Level gauge

Description

[0001] The invention relates to a compact and modular level measuring device.

[0002] In process automation technology, appropriate field devices are used to record relevant process parameters. To record the respective process parameters, suitable measurement principles are implemented in the corresponding field devices to record process parameters such as level, flow, pressure, temperature, pH value, redox potential, or conductivity. Endress + Hauser manufactures and distributes a wide variety of such field device types.

[0003] Non-contact measurement methods have become established for level measurement of filling materials in containers because they are robust and low-maintenance. Another advantage of non-contact measurement methods is their ability to measure the fill level virtually continuously. Therefore, radar-based measurement methods are predominantly used in 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). One established measurement method is FMCW. (“Frequency Modulated Continuous Wave”). The FMCW-based level measurement method is described, for example, in the published patent application DE 10 2013 108 490 A1.

[0004] By design, the antenna array of radar-based level gauges must be mounted in direct contact with the interior of the container, as no barrier impermeable to radar signals may be present between the antenna array and the medium. The electronic modules of the level gauge, such as the radar-specific high-frequency module for high-frequency signal generation and other units for data processing and transmission, are housed outside the container in a separate device housing. Especially for explosion protection purposes, spatial separation between the active, i.e., powered modules, and the passive antenna array is often required. For this purpose, the device housing includes a gauge neck, via which the antenna array is mechanically connected to the device housing. A corresponding explosion protection barrier is arranged in the gauge neck between the antenna array and the antenna array.In addition to or as an alternative to explosion protection requirements, the measuring device neck may need to fulfill additional protective functions: Depending on the application, high temperatures, high pressure, or hazardous gases may be present inside the container. Therefore, depending on the application, the measuring device neck must function as a pressure seal, temperature barrier, and / or media seal.

[0005] To ensure that the device housing and its (interface) modules can serve as a platform for other field device types besides level measuring devices, and to allow for a more compact overall device housing, the high-frequency module specific to radar-based level measuring devices can be relocated to the device neck. However, the spatial conditions within the device neck are extremely limited due to thermal and explosion protection requirements. For this reason, accommodating the radar-specific high-frequency module in the device neck is difficult. Connecting the high-frequency module to the antenna array is also challenging, particularly with a modular design, as the connection must be detachable, and any plug connections between the corresponding waveguide segments increase the risk of high-frequency interference.

[0006] WO 2020 / 120059 A1 describes a radar-based level measuring device according to the prior art, in which a waveguide segment is connected to an antenna via a feedthrough via a radio frequency connection.

[0007] The invention is therefore based on the object of providing a compact and modular level measuring device.

[0008] The invention solves this problem by a radar-based level measuring device that is used to determine a level in a container and comprises the following components: An antenna arrangement which can be controlled via a waveguide-shaped high-frequency connection, by means of which a radar signal can be transmitted towards the filling material, and by means of which a corresponding reception signal can be received after reflection of the radar signal at the filling material surface, a high-frequency module, with ∘ a transmitting / receiving unit which is designed to generate the radar signal according to a defined measuring principle and to determine the filling level after reflection of the radar signal at the filling material surface based on the corresponding reception signal according to the implemented measuring principle, further with ∘ an electronics encapsulation in which the transmitting / receiving unit is arranged, so that the transmitting / receiving unit and the second waveguide segment can be enclosed by means of a potting within the electronics encapsulation for the purpose of explosion protection until the feedthrough, and with ∘ a waveguide segment,which is connected to the transmitting / receiving unit for transmitting the radar signals in such a way that the waveguide segment is guided out of the electronics encapsulation; a device housing adjacent to the antenna arrangement, in which the radio-frequency module is arranged, or in whose measuring device neck the radio-frequency module is arranged; and a spring element which prestresses the radio-frequency module or the electronics encapsulation relative to the device housing or the measuring device neck in such a way that the guided waveguide segment is pressed against the radio-frequency connector with a corresponding force in the direction of a common waveguide axis. According to the present invention, the waveguide segment is designed as a hollow guide segment.

