Fill level measuring device

Abstract

This invention relates to a high-temperature resistant radar-based fill level measurement device (1) with a transmitting / receiving component (11) for efficiently transmitting and receiving radar signals (S) in different frequency bands. HF1,2 R HF1,2 For this purpose, the transmitting / receiving component (11) is based on a waveguide (111), by means of which the temperature-sensitive high-frequency unit of the horizontal measuring device (1) is spaced apart from the potentially hot contents (2). Radar signal (S HF1,2 R HF1,2 The signal is transmitted and received via the end region of the waveguide (111). According to the invention, the waveguide (111) has an inner cross-section (D) through which only the lowest frequency radar or received signal (S) is transmitted. HF1 R HF1 ) is specifically propagated in the fundamental mode, while higher frequency band radar or received signals (S HF2 R HF2 The signal must propagate predominantly in a higher-order mode. To ensure that all frequency bands remain at a common phase center in the end region and are thus transmitted efficiently, according to the invention, an adjustment element (112) is arranged there, which directs the transmission of the radar signal (S) in the higher frequency band of the transmission direction. HF2 The mode is converted to a lower order mode. As a result of this design, the transmit / receive component (11) can be designed compactly and efficiently.

Description

Technical Field

[0001] This invention relates to a radar-based fill level measuring device suitable for a variety of applications. Background Technology

[0002] In process automation technology, field devices are used to record relevant process parameters. To record desired process parameters, appropriate measurement principles are implemented in the field devices. Examples of these process parameters include, for instance, fill level, flow rate, pressure, temperature, pH value, redox potential, and conductivity. Various types of field devices are manufactured and sold by the Endershaus Group.

[0003] For measuring the fill level of fill material in containers, non-contact measurement methods have proven themselves due to their robustness and low maintenance costs. Another advantage of non-contact measurement methods is their ability to virtually continuously measure the fill level. Therefore, for continuous fill level measurements, radar-based measurement methods are primarily used. In such cases, the term " radar In the context of this invention, "signal" means, therefore, electromagnetic waves with frequencies between 0.1 GHz and 300 GHz. Essentially, the higher the frequency, the higher the achievable measurement resolution. Established as measurement methods are the pulse travel time method and the FMCW ("Frequency Modulated Continuous Wave") method. More information on radar-based fill level measurements can be found, for example, in… Radar Level Detection, Peter Devine, 2000 Found in ”.

[0004] Typical frequency bands permitted for radar-based fill level measurements are located at 26 GHz, 60 GHz, 80 GHz, and 120 GHz, and increasingly at 180 GHz and 240 GHz. In such cases, higher frequency bands are advantageous for many applications because, for a given antenna size, higher beam focusing is achieved, and generally more bandwidth is available, which can be used for greater range resolution. One such application is highly accurate fill level measurements in refining tanks.

[0005] However, radar signals with higher frequencies or higher bands also have various known drawbacks that can lead to deterioration or error in the measured fill level values ​​in specific applications. These drawbacks are largely due to the interaction between radar measurements and the fill material being measured, the gaseous environment surrounding the fill material, and are also partly related to container shape, environmental conditions, installation conditions, and regulatory specifications. In particular, fill level measurement in grain silos is an application where a wide beamcone and therefore a low frequency band are advantageous: the particulate characteristics of these fill materials cause high diffuse reflection of the radar signal, thus, in the case of a narrow beamcone and high frequency band, the reflected received signal can be diverted far away from the vertical direction, making it unreceived by the antenna of the fill level measuring equipment.

[0006] To leverage the advantages of different frequencies and bands, WO 2023099269 A1 describes a fill level measuring device capable of determining fill levels in a large number of distinct frequency bands, depending on the situation or application. However, in such cases, using the same antenna to transmit and receive radar signals from different frequency bands presents problems, as the antenna is optimized for a specific frequency. A trade-off arises with broadband designs for antennas targeting all frequency bands. The application of multiple antennas in the transmitting / receiving unit increases the space consumption of the fill level measuring device. This situation is further complicated by fill level measurements in containers with increased process temperatures, as high-frequency units are particularly susceptible to the effects of high temperatures. Summary of the Invention

[0007] Therefore, the object of the present invention is to provide a radar-based fill level measurement device that is applicable to multiple frequency bands that are significantly different from each other and overcomes the above-mentioned disadvantages.

