Method for producing a radar-based fill-level meter

Abstract

The invention relates to a method for simply manufacturing a radar-based fill-level meter (1), comprising the following method steps: two-component injection molding of an antenna main body (11) and a seal (110) which is arranged on the antenna main body (11) around the incoupling region (112) for the horn antenna (111); subsequently metallizing the antenna main body (11); fastening a radar module (12) to the antenna main body (11) so that the horn antenna (111) is sealed, and; as a final step, potting the radar module (12) on the antenna main body (11) so that the horn antenna (111) is omitted. The invention therefore makes use of the fact that an antenna main body (11) having efficient sealing of the waveguide (112) with respect to the potting (14) can be obtained by means of two-component injection molding with little manufacturing effort.

Description

[0001] Manufacturing process for a level measuring device

[0002] The invention relates to a method for the simplified manufacture of a radar-based level measuring device.

[0003] In process automation technology, field devices are used to acquire relevant process parameters. Suitable measurement principles are implemented in these field devices to acquire process parameters such as fill level, flow rate, pressure, temperature, pH value, redox potential, or conductivity. The Endress+Hauser Group manufactures and distributes a wide variety of field device types and variants.

[0004] Non-contact measurement methods have become established for measuring the fill level of contents in containers due to their robustness and low maintenance requirements. A further advantage of non-contact measurement methods is their ability to measure the fill level almost continuously. Therefore, radar-based measurement methods are predominantly used in the field of continuous level measurement (in the context of this patent application, the term "radar" refers to signals or electromagnetic waves with frequencies between 0.03 GHz and 300 GHz). In principle, the higher the frequency, the higher the measurement resolution achievable. The pulse transit-time method and FMCW ("Frequency Modulated Continuous") have become established measurement methods. Radar-based level measurement is described in more detail, for example, in "Radar Level Detection," Peter Devine, 2000.

[0005] For explosion protection reasons, the radar module of the level gauge must be encapsulated as standard practice, with potting the radar module in a soft resin being one of the established methods. However, this presents a manufacturing challenge because the waveguide or horn antenna, through which the radar signal is transmitted from the level gauge, must remain outside the potting compound for high-frequency reasons. The invention therefore aims to simplify the manufacturing of radar-based level gauges in light of these requirements.

[0006] The invention solves this problem by a method for manufacturing a radar-based level measuring device, which comprises the following process steps:

[0007] - Two-component injection molding, such that an antenna base body, which has a horn antenna with a waveguide-shaped coupling area along a device axis, is formed with at least one first seal arranged circumferentially around the coupling area,

[0008] - Metallization of the antenna base body,

[0009] - Attaching a radar module to the coupling area so that the horn antenna is sealed by the first seal, and

[0010] - Encapsulation of the radar module on the antenna base body, so that the coupling area remains unaffected, whereby a silicone gel, for example, can be used as the encapsulation.

[0011] The invention is therefore based on the finding that, by means of two-component injection molding, an antenna base body with efficient sealing of the waveguide against the potting compound can be achieved with low manufacturing effort.

[0012] Within the scope of the invention, the process of "two-component injection molding," or more precisely, multi-material injection molding, generally refers to the injection molding-based manufacturing of a workpiece consisting of two spatially adjacent materials, for example, to achieve a hard-soft bond. In a first injection molding step, the first material is injected into the mold in such a way that a defined space remains for the second material to fill. Subsequently, after the first material has cooled, the second material is injected into the same mold in a second injection molding step, so that it is completely filled. The two materials do not mix extensively, but rather bond only at their interface.The two-component injection molding process is also described in more detail in the internet-based encyclopedia "Wikipedia" under the term "multi-component injection molding".

[0013] The invention is particularly advantageous when the antenna base is manufactured from polycarbonate using injection molding and a thermoplastic elastomer is used as the sealing material for at least the first seal. When using this material combination, the silicone gel-based potting compound can cure particularly efficiently.