[0009] The spring element according to the invention ensures a gap-free and thus low-interference connection of the high-frequency module to the antenna array via the waveguide segment or the corresponding high-frequency connector, thereby simplifying the modular design of the level gauge. The compression reduces susceptibility to RF interference because the high-frequency connector and the waveguide segment are designed as hollow guides. The inventive principle of compression of the waveguide segment can also be applied if a positive-fit galvanic isolation is arranged on both sides between the high-frequency connector and the waveguide segment to electrically decouple the antenna array.

[0010] The inventive pressing of the electronic module is particularly advantageous when the device housing includes a measuring device neck as thermal decoupling from the antenna array. In this case, the high-frequency module to be connected to the antenna array can be arranged in the measuring device neck – under the inventive prestressing. On the one hand, this saves space in the actual device housing. On the other hand, this design minimizes the length of the high-frequency path between the antenna array and the high-frequency module, thus further reducing the susceptibility to RF interference during level measurement.

[0011] For the purposes of the invention, it is not predetermined whether the high-frequency module or its waveguide segment is pressed against the high-frequency connection by the spring element under pressure or under tension. Accordingly, the spring element can be designed either as a compression spring or as a tension spring. If the spring element is designed as a compression spring, the compression spring for preloading the high-frequency module must be arranged within the device housing or within the measuring device neck on an outer side of the electronics encapsulation opposite the waveguide segment. If the spring element is designed as a tension spring, the tension spring for preloading the high-frequency module must be arranged within the device housing or within the measuring device neck on an outer side of the electronics encapsulation facing the waveguide segment.Depending on the design, the spring element can be designed as one or more wave springs, spiral springs or disc springs.

[0012] To ensure easy and secure insertion of the high-frequency module into the device housing or the measuring device neck during production, it is recommended to design the level gauge with at least one such guide element. This guides the high-frequency module within the device housing or the measuring device neck along the common waveguide axis of the high-frequency connector or waveguide segment. This ensures that the waveguide segment docks precisely onto the high-frequency connector during installation.

[0013] Under the terms "Unit" or "Module"In the context of the invention, "electronic circuit" is understood to mean, in principle, any electronic circuit that is suitably designed for the intended purpose, e.g., for high-frequency generation or as an interface. Depending on the requirements, the corresponding unit may comprise an analog circuit for generating or processing corresponding analog signals. However, the unit may also comprise a digital circuit, such as an FPGA or a storage medium in conjunction with a program. The program is designed to carry out the corresponding method steps or to apply the necessary computing operations of the respective unit. In this context, different electronic units or modules of the measuring device within the meaning of the invention may potentially also access a common physical memory or be operated using the same physical digital circuit.Specifically, the transmitting / receiving unit for controlling the antenna arrangement via the waveguides can be based on the FMCW or pulse transit time method, for example.

[0014] The invention is explained in more detail with reference to the following figures. They show: Fig. 1 : A radar-based level gauge on a container, Fig. 2 : a cross-sectional view of the level measuring device according to the invention, and Fig. 3 : a detailed view of the level gauge in the area of ​​the waveguide segment.

[0015] For a basic understanding of radar-based level measurement, Fig. 1A container 3 containing a medium 2 is shown, the fill level L of which is to be determined. Depending on the type of medium 2 and the area of ​​application, the container 3 can be up to more than 100 m high. The conditions within the container 3 also depend on the type of medium 2 and the area of ​​application. For example, exothermic reactions can lead to high temperatures and pressures. For dusty or flammable substances, appropriate explosion protection conditions must be observed inside the container.

[0016] In order to be able to determine the fill level L independently of the prevailing conditions, a radar-based level measuring device 1 is mounted on the container 3 at a known installation height h above the filling material 2. The level measuring device 1 is fastened or aligned to a corresponding (flange) opening of the container 3 in such a way that an antenna arrangement 10 of the level measuring device 1 is directed vertically into the container 3 towards the filling material 2. The remaining device housing 13 of the level measuring device 1, in which the electronic components 11 are accommodated, is arranged outside the container feedthrough. The spatial separation of the electronic components 11 in the device housing 13 from the antenna arrangement 10 and from the container interior by a measuring device neck 131 ensures, on the one hand, explosion protection within the container 3. On the other hand, the electronic components 10 are located in the device housing 13 orin the measuring device neck 131, protected from temperature and pressure stress from the container interior. As in . Fig. 1 and Fig. 2 As indicated, the measuring device neck 131 has corresponding cooling fins for thermal decoupling of the device housing 13.