[0008] This invention achieves this objective using a transmitter / receiver for a radar-based fill level measurement device, by means of which the radar signal of the transmitter / receiver can be transmitted in at least two distinct frequency bands and received as a corresponding received signal after reflection. For this purpose, the transmitter / receiver includes: - Hollow conductor, which has o At least one coupling structure, through which radar signals can be coupled into the hollow conductor, and received signals can be coupled out of the hollow conductor. The inner cross section is selected such that the lowest frequency radar signal and the received signal can propagate specifically in one of their fundamental modes, and o First end region, through which radar signals can be transmitted and received. - A matching element, disposed at the first end region, is designed to convert the high-frequency radar signal in the output direction into at least one lower-order mode, particularly into the fundamental mode. In a scientific context, for example in... "Flexible Radar Front End with Multimodal Transition at 300 GHz "A flexible radar front-end with multi-mode conversion"; M. Geiger et al.; 2020 IEEE / MTT-S International Microwave Symposium (IMS) The core working principle was disclosed in the text.

[0009] The advantage of the transmitting / receiving device of the present invention is that, when the dimensions of the inner cross section are designed such that radar signals and received signals in the high-frequency band can propagate in higher-order modes according to the following formula, radar signals can be transmitted and received in all frequency bands with a shared phase center: , From an optical perspective, this makes it simpler to position the focusing radar lens in front of the first end region of the hollow conductor, so as to focus radar signals across all frequency bands more effectively in the output direction. In this way, the overall transmitting / receiving device can be designed more compactly. Particularly advantageous in this respect is positioning the radar lens in front of the first end region of the hollow conductor, ensuring that the beam angle of the radar signal in the lowest frequency band completely covers the radar lens, thereby achieving the highest possible signal strength.

[0010] To convert high-frequency radar signals into lower-order modes, the matching element can be made of a dielectric material, and / or the matching element can be designed to taper or taper in the emission direction. The matching element can be fixed to a hollow conductor, for example, by providing a corresponding segment on the matching element that protrudes into a first end region and thus fixes the matching element there.

[0011] The cross-sectional shape of the hollow conductor is not fixed and predetermined within the scope of this invention. For example, the shape can be square. However, advantageously, the hollow conductor has a circular inner cross-section because, in such a case, the matching element is also designed rotationally symmetrically to simplify manufacturing and mounting on the hollow conductor.

[0012] The transmitting / receiving device of the present invention is perfectly suited for radar-based filling level measurement of filling materials. A corresponding filling level measuring device includes: - A high-frequency unit, designed, in particular according to the FMCW method, to generate radar signals in at least two mutually defined frequency bands and to process the corresponding received signals, and - An evaluation unit designed to determine the fill level based on the received signal in at least one frequency band.

[0013] - The transmitting / receiving device of the present invention is used to transmit radar signals toward the filling material in such a situation, and to receive the corresponding received signal after the radar signal is reflected from the surface of the filling material.

[0014] In this way, the fill level measuring device can effectively measure within each clearly separated frequency band, depending on the application. In such cases, within the scope of the invention, frequency bands are always clearly defined from each other when their center frequencies are at least twice the distance and the bandwidth of each band is narrower than one-fifth of its center frequency. Within the scope of the invention, clear demarcation is also provided when the center frequencies of the frequency bands are at least four times the distance and the bandwidth of each band is narrower than half the center frequency. In such cases, the center frequency of the frequency band is defined as the frequency located at the exact center of the frequency band. According to this definition, for example, the frequency band extends with a center frequency of 26 GHz and the bandwidth of 2 GHz correspondingly extends from 25 GHz to 27 GHz.

