TDR level gauge and method for operating a TDR level gauge

Description

[0001] The invention relates to a TDR (Time Domain Reflectometry) level gauge for measuring the fill level of a medium in a container, comprising at least one transmitter unit for emitting a pulsed electromagnetic measurement signal, at least one receiver unit for receiving at least one reflection signal, at least one evaluation unit for evaluating the at least one reflection signal, and at least one waveguide, wherein the waveguide has at least one conductor for guiding the measurement signal and the reflection signal, wherein the waveguide has at least two waveguide sections, each waveguide section having at least one functional waveguide cross-sectional area, wherein the functional waveguide cross-sectional area corresponds to the cross-sectional area of ​​the at least one conductor, wherein at least one reference reflector is provided, and wherein the reference reflector is designed and arranged as follows:that during operation at least part of the measurement signal is reflected at least once by at least one reference reflector.

[0002] Furthermore, the invention relates to a method for operating a TDR level gauge for measuring the fill level of a medium in a container, wherein the TDR level gauge comprises at least one transmitter unit for emitting an electromagnetic measurement signal, at least one receiver unit for receiving at least one reflected reflection signal, at least one evaluation unit for evaluating the at least one reflected signal, and at least one waveguide, wherein the waveguide comprises at least one conductor for guiding the measurement signal and the reflected signal, wherein the waveguide comprises at least two waveguide sections, each waveguide section comprising at least one functional waveguide cross-sectional area, wherein the functional waveguide cross-sectional area corresponds to the cross-sectional area of ​​the at least one conductor.wherein at least one reference reflector is provided and wherein the reference reflector is designed and arranged such that, during operation, at least a part of the measurement signal is reflected at least once by the at least one reference reflector.

[0003] Prior art time-domain reflectometry (TDR) level gauges use the principle of TDR to measure the level of a medium, preferably a liquid, in a container. The distance between a transmitter and the surface of the medium is determined based on the travel time of a measurement signal emitted by the transmitter and reflected from the surface. From this measured distance, and given the container's depth, the level of the medium in the container is then determined. Crucial for accurate level determination is knowledge of the propagation speed of the measurement signal transmitted towards the medium.

[0004] The propagation speed of the measurement signal depends in particular on the permittivity ε of the medium through which the measurement signal moves.

[0005] In one type of TDR level measurement, a waveguide carries the measurement signal from the transmitting unit towards the medium and also carries the reflected signal from the medium's surface to the receiving unit. Depending on the application, particularly the parameters of the measurement environment, and the medium being measured, the measurement signal may pass through regions with varying permittivities above the medium. This occurs, for example, when a temperature gradient exists above the medium in the container.

[0006] To determine the permittivity distribution above the medium, it is known from the prior art of US patent 7,525,476 B1 to arrange reference reflectors in the form of cylindrical or otherwise shaped bodies at fixed intervals along the waveguide. Due to the change in impedance, the measurement signal propagating along the waveguide is also reflected by the reference reflectors. Based on knowledge of the distance traveled between the transmitting or receiving unit and the respective reference reflector, as well as the travel time of the measurement signal reflected by the reference reflector, the permittivity ε of the medium surrounding the waveguide above the reference reflector can be determined. This information can be used to correct the propagation speed of the measurement signal along the waveguide and thus to correct the level determination of the medium.

[0007] From the publication DE 20 2005 020 158 U1 it is also known to design the reference reflector as a local defect in the form of an opening, a notch, a protrusion or an aperture in the waveguide.

[0008] Furthermore, the publication EP 0 534 654 B1 discloses the design of the reference reflector as a discontinuity in the form of, for example, a collar surrounding the waveguide or in the form of a connection of separately designed waveguide parts.

[0009] The publication EP 3 173 750 A1 discloses a level measuring device for measuring the level of a medium in the presence of an atmosphere that influences the travel time of electromagnetic waves, using an electromagnetic wave based on a travel-time principle. The device comprises an evaluation unit, a transmitter and receiver for transmitting and receiving electromagnetic waves, at least one measuring probe, and at least one reference point. The evaluation unit is configured to take into account changes in the geometry of the reference point depending on the ambient conditions when processing the travel time of a signal reflected at the reference point. The reference points can also be designed as tapered sections of the measuring probe.