[0014] The metallization of the antenna base serves to establish the electrical conductivity required for transmitting and receiving radar signals inside the horn antenna. This metallization can be achieved, for example, by chemical vapor deposition (CVD) or physical vapor deposition (PVD), such as sputtering. In this regard, it has been found within the scope of the invention that the inherent metallization of the seal does not adversely affect its sealing performance or its mechanical stability.

[0015] In order for the antenna base to function as a potting cup on the surface facing away from the horn antenna and where the radar module is located, the antenna base must be designed accordingly. A two-part design of the antenna base is conceivable, with a potting frame attached to a corresponding outer contour of the antenna base on the surface facing away from the waveguide. In this case, any gap between the antenna base or its outer contour and the potting frame must be sealed by a corresponding second seal. Within the scope of the invention, it is particularly advantageous if, during the injection molding of the first seal along the outer contour, the second, circumferential seal is simultaneously injection molded to create a gap-free seal between the antenna base and the potting frame at the outer contour.Therefore, during the manufacturing of the level gauge, the potting frame must be attached to the surface of the antenna base facing away from the waveguide before the radar module is potted. It goes without saying that instead of a two-part design consisting of the antenna base and the potting frame, a one-piece design can also be chosen, in which the potting cup is formed solely by the antenna base.

[0016] A radar-based level measuring device for determining the fill level of a product manufactured according to the method of one of the preceding embodiments comprises at least the following components:

[0017] - An antenna base body manufactured by two-component injection molding, which forms a horn antenna with a waveguide-shaped coupling area along a device axis, with a first seal formed around the coupling area,

[0018] - a radar module arranged at the coupling area in such a way as to transmit radar signals to the contents via the horn antenna, in particular according to the FMCW method, o receive corresponding received signals after their reflection at the surface of the contents, and o determine the fill level on the basis thereof, and

[0019] - a potting compound that encapsulates the radar module on the antenna base in such a way that the coupling area is excluded from this.

[0020] Within the scope of the invention, the term "module" is generally understood to mean any configuration or encapsulation of electronic circuits required for the specific application, e.g., for high-frequency signal processing or as an interface. Depending on the application, the corresponding module may therefore include analog circuits for generating or processing analog signals. However, the module may also include digital circuits, such as FPGAs, microcontrollers, or storage media, in conjunction with appropriate programs. The program is designed to execute the necessary process steps or perform the required arithmetic operations. In this context, various electronic circuits within the module, as defined by the invention, can potentially access a common physical memory or be operated using the same physical digital circuit.The various electronic circuits of the module can preferably be arranged on a common circuit board.

[0021] The invention is explained in more detail using the following figures. They show:

[0022] Fig. 1: A level measuring device according to the invention on a container,

[0023] Fig. 2: a perspective view of the antenna base body according to the invention, and

[0024] Fig. 3: a sectional view through the level measuring device according to the invention.

[0025] For a basic understanding of the invention, Fig. 1 shows a container 3 with a substance 2, the fill level L of which is to be determined. Depending on the type of substance 2 and the application, the container 3 can be more than 100 m high. The conditions inside the container 3 also depend on the type of substance 2 and the application. For example, in the case of exothermic reactions, high temperature and pressure stresses may occur. For dusty or flammable substances, appropriate explosion protection measures must be observed inside the container.

[0026] The level measuring device 1 is usually connected via a separate interface module, which uses protocols such as "4-20 mA", "PROFIBUS", "HART", "Bluetooth" or "Ethernet". 1The system is implemented and connected to a higher-level unit 4, such as a local process control system or a decentralized server system. The measured fill level value L can be transmitted via this connection, for example, to control the inflow or outflow of the container 3. Other information about the general operating status of the level gauge 1 can also be communicated.

[0027] In order to determine the fill level L independently of the prevailing conditions, the level gauge 1 is mounted above the contents 2 at a known installation height h above the bottom of the container 3. The level gauge 1 is optionally attached to a corresponding opening in the container 3 in a pressure- and media-tight manner, such that the housing 10 of the level gauge 1 remains essentially outside the container 3.

[0028] Radar signals SHF are transmitted via a horn antenna 111 of the level gauge 1 within a predefined frequency band, for example at 80 GHz, along a device axis a in the direction of the surface of the material 2. After reflection from the surface of the material, the level gauge 1 receives the reflected received signals RHF again via the horn antenna 111. The signal propagation time t between transmission and reception of the respective radar signal SHF, RHF is given by proportional to the distance d between the level gauge 1 and the contents 2, where the variable "c" represents the radar propagation speed, which is at least roughly known. The signal travel time t can be determined by the level gauge 1, for example, using the FMCW or pulse travel time method. This allows the level gauge 1 to assign the measured travel time t to the respective distance d, for example, based on appropriate calibration. Furthermore, the level gauge 1 can determine the fill level L according to d = h - L, provided the installation height "h" is stored in the level gauge 1. To determine the signal travel time t or the corresponding fill level value L based on the incoming received signal RHF, ZU its preprocessing, and to generate the transmitted radar signal SHF, the level gauge 1 includes a corresponding radar module 12, in which, for example, the FMCW or pulse travel time measurement principle is implemented.If the FMCW method is implemented, the radar module 12 can, for example, be based on a PLL (phase-locked loop) on the transmit side. On the receive side, the radar module 12 can, in this case, include Fourier transform logic. This serves to identify the frequency maximum in the intermediate frequency signal corresponding to the signal propagation time t, which is characteristic of FMCW and is obtained after mixing the received signal RHF with the transmitted radar signal SHF.

[0029] The manufacturing process and the construction of the level gauge 1 according to the invention are explained in more detail with reference to the oblique view in Fig. 2 and the sectional view of the level gauge 1 in Fig. 3: Accordingly, the horn antenna 111 is formed by a plastic-based antenna base body 11, wherein the axis of symmetry of the cone-segment-shaped interior of the horn antenna 111 defines the device axis a. Furthermore, the antenna base body 11 comprises a waveguide-shaped coupling area 112, which extends along the device axis a to the horn antenna 111. The coupling area 112 serves to couple the radar signals SHF generated by the radar module 12 into the horn antenna 111 for transmission, and to couple the received signals RHF received via the horn antenna 111 into the radar module 12.

[0030] The antenna base body 11 is manufactured as the first injection molding step using a two-component injection molding process, for which, for example, polycarbonate or a comparable plastic can be used as the material. The second injection molding step serves to form a first seal 110, which is arranged circumferentially around the coupling area 112 on a surface facing away from the horn antenna 111. In the embodiment shown in Fig. 2 and Fig. 3, a second, circumferential seal 110' is formed simultaneously along an outer contour of the antenna base body 11 in this second injection molding step. The terms "outer contour" and "circumferential" in Fig. 2 and Fig. 3 refer to the device axis a.To ensure that both the first seal 110 and the second seal 110' are formed in the second injection molding step, the first injection molding step is designed such that a corresponding connecting channel 110" is formed between the seals 110 and 110' in the antenna base body 11. A thermoplastic elastomer can be used as the injection molding material for the seals 110 and 110'.

[0031] After completion of the two-component injection molding, the antenna base body 11 is metallized using a suitable deposition process, such as PECVD (Plasma Enhanced Chemical Vapor Deposition) or PVD (Physical Vapor Deposition). This serves to create electrical conductivity on the inner wall of the horn antenna 111 and the waveguide 112, which is essential for transmitting and receiving the radar signals S and RHF, respectively. Following metallization, the radar module 12 can be attached planarly to the first seal 110 at the coupling area 112, for example, by means of a screw connection. As indicated in Fig. 3, the radar module 12 is based on a circuit board.