[0015] The term "in the context of this invention" unit "In principle, this means providing any set of circuits for specific applications, such as as an interface or for high-frequency signal processing. Therefore, depending on the application, the unit can include corresponding analog circuitry for generating or processing corresponding analog signals. However, the unit can also include digital circuitry, such as an FPGA, microcontroller, or storage medium, that cooperates with a corresponding program. In such cases, the program is designed to perform the required method steps or apply necessary computer operations. In this context, within the scope of this invention, different electronic circuits within the unit can also operate using shared physical memory or by means of the same physical digital circuitry. In such cases, it is not important whether the different electronic circuits within the unit are arranged on a shared circuit board or on multiple connected circuit boards." Attached Figure Description

[0016] The invention will now be explained in more detail with reference to the accompanying drawings, which are shown below: Figure 1 The present invention is a fill level measuring device installed on a container. Figure 2 The present invention relates to a transmitting / receiving device for low-frequency applications, and... Figure 3 It is a transmitting / receiving device used in the high-frequency band. Detailed Implementation

[0017] In order to understand the principle of the invention, Figure 1A container 3 containing filler material 2 is shown, whose fill level L will be determined by a radar-based fill level measuring device 1. In this case, depending on the type of filler material 2 and the field of application, the container 3 can be up to 100 m high. The optimal frequency band for the fill level measuring device 1 to determine the fill level depends on the type of filler material 2 and the field of application: in the case of coarse-particle filler material 2 and corresponding diffuse reflection, a relatively low frequency band, for example, at 6 GHz tends to be most suitable. In the case of foamed filler material, the low frequency band is also best because foam does not reflect. In the case of a refining tank as container 3, due to the flat surface of the filler material, and thus the highest possible frequency band, is advantageous because this inherently achieves a potentially greater range resolution.

[0018] Typically, the fill level measuring device 1 is connected via a separate interface unit, such as, for example, " 4-20mA " PROFIBUS " HART "or" Ethernet It connects to the upper-level unit 4, such as, for example, a local process control system or a decentralized server system. In this way, it is possible to transmit the measured fill level value L, for example, to control the inflow and / or outflow of container 3. However, other information about the overall operating status or parameterization for the fill level measuring device 1 can also be transmitted via the interface.

[0019] To determine the fill level L, the fill level measuring device 1 is mounted above the fill material 2 at a known installation height h above the bottom plate of the container 3. In this case, the fill level measuring device 1 is fixed and oriented at the appropriate port of the container 3 in a pressure-sealed and fill material-sealed manner, such that the transmitting / receiving device 11 of the fill level measuring device 1 is guided vertically downward into the container 3 in the direction of the fill material 2.

[0020] With the aid of the transmitting / receiving device 11, the radar signal S HF1,2 It is transmitted within a predetermined frequency band in the direction of the surface of the filling material 2, and is therefore emitted. In radar signal S HF1,2 After being reflected from the surface of the filling material, the filling level measuring device 1 then receives the reflected signal R via the transmitting / receiving device 11. HF1,2 Under such circumstances, the corresponding radar signals S and R are transmitted and received. HF1,2 The signal travel time t between them is based on the following formula:

[0021] The distance d between the filling level measuring device 1 and the filling material 2 is proportional to the distance c between them, where c is related to the filling material and is generally at least roughly known to the radar signals S and R. HF1,2The propagation speed. The signal travel time t can be determined by a fill level measuring device 1, for example, by means of the FMCW method or by means of the pulse travel time method. In the case of the FMCW method, in the radar signal S, R HF1,2 The intermediate frequency signal IF obtained in each case during reception and mixing. 1,2 frequency f IF1,2 According to the following formula:

[0022] The signal travel time t between transmission and reception is derived. In each case, the term... It transmits radar signal S HF1,2 The frequency change rate is a preset and therefore known frequency within the corresponding frequency band. In such a case, the intermediate frequency signal IF 1,2 frequency f IF1,2 For example, it can be determined through its Fourier transform. In this way, the fill level measuring device 1 can determine the distance d, for example, based on the calibration corresponding to the measured travel time t. In this way, the fill level measuring device 1 can further determine the fill level L according to the following formula using the installation height h provided as a parameter in the fill level measuring device 1: .

