Fill level measuring device

Abstract

The invention relates to a calibration device (5) for calibrating a radar-based fill level measuring device (1) or a high-frequency module thereof. To this end, the device (5) is based on a platform (51). A hollow conductor (52) extends within a flat plane (A) of the platform (51). The hollow conductor (52) is characterized by an input coupling region (521), an end region (522) for reflecting a radar signal (S HF , R HF ) and a calibration path (d kal ) extending therebetween. According to the invention, the hollow conductor (52), and thus the calibration path (d kal ), is nested in a spiral shape. In this way, a very compact design is achieved in terms of the length of the calibration path (d kal ) and the hollow conductor (52), such that the calibration device (5) can also be used for recalibration at the place of use of the fill level measuring device (1).

Description

Technical Field

[0001] This invention relates to the calibration of a radar-based fill level measurement device and the calibration of its high-frequency module. Background Technology

[0002] In process automation technology, appropriate field devices are used to record relevant process parameters. To record these parameters, suitable measurement principles are implemented in the field devices. Examples of process parameters include fill level, flow rate, pressure, temperature, pH, redox potential, and conductivity. The Endress+Hauser Group manufactures and sells a wide variety of field device types and variations.

[0003] For measuring the fill level of media in containers, non-contact measurement methods have proven effective because they are robust and require minimal maintenance. For example, see "Radar Level Detection, Peter Devon, 2000" (…). Radar Level Detection, Peter Devine, 2000) More detailed information on radar-based fill level measurement can be found in [the relevant document / reference]. A major advantage of radar-based fill level measurement is its ability to measure fill levels nearly continuously. Therefore, radar-based measurement methods are primarily used in the field of continuous fill level measurement. In this context, within the background of this invention, the term "radar" refers to a signal or electromagnetic wave with a frequency between 0.03 GHz and 300 GHz. In principle, the larger the absolute bandwidth and the higher the frequency, the higher the achievable measurement resolution. Established radar measurement methods include the pulse propagation time method and FMCW ("..."). Frequency Modulated Continuous Wave ")Law.

[0004] However, to ensure the potential high resolution of radar measurements, it is essential to calibrate the fill level measuring device, and consequently its high-frequency module, at least during manufacturing.

[0005] In cases of mandatory calibration for fill level measurements, the fill level measuring device must be recalibrated at specified intervals during measurement operations. The challenge here is that this requires removing the fill level measuring device from its location of use and establishing a suitable calibration path. In this case, the calibration path's length depends on the measurement range. Summary of the Invention

[0006] Therefore, one object of the present invention is to provide the most efficient possible calibration of a radar-based fill level measurement device under these boundary conditions.

[0007] This invention achieves this objective through a calibration device that enables the independent calibration of a radar-based fill level measurement device, and consequently, its high-frequency module. To this end, the calibration device includes: - Platform, which includes sections of flat surface. - A hollow conductor that extends within a segment in a plane and has o Input coupling region, o The terminal region of radar signal reflection, which is opposite to the input coupling region, and o is the defined calibration path located within it.

[0008] In this configuration, the device is characterized by hollow conductors, and consequently calibration paths, formed in a helical nesting pattern in a plane. This can be achieved by constructing the hollow conductors as semi-circular base segments, giving them a toroidal helical shape. Alternatively, the hollow conductors can be segmented into straight base segments arranged at defined angles relative to the next base segment and connected to each other by circular connecting segments, giving the hollow conductors a rectangular, hexagonal, or octagonal helical shape. In these cases, all connecting segments of the hollow conductors can have the same radius. The advantage of the helical design in terms of calibration path length is that the calibration path can be designed to be very compact overall. With the same platform segment size, the calibration path can also be selectively doubled by constructing the hollow conductors along the helix as two parallel hollow conductor routes, wherein the two parallel routes are connected at the center of the helix by a connecting route.

[0009] Overall, due to the absence of discontinuities in the routing of the hollow conductor, the calibration device of this invention exhibits low radar attenuation. This, in turn, achieves a high signal-to-noise ratio and thus enables high-resolution calibration, which can be performed based on the following method steps: - The radar signal is coupled into the hollow conductor via a filling level measuring device and its high-frequency module through the input coupling region. - After the radar signal is reflected in the terminal region, the corresponding received signal is output from the hollow conductor, and - Calibration is performed based on the known calibration path of the received signal and the hollow conductor.

[0010] In this case, due to the compact construction of the calibration device, the method can be performed not only during the manufacturing of the fill level measuring device, but also in the context of measurement operations, so as to, for example, recalibrate the fill level measuring device.

[0011] In principle, the fill level measuring device to be calibrated can be most easily adjacent to the calibration device when the input coupling area is located on the outside of the platform and thus opposite to the center of the helix.

