Mode converter for filling level radar

Abstract

A mode converter for a level radar includes an input line introducing a high-frequency signal into the mode converter; a helix structure into which a conductor of the input line projects and which includes a plurality of helical electrical conductors; and a waveguide which encloses the helix structure. The helix structure is configured to convert the high-frequency signal from the input line into an H01 mode in the waveguide.

Claims

1. A mode converter for a level radar, comprising: an input line introducing a high-frequency signal into the mode converter; a helix structure into which an internal conductor of a coaxial cable of the input line projects, the helix structure including a plurality of helical electrical conductors; and a waveguide enclosing the helix structure; wherein the helix structure is configured to convert the high-frequency signal from the input line into an H01 mode in the waveguide.

2. The mode converter according to claim 1, wherein the conductor projects into the helix structure by more than 10% of the length of the helix structure.

3. The mode converter according to claim 1, wherein the waveguide is formed by a housing of the level radar.

4. The mode converter according to claims 1, wherein the helix structure is carried by a dielectric body which is arranged in the waveguide and wherein the dielectric body carries the helix structure on the outside thereof.

5. A level radar, comprising: a mode converter according to claim 1.

6. The mode converter according to claim 1, further comprising: a dielectric body including a first cylindrical portion which is enclosed by the helix structure; and a socket in the first cylindrical portion, the socket configured to receive the internal conductor of the coaxial cable.

7. The mode converter according to claim 6, further comprising: a second cylindrical portion having a greater diameter than a diameter of the first cylindrical portion, in which the first cylindrical portion including the helix structure is received.

8. The mode converter according to claim 7, further comprising: a conical portion situated between the first cylindrical portion and the second cylindrical portion.

9. The mode converter according to claim 7, further comprising: an emission cone connecting to the second cylindrical portion in such a way that a shoulder is formed on the second cylindrical portion.

10. A method for manufacturing a mode converter, comprising the steps of: providing a carrier body; including an input line introducing a high-frequency signal into the mode converter; applying a metallic helix structure to the carrier body by metallizing a plurality of helical strips on the outside of the carrier body using laser direct structuring of the carrier body, the metallic helix structure shaped and sized for an internal conductor of a coaxial cable of the input line to project into the metallic helix structure, the metallic helix structure including a plurality of helical electrical conductors; and including a waveguide enclosing the metallic helix structure, wherein the metallic helix structure is configured to convert the high-frequency signal from the input line into an H01 mode in the waveguide.

11. The method according to claim 10, wherein the carrier body is made of a plastics material which is suitable for metallization by a laser direct structuring.

12. The method according to claim 11, wherein the entire converter body is made of the plastics material.

13. The method according to claim 10, further comprising the step of: attaching the carrier body to a further plastics material body in such a way that the carrier body forms a first portion of the converter body to which the helix structure is applied and the further plastics material body forms at least a second portion by which the converter body is configured to be fixed to a housing.

14. The method according to claim 13, wherein the carrier body is a solid cylinder in such a way that the converter body merely includes the plastics material of the carrier body in the first portion in the interior of the helix structure.

15. The method according to claim 13, wherein the carrier body is a hollow cylinder and the carrier body is attached to the further plastics material body by being slid onto the further plastics material body.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows schematically a container comprising a level radar in accordance with an embodiment of the invention.

(2) FIG. 2 shows a longitudinal section through a mode converter in accordance with an embodiment of the invention.

(3) FIG. 3 is a three-dimensional view of a mode converter in accordance with an embodiment of the invention.

(4) FIG. 4 is a three-dimensional view of a converter body in accordance with an embodiment of the invention.

(5) FIG. 5 is a longitudinal section through a converter body in accordance with an embodiment of the invention.

(6) FIG. 6 is a longitudinal section through a converter body in accordance with an embodiment of the invention.

(7) FIG. 7 is a longitudinal section through a converter body in accordance with an embodiment of the invention.

(8) FIG. 8 is a flow chart for a method for manufacturing a converter body in accordance with an embodiment of the invention.

(9) Identical or similar parts are provided with like reference numerals.

DETAILED DESCRIPTION OF EMBODIMENTS

(10) FIG. 1 shows a container 10 comprising a level radar 12 which measures the fill level in the container. The level radar 12 is attached to the upper end of a bypass line 14, in which a liquid 16 is at exactly the same height as in the interior of the container 10.

(11) The level radar 12 comprises an emission device 18, which is connected to a control system 22 of the level radar 12 via a coaxial line 20. It is possible for the control system 22 to be attached to the emission device 18 directly or to be located at a distance therefrom.

(12) To measure the distance of the emission device 18 from the surface of the liquid 16, the control system 22 generates pulses of a high-frequency signal, which are conveyed to the emission device 18 via the coaxial line 20. The emission device 18 radiates pulses of the high-frequency signal into the bypass line 14 as radar pulses 24, which are subsequently reflected back at the surface of the liquid and received again by the emission device 18. The reflected radar pulses are fed into the coaxial line 20 by the emission device 18 as a reflected high-frequency signal and transferred back to the control system 22. The control system 22 subsequently determines the distance from transit time differences between the pulses. However, it is also possible for the distance to be determined by another method, such as FMCW. In FMCW, the distance is determined by way of the frequency shift between the sent and the received signal.

(13) The high-frequency signal is transferred into the coaxial line 20 as a TEM guide wave. The emission device 18 comprises a mode converter 30, which is configured to convert the TEM guide wave into the H01 mode of a waveguide, which is subsequently emitted as a radar signal. Conversely, the mode converter 30 can convert the reflected signal of the H01 mode back into a TEM guide wave upon receipt.

(14) Since the H01 mode does not have any portions of the electric field at the edge of the bypass pipe 14, which is generally made of metal and forms a waveguide for the radar signal, no longitudinal currents which might be interfered with by disruptions in the bypass pipe 14 (such as slits or openings) flow in the bypass pipe 14. The H01 mode is thus not interfered with, or only slightly, by these disruptions, and this increases the signal quality of the reflected high-frequency signal.

(15) FIG. 2 shows an emission device 12 and in particular a mode converter 30 in greater detail. The mode converter 30 comprises a housing 32, which at one end thereof has an opening 34, through which a converter body 36 is inserted into the housing 32. At the other end thereof, the housing 32 is sealed using a cover 38, which is for example screwed to the housing 32.

(16) The cover 38 comprises an opening 40 or hole 40, through which the coaxial line 20 is passed into the interior 42 of the housing 32. In the hole 40, a plug 44 such as a 3.5 mm plug may for example be attached, to which a cable for the coaxial line 20 can be connected. The internal conductor 46 of the coaxial line 20 projects into the interior of the housing and into the converter body 36. For this purpose, the converter body 36 comprises a socket 48 for the internal conductor 46. The internal conductor 46 may be considered an input conductor of the mode converter 30.

(17) The housing 32, the cover 38 and the converter body 36 are substantially rotationally symmetrical about an axis A. The hole 40 in the cover 38, the plug 44, and the opposing opening 34 in the housing 32 are arranged along the axis A.

(18) The interior 42 of the housing 32 is cylindrical (the cylinder axis being coincident with the axis A), in such a way that a circular waveguide 49, in which the converter body 36 (or the front portion thereof) and the internal conductor 46 are arranged, is formed in the interior of the housing 32.

(19) An antenna horn 50 is attached to the end of the housing 32 comprising the opening 34, and comprises a first flange 52 at one end thereof for fastening to the housing 32 and a second flange 54 at the other end thereof for fastening to a container 10 (for example to the bypass line 14). The antenna horn 50 can be screwed to the housing 32 by means of the flange 52.

(20) The antenna horn 50 comprises a conical portion 56, which widens outwards from a diameter somewhat smaller than the external diameter of the opening 34 to an outer opening 57. The antenna horn 50 can be adapted to a desired pipe diameter (for example of the bypass line 14) at the open face or the face comprising the outer opening 57 or have the same diameter as the bypass line 14. The pipe diameter may be 82.5 mm.

(21) The antenna horn 50 may also be rotationally symmetrical about the axis A.

(22) On the converter body 36 there is a helix structure 58, which is configured to convert a TEM guide wave from the coaxial cable 20 and an H01 mode in the waveguide 49 into one another.

(23) FIG. 3 shows the converter body 36, comprising the helix structure 58, and the volumes 60, 62, 64 in which the high-frequency signal is guided in greater detail in three dimensions. The volume 60 is the space between the casing of the coaxial cable 20 and the internal conductor 46 through which the TEM guide wave enters (and leaves) the mode converter 30. The volume 60 may for example be filled with a dielectric plastics material.

(24) The volume 62 is an air region between the converter body 36 or between the helix structure 58 and the inner face of the housing 32 or of the waveguide 49. The electrical field which is converted into the H01 mode may form in the volume 62.

(25) The volume 64 is the interior of the antenna horn 50 by means of which the radar signal is directed into the container 10 or into the bypass line 14 or by means of which the reflected signal is focussed and passed back into the waveguide 49.

(26) An enlargement of the converter body 36 comprising the helix structure 58 is additionally shown in FIG. 4. The helix structure 58 comprises a plurality of electrically conductive strips 68, formed in the same manner, which enclose the axis A in a helix or coil shape. The helix structure 58 or the strips 68 are arranged on a body 70 made of plastics material and/or a dielectric material, which provides the majority of the converter body 36.

