Method for determining a permittivity of a medium by means of a calibration device and a radar-based fill level measuring apparatus, calibration device and system

Abstract

The invention relates to a method for determining a permittivity of a medium (3) by means of a calibration device (1) and a radar-based fill level measuring apparatus (2), wherein the method comprises at least the following steps: - providing a reference environment in the hollow waveguide (5), in-coupling a first radar signal having at least one first frequency into the hollow waveguide (5) and out-coupling a first received signal, in-coupling a second radar signal having at least one second frequency into the hollow waveguide (5) and out-coupling a second received signal, - introducing the calibration device (1) into a container (9) containing the medium (3) such that the hollow waveguide (5) is filled with the medium (3), in-coupling the first radar signal into the hollow waveguide (5) and out-coupling a third received signal, - in-coupling the second radar signal into the hollow waveguide (5) and out-coupling a fourth received signal, - determining a permittivity of the medium (3) on the basis of the first, second, third and fourth received signals.

Description

[0001] Method for determining the permittivity of a medium using a calibration device and a radar-based level gauge, calibration device and system

[0002] The invention relates to a method for determining the permittivity of a medium using a calibration device and a radar-based level measuring device, a calibration device and a system.

[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 level measurement methods have become established for measuring the fill level of contents in containers due to their robustness and low maintenance requirements. Radar-based level measurement is described in more detail, for example, in "Radar Level Detection," Peter Devine, 2000. A key advantage of radar-based level measurement is its 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 invention, the term "radar" refers to signals or electromagnetic waves with frequencies between 0.03 GHz and 300 GHz. By design, the higher the absolute bandwidth or frequency, the higher the measurement resolution achievable. Pulse time-of-flight measurement and FMCW (Frequency Modulated Continuous Wave) have become established measurement methods.

[0005] The permittivity of a medium in a container of a process plant is often unknown. This is due, firstly, to the fact that the medium is subject to chemical processes, for example, and its permittivity changes during the process, and secondly, to the fact that determining the permittivity of aggressive and hazardous media is complex. However, knowledge of the medium's permittivity is a prerequisite for the design and selection of a radar-based level gauge intended to monitor the medium's level, since the frequency range of the radar-based level gauge should ideally be matched to the permittivity of the medium due to the frequency dependence of permittivity. Therefore, the object of the present invention is to provide a method, a calibration device, and a system that enable a simple determination of the permittivity of a medium in a container.

[0006] According to the invention, the problem is solved by a method according to claim 1, a calibration device according to claim 8 and a system according to claim 12.

[0007] With regard to the method, the problem is solved according to the invention by a method for determining a permittivity of a medium by means of a calibration device and a radar-based level measuring device, wherein the radar-based level measuring device is configured to emit radar signals with a frequency from a predetermined frequency range and to receive a received signal after a reflection of the respective radar signal, wherein the method comprises at least the following steps:

[0008] Providing the calibration device with a base body and a waveguide arranged in the base body, wherein the waveguide has an input region, an end region and a calibration section of predetermined length running between the input region and the end region, wherein the end region is configured to reflect a radar signal,

[0009] Place a reference environment in the waveguide; couple a first radar signal with at least one first frequency into the waveguide and couple out a first received signal after reflection of the first radar signal at the end region; couple a second radar signal with at least one second frequency into the waveguide and couple out a second received signal after reflection of the second radar signal at the end region; place the calibration device into a container containing the medium so that the waveguide is filled with the medium; couple the first radar signal into the waveguide and couple out a third received signal after reflection of the first radar signal at the end region; couple the second radar signal into the waveguide and couple out a fourth received signal after reflection of the second radar signal at the end region.

[0010] Determining the permittivity of a medium based on the first, second, third, and fourth received signals. The method according to the invention thus enables the determination of the medium's permittivity using a calibration device and a radar-based level measuring device. By first providing a reference environment within the waveguide and then filling the waveguide with the medium in the container, the permittivity of the medium can be determined. The first and second received signals serve as reference signals. The reference environment can be provided by filling or evacuating the waveguide with a reference medium. By comparing the reference signals with the third and fourth received signals, the permittivity of the medium can then be determined. The medium can be liquid or gaseous.

[0011] The container is, for example, a tank, a vessel, or a pipe; in particular, the container is located within a process plant. Advantageously, the permittivity of the medium can thus be investigated directly in the container. It is therefore unnecessary to transfer the medium from the container to a laboratory vessel or to prepare the medium in a laboratory and determine its permittivity there. Determining the permittivity of the medium directly in the container is particularly advantageous for aggressive media and media that are harmful to humans or the environment and which can only be transferred to a laboratory with considerable effort.