[0023] To base on the low-frequency intermediate frequency signal IF 1,2 The signal travel time t and the corresponding fill level value L are determined. The fill level measuring device 1 includes a correspondingly designed evaluation unit, in which, for example, the FMCW measurement principle or the pulse travel time measurement principle is implemented. This is used to generate the radar signal S. HF1,2 and used to generate the corresponding intermediate frequency signal IF 1,2 This is a high-frequency unit connected to the transmitter / receiver 11. In this case, for implementing the FMCW method, the high-frequency unit can include a transmitter side, such as a correspondingly designed phase-controlled control loop (“…”). PLL or phase-locked loop In this case, a mixer and subsequent Fourier transform logic are used on the receiving side of the high-frequency unit to record the intermediate frequency signal IF corresponding to the distance d. 1,2 frequency f IF1,2 .

[0024] Radar signal S HF1,2The selection of the center frequency and bandwidth depends explicitly on the field of use, and especially on the type of filling material 2: for highly accurate measurements of the filling level, such as, for example, in oil storage tanks, the highest possible bandwidth is inherently advantageous, while in the case of non-uniform or wavy filling material surfaces, the widest possible beam angle of the transmitting / receiving device 11, i.e., a relatively low bandwidth, is advantageous. In such cases, according to the concept of " Beam horn This means that the transmitting / receiving device 11 has a solid angle of equal transmit strength or receive sensitivity, for example, -3dB.

[0025] In order to be usable under these application conditions, Figure 1 The fill level measuring device 1 shown is capable of transmitting radar signals S in two different frequency bands. HF1 S HF2 In this case, the frequency bands do not overlap but are clearly defined from one another. The selection of the frequency band for which the fill level measuring device 1 determines the fill level value L can be manually predetermined, or the fill level measuring device 1 can select the most suitable frequency band. In the second case, the fill level measuring device 1 can be designed such that it independently selects the core frequency band based on certain parameters, such as, for example, the possible rate of change of the fill level value L. This is also described in DE 10 2021 131 690 A1.

[0026] For signal generation in different frequency bands, the fill level measuring device 1 therefore includes two separate high-frequency units, which are designed to generate corresponding radar signals S in the two frequency bands. HF1,2 And after reflection, the corresponding received signal R is received and processed. HF1,2,3 In this case, the first high-frequency unit operates, for example, at a center frequency of 180 GHz and in the corresponding first frequency band. The second high-frequency unit generates the corresponding second radar signal S in the lowest frequency band with a center frequency of 26 GHz. HF2 .

[0027] Regarding the potential temperature load inside container 3, it is important that the fill level measuring device 1 is configured such that, in particular, the high-frequency unit is thermally protected from this effect. In this respect, Figure 2 and Figure 3 The design of the transmitter / receiver device 11 of the present invention is shown, which prevents thermal load and simultaneously achieves efficient transmission and reception in all frequency bands: In this case, the transmitter / receiver device 11 is based on the radar signal S used for transmission. HF1,2 and the received signal R HF1,2The hollow conductor 111 contains signals that are coupled into and out of the high-frequency unit via coupling structures 1111 within it. In this case, the length l of the hollow conductor 111 is designed to provide effective thermal isolation.

[0028] exist Figure 2 In the illustrated embodiment, the coupling structure 1111 is arranged in the end region of the hollow conductor 111, spaced apart from the interior of the container 3. Furthermore, in contrast to this illustrated embodiment, the option is for the coupling structure 1111 to be laterally coupled into and out of the hollow conductor 111, and / or to provide separate coupling structures for each frequency band. Since the coupling structure 1111 is connected to each high-frequency unit and is therefore arranged in the end region of the hollow conductor 111 away from the process, the high-frequency units are correspondingly protected by the hollow conductor 111 from the effects of heat from the interior of the container 3.