[0010] Based on this prior art, the present invention aims to provide a TDR level gauge that is both particularly reliable and exceptionally simple in design. Furthermore, the invention aims to provide a corresponding method for operating such a TDR level gauge.

[0011] According to a first teaching of the invention, the aforementioned problem is solved by a TDR level sensor according to claim 1. It was discovered according to the invention that a reference reflector can be designed particularly simply by the waveguide itself being configured as a reference reflector in at least one section. Advantageously, this eliminates the need for additional bodies attached to the waveguide to generate a reference reflection.

[0012] The at least two waveguide sections, between which the reference reflector is arranged, are arranged directly following one another in the direction of propagation of the measurement signal.

[0013] Furthermore, the waveguide cross-sectional areas, between which the reference reflector is arranged, are involved in guiding the measurement signal during operation.

[0014] According to a further embodiment, the transmitting unit and the receiving unit are designed as one unit, namely as a transmitting / receiving unit.

[0015] According to the invention, at least two reference reflectors are provided, wherein the at least two reference reflectors are configured as a transition between two waveguide sections with different sizes of functional waveguide cross-sectional areas. According to this configuration, the permittivity of the medium surrounding the waveguide can be determined in at least two regions, so that a permittivity distribution within the container can be determined with particular accuracy.

[0016] The functional waveguide cross-sectional area can, for example, be rotationally symmetrical, in particular circular, or oval or rectangular, in particular square.

[0017] According to one embodiment, the waveguide has exactly one conductor carrying the measurement signal.

[0018] According to another embodiment, the waveguide has at least two conductors carrying the measurement signal.

[0019] According to the invention, the at least two reference reflectors are configured as a tapered section of the at least one conductor of the waveguide involved in guiding the measurement signal, i.e., viewed in the direction of propagation of the measurement signal, as a reduction in the size of the functional waveguide cross-sectional area while maintaining the shape of the functional waveguide cross-sectional area. Furthermore, another reference reflector can also be configured as a thickening section of the at least one conductor of the waveguide involved in guiding the measurement signal, i.e., viewed in the direction of propagation of the measurement signal, as an increase in the size of the functional waveguide cross-sectional area while maintaining the shape of the functional waveguide cross-sectional area.

[0020] It is also conceivable that at least one reference reflector is arranged within the medium during operation, so that a permittivity distribution within the medium, for example a multiphase medium, can also be recorded.

[0021] It is particularly advantageous if the transition in shape and / or size between the functional waveguide cross-sectional areas is at least partially discontinuous. In this configuration, the reference reflection signal reflected at the transition is particularly narrow, resulting in a particularly accurate determination of the propagation time and thus the permittivity of the medium surrounding the waveguide section. It is also conceivable that the transition in shape and / or size between the functional waveguide cross-sectional areas is at least partially step-like. According to this configuration, depending on the number and size of the steps, the reference reflector generates at least two immediately successive reference reflection signals or a spatially or temporally extended reference reflection signal.This design has the advantage that the reference reflection signal can be distinguished particularly well from the reflection signal reflected at the surface of the medium during evaluation.

[0022] According to a further embodiment, the transition in shape and / or size between the functional waveguide cross-sectional areas is at least partially designed as a transition region, i.e., continuously. This embodiment has the advantage that the reference reflection signal is temporally and / or spatially extended and thus distinguishable from the reflection signal reflected at the surface of the medium.

[0023] A particularly advantageous feature is the spatially extended transition in shape and / or size between the functional waveguide cross-sectional areas, at least partially, in the direction of propagation of the measurement signal. For example, the transition can be designed as a staggered step or a staggered discontinuity.

[0024] According to the invention, at least two reference reflectors are provided, wherein the at least two reference reflectors are configured as successive tapers of the at least one conductor of the waveguide involved in guiding the measurement signal. It is also advantageous if at least three or more reference reflectors are provided, each configured as a taper, preferably with a discontinuous transition, of the at least one conductor of the waveguide involved in guiding the measurement signal.