[0012] To achieve efficient input coupling, especially when the hollow conductor has a rectangular cross-section, a polarization filter can be placed in the input coupling region. In this case, the polarization filter is located before the input coupling region, and the polarization filter can be designed to couple the radar signal into the hollow conductor via a dielectric waveguide or dielectric lens.

[0013] In principle, hollow conductors require a conductive inner surface. This can be achieved, for example, by making a platform from a conductive material—such as aluminum, copper, or stainless steel—or by applying a conductive coating—such as a silver coating—to the inner surface of the hollow conductor.

[0014] The planar arrangement of the hollow conductors facilitates the manufacture of the calibration device because the platform can be implemented in two parts, separated in the assembled state by a plane extending from the hollow conductors. In this case, the hollow conductors can be manufactured, for example, by milling the surfaces of the platform portions. The cross-sectional diameter and shape of the hollow conductors are then determined according to the frequency of the radar signal and, consequently, the desired mode.

[0015] By arranging an airtight sealing window at the input coupling region, the hollow conductor can be evacuated or filled with inert gas, further improving the signal-to-noise ratio of the calibration device. Furthermore, it is advantageous when the inner surface of the hollow conductor has a corrosion-prone coating—such as silver.

[0016] To not only provide a calibration path, the hollow conductor can be structurally modified to have radar disturbance points at one or more defined locations, particularly in the form of narrowed or widened cross-sections. For high-frequency signals, these radar disturbance points thus function similarly to the reflective end regions of the hollow conductor.

[0017] Referring to this invention, the term "module" generally refers to any group of circuits configured for a specific application, such as as an interface or for high-frequency signal processing. Thus, depending on the application, a particular module may include corresponding analog circuitry for generating or processing corresponding analog signals. However, a particular module may also include digital circuitry, such as an FPGA, microcontroller, or storage medium that works in conjunction with a corresponding program. In this case, the program is designed to perform the required method steps or implement the required computer operations. In this context, within the scope of this invention, different electronic circuits within a module may also use a shared physical memory or operate by means of the same physical digital circuitry. In this case, it is not important whether the different electronic circuits within the module are arranged on a shared circuit board or on multiple interconnected circuit boards. Attached Figure Description

[0018] The invention will now be explained in more detail with reference to the accompanying drawings, which are shown below: Figure 1 A radar-based fill level measuring device located on the container. Figure 2 An exploded view of the first embodiment of the calibration device of the present invention, and Figure 3 A plan view of a second embodiment of the calibration device of the present invention. Detailed Implementation

[0019] In order to understand the invention in principle, Figure 1 A container 3 with filler 2 is shown, its fill level. L The fill level will be determined by a radar-based fill level measuring device 1. In this case, depending on the type of filler 2 and the application area, the container 3 can reach a height of 100 m. The fill level measuring device 1 determines the fill level accordingly. L Optimal frequency band f 1,2,3 Depending on the type of filler 2 and the application area: in the case where filler 2 is a coarse-grained filler and diffuse reflection occurs accordingly, for example, in the relatively low frequency band of 6 GHz. f 1,2,3 This is often appropriate. Similarly, in the case where filler 2 would bubble, a lower frequency band is better because the foam will not reflect light in this situation. In the case of container 3 being a refinery storage tank, due to the flat surface of the filler, a higher frequency band, such as 80 GHz or 180 GHz, is preferable. f 1,2,3 This is advantageous because it itself enables potentially higher distance resolution.

[0020] Typically, the fill level measuring device 1 is connected to the upper-level unit 4 via a separate interface module, in which, for example, " 4-20 mA "", PROFIBUS "", HART "or" Ethernet The higher-level unit 4 is, for example, a local process control system or a distributed server system. In this way, for example, it is possible to transmit measured fill level values. L Or only transmission distance d This allows for control of the inflow and / or outflow of container 3. It can also transmit other information regarding the general operating status of the fill level measuring device 1.

[0021] To determine the fill level L The filling level measuring device 1 is installed above the bottom of container 3 at a known installation height. hIt is positioned above the filler 2. In this case, the fill level measuring device 1 is fixed and oriented at the appropriate interface of the container 3 in a pressure-resistant and sealed manner relative to the filler, such that only the electrically passive antenna is located in the container 3 and is vertically downward along the direction of the filler 2. The active component of the fill level measuring device 1 is located in a separate housing outside the container 3, which is fixed to the interface of the container 3, for example, via a flange.