(27) At the input side 72 thereof, the converter body 36 comprises a conical end 74, which serves to centre the converter body 36 by way of the hole 40 in the cover 38. The coaxial line 20 is also located in the input side 72 of the converter body 36, but the internal conductor 46 thereof may still project up to approximately halfway into the helix structure 58.

(28) The conical end 74 of the converter body 36 widens to a first cylindrical portion 76 on which the helix structure 58 is arranged.

(29) On the output side 78, the converter body 36 widens into a conical portion 80, so as subsequently to become cylindrical again. This second cylindrical portion 82 has a greater diameter than the first cylindrical portion 76.

(30) In this context, the conical portion 80 provides pressure bracing against the container pressure in the container 10. The opening 34 in the housing 32 has a correspondingly conical portion so as to receive the conical portion 80.

(31) The second cylindrical portion 82 is used for sealing. The second cylindrical portion 82 comprises two annular grooves 84, which extend radially around the converter body 36 and in which seals 86 are arranged. The seals 86 may be two or more O-rings, for example made of FKM or FFKM (Kalrez).

(32) After the second cylindrical portion 82, the converter body 36 tapers, forming a shoulder 88 which is supported against the antenna horn 50 or the flange 52 thereof. In this way, the converter body 36 is prevented from falling out or being pulled out of the housing 32 by a vacuum or negative pressure in the container 10.

(33) After the taper, the converter body 36 comprises a cone tip 90 via which the H01 wave is coupled out into the antenna horn 50.

(34) As is shown in FIGS. 5 to 7, the converter body 36 comprising the applied helix structure 58 may be formed in one piece, two pieces or a plurality of pieces.

(35) FIG. 5 shows that the helix structure 58 can be applied to a pipe or a hollow cylinder 92 made of a first material as a carrier body 94. The pipe 92 is subsequently slid onto a further body 96 of a second material. The pipe 92 and the further body 96 together form the dielectric body 70 of the converter body 36.

(36) The first material may be a material suitable for LDS, such as the material TECACOMP PEEK LDS from Ensinger. The second material may be a standard PEEK, such as TECAPEEK Natur from Ensinger.

(37) FIG. 6 shows that the helix structure 58 can be applied to a solid cylinder 98 of a first material as a carrier body 94. The entire input face 72 of the converter body 36 comprising the helix structure 58 may be made of the first material and connected, for example via a thread 100, to the second body 96 of a second material. The materials may be the same materials as those of FIG. 5.

(38) A potential advantage of a two-part construction, as shown in FIGS. 5 and 6, is that only the part or the carrier body 94 comprising the helix structure 58 has to be manufactured from the material suitable for LDS, and the remainder or the further body 96, in other words particularly the part of the adaptation cone 90 contacting the medium, may favourably be manufactured from an industrially known and accepted material, such as PEEK natur (without unknown additives) or PTFE, from a semi-finished product, for example by machining by turning.

(39) FIG. 7 shows a single-piece construction for the converter body 36; in this context the entire body 70 of the converter body may be made of the same material, such as the first material from FIGS. 5 and 6.

(40) FIG. 8 is a flow chart for a method by which a converter body 36 can be manufactured.

(41) In step 110, a carrier body 94 for the helix structure is provided; for example, the carrier body 94 may be injection-moulded from a material suitable for LDS in the form of a hollow cylinder 92, a solid cylinder 98 or the entire converter body 36. Machining by cutting from a semi-finished product is also possible.

(42) In step 112, the helix structure 58 is applied to the carrier body 94 by metallisation. For example, the helix structure 58 can be drawn in advance on a carrier body 94 of a material suitable for LDS, using a laser, and the helical strips 68 can subsequently be deposited at the locations prepared by the laser, for example in an electroless chemical bath.

(43) If the carrier body 94 provides the entire dielectric body 70 of the converter body 36, the method ends after this step.

(44) Otherwise, in a further step 114, a further plastics material body 96 of a second material can be provided. For example, the further plastics material body 96 can be manufactured from a semi-finished product of the second material by machining by cutting. It is also possible to injection-mould the further plastics material body 96 from the second material.

(45) Subsequently, in step 116, the carrier body is attached to the further plastics material body 96. For example, the carrier body 94 may be a solid cylinder 98 and be screwed to the further plastics material body 96. It is also possible for the carrier body 94 to be a hollow cylinder 92 and for the carrier body 92 to be slid onto the further plastics material body 96.

(46) It should additionally be noted that expressions such as comprising or the like do not exclude the possibility of further elements or steps, and a and an do not exclude the possibility of a plurality. It should further be noted that features or steps disclosed with reference to any one of the above embodiments may also be used in combination with other features or steps of other embodiments disclosed above. Reference numerals in the claims should not be interpreted as limiting.