[0012] Alternatively, the reference environment can be provided by filling the waveguide with the medium; in this case, the waveguide may already be placed in the container. If the waveguide has already been filled with the medium as the reference environment for determining the two reference signals, the third and fourth received signals can be determined during a process within the container in which the permittivity of the medium changes relative to the reference environment.

[0013] The first and second frequencies are preferably different frequencies. The waveguide can have an electrically conductive inner surface. This can be achieved, for example, by manufacturing the base body from an electrically conductive material such as aluminum, copper, or stainless steel, or by coating the inner surface of the waveguide with an electrically conductive material, such as gold or platinum. The waveguide can have a radar interference feature at one or more defined positions, particularly in the form of a cross-sectional narrowing or widening. From a high-frequency perspective, the radar interference features have the same function as the radar-reflecting end region of the waveguide and thus enable the measurement of multiple calibration sections. The waveguide can be arranged in a planar plane. The waveguide, or...The calibration section can be straight, simply or multiply curved, or spirally shaped. One possible embodiment of the calibration device is described in patent application DE 102024111089.9, to which the present application refers in full.

[0014] In one embodiment, a radar-based level gauge is selected from several available options based on the permittivity of the medium. This radar-based level gauge is designed to monitor the medium with the determined permittivity. Specifically, a radar-based level gauge is selected whose frequency range enables monitoring of the determined permittivity. In particular, a radar-based level gauge is selected whose frequency range exhibits the greatest sensitivity to the determined permittivity. Thus, a radar-based level gauge optimally suited for the medium can be selected.

[0015] In one embodiment, the dispersion is determined from the first and second received signals, and the permittivity of the medium is then determined from the dispersion, the third, and the fourth received signals. Dispersion describes the frequency dependence of the propagation speed of a radar signal in the waveguide. Since the first and second radar signals have different frequencies, they propagate at different speeds in the waveguide, resulting in a frequency shift of the first received signal relative to the second. Dispersion occurs both when measuring the reference environment and in the waveguide filled with the medium. By determining the dispersion based on the reference measurement, the third or fourth received signal can be corrected for the dispersion.

[0016] In one embodiment, the permittivity of the medium is determined by comparing the first received signal and the third received signal, as well as by comparing the second received signal and the fourth received signal.

[0017] In one embodiment, the permittivity of the medium is determined based on a frequency, a phase and / or an amplitude of the first received signal, based on a frequency, a phase and / or an amplitude of the second received signal, based on a frequency, a phase and / or an amplitude of the third received signal and based on a frequency, a phase and / or an amplitude of the fourth received signal.

[0018] In one embodiment, the predetermined length of the calibration section is adapted to the height of the container. The length of the calibration section can essentially correspond to the height of the container. This makes it possible to verify whether the fill level in the container can be monitored with a radar-based level gauge. At great container heights, it is possible that only a very weak received signal is coupled out after reflection at the end of the section.

[0019] In one embodiment, the first and second frequencies are selected from two end regions of the given frequency range. This selection achieves the largest possible frequency separation between at least the first and second frequencies, thus simplifying the calculation of the dispersion based on the first and second received signals.

[0020] With regard to the calibration device, the problem is further solved according to the invention by a calibration device with a base body, a waveguide arranged in the base body with an input area, an end area and a calibration section of a predetermined length running between the input area and the end area, wherein the end area is designed to reflect a radar signal, and a first opening in the end area.

[0021] The calibration device according to the invention can be used to determine the permittivity of a medium in a container according to the method according to the invention. The embodiments of the calibration device according to the invention apply mutatis mutandis to the method according to the invention and vice versa.

[0022] The calibration device can be inserted into the container. The first opening at the end allows medium to escape from the waveguide and thus fill the waveguide with the medium. If the waveguide is to be evacuated, filled with a reference medium, or filled with the medium itself, the first opening can have a valve or a sealing device. If the waveguide is evacuated, the absolute pressure inside the waveguide is zero, whereby "zero absolute pressure" as used in the application is understood to mean a vacuum with a pressure of less than 100 mbar, and in particular less than 10 mbar, that can be achieved with reasonable effort. The reference medium is preferably a gas, for example, a noble gas.

[0023] The waveguide can have an electrically conductive inner surface. This can be achieved, for example, by manufacturing the base body from an electrically conductive material such as aluminum, copper, or stainless steel, or by applying an electrically conductive coating to the inner surface of the waveguide, such as a silver coating. The waveguide can have a radar interference feature at one or more defined locations, particularly in the form of a cross-sectional narrowing or widening. From a high-frequency perspective, these radar interference features have the same function as the reflective end region of the waveguide, thus enabling the measurement of multiple calibration sections. The waveguide can be arranged in a planar plane. The waveguide or calibration section can be straight, simply or multiply curved, or spiral. The waveguide can have a rectangular or circular cross-section.