[0032] The two seals 110, 110' serve to encapsulate the radar module 12, which is attached to the antenna base 11, for explosion protection purposes by potting 14. The first seal 110, located between the antenna base 11 and the radar module 12, prevents any of the potting compound from penetrating the interior of the waveguide 112 and the horn antenna 111 during the potting process. To enable the complete potting of the radar module 12, a potting cup must be formed on the surface of the antenna base 11 facing away from the horn antenna 111. In the embodiment shown in Figures 2 and 3, this is achieved using a separate potting frame 13, which, at least in its end region, is designed to correspond to the outer contour of the antenna base 11.The potting frame 13 can be attached to the antenna base 11 at this end, for example, by means of a snap-fit ​​connection 113, so that the second seal 110' seals the outer contour between the potting frame 13 and the antenna base 11 without a gap. This creates a suitable potting cup for the potting compound 14 on the surface of the antenna base 11 facing away from the horn antenna 111. A curing silicone gel can be used as the potting compound. Curing is promoted by the fact that the seals 110, 110' are made of thermoplastic elastomer and that the antenna base 11 is made of polycarbonate. Contrary to the illustration in Fig. 3, the components of the level gauge 1 shown are enclosed by the housing 10, whereby the housing material must be sufficiently transparent to the radar signals S and RHF. Overall, this is characterized by the design shown in Fig. 2 and Fig. 3.3 level measuring devices 1 are manufactured by a simple manufacturing process, whereby the level measuring device 1 can comply with common explosion protection requirements due to the encapsulation.

[0033] Reference symbol list

[0034] 1 level gauge

[0035] 2 Filling material

[0036] 3 containers

[0037] 4 Parent unit 10 Housings

[0038] 11 Antenna base bodies

[0039] 12 Radar module

[0040] 13 Potting frame 14 Potting

[0041] 110 First seal 110' Second seal 110" Connecting channel 111 Horn antenna

[0042] 112 Coupling area

[0043] 113 Snap-in connection a Device axis d Distance h Installation height

[0044] L level

Claims

Patent claims 1. Method for manufacturing a radar-based level measuring device (1) comprising the following process steps: - Two-component injection molding, such that an antenna base body (11) which has a horn antenna (111) with a waveguide-shaped coupling area (112) along a device axis (a) is formed with at least one first seal (110) arranged around the coupling area (112), - Metallization of the antenna base body (11 ), - Attaching a radar module (12) to the coupling area (112) so that the coupling area (112) is sealed, and - Encapsulation of the radar module (12) on the antenna base body (11) so that the coupling area (112) remains unaffected.

2. Method according to claim 1, wherein a silicone gel is used as the potting compound (14).

3. Method according to one of the preceding claims, wherein the antenna base body (11) is manufactured by injection molding of polycarbonate.

4. Method according to one of the preceding claims, wherein a thermoplastic elastomer is used as the sealing material for the at least first seal (110).

5. A method according to any of the preceding claims, comprising the following method step, which is carried out before the potting of the radar module (12): - Attaching a potting frame (13) to a surface of the antenna base body (11) facing away from the horn antenna (111), wherein during injection molding a second, circumferential seal (110') is potted along an outer contour of the antenna base body (11). is so that the antenna base body (11 ) seals without gaps to the potting frame (13) at the outer contour.

6. Method according to one of the preceding claims, wherein the antenna base body (11 ) and the seal (110, 110') are metallized by chemical vapor deposition or by cathode sputtering.

7. Radar-based level measuring device (1 ) for determining a level (L) of a fill material (2) manufactured according to the method according to one of the preceding claims, comprising the following components: - An antenna base body (11) which forms a horn antenna (111) with a waveguide-shaped coupling area (112) along a device axis (a), with a first seal (110) which is formed around the coupling area (112), - a radar module (12) arranged at the coupling area (112) in such a way as to transmit radar signals (SHF) to the fill material (2) via the horn antenna (111) in particular according to the FMCW method, o receive corresponding received signals (RHF) after their reflection at the surface of the fill material, and o determine the fill level (L) on the basis of this, and - a potting compound (14) by which the radar module (12) is encapsulated on the antenna base body (11) in such a way that the coupling area (112) is excluded from this.

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