[0022] The fill level measuring device 1 transmits radar signals S via an antenna in a defined frequency band (e.g., 6 GHz or 180 GHz) toward the surface of the filler 2. HF In radar signal S HF After being reflected off the surface of the filler, the fill level measuring device 1 receives the reflected signal R via an antenna. HF In this situation, transmitting and receiving radar signals S HF R HF The signal propagation time t between them is determined by the following formula:

[0023] The distance d between the filling level measuring device 1 and the filling material 2 is proportional to the distance d, where c is a radar signal S that depends on the medium and is generally at least roughly known. HF R HF The propagation speed. The signal propagation time t can be determined, for example, by the fill level measuring device 1 using the FMCW method or the pulse propagation time method. In this way, the fill level measuring device 1 can specify an appropriate distance d based on the corresponding calibration of the measured propagation time t. Subsequently, the fill level measuring device 1 can determine the fill level L according to the following formula:

[0024] When the installation height h is given in the filling level measuring device 1 or in the upper unit 4.

[0025] Due to radar signals S HF , R HF speed of spread c The propagation time of the signal in the fill level measuring device 1 is only roughly known and is also affected by the internal signal routing; therefore, calibration is necessary to determine the propagation time of the signal. t With distance d The relationship between them.

[0026] Therefore, at least in the process of manufacturing the fill level measuring device 1, a defined and known calibration path d is used. kalCalibration is performed. In this case, calibration can be performed using the complete fill level measuring device 1 after manufacturing is complete, or earlier using only the high-frequency module. This allows for the calibration path d to be... kal Fill level measuring device 1 is used for different variations of high-frequency modules of the same type. Especially in forced calibration applications, periodic recalibration of fill level measuring device 1 is required during measurement operations.

[0027] In principle, by following the calibration path d kal Transmitting radar signal S HF And in the calibration path d kal After reflection at the appropriate end region 522, the corresponding received signal R is received. HF The calibration is performed accordingly. As a result of the calibration, the propagation time t and calibration path d are measured by the fill level measuring device 1. kal The two pairs are matched according to the following formula:

[0028] Required calibration path d kal The length of the calibration path depends decisively on the desired measurement range, which can reach 100m. Therefore, especially in cases where recalibration is required during measurement operations, providing a sufficiently long calibration path is crucial. kal This could become a problem. The following will be based on... Figure 2 The exploded diagram explains the calibration device 5 of the present invention in more detail, taking into account the desired calibration path d. kal The design is compact: accordingly, the calibration device 5 is based on a metal platform 51 consisting of two parts. In the illustrated embodiment, the platform 51 and its two parts 51a and 51b have a basic rectangular shape.

[0029] from Figure 2 As can be seen from the exploded view, each of the two parts 51a and 51b has a flat rectangular surface. In the assembled state, the two parts 51a and 51b are adjacent to each other planarly at these surfaces, and their basic rectangular shapes coincide. In this way, a rectangular segment A of flat plane is defined. Within the planar segment A, a calibration path d is formed along the adjacent surfaces. kal The hollow conductor 52. Due to the planar arrangement of the hollow conductor 52, the hollow conductor 52 can be manufactured by milling the surface of one of the portions 51a and 51b, or by milling overlapping portions 51a and 51b.

[0030] exist Figure 2In the embodiment shown, the two parts 51a and 51b of the platform 51 are connected to each other by screw connection 525, wherein the screw holes for the connection are arranged next to the hollow conductor 52.

[0031] Unlike the illustrated embodiment, the two portions of platform 51 do not need to be made of conductive material, provided that the inner surface of the hollow conductor 52 is conductive. In the case of non-metallic portions 51a and 51b, these portions can be prepared, for example, by sputtering deposition or chemical vapor deposition (“CVD”), thereby providing a conductive coating (such as, in particular, silver) to form the inner surface of the hollow conductor 52.

[0032] According to the present invention, the hollow conductor 52 is helical, wherein, in Figure 2 In the example of the illustrated embodiment, the spiral shape is composed of straight base segments 523, which are arranged at right angles to the next base segment 523. Each base segment is connected by a quarter-circular connecting line segment 524, thus forming a nested rectangular spiral. A reflected radar signal S is located at the center of the spiral. HF R HF The end region 522 of the hollow conductor 52. Opposite to the end region 522, and thus located at the edge of the rectangular platform 51, is the input coupling region 521, in which the horizontal measuring device 1 is filled, and its high-frequency module can be connected for coupling at this input coupling region 521. Therefore, the calibration path d kal The input coupling region 521 is defined by a hollow conductor 52 between the input coupling region 521 and the terminal region 522. For this purpose, the radar signal S can be transmitted, for example, via a dielectric waveguide that can be inserted into the input coupling region 521. HF R HF It is coupled into the hollow conductor 52. Figure 2 What is not explicitly shown is that the hollow conductor can also be structurally sealed at the input coupling region 521 through a radar-transparent window, so that the hollow conductor 52 can be evacuated or supplied with inert gas to interfere with radar transmission less.

[0033] Figure 3 Another embodiment of the calibration device 5 of the present invention is shown. In this case as well, the input coupling region 521 is arranged at the edge of the rectangular platform 51, thus opposite to the center of the spiral. However, with... Figure 2 Unlike other structures, the hollow conductor 52 is divided into semi-circular base segments 523', thereby calibrating the hollow conductor 52 and the path d. kalA circular spiral shape is formed. Furthermore, the hollow conductor 52 is divided into two parallel hollow conductor routes 52a and 52b along the spiral. They are connected to each other at the center of the spiral via a connecting route 52c for high-frequency transmission. Therefore, in this embodiment, the reflective end region 522 of the hollow conductor 52 is also located at the edge of the rectangular platform 51, adjacent to the input coupling region 521. Since the hollow conductor routes 52a and 52b are arranged in parallel within the spiral, the calibration path d is optimized without increasing the basic area of ​​the platform 51. kal The length is doubled.

[0034] List of reference numerals

[0035] 1. Fill level measuring device

[0036] 2. Filler

[0037] 3 containers

[0038] 4. Upper-level unit

[0039] 5. Calibration device

[0040] 51 Platform

[0041] 52 Hollow Conductor

[0042] 521 Input coupling region

[0043] 522 Terminal Region

[0044] 523 base segment

[0045] 524 Connecting segment

[0046] 525 screw connection

[0047] A Planar Section

[0048] d Distance, spacing

[0049] h Installation height

[0050] L fill level

[0051] R HF Received signal

[0052] S HF radar signals

Claims

1. A calibration device (5) for calibrating a radar-based fill level measuring device (1) or its high-frequency module, the calibration device (5) comprising: - Platform (51), said platform (51) includes a section of a flat plane (A), - A hollow conductor (52) extending within the segment in the plane (A) and having o Input coupling region (521), o Radar signal (S HF R HF The end region of the reflection (522), and o The defined calibration path (d) located within it kal ), Its features are, The hollow conductor (52), and further the calibration path (d) kal It is formed by spiral nesting.

2. The apparatus according to claim 1, wherein, The hollow conductor (52) is segmented into semi-circular base segments (523′), so that the hollow conductor (52) has an annular spiral shape.

3. The apparatus according to claim 1, wherein, The hollow conductor (52) is segmented into straight base segments (523), which are arranged at a defined angle relative to the next base segment (523) and connected to each other by circular connecting segments (524), such that the hollow conductor has a spiral shape, especially rectangular, hexagonal or octagonal.

4. The apparatus according to claim 3, wherein, All connecting segments (524) of the hollow conductor (52) have the same radius.

5. The apparatus according to any one of the preceding claims, wherein, The input coupling region (521) is located at the hollow conductor (52) and is opposite to the center of the spiral.

6. The apparatus according to claim 5, wherein, The hollow conductor (52) is segmented along the spiral into two parallel hollow conductor routes (52a, 52b), which are connected at the center of the spiral by a connecting route (52c).

7. The apparatus according to any one of the preceding claims, in, The platform (51) is made of a conductive material, particularly aluminum, copper or stainless steel, and / or the hollow conductor (52) has a conductive coating, particularly a silver coating.

8. The apparatus according to any one of the preceding claims, wherein, The platform (51) is implemented as two parts such that, in the assembled state, the two corresponding parts (51a, 51b) of the platform (51) are separated by the plane (A).

9. The apparatus according to any one of the preceding claims, Also includes: - An airtight sealing window, said airtight sealing window being arranged at the input coupling area (521), The hollow conductor (52) is either evacuated or filled with an inert gas.

10. The apparatus according to any one of the preceding claims further comprises: - A polarization filter, which is arranged before the input coupling region (521) and is particularly designed to transmit the radar signal ( ) via a dielectric waveguide or dielectric lens. S HF ) is coupled into the hollow conductor (52), The hollow conductor (52) has a rectangular cross-section.

11. The apparatus according to any one of the preceding claims, wherein, The hollow conductor (52) has a radar disturbance point at at least one defined location, particularly a radar disturbance point in the form of a change in the cross-section of the hollow conductor.

12. A method for calibrating a radar-based fill level measuring device (1) or its high-frequency module using the apparatus (5) according to any one of the preceding claims, wherein, The method includes the following steps: - The radar signal (S) is transmitted via the input coupling region (521). HF ) is coupled into the hollow conductor (52), - In the radar signal (S HF After being reflected on the end region (522), the corresponding received signal (R) is output and coupled. HF ),as well as - Based on the received signal (R) HF ) and the known calibration path (d) of the hollow conductor (52). kal (To perform calibration) 13. The method according to claim 12, wherein the method is performed during the manufacture of the fill level measuring device (1) or in the context of a measurement operation.

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