[0017] Due to the arrangement on the container 3, the level measuring device 1 is able to transmit radar signals S HF vertically in the direction of the surface of the filling material 2 via the antenna arrangement 10. After reflection at the filling material surface, the level measuring device 1 receives the reflected radar signals R HF in turn via the antenna arrangement 10. The signal propagation time between transmission and reception of the respective radar signal S HF , R HF is proportional to the distance d between the level measuring device 1 and the filling material 2, wherein the signal propagation time can be determined by the level measuring device 1, for example, using the FMCW or the pulse propagation time method. Accordingly, the level measuring device 1 can assign the measured propagation time to the respective distance d, for example based on a corresponding calibration. The level measuring device 1 can thereby d = h − L in turn determine the fill level L, provided that the installation height h is stored in the level measuring device 1.

[0018] Typically, the level measuring device 1 is connected to a higher-level unit 4, such as a process control system, via an interface module, such as "PROFIBUS," "HART," or "Wireless HART," housed in the device housing 13. This can be used to transmit the level value L, for example, to control the inflow or outflow of the container 3 if necessary. However, other information about the general operating status of the level measuring device 1 can also be communicated.

[0019] As in Fig. 2As outlined, the antenna arrangement 10 within the level measuring device 1 is controlled using high frequency technology by a high-frequency module 11, 12, 120. In this case, the FMCW or pulse transit time measuring principle, for example, is implemented in a correspondingly designed transmitting / receiving unit 11 of the high-frequency module 11, 12, 120 to determine the signal propagation time based on the incoming received signal R HF. In addition, the transmitting / receiving unit 11 serves to generate the radar signal S HF to be transmitted. For this purpose, the transmitting / receiving unit 11 in the embodiment shown is arranged within the measuring device neck 131, for example as a monolithically encapsulated SMD component on a side of a printed circuit board facing the antenna arrangement 10.

[0020] The printed circuit board, including the transmitting / receiving unit 11, is enclosed by an electronics encapsulation 12 of the high-frequency module 11, 12, 120. The electronics encapsulation 12 can be made of a plastic such as PC, PE, PP, or PA. This allows, on the one hand, the printed circuit board, including the transmitting / receiving unit 11, to be additionally encapsulated with a potting compound for explosion protection purposes (not explicitly mentioned in Fig. 2 On the other hand, the coupling of the transmitting / receiving unit 11 to the antenna arrangement 10 according to the invention is made possible by means of the high-frequency module 11, 12, 120. For this purpose, the antenna arrangement in the case of the Fig. 2 In the embodiment shown, the high-frequency connection 100 is a straight waveguide segment 100, via which the antenna arrangement 10 can be contacted by the high-frequency module 11, 12, 120.

[0021] For transmitting the radar signals S HF , R HF from or to the transmitting / receiving unit 11, the high-frequency module 11, 12, 120 is assigned a likewise rectilinear waveguide segment 120, which, in the fully assembled state of the level measuring device 1, extends orthogonally from the transmitting / receiving unit 11 to the high-frequency connection 100 with respect to the circuit board. The waveguide segment 120 is attached to a feedthrough 121 of the electronics encapsulation 12 via a screw connection 122 in such a way that the waveguide segment 120 is guided outward through the wall of the electronics encapsulation 12. For this purpose, the waveguide segment 120 has an external thread around the cavity aligned in the waveguide axis a, so that the waveguide segment 120 is countered by a corresponding nut from the outside against the electronics encapsulation 12, as shown in Fig. 2 is the case. Instead of the Fig. 2The waveguide segment 120 can also be fastened to the feedthrough of the electronics encapsulation 12 using an alternative fastening method, for example by means of a pin, using the screw connection 122 shown.

[0022] In addition, the circuit board on which the transmit / receive unit 11 is arranged within the electronics encapsulation 12 is mounted to the waveguide segment 120 by means of at least one fastening means. This fastening means can be an adhesive connection or, again, a pin or screw connection. As a result, the circuit board or the transmit / receive unit 11 is self-supporting within the electronics encapsulation 12. This means that, due to the indirect fixation via the waveguide segment 120, the transmit / receive unit 11 does not require direct fixation to the electronics encapsulation 12. This allows the circuit board and thus the electronics encapsulation 12 as a whole to be designed very compactly, thus simplifying the accommodation of the high-frequency module 11, 12, 120 in the measuring device neck 131.

[0023] As in Fig. 2As shown, in addition to the transmitting / receiving unit 11, further printed circuit boards 15 can also be arranged within the electronics encapsulation 12 of the high-frequency module 11, 12, 120. These can, as shown in the illustration, be electrically connected, for example by means of a mechanically flexible cable harness, to the circuit board on which the transmitting / receiving unit 11 is arranged. The transmitting / receiving unit 11 and any further printed circuit boards 15 for manufacturing the high-frequency module 11, 12, 120 can be inserted from a side of the electronics encapsulation 12 facing away from the feedthrough 121, for example by means of an assembly aid which is designed as a negative mold of the transmitting / receiving unit 11 or the further printed circuit boards 15.

[0024] In the assembled state, i.e. as soon as the high-frequency module 11, 12, 120 is inserted into the measuring device neck 131, the high-frequency connection 100, designed as a waveguide, and the waveguide segment 120 of the high-frequency module 11, 12, 120 are so precisely adjacent to one another (or the high-frequency connection 100 and the waveguide segment 120 are so precisely adjacent to a galvanic isolation 140 arranged between them) that the waveguide segments 100, 120 form a common waveguide axis a. This achieves a loss-free transmission of the radar signals S HF between the antenna arrangement 10 and the transmitting / receiving unit 11. Accordingly, the high-frequency module 11, 12, 120 is Fig. 2The embodiment shown is designed such that the electronics encapsulation 12, when inserted into the measuring device neck 131 (from the end region facing away from the antenna arrangement 10), is guided in the direction of the waveguide axis a of the waveguide segments 100, 120. For this purpose, a corresponding guide element 14 is formed radially symmetrically around the second waveguide segment 120 in this area, in an extension to the electronics encapsulation 12 and corresponding to the inner wall of the measuring device neck 131.

[0025] The Fig. 2The optional galvanic isolation 140 made of plastic or ceramic shown serves to electrically decouple the antenna arrangement 10 from the transmitting / receiving unit 11 or from the other electronic components in the device housing 13. For this purpose, the galvanic isolation 140 is arranged precisely between the radio-frequency connection 100 and the waveguide segment 120, wherein the galvanic isolation 140 is made of an electrically insulating material such as a ceramic or plastic and has a feedthrough corresponding to the inner cross-section of the waveguides 100, 120.

[0026] In order to ensure that the high-frequency connection 100 of the antenna arrangement 10 and the waveguide segment 120 of the high-frequency module 1, 12, 120 adjoin one another or the galvanic isolation 140 without a gap when the electronics encapsulation 12 is inserted, a spring element 130 presses the electronics encapsulation, guided by the guide element 14, from the interior of the measuring device neck 131 towards the antenna arrangement 10 in such a way that the waveguide segment 120 is pressed against the waveguide of the high-frequency connection 100 with the corresponding spring force. This in turn ensures loss-free signal transmission. Fig. 2 In the embodiment shown, the spring element 130 is designed as a wave spring. The wave spring 130 is clamped inside the measuring device neck 131 between a groove or a retaining ring 132 and the outer side of the electronics encapsulation 12 facing away from the waveguide segment 120.

[0027] In contrast to the Fig. 2 In the embodiment shown, it is also conceivable to design the spring element 130, 133 as a tension spring 133 and to clamp it in the device neck 131 between the antenna arrangement 10 and the electronics encapsulation 12 in order to pull the second waveguide segment 120 against the first waveguide segment 100 with the corresponding spring force. Such a possibility for the inventive fixing of the high-frequency module 11, 12, 120 is shown in Fig. 3illustrated: In the embodiment shown there, a spring ring 133 is provided on the outside of the electronics encapsulation 12 at the level of the waveguide segment 120. The spring ring 133 is designed to press against the guide element 14 of the electronics encapsulation 12 from the inside when the high-frequency module 11, 12, 120 is inserted into the measuring device neck 131, so that an annular outer bead of the guide element 14 snaps outwards into a corresponding groove in the measuring device neck 131. The positions of the spring ring 133, the outer bead, and the groove are selected so far down that the waveguide segment 120 is in turn pressed against the high-frequency connection 100 of the antenna arrangement 10 with a defined tensile stress and without a gap.

[0028] Regardless of the design of the spring element 130, 133 as a tension spring 133 or a compression spring 130, the clamping not only ensures a gap-free seal between the waveguides 100, 120 but also ensures that the electronics encapsulation 12 is fixed within the measuring device neck 12. In this context, the inventive pressing of the waveguide segment 120 against the radio-frequency connector 100 can also be implemented if the electronics encapsulation 12 is housed directly in the device housing 13. This can be the case if the device housing 13 of the level measuring device 1 does not include a measuring device neck 131, or if the waveguide-shaped radio-frequency connector 100 extends through the entire measuring device neck 131. In addition, the pressing of the individual waveguide segments 100, 120 according to the invention can also be implemented if they are not designed as waveguides, but for example as dielectric waveguides. List of reference symbols

[0029] 1Level measuring device 2Filling material 3Container 4Superordinate unit 10Antenna arrangement 11Transmitter / receiver unit 12Electronics encapsulation 13Device housing 14Guide element 15Printed circuit board 100High-frequency connection 120Waveguide segment 121Feedthrough in the electronics encapsulation 122Screw connection 130Spring element 131Measuring device neck 132Retaining ring 133Spring ring 140Galvanic isolation aWaveguide axis dDistance hInstallation height LLevel R HF Reflected radar signal S HF Radar signal

Claims

1. A radar-based fill level meter for determining a fill level (L) of a filling material (2), comprising the following components: - An antenna assembly (10), which can be activated via a high-frequency connection (100) in the form of a waveguide, o with which a radar signal (SHF) can be sent in the direction of the filling material (2), and ∘ with which a receive signal (RHF) can be received once the radar signal (SHF) has been reflected on the surface of the filling material, - a high-frequency module (11, 12, 120), with o a transmitter / receiver unit (11), which is configured to generate the radar signal (SHF) and, once it has been reflected on the surface of the filling material, to determine the filling level (L) based on the corresponding receive signal (RHF), with o electronic encapsulation (12), in which the transmitter / receiver unit (11) is arranged, and with o a waveguide segment (120), which is connected to the transmitter / receiver unit (11) in order to transmit the radar signals (SHF, RHF) in such a way that the waveguide segment (120) is guided out of the electronic encapsulation (12), - a device housing (13) connected to the antenna assembly (10), in which the high-frequency module (11, 12, 120) is arranged, and - a spring element (130, 133), which is used to preload the high-frequency module (11, 12, 120) opposite the device enclosure (13) in such a way that the waveguide segment (120) is pressed against the high-frequency connection (100) with a corresponding force in the direction of a shared waveguide axis (a).

2. The fill level meter as claimed in claim 1, wherein the spring element (130, 133) is configured as a pressure spring (130), which is arranged on an outer side of the electronic encapsulation (12) opposite the waveguide segment (120) in order to preload the high-frequency module (11, 12, 120) inside the device housing (13).

3. The fill level meter as claimed in claim 1, wherein the spring element (130, 132) is configured as a tension spring (133), which is arranged on an outer side of the electronic encapsulation (12) facing toward the waveguide segment (120) in order to preload the high-frequency module (11, 12, 120) inside the device housing (13).

4. The fill level meter as claimed in one of the preceding claims, wherein the spring element (130, 133) is configured as a wave spring (130), a spiral spring, a disk spring and / or a spring washer (133).

5. The fill level meter as claimed in one of the preceding claims, wherein the device housing (13) is connected to the antenna assembly (10) via a measuring device neck (131), in which the high-frequency module (11, 12, 120) is arranged.

6. The fill level meter as claimed in at least one of the preceding claim, wherein at least the transmitter / receiver unit (11) is sealed inside the electronic encapsulation (12) using the potting compound.

7. The fill level meter as claimed in one of the preceding claims, comprising: At least one guide element (14), which is configured to guide the high-frequency module (11, 12, 120) inside the device housing (13) or inside the measuring device neck (131) along the shared waveguide axis (a).

8. The fill level meter as claimed in at least one of the preceding claims, wherein galvanic separation (140) with a positive connection on both sides is arranged between the high-frequency connection (100) and the waveguide segment (120).