[0025] According to a further embodiment, at least two additional reference reflectors are provided, wherein the at least two additional reference reflectors are configured as a thickening of the at least one conductor of the waveguide involved in guiding the measurement signal. It is also advantageous if at least one reference reflector is configured as a tapered section and at least one reference reflector is configured as a thickening of the at least one conductor of the waveguide involved in guiding the measurement signal. According to a non-inventive embodiment, at least three or more reference reflectors are provided, each configured as a thickening, preferably with a discontinuous transition, of the at least one conductor of the waveguide involved in guiding the measurement signal.

[0026] According to a further embodiment, the position of a reference reflector on the waveguide is determined depending on the dimensions of the waveguide and the measurement environment and / or the temperature distribution expected in the container during operation. For example, it is advantageous to have at least two reference reflectors, arranged at regular intervals along the waveguide. For example, the distance from the point where the measurement signal is coupled into the container to the first reference reflector, or the distance between the reference reflectors, is 1 m.

[0027] According to a particularly preferred embodiment, the distance between the point where the measurement signal is coupled into the container, or the distance between the individual reference reflectors, is designed as a multiple of the wavelength of the measurement signal. Preferably, the incident measurement signal and the reflected signal are superimposed in a constructive manner.

[0028] According to a further embodiment, the distance between the point where the measurement signal is coupled into the container, or the distance between the individual reference reflectors, does not correspond to a multiple of the wavelength. This embodiment has the advantage that the reflection signal reflected at the surface of the medium is particularly easy to distinguish from the reference reflection signals.

[0029] According to a further embodiment of the level measuring device, at least two reference reflectors are provided, which are arranged at irregular intervals along the waveguide.

[0030] Furthermore, it is advantageous if at least the transition between the functional waveguide cross-sectional areas, which forms a reference reflector, is designed as a single piece. Particularly preferably, the at least one conductor in the propagation direction of the measurement signal has no material transitions or joints. The at least one conductor of the waveguide is preferably manufactured from a single workpiece.

[0031] The waveguide is particularly preferably manufactured from a single workpiece.

[0032] According to a further embodiment, the waveguide is designed as a coaxial conductor comprising at least one inner conductor and at least one outer conductor, wherein the at least two reference reflectors are formed by the at least one inner conductor.

[0033] Furthermore, it is advantageous if the waveguide is designed as a coaxial conductor comprising at least one inner conductor and at least one outer conductor, wherein the at least two reference reflectors are formed by the at least one outer conductor.

[0034] It is also conceivable that the waveguide is designed as a coaxial conductor comprising at least one inner conductor and at least one outer conductor, wherein at least one reference reflector is formed by the at least one outer conductor and wherein at least one reference reflector is formed by the at least one inner conductor.

[0035] Particularly preferred are the reference reflector formed by the inner conductor and the reference reflector formed by the outer conductor arranged at the same height.

[0036] It is also advantageous if the reference reflector formed by the inner conductor and the reference reflector formed by the outer conductor are arranged at different heights.

[0037] Alternatively, the waveguide can be designed as a simple mono probe or as a double probe.

[0038] If the waveguide is designed as a double probe comprising a first and a second conductor, the at least two reference reflectors are preferably formed by one conductor.

[0039] Alternatively, if the waveguide is designed as a double probe comprising a first and a second conductor, at least one reference reflector is formed by the first conductor and at least one reference reflector is formed by the second conductor.

[0040] It is particularly preferred that the reference reflector formed by the first conductor and the reference reflector formed by the second conductor are arranged at the same height.

[0041] It is also advantageous if the reference reflector formed by the first conductor and the reference reflector formed by the second conductor are arranged at different heights.

[0042] According to a second teaching of the invention, the problem derived at the outset is solved by a method according to claim 10.

[0043] The procedure includes the following steps: Emitting a measurement signal along the waveguide by the transmitting unit, receiving at least one reflection signal by the receiving unit, wherein the reflection signal corresponds to at least one reflection of the measurement signal at the at least one reference reflector, receiving at least one further reflection signal by the receiving unit, wherein the further reflection signal corresponds to a reflection of the measurement signal at the surface of the medium to be measured, determining at least one permittivity ε of the medium surrounding a waveguide section from the travel time of the at least one reflection signal by the evaluation unit, wherein the reflection signal corresponds to a reflection of the measurement signal at the at least one reference reflector,Determining a correction factor for the propagation speed of the measurement signal along the waveguide based on the at least one permittivity ε and determining the fill level of the medium in the container from the transit time and the corrected propagation speed of the at least one further reflection signal, wherein the further reflection signal corresponds to a reflection of the measurement signal at the surface of the medium to be measured.