[0024] In one embodiment, the end area has an end structure designed to reflect the radar signal.

[0025] In one embodiment, the final structure is designed as a comb structure.

[0026] In one embodiment, the calibration device has a second opening in the coupling area. Like the first opening, the second opening serves to fill the waveguide with medium. For example, the medium can enter the waveguide through the second opening and exit through the first opening.

[0027] With regard to the system, the problem is further solved according to the invention by a system with a calibration device according to one of the previous embodiments, a radar-based level measuring device, which is designed to emit radar signals with a frequency from a predetermined frequency range and to receive a received signal after a reflection of the respective radar signal.

[0028] The system according to the invention can be used to determine the permittivity of a medium in a container according to the method according to the invention. The embodiments of the system according to the invention apply mutatis mutandis to the method according to the invention and vice versa.

[0029] Based on the determined permittivity, a radar-based level gauge can then be selected from a group of several radar-based level gauges designed to monitor the determined permittivity. The system can be designed such that the medium can enter the waveguide. The system can have a third opening through which the medium can enter the coupling area.

[0030] In one embodiment, the system includes a polarization filter connected to the coupling area. The polarization filter can be configured to filter the polarization of a radar signal emitted by the radar-based level gauge. This allows, for example, the elimination of interference signals before the radar signal is coupled into the waveguide. For the purposes of this application, interference signals are defined as those components of the emitted radar signal that cause unwanted reflections within the calibration device or the waveguide. The polarization filter can have an input into which a radar signal from the radar-based level gauge can be coupled, and an output from which a filtered radar signal can emerge.

[0031] In one embodiment, the polarization filter is designed such that the medium can enter the waveguide through the polarization filter. For this purpose, the polarization filter can have a side input with a third opening. This side input can serve to guide interference signals, which have been filtered out of the radar signal, out of the polarization filter. The medium can enter the polarization filter through the third opening and enter the waveguide through the coupling region. The coupling region can be designed such that the medium can enter the waveguide from the polarization filter.

[0032] In one embodiment, the polarization filter is an orthomode transducer.

[0033] The invention will now be explained in more detail with reference to the following figures, Figs. 1-4. They show:

[0034] Fig. 1 : an embodiment of a calibration device according to the invention.

[0035] Fig. 2: one embodiment of the end area.

[0036] Fig. 3: an embodiment of a system according to the invention.

[0037] Fig. 4: one embodiment of a polarization filter.

[0038] Figure 1 shows an embodiment of a calibration device 1 according to the invention. The calibration device 1 can be used to carry out the method according to the invention. The calibration device 1 comprises a base body 4 and a waveguide 5 arranged therein. The waveguide 5 comprises an input region 6, an end region 7, and a calibration section 8 of a predetermined length extending between the input region 6 and the end region 7. The end region 7 is configured to reflect radar signals. For example, the end region 7 can have an end structure 12 for this purpose. Such an end structure 12 is shown in Figure 2, which shows a cross-section of the waveguide 5, which is configured as a rectangular waveguide by way of example in Figure 2. The end structure 12 is optionally configured as a comb structure in Figure 2.

[0039] To fill the calibration device 1 with the medium 3, the calibration device 1 can have a first opening 10 in the end region 7. The calibration device 1 can also have a second opening 13 in the coupling region 7. The medium can thus enter the waveguide 5 through the first opening 10 or the second opening 13 and exit through the other opening. In this way, the waveguide 5 can be easily filled with the medium 3.

[0040] Fig. 3 shows an embodiment of the system 14 according to the invention, comprising a calibration device 1 and a radar-based level gauge 2. The radar-based level gauge 2 is configured to transmit radar signals at a frequency from a predetermined frequency range and to receive a received signal after reflection of the respective radar signal. The radar-based level gauge 2 can have a transmit-receive arrangement configured to transmit the radar signals and to receive the received signals. Furthermore, the radar-based level gauge 2 can have at least one high-frequency unit configured to generate a radar signal. A processing unit can be arranged in the radar-based level gauge 2, which, for example, is configured to determine the level based on the received signals.The computing unit can also be designed to determine the permittivity of the medium based on the first received signal, the second received signal, the third received signal, and the fourth received signal.

[0041] System 14 can be connected to a higher-level unit 19, either wirelessly or via a wired connection. For this purpose, the radar-based level sensor 12 can include an interface module implementing, for example, "4-20 mA", "PROFIBUS", "HART", or "Ethernet" to exchange information with the higher-level unit 19, such as a local process control system or a decentralized server system. For example, the measured level value can be transmitted, perhaps to control the inflow or outflow of the container 9. Other information about the general operating status of the level sensor 2 can also be communicated.

[0042] The radar-based level gauge 2 can be attached to the container 9 in a pressure- and media-tight manner, particularly to a corresponding opening. The level gauge 2 can be oriented such that only a transmitting / receiving arrangement, for example, an electrically passive antenna, is directed vertically downwards into the container 9 towards the medium 3. The active components of the level gauge 2 are located outside the container 9 in a separate housing, which is attached to the opening of the container 9, for example, via a flange.

[0043] The system 14 can be placed in a container 9 to carry out the method according to the invention. The container 9 can, for example, be a tank or a pipe. The system 14 can be attached to the container 9 such that the waveguide can be filled with the medium 3. For example, the system 14 is arranged such that at least the calibration device 1 is immersed in the medium 3.

[0044] To fill the waveguide 5 with the medium 3, the calibration device 1 can have a first opening 10 and a second opening 13. However, instead of the second opening 13, the system 14 according to the invention can be configured such that the waveguide 5 can be filled with the medium 3. In particular, the system 14 can have at least two openings that serve for the entry and exit of the medium 3. The at least two openings can be arranged in the calibration device 1, as already described. However, the system 14 can also have further components, each provided with at least one opening; preferably, the first opening 10 is arranged in the end region 7 of the calibration device 1.

[0045] For example, the system 14 can include a polarization filter 15, which is shown by way of example in Figs. 3 and 4. The polarization filter 15 can be arranged between the radar-based level gauge 2 and the calibration device 1. In particular, the polarization filter 15 is connected to the coupling area 6. An unfiltered UHF radar signal can enter the polarization filter 15 via an input 20, and a filtered RHF radar signal can exit the polarization filter 15 via the output 21. Filtered-out JHF interference signals can be routed out of the polarization filter 15 via the side input 16.

[0046] The polarization filter 15 can be configured such that the medium 3 can enter the waveguide 5 through the polarization filter 15. The polarization filter 15 can thus have a third opening 17, which is, for example, arranged in a side inlet 16 of the polarization filter 15. The polarization filter 15 can have an interior 23 and a fourth opening 22 in an outlet 22 of the polarization filter 15, which is arranged, in particular, facing the coupling area 6. In this way, the medium 3 can enter the interior 23 through the third opening 16 and enter the coupling area 6 and the waveguide 5 through the fourth opening 22. The polarization filter 15 is, in particular, an orthomode transducer. The method according to the invention can be carried out using the system 14. The method according to the invention provides, in a first step, the calibration device 1.In a further step, a reference environment is provided in the waveguide 5; for example, the waveguide 5 is evacuated and filled with a reference medium, such as a noble gas. In this state of the waveguide 5, a first radar signal with at least one frequency is coupled into the waveguide 5, and a first received signal is coupled out after reflection of the first radar signal at the end section 7; in addition, a second radar signal with at least one frequency is coupled into the waveguide 5, and a second received signal is coupled out after reflection of the second radar signal at the end section 7.

[0047] The first and second received signals serve as reference signals. For example, dispersion can be determined using the first and second received signals. Dispersion is determined, in particular, by comparing the first and second received signals; specifically, dispersion is determined using the frequency, phase, and / or amplitude of the first received signal and the frequency, phase, and / or amplitude of the second received signal.

[0048] In a further process step, at least the calibration device 1 is placed in a container 9 containing a medium 3, so that the waveguide 5 is filled with the medium 3. In the waveguide 5 filled with medium 3, the first radar signal is coupled in, and a third received signal is coupled out after reflection of the first radar signal at the end section 7. Simultaneously, the second radar signal is coupled in, and a fourth received signal is coupled out after reflection of the second radar signal at the end section 7.

[0049] The permittivity of medium 3 is then determined using the first, second, third, and fourth received signals. Once the dispersion has been determined, the permittivity can be calculated based on the dispersion, the third received signal, and the fourth received signal. For example, the third and fourth received signals can be corrected for dispersion, and the permittivity can then be determined by comparing the corrected third and fourth received signals. Specifically, the frequency, phase, and / or amplitude of the corrected third received signal and the frequency, phase, and / or amplitude of the corrected fourth received signal are compared. Based on the determined permittivity of medium 3, several options can then be selected.

[0050] radar-based level gauges, such radar-based

[0051] A level measuring device should be selected which is designed for monitoring medium 3 or which has the highest sensitivity for the determined permittivity.

[0052] Reference symbol list

[0053] 1 Calibration device

[0054] 2 Radar-based level gauge

[0055] 3 Medium

[0056] 4 basic shapes

[0057] 5 waveguides

[0058] 6 Coupling area

[0059] 7 End area

[0060] 8 Calibration section

[0061] 9 Container

[0062] 10 first opening

[0063] 12 Final structure

[0064] 13 second opening

[0065] 14 System

[0066] 15 polarization filters

[0067] 16 Side entrance

[0068] 17 third opening

[0069] 18 basic segments

[0070] 19 higher-level unit

[0071] 20 Entrance

[0072] Exit 21

[0073] 22 fourth opening

[0074] 23 Interior

Claims

Patent claims 1. Method for determining a permittivity of a medium (3) using a calibration device (1) and a radar-based level measuring device (2), wherein the radar-based level measuring device (2) is configured to emit radar signals with a frequency from a predetermined frequency range and to receive a received signal after reflection of the respective radar signal, wherein the method comprises at least the following steps: Providing the calibration device (1) with a base body (4) and a waveguide (5) arranged in the base body (4), wherein the waveguide (5) has an input region (6), an end region (7) and a calibration section (8) of a predetermined length running between the input region (6) and the end region (7), wherein the end region (7) is configured to reflect a radar signal, Providing a reference environment in the waveguide (5), o Coupling a first radar signal with at least a first frequency into the waveguide (5) and coupling out a first received signal after reflection of the first radar signal at the end region (7), o Coupling a second radar signal with at least a second frequency into the waveguide (5) and coupling out a second received signal after reflection of the second radar signal at the end region (7), Inserting the calibration device (1) into a container (9) containing the medium (3) so that the waveguide (5) is filled with the medium (3), coupling the first radar signal into the waveguide (5) and coupling out a third received signal after reflection of the first radar signal at the end section (7), coupling the second radar signal into the waveguide (5) and coupling out a fourth received signal after reflection of the second radar signal at the end section (7), Determining the permittivity of the medium (3) using the first received signal, the second received signal, the third received signal and the fourth received signal.

2. Method according to claim 1, wherein, based on the permittivity of the medium (3), one such radar-based level measuring device is selected from several available radar-based level measuring devices. A level measuring device is selected which is designed for monitoring the medium (3) with the determined permittivity.

3. Method according to one of the preceding claims, wherein a dispersion is determined on the basis of the first received signal and the second received signal, and the permittivity of the medium (3) is determined on the basis of the dispersion, the third received signal and the fourth received signal.

4. Method according to one of the preceding claims, wherein the permittivity of the medium (3) is determined by comparing the first received signal and the third received signal as well as comparing the second received signal and the fourth received signal.

5. Method according to one of the preceding claims, wherein the permittivity of the medium (3) is determined based on a frequency, a phase and / or an amplitude of the first received signal, based on a frequency, a phase and / or an amplitude of the second received signal, based on a frequency, a phase and / or an amplitude of the third received signal and based on a frequency, a phase and / or an amplitude of the fourth received signal.

6. Method according to one of the preceding claims, wherein the predetermined length of the calibration section (8) is adapted to a height of the container (9).

7. Method according to one of the preceding claims, wherein the first frequency and the second frequency are selected from two end ranges of the specified frequency range.

8. Calibration device (1) with a base body (4), a waveguide (5) arranged in the base body (4), wherein the waveguide (5) has a coupling area (6), an end area (7) and a calibration section (8) of a predetermined length running between the coupling area (6) and the end area (7), wherein the end area (7) is designed to reflect a radar signal and a first opening (10) in the end area (7).

9. Calibration device (1) according to claim 8, wherein the end region (7) has an end structure (11) which is designed to reflect the radar signal.

10. Calibration device (1) according to claim 9, wherein the end structure (11) is designed as a comb structure (12).

11. Calibration device (1) according to one of claims 8-10, wherein the calibration device (1) has a second opening (13) in the coupling area (6).

12. System (14) comprising a calibration device (1) according to one of claims 8-11, a radar-based level measuring device (2) which is configured to emit radar signals with a frequency from a predetermined frequency range and to receive a received signal after reflection of the respective radar signal.

13. System (14) according to claim 12, wherein the system (14) comprises a polarization filter (15) which is connected to the coupling area (6).

14. System (14) according to claim 13, wherein the polarization filter (15) is configured such that a medium (3) can enter the waveguide (5) through the polarization filter (15).

15. System (14) according to one of claims 13-14, wherein the polarization filter (15) is an orthomode transducer.

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