Fill-level measuring device

Abstract

The invention relates to an easily producible, heat-resistant and explosion-protection-compliant fill-level measuring device (1) for a highly precise fill-level measurement, comprising the following components for this purpose: an IC-based high-frequency unit (10) which is designed to generate radar signals (SHF) at 100 GHz or more, emit said radar signals along a beam axis (a) towards the filling material (2) and receive corresponding received signals (RHF) after the radar signals are reflected on the filling material surface; and an evaluation unit which determines the fill level (L) at least on the basis of the received signal (RHF). According to the invention, the fill-level measuring device (1) is characterized by an encapsulation (11) which encapsulates the high-frequency unit (10) and at the same time surrounds a radar lens (111) positioned in the beam axis (a). The encapsulation minimizes the components and thus simplifies the adjustment of the IC in relation to the radar lens (111).

Description

[0001] Level measuring device

[0002] The invention relates to a radar-based level measuring device.

[0003] 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. The Endress+Hauser Group manufactures and distributes a wide variety of field device types and variants.

[0004] Non-contact measuring methods have become established for level measurement of filling materials in containers because they are robust and low-maintenance. A further advantage of non-contact measuring methods is their ability to measure the fill level virtually continuously. Therefore, radar-based measuring methods are predominantly used for 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 that can be achieved. The pulse transit time method and FMCW ("Frequency Modulated Continuous Wave") have become established measurement methods. Radar-based level measurement is described in more detail, for example, in "Radar Level Detection, Peter Devine, 2000".

[0005] Typical frequency bands approved for radar-based level measurement are 26 GHz, 60 GHz, 80 GHz, and 120 GHz, and increasingly also 180 GHz and 240 GHz. Higher frequency bands are advantageous for many applications because, for given antenna dimensions, greater beam focusing is achieved and generally more bandwidth is available, which can be used for greater range resolution. For higher frequencies above 100 GHz, the device's internal radio-frequency unit, which generates and processes the radar signals, is implemented in the form of integrated circuits. The radar signals are transmitted or received directly via the IC package (better known as "AiP = Antenna in Package") or even directly on the semiconductor chip ("AoC = Antenna on Chip").The structures for such integrated antennas must be kept small due to the limited chip area, resulting in a correspondingly wide radiation angle. This is what the term "radiation angle" refers to. 1 In the context of the present invention, this generally refers to the solid angle at which the respective antenna exhibits a defined, equal transmission intensity or reception sensitivity of, for example, -3 dB relative to a corresponding beam axis. The beam axis, in turn, is the vector along which the radar signal is transmitted with the highest intensity. The term "beam axis" refers to the vector along which the radar signal is transmitted with the maximum intensity.

[0006] In order to transmit the radar signals with sufficient focus towards the filling material despite IC-based radiation, a focusing radar lens must be installed upstream of the radio-frequency unit at such high frequencies, which, however, leads to increased design and manufacturing complexity. A further design conflict arises in this context from the fact that the radio-frequency unit must be encapsulated in accordance with explosion protection regulations. An alternative approach, in which the radar signals from the radio-frequency unit are not freely emitted towards the radar lens, is described in the publication WO 2023 / 285300 A1: There, the radar signals from the radio-frequency unit are coupled into an antenna via a dielectric waveguide. However, the problem with this approach is the small waveguide cross-section at high frequencies, which leads to a correspondingly delicate design and, consequently, difficult manufacturing.

[0007] The invention is therefore based on the object of providing a radar-based level measuring device that overcomes these disadvantages. The invention achieves this object by means of a level measuring device for determining the level of a product, which comprises at least the following components:

[0008] - A high-frequency unit designed to o generate radar signals and radiate them along a beam axis towards the filling material and o receive corresponding signals after their reflection at the filling material surface,

[0009] - an evaluation unit designed to determine the fill level based at least on the received signal, and

[0010] - a potting encapsulation which encapsulates at least the high-frequency unit, with o a first radar lens arranged in the beam axis.

[0011] This inventive design enables simple production of the level measuring device based on the following process steps:

[0012] - Provision of the high-frequency unit, the potting cup and the housing,

[0013] - Inserting the high-frequency unit into the potting cup,

[0014] - Pouring the casting compound into the casting cup, and

[0015] - Inserting the potting cup into the housing.

[0016] This eliminates the need for handling a delicate waveguide or adjusting the first radar lens relative to the radio-frequency unit. If the first radar lens is not encapsulated as a hybrid component in the encapsulation, but rather as a monolithic component of the encapsulation, a further manufacturing step is eliminated. The first radar lens and / or the encapsulation can be made of materials such as PTFE, PEEK, PEI, PFA, or PEE to achieve the appropriate refraction of the radar signals.

[0017] The inventive design of the level measuring device is particularly advantageous if the high-frequency unit is designed as an IC and the signals are accordingly generated or processed in a frequency band at 100 GHz or more, in particular at 180 GHz. In this case, the inventive design of the level measuring device enables focused radiation of the radar signals, even though these are emitted or received by the IC at a wide radiation angle. In this context, it is advantageous if the potting frame and the high-frequency unit are designed such that a hermetic cavity is formed between the first radar lens and the high-frequency unit. This ensures that the cavity remains potted-free during potting, so that the transmission of the radar signals is not restricted during measuring operation.

[0018] If the focusing by the first radar lens is not sufficient or if an aperture that focuses too strongly would be necessary for this, it is possible within the scope of the invention to arrange a second radar lens behind the first radar lens in the beam axis in relation to the high-frequency unit and to align it accordingly. This is particularly suitable if the housing of the level measuring device, in which the high-frequency unit is arranged, per se comprises a housing neck in order to distance the high-frequency unit from the possibly hot interior of the container. In this case, the second radar lens can be structurally arranged at the end region of the housing neck that faces towards the filling material. As a result, the first radar lens or the high-frequency unit is correspondingly distanced from the second radar lens and the interior of the container by the housing neck, or vice versa.Furthermore, it is advantageous in this case if the first radar lens has such an aperture and is spaced so far from the second radar lens that the radiation angle of the first radar lens is congruent with an outer contour of the second radar lens. This ensures that the radar signals are transmitted and received with maximum efficiency in terms of transmission / reception power. It goes without saying that, for further optimized focusing, a third radar lens can be arranged in the housing neck between the first radar lens and the third radar lens. The efficiency, especially when transmitting the radar signals, can also be increased by designing the first radar lens in such a way that it does not reflect the radar signal transmitted by the high-frequency unit as much as possible. This can be achieved in several ways:

[0019] - The first radar lens can be designed in such a way that it has a slight tilt relative to the beam axis, i.e. between 0.2° and a maximum of 15°.

[0020] - The first radar lens can have a coating or a particularly groove-shaped structure with a depth of particularly one quarter of the wavelength of the radar signal on a surface facing the high-frequency unit.

[0021] - The first radar lens can be structurally divided into two halves with respect to the beam axis, which in turn are offset from each other by a quarter of the wavelength of the radar signal with respect to the beam axis.

[0022] The term “unity 1In the context of the invention, any design or encapsulation of those electronic circuits is generally understood to mean any design or encapsulation of those electronic circuits that is required for the specific intended use, e.g. for high-frequency signal processing or as an interface. Depending on the intended use, the corresponding unit can therefore comprise corresponding analog circuits for generating or processing corresponding analog signals. However, the unit can also comprise digital circuits, such as FPGAs, microcontrollers or storage media in conjunction with corresponding programs. The program is designed to carry out the required method steps or apply the necessary computing operations. In this context, different electronic circuits of the unit within the meaning of the invention can potentially also access a common physical memory or be operated using the same physical digital circuit.It is irrelevant whether different electronic circuits within the unit are distributed on a common circuit board or on several connected circuit boards. The invention is explained in more detail with reference to the following figures. It shows:

[0023] Fig. 1 : A radar-based level gauge on a container, and

[0024] Fig 2. A sectional view of the level measuring device according to the invention.

[0025] To provide a basic understanding of the level measuring device 1 according to the invention, Fig. 1 shows a container 3 containing a medium 2 whose fill level L 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 temperature and pressure loads. For dusty or flammable substances, appropriate explosion protection conditions must be observed inside the container.

[0026] As a rule, the level measuring device 1 is connected to a separate interface unit, in which the protocol can be “4-20 mA”, “PROFIBUS”, “HART 1, or "Ethernet is implemented, 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, for example, to control inflows or outflows of the container 3 if necessary. However, other information about the general operating status of the level measuring device 1 can also be communicated.

[0027] In order to be able to determine the fill level L independently of the prevailing conditions, the fill level measuring device 1 is mounted above the filling material 2 at a known installation height h above the brine of the container 3. The fill level measuring device 1 is attached to a corresponding opening of the container 3 in such a pressure- and media-tight manner that only a second radar lens 12 of the fill level measuring device 1 is directed vertically downwards into the container 3 towards the fill material 2, while the other components of the fill level measuring device 1 are arranged outside the container 3 in a separate housing 13.

[0028] Radar signals SHF are transmitted within a predefined frequency band via the second radar lens 12 in the direction of the surface of the filling material 2. After reflection at the filling material surface, the level measuring device 1 receives the reflected reception signals RHF again via the second radar lens 12. The signal propagation time t between transmission and reception of the respective radar signal SHF, RHF is according to proportional to the distance d between the level measuring device 1 and the filling material 2, whereby the variable “c” represents the at least roughly known radar propagation speed. The signal propagation time t can be determined by the level measuring device 1, for example, using the FMCW or pulse propagation time method. This allows the level measuring device 1 to assign the measured propagation time t to the respective distance d, for example on the basis of an appropriate calibration. The level measuring device 1 can then determine the filling level L according to d - h - L, provided that the installation height “h” is stored in the level measuring device 1. To determine the signal propagation time t or the corresponding filling level value L based on the incoming received signal RHF, the level measuring device 1 comprises an appropriately designed evaluation unit, in which the corresponding measuring principle (FMCW or the pulse propagation time method) is implemented.A corresponding high-frequency unit 10 in the level gauge 1 is used to generate the transmitted radar signal SHF and to preprocess the received signal RHF. If the FMCW method is implemented, the high-frequency unit 10 can be based on a PLL ("Phase Locked Loop") on the transmit side, for example. On the receive side, the high-frequency unit 10 can in this case include a Fourier transformation 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 frequency or frequency band in which the high-frequency unit 10 of the level measuring device 1 generates the radar signal SHF is selected primarily depending on the nature of the filling material 2: In the case of high-precision level measurement, a comparatively high frequency band, for example, 180 GHz, is implemented. An inventive design of the level measuring device 1, which is easy to manufacture even at such a high frequency band, has explosion protection compliance, and can be designed to be temperature-resistant, is explained in more detail with reference to Fig. 2:

[0030] Basically, the IC-based radio-frequency unit 10 comprises a printed circuit board substrate 100, which in turn is arranged in the housing 13. As a result, the beam axis a, under which the radar signals S, RHF are emitted or received by the IC, is aligned orthogonally to the printed circuit board substrate 100. The printed circuit board substrate 100 and the radio-frequency unit 10 are in turn fixed within the housing 13 in a potting encapsulation 11. This is filled with a potting compound (not explicitly shown) during the manufacturing process in order to encapsulate the radio-frequency unit 10 in compliance with explosion protection regulations.

[0031] According to the invention, the encapsulation 11 is designed in alignment with the beam axis a in the form of a focusing, first radar lens 111, wherein the first radar lens according to Fig. 2 represents a monolithic component of the encapsulation 11. This eliminates the need for a separate component. By fixing the circuit board substrate 100 within the encapsulation 11, the adjustment of the first radar lens 111 with respect to the beam axis a is also facilitated, since the alignment of the circuit board substrate 100 is predetermined by corresponding stop points in the encapsulation 11. In the embodiment shown, the housing 13 of the level measuring device 1 comprises a housing neck 131, so that the high-frequency unit 10 is spaced from the interior of the container for its thermal protection.The end region of the housing neck 131 which, in the assembled state, faces away from the container interior adjoins the first radar lens 111 in alignment with the beam axis a. The opposite end region of the housing neck 131, which faces the filling material 2, is closed off by the second radar lens 12, wherein the second radar lens 12 is in turn arranged and aligned in the same beam axis a as the first radar lens 111.

[0032] As shown schematically in Fig. 2, the aperture and thus the radiation angle of the first radar lens 111 is matched to the length of the housing neck 13 and the contour of the second radar lens 12 in that the second radar lens 12 is aligned according to aiu ~ N * HFis illuminated approximately across its entire cross-section. Thus, the total cross-section of the second radar lens 12 in this case corresponds to an integer multiple N of the number of wavelengths HF of the radar signals SHF. Due to the generally reciprocal radar properties, the radiation angle at the first radar lens 111 is independent of whether transmission or reception is taking place.

[0033] The second radar lens 12 is also designed to be focused, so that the resulting radiation angle of the radar signals S, RHF towards the filling material 2 is further focused compared to the radiation angle of the first radar lens 111. Since plastics such as PTFE, PEEK, PEI, PFA, or PEE cause a corresponding refraction of the radar signals S, RHF due to their dielectric value, the radar lenses 12, 111 or the potting cup 11 can be manufactured from these materials, for example, by injection molding or hot stamping.

[0034] In the embodiment of the potting cup 11 according to the invention shown in Fig. 2, the potting cup 11 is designed such that after inserting the printed circuit board substrate 100 into the potting cup 11, a hermetic cavity 112 is formed between the first radar lens 111 and the radio-frequency unit 10. The advantage of this is that during the subsequent potting of the potting cup 11 with, for example, casting resin, the cavity 111 remains free of casting resin. Thus, the radar signal path along the

[0035] Beam axis a not affected by any casting compound.

[0036] List of reference symbols

[0037] 1 level gauge

[0038] 2 Filling material

[0039] 3 containers

[0040] 4 Superior unit

[0041] 10 High frequency unit

[0042] 11 Encapsulation

[0043] 12 Second radar lens

[0044] 13 housings

[0045] 100 PCB substrate

[0046] 111 First radar lens

[0047] 112 Cavity

[0048] 131 Housing neck a Beam axis d Distance h Installation height

[0049] L Fill level

[0050] RHF reception signals

[0051] SHF radar signals at the beam angle of the first radar lens

Claims

Patent claims 1. Level measuring device for determining a level (L) of a filling material (2), comprising the following components: - A high-frequency unit (10) which is designed to o generate radar signals (SHF) and to radiate them along a beam axis (a) towards the filling material (2) and o receive corresponding reception signals (RHF) after their reflection at the filling material surface, - an evaluation unit designed to determine the fill level (L) based on at least the received signal (HF), and - a potting encapsulation (11) which encapsulates at least the high-frequency unit (10), with a first radar lens (111) arranged in the beam axis (a).

2. Level measuring device according to claim 1, wherein the first radar lens (111) is enclosed in the encapsulation (11).

3. Level measuring device according to claim 1, wherein the first radar lens (111) is designed as a monolithic component of the encapsulation (11).

4. Level measuring device according to one of the preceding claims, wherein the first radar lens (111) and / or the encapsulation (111) is made of PTFE, PEEK, PEI, PFA or PEE.

5. Level measuring device according to one of the preceding claims, wherein the high-frequency unit (10) is designed to generate or process the signals (S, RHF) in a frequency band at least 100 GHz, in particular at 180 GHz.

6. Level measuring device according to one of the preceding claims, wherein the encapsulation (11) is designed such that a hermetic cavity (112) is formed between the first radar lens (111) and the high-frequency unit (10).

7. Level measuring device according to one of the preceding claims, comprising: - A second radar lens (12) arranged and aligned with respect to the high frequency unit (10) behind the first radar lens (111) in the beam axis (a).

8. Level measuring device according to claim 7, comprising: - A housing (13) with a housing neck (131) through which the second radar lens (12) is spaced from the first radar lens (111) or from the high-frequency unit (10).

9. Level measuring device according to claim 7 or 8, wherein the first radar lens (111) has such an aperture and is spaced so far from the second radar lens (12) that the radiation angle (am) of the first radar lens (111) is congruent with an outer contour of the second radar lens (12).

10. Level measuring device according to one of the preceding claims, wherein the first radar lens (111) has a defined tilt of in particular between 0.2° and 15° relative to the beam axis (a), and / or wherein the first radar lens (111) has a coating or a particularly groove-shaped structure with a depth of in particular a quarter of the wavelength of the radar signal (SHF, RHF) on a surface facing the high-frequency unit (10).

11. Method for manufacturing the level measuring device 1 according to at least one of the preceding claims, comprising the following method steps: - Providing the high-frequency unit (10), the potting cup (11) and the housing (13), - Inserting the high-frequency unit (10) into the potting cup (11), - Filling the casting compound into the casting cup (11 ), and - Insert the potting cup (11) into the housing (13).

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