[0044] The TDR level measuring device is particularly preferably designed according to one of the previously described embodiments.

[0045] In detail, there are numerous possibilities for designing and further developing the level measuring device and the method according to the invention. Reference is made to both the claims subordinate to the independent claims and to the following description of preferred embodiments in conjunction with the drawing. The drawing shows Fig. 1 a first embodiment of a level measuring device, Fig. 2 a second embodiment of a waveguide, Fig. 3 a third embodiment of a waveguide, Fig. 4 a fourth embodiment of a waveguide, Fig. 5 a fifth embodiment of a waveguide, Fig. 6 a sixth embodiment of a waveguide, Fig. 7 a seventh embodiment of a waveguide, Fig. 8 an eighth embodiment of a waveguide and Fig. 9 a first embodiment of a method according to the invention.

[0046] InFig. 1 Figure 1 shows a first embodiment of a TDR level measuring device 1 for measuring the level of a medium in a container, comprising at least one transmitter 3 for emitting a pulsed electromagnetic measurement signal, a receiver 4 for receiving at least one reflection signal, an evaluation unit 5 for evaluating the at least one reflection signal and a waveguide 6 for guiding the measurement signal and the reflection signal.

[0047] The waveguide 6 is configured section by section as a reference reflector 7, with each reference reflector 7 being formed by a discontinuous transition between two waveguide sections with different sizes of functional waveguide cross-sectional areas 8. In the illustrated embodiment, two reference reflectors 7 are present, each configured as a narrowing of the waveguide 6. The functional waveguide cross-sectional areas 8 in the individual waveguide sections are each circular in shape.

[0048] Based on the known position of the reference reflectors 7 or the known length of the individual waveguide sections and the measured transit time of the reflection signals reflected at the reference reflectors 7, the permittivity ε r3 or ε r2 of the medium surrounding the corresponding waveguide sections can be determined, which can be used to correct the propagation speed of the measurement signal and thus to determine the fill level of the medium in the container.

[0049] According to another embodiment, at least one reference reflector 7 is also arranged in the medium, so that the permittivity ε rM of the medium can also be determined.

[0050] Fig. 2 Figure 1 shows a second embodiment of a waveguide 6 with a reference reflector 7, wherein the transition of the size of the functional waveguide cross-sectional area 8 is designed as a spatially extended continuous transition region.

[0051] Fig. 3 Figure 1 shows a third embodiment of a waveguide 6 with two reference reflectors 7, wherein one reference reflector 7 is designed as a spatially extended narrowing of the waveguide 6 and wherein a second reference reflector 7 is designed as a thickening with a spatially extended transition region.

[0052] In Fig. 4 Figure 1 shows another embodiment of a waveguide 6, wherein the reference reflector 7 is configured as a transition between two waveguide sections with different shapes of the functional waveguide cross-sectional areas 8. In detail, the functional waveguide cross-sectional area 8 is circular in a first waveguide section and oval in a second waveguide section.

[0053] Fig. 5 Figure 1 shows another embodiment of a waveguide 6 with a reference reflector 7, wherein the reference reflector 7 is designed as a step-shaped transition of the size of the functional waveguide cross-sectional areas 8 of a first and a second waveguide section.

[0054] In Fig. 6 Figure 1 shows another embodiment of a waveguide 6 with a reference reflector 7, wherein the reference reflector 7, designed as a transition between two waveguide sections with different sizes of the functional waveguide cross-sectional areas 8, is designed with a stepped offset and is thus designed as a spatially extended transition area.

[0055] The in Fig. 7 The waveguide 6 shown is designed as a coaxial conductor comprising an inner conductor 16 and an outer conductor 17. The outer conductor 17 has holes 15 for the passage of the medium to be measured. The inner conductor 16 is configured section by section as a reference reflector 7.

[0056] The Fig. 8 The waveguide 6 shown is also designed as a coaxial conductor comprising an inner conductor 16 and an outer conductor 17. The outer conductor 17 has holes 15 for the passage of the medium to be measured. In addition, the outer conductor 17 is partially configured as a reference reflector 7.

[0057] In Fig. 9 Figure 1 shows a first embodiment of a method 2 according to the invention for operating a TDR level gauge 1 for measuring the fill level of a medium in a container. The TDR level gauge 1 is configured as shown in Figure 2. Fig. 1 depicted and designed. Procedure 2 comprises the following steps:9. Transmission of a measurement signal along the waveguide 6 by the transmitting unit 3, 10. Receipt of a first reflection signal by the receiving unit 4, wherein the reflection signal corresponds to a reflection of the measurement signal at the first reference reflector 7, 10. Receipt of a second reflection signal by the receiving unit 4, wherein the reflection signal corresponds to a reflection of the measurement signal at the second reference reflector 7, 11. Receipt of a further reflection signal by the receiving unit 4, wherein the reflection signal corresponds to a reflection of the measurement signal at the surface of the medium to be measured, 12. Determination of the permittivity εr3 and εr2 of the medium surrounding the respective waveguide sections from the transit time of the first and second reflection signals by the evaluation unit 5.Determine 13 a correction factor for the propagation speed of the measurement signal along the waveguide 6 based on the determined permittivities ε r3 and ε r2, and determine 14 the fill level of the medium in the container from the transit time and the corrected propagation speed of the at least one further reflection signal, wherein the further reflection signal corresponds to a reflection of the measurement signal at the surface of the medium to be measured.

[0058] The presented method 2 has the advantage that, due to the consideration of the permittivity distribution above the medium or the adaptation of the propagation speed of the measurement signal or the reflection signal to this permittivity distribution, the determination of the fill level of the medium to be measured is particularly reliable. Reference symbol

[0059] 1 TDR level gauge 2 Procedure for operating a TDR level gauge 3 Transmitting unit 4 Receiving unit 5 Evaluation unit 6 Waveguide 7 Reference reflector 8 Functional waveguide cross-sectional area 9 Transmitting a measurement signal 10 Receiving a first reflection signal 11 Receiving a second reflection signal 12 Determining the permittivity 13 Determining a correction factor 14 Determining the level 15 Hole 16 Inner conductor 17 Outer conductor

Claims

1. A TDR fill level measuring device (1) for measuring the fill level of a medium in a container, comprising at least one transmitting unit (3) for transmitting a pulse-shaped electromagnetic measuring signal, at least one receiving unit (4) for receiving at least one reflection signal, at least one evaluation unit (5) for evaluating the at least one reflection signal and at least one waveguide (6), wherein the waveguide (6) has at least one conductor for guiding the measuring signal and the reflection signal, wherein the waveguide has at least two waveguide sections, wherein each waveguide section has at least one functional waveguide cross-sectional face (8), wherein the functional waveguide cross-sectional face (8) corresponds to the cross-sectional face of the at least one conductor, wherein at least one reference reflector (7) is present, and wherein the reference reflector (7) is designed and arranged in such a manner that at least a part of the measuring signal is reflected at least once on the at least one reference reflector (7) during operation, wherein the at least one reference reflection (7) is formed by a transition between two waveguide sections having different shapes and / or different sizes of the functional waveguide cross-sectional face (8), wherein at least two reference reflectors (7) are provided, characterized in that the at least two reference reflectors (7) are designed as successive tapers of the at least one conductor of the waveguide (6) involved in guiding the measuring signal, so that the functional waveguide cross-sectional area of the second waveguide section is smaller than the functional cross-sectional area of the first waveguide section and so that the functional waveguide cross-sectional area of the third waveguide section is smaller than the waveguide cross-sectional area of the second waveguide section.

2. TDR fill level measuring device (1) according to claim 1, characterized in that the transition of the form and / or size between the functional waveguide cross-sectional faces (8) is designed at least partially step-like.

3. TDR fill level measuring device (1) according to claim 1 or 2, characterized in that the transition of the form and / or size between the functional waveguide cross-sectional faces (8) is continuously designed at least partially in the form of a transitional section.

4. TDR fill level measuring device (1) according to any one of claims 1 to 3, characterized in that the transition of the form and / or size between the functional waveguide cross-sectional faces (8) is at least partially spatially extended in the direction of the propagation of the measuring signal.

5. TDR fill level measuