resonant impedance value Z R = 200 ohms. This conversion is therefore carried out before the fill level 5 of the filling medium 6 is detected, ie before the fill level sensor 1 is used productively.

[0049] Along the transmission direction 22, the terminal circuit 20, the resonant circuit 19 and the antenna 10 have a terminal input impedance Z E The terminal circuit 20 sets the terminal input impedance Z E The line impedance value is set to 50 ohms. Since the line impedance of the feeder 9 is equal to the terminal input impedance Z E The same, so the electromagnetic wave is not reflected at the transition from the feed line 9 to the feeder 11.

[0050] Therefore, the main components of the power feeder 11 , namely the cylindrical inner conductor 14 , the hollow cylindrical outer conductor 15 , the annular dielectric 17 and the annular high-frequency absorber, are coaxially configured.

[0051] Controller 12 is configured to detect changes in the near-field around antenna 10 caused by changes in the fill level 5 of filling medium 6 in interior space 4 of container 3, as radiated by the electromagnetic waves. Because filling medium 6 and air have different dielectric constants, changes in the fill level 5 of filling medium 6 in interior space 4 of container 3 cause changes in the near-field near antenna 10. These changes in the near-field also cause changes in the adaptation of antenna 10, resulting in changes in the reflected power as a function of frequency. Changes in the near-field around antenna 10, caused by changes in the fill level 5 of medium 6, for example, toward antenna 10, result in a decrease in the resonant frequency. In the present embodiment, controller 12 is connected to feeder line 9 to detect changes in the reflected power.

[0052] The controller 12 is further configured to detect the fill level of the filling medium 6 in the interior space 4 by analyzing the detected changes in the near field. The controller 12 is also configured to report the detected fill level of the filling medium 6.

[0053] Figure 3a is a longitudinal section of an embodiment of the modal filter 13, and Figure 3b The figure is a perspective view of the modal filter 13. The modal filter 13 is configured to prevent electromagnetic waves of higher modes from propagating in the interior 4 of the container 3. The modal filter 13 has a flange 24 and a horn portion 25, which defines a horn interior space 26. The horn interior space 26 guides the electromagnetic waves radiated by the antenna 10. In this embodiment, the flange 24 is used to position the modal filter 13 on the feeder 11. In other embodiments, the flange is used to position the modal filter 13 on the wall 2 of the container 3. If the modal filter 13 is positioned, the antenna 10 extends into the horn interior space 26. The horn interior space 26 continuously widens along the transmission direction 22.

[0054] In this embodiment, horn interior 26 is rotationally symmetrical with respect to propagation direction 22. Therefore, all cross-sections of horn interior 26 relative to propagation direction 22 are circular. In particular, cross-section 27 of horn interior 26 relative to propagation direction 22 is circular, and radius 28 of cross-section 27 is determined to prevent the propagation of higher-mode electromagnetic waves in interior 4 of container 3, taking into account the geometry of interior 4 of container 3 and the assumed highest dielectric constant of filler medium 6. Radius 28 is the minimum radius of horn interior 26. Antenna 10 passes through cross-section 27. In other words, the antenna is located in horn interior 26 at a position where the radius of the horn interior is minimum.

[0055] The trumpet 13 has three recesses 29 for the filling medium 6 to enter the trumpet interior 26. This ensures that changes in the filling level 5 of the filling medium 6 in the region of the trumpet 25 do not lead to air bubbles in the trumpet interior 26, but rather that the trumpet interior 26 is filled with the filling medium 6 corresponding to the filling level 5 of the filling medium 6.

[0056] Reference numerals

[0057] 1 level sensor

[0058] 2 walls

[0059] 3 Containers

[0060] 4 Internal Space

[0061] 5 Material level

[0062] 6 Filling medium

[0063] 7 holes

[0064] 8 Generator

[0065] 9 Feeders

[0066] 10 Antenna

[0067] 11 Power Feeder

[0068] 12 Controller

[0069] 13 Modal Filters

[0070] 14 Inner conductor

[0071] 15 Outer conductor

[0072] 16 heat sink

[0073] 17 Dielectric

[0074] 18 High-frequency absorber

[0075] 19 Resonant Circuit

[0076] 20 Terminal Circuit

[0077] 21 Feed dielectric

[0078] 22 Transmission direction

[0079] 23 parts

[0080] 24 flange

[0081] 25 Speaker

[0082] 26 Speaker Internal Space

[0083] 27 cross section

[0084] 28 Radius

[0085] 29 blank space

[0086] Z R Resonant input impedance

[0087] Z E Terminal input impedance.