[0029] Through the opposing first end regions of the hollow conductor 111, and therefore, in the installed state of the filling level measuring device 1 facing this end region of the filling material 2, the radar signal S HF1,2 It was emitted and received signal R after reflection from filling material 2. HF1,2 The signal is received. In this case, the hollow conductor 111 has an inner cross-section D according to the invention, through which the lowest frequency radar signal and the received signal S are transmitted. HF1,2 R HF1,2 It can propagate specifically in one of the fundamental models, therefore, for example, in the case of a circular cross-section shape, it is TE. 11 Or, in the case of a rectangular cross-section, it is TE. 10 Therefore, the inner section D needs to be selected according to the following formula for the cutoff frequency (therefore, in the case of a rectangular section shape, the diameter or side length).

[0030]

[0031] in It is radar signal S HF1 R HF1 Wavelength in the low-frequency band. On the other hand, dimensional design is performed according to the following formula:

[0032] To ensure radar signal S HF1 It propagates in the low-frequency band, or specifically radiates in the fundamental mode. This is capable of... Figure 2 The low-frequency E-field distribution was observed in the hollow conductor 111 and in the external radiation in front of the hollow conductor 111.

[0033] Figure 3 The diagram illustrates radar signal S. HF2 The corresponding E-field distribution in the high-frequency band: It can be seen that due to the above-mentioned dimensional design of the inner cross-section D, the radar signal S in the high-frequency band... HF2 It does not propagate exclusively in the fundamental mode within the hollow conductor 111 because the above formula requires the following relationship: .

[0034] Therefore, high-frequency transmission dominates in higher-order modes because the inner cross-section D is "too wide" for high-frequency bands for pure single-mode transmission. Therefore, according to the invention, a dielectric matching element 112 is arranged at the first end region, by means of which the high-frequency radar signal S... HF2 The signal is converted into a lower-order mode in the emission direction, among which the fundamental mode is the dominant mode. The radar signal S generated in the lower frequency band... HF2 Its mode is unaffected by the matching element 112 because the structural size of the matching element 112 is at least 1:16 smaller than the wavelength of the low-frequency band.

[0035] The function of the matching element 112 depends on both its material properties and its shape: Figure 2 and Figure 3 The shape of the matching element 112 in the embodiment illustrated in the figure tapers in a stepped manner in the emission direction. In this case, the number of steps depends on the number of different frequency bands, wherein the radar signals S, R... HF1,2 It is transmitted and received. Therefore, Figure 2 and Figure 3 The embodiment of the matching element 112 illustrated herein has a shape consisting of two steps. The dimension of the step height, i.e., the tapering, depends on the material of the matching element 112: the higher the dielectric constant of the material, the smaller the step height. Suitable materials include, in particular, PTFE, PFA, and PEEK.

[0036] exist Figure 2 and Figure 3 In the case of the embodiment of the matching element 112 shown, its fixation on the first end region of the hollow conductor 111 occurs by means of two segments 1121, which are designed as integral parts of the matching element 112 and protrude to form a shape-interlocking connection with the inner cross section D in the first end region of the hollow conductor 111.

[0037] In summary, due to the matching element 112, according to the present invention, the radar signals S of the two frequency bands... HF1,2 It is transmitted with a shared phase center. In this way, the shared radar lens 113 can be used for radar signals S and R in two frequency bands. HF1,2The shared radar lens 113 is positioned in front of the hollow conductor 11 in the emission direction. For example, in... Figure 2 and Figure 3 As can be observed, in this configuration, the transmitting / receiving device 11 is designed such that the first filling material 2 and the matching element 112 facing the end region of the hollow conductor 11 are located at the focal point of the radar lens 113. Using the radar lens 113, radar signals S and R can then be transmitted. HF1,2 A greater focus allows for the recording of greater distances, d.

[0038] List of reference numerals in the attached figures

[0039] 1. Fill level measuring equipment

[0040] 2. Filler material

[0041] 3 containers

[0042] 4. Upper-level unit

[0043] 11 Transmitter / Receiver

[0044] 111 Hollow conductor

[0045] 112 Matching Components

[0046] 113 Radar Lens

[0047] 1111 Coupled Structure

[0048] 1121 Section of the matching element

[0049] c. Propagation speed of radar signals

[0050] D inner section

[0051] d Distance

[0052] f IF1,2,3 The frequency of the intermediate frequency signal Frequency change rate of transmitted radar signals h Installation height L fill level R HF1,2 Received signal S HF1,2 radar signals wavelength of radar signal

Claims

1. A transmitting / receiving device (11) for a radar-based fill level measuring device (1), by means of said transmitting / receiving device (11), a radar signal (S HF1,2 The radar signal (S) can be transmitted in at least two different frequency bands, and the radar signal (S) HF1,2 After reflection, it can be used as the corresponding received signal (R). HF1,2 The transmitter / receiver (11) is received, and includes: - Hollow conductor (111), said hollow conductor (111) having: o At least one coupling structure (1111), the radar signal (S HF1,2 The received signal (R) can be coupled into the hollow conductor (111) via the at least one coupling structure (1111), and the received signal (R) HF1,2 It can couple out the hollow conductor (111). The inner cross section (D) is selected such that the lowest frequency radar signal and the received signal (S) are at the lowest frequency band. HF1 R HF1 It can propagate specifically through one of its fundamental models, and o First end region, via the radar signal (S) in the first end region HF1,2,3 ) can be transmitted and the received signal (R) HF1,2 It can be received. - Matching element (112), said matching element (112) is arranged at the first end region, said matching element (112) is designed to transmit high-frequency radar signals (S) in the emission direction. HF2 It is converted into at least one lower-order mode, especially one of its fundamental modes.

2. The transmitting / receiving device according to claim 1, wherein, The inner cross section (D) is selected such that the high-frequency radar signal and the received signal (S) are both... HF1 R HF1 It can propagate in higher order modes.

3. The transmitting / receiving device according to claim 1 or 2, comprising: - A focusing radar lens (113), which is arranged in particular in front of the first end region of the hollow conductor (111) such that the matching element (112) is located at the focal point of the radar lens (113).

4. The transmitting / receiving apparatus according to claim 1, 2 or 3, wherein, The matching element (112) is made of dielectric material.

5. The transmitting / receiving device according to claim 4, wherein, The matching element (112) is tapered or stepped in the emission direction.

6. The transmitting / receiving apparatus according to claim 4 or 5, wherein, The matching element (112) includes at least one segment (1121) that protrudes into the first end region of the hollow conductor (111) in such a way that the matching element (112) is secured to the hollow conductor (111).

7. The transmitting / receiving apparatus according to any one of the preceding claims, wherein, The hollow conductor (111) has a rotationally symmetric inner cross section (D).

8. A fill level measuring device for determining the fill level (L) of filler material (2), comprising: - A high-frequency unit, which is designed, in particular according to the FMCW method, to generate radar signals (S) in two frequency bands. HF1,2 ), and process the corresponding received signal (R) HF1,2 ), - According to at least one of the preceding claims, the transmitting / receiving device (11), by means of the transmitting / receiving device (11), the radar signal (S HF1,2,3 The signal (R) can be transmitted to the filling material (2) and, after being reflected from the surface of the filling material, the corresponding received signal (R) HF1,2 ) can be received, and - An evaluation unit, said evaluation unit being designed to evaluate signals received in at least one frequency band (R HF1,2 The fill level (L) is determined by this method.

9. The fill level measuring device according to claim 8, wherein the fill level measuring device is designed to simultaneously or periodically alternately transmit and receive the radar signals (S) in at least two different frequency bands. HF1,2,3 ).

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