Claims

1. A level sensor (1) for detecting the level of a filling medium in a container, - wherein the fill level sensor (1) comprises: a generator (8) with a feed line (9), an antenna (10), a feeder (11) and a controller (12), - wherein the generator (8) is designed to generate electromagnetic waves having a resonant frequency and output the electromagnetic waves via the feed line (9), the feed line having a line impedance having a line impedance value, - wherein the feeder (11) is arranged between the feeder line (9) and the antenna (10) and is configured to transmit the electromagnetic waves from the feeder line (9) toward the antenna (10), - wherein the antenna (10) is designed to radiate the electromagnetic waves into a container having a filling medium, - wherein the electromagnetic wave is transmitted in a transmission direction (22) from the feeder (9) via the feeder (11) towards the antenna (10), and wherein the controller (12) is configured to detect changes in a near field around the antenna (10) caused by changes in a filling level of a filling medium in a container of electromagnetic waves radiated by the antenna (10) and is configured to detect the filling level of the filling medium in the container by analyzing the detected changes in the near field, It is characterized by: - the feeder (11) has a resonant circuit (19), The resonant circuit (19) and the antenna (10) have a common resonant input impedance (Z) along the transmission direction (22). R ), and the resonant circuit (19) will resonate the input impedance (Z R ) is converted into a real impedance with a predetermined resonant impedance value, and - the antenna (10) has an antenna resonance frequency that is different from the resonance frequency.

2. The material level sensor (1) according to claim 1, characterized in that The feeder (11) has a terminal circuit (20); and the terminal circuit (20), the resonant circuit (19) and the antenna (10) together have a terminal input impedance (Z) along the transmission direction (22). E ), and the terminal circuit (20) changes the terminal input impedance (Z E ) is set to the line impedance value.

3. The material level sensor (1) according to claim 2, characterized in that The terminal circuit (20) has a quarter-wavelength line.

4. The material level sensor (1) according to claim 3, characterized in that The quarter-wavelength line is realized using an air gap.

5. The fill level sensor (1) according to any one of claims 1 to 4, characterized in that The antenna resonant frequency is greater than the resonant frequency.

6. The fill level sensor (1) according to any one of claims 1 to 4, characterized in that The resonant frequency is in the frequency range of microwaves.

7. The fill level sensor (1) according to any one of claims 1 to 4, characterized in that The antenna (10) is configured to be in direct contact with the filling medium.

8. The fill level sensor (1) according to any one of claims 1 to 4, characterized in that The controller (12) is designed to report the detected fill level of the filling medium.

9. The material level sensor (1) according to claim 2 or 3, characterized in that The feeder (11) has a cylindrical inner conductor (14) and a hollow cylindrical outer conductor (15) for transmitting the electromagnetic wave, and the outer conductor (15) and the inner conductor (14) are coaxially arranged with each other.

10. The material level sensor (1) according to claim 9, characterized in that A portion (23) of the inner conductor (14) forms the antenna (10).

11. The material level sensor according to claim 9, characterized in that: The resonant circuit (19) and / or the terminal circuit (20) are arranged between the inner conductor (14) and the outer conductor (15).

12. The material level sensor (1) according to claim 9, characterized in that The outer conductor (15) has a heat sink (16).

13. The fill level sensor (1) according to any one of claims 1 to 4, characterized in that The resonant circuit (19) comprises a dielectric (17) and a high-frequency absorber (18).

14. The material level sensor (1) according to claim 13, characterized in that The dielectric (17) is glass.

15. The material level sensor (1) according to claim 14, characterized in that The glass is a metallic molten glass.

16. The material level sensor (1) according to claim 13, characterized in that The dielectric (17) is also a process window.

17. The fill level sensor (1) according to any one of claims 1 to 4, characterized in that The resonant impedance value is in the range of 150 ohms to 300 ohms.

18. The fill level sensor (1) according to any one of claims 1 to 4, characterized in that The fill level sensor (1) has a modal filter (13) at the antenna (10); and the modal filter (13) is configured to avoid waveguide modes in the container.

19. The material level sensor (1) according to claim 18, characterized in that The modal filter (13) has a horn portion (25) having a horn internal space (26); the antenna (10) extends into the horn internal space (26); and the horn internal space (26) continuously widens along the transmission direction (22).

20. The level sensor (1) according to claim 19, characterized in that The cross section (27) of the horn interior (26) relative to the transmission direction (22) is circular; and the radius (28) of the cross section (27) is determined in such a way as to avoid excitation of waveguide modes in the container, taking into account the geometry of the interior of the container and the highest dielectric constant to be assumed for the filling medium.

21. The level sensor (1) according to claim 20, characterized in that The radius (28) is the minimum radius of the horn interior space (26).

22. The fill level sensor (1) according to any one of claims 19 to 21, characterized in that The horn portion (25) has a recess (29) for allowing a filling medium to enter the horn inner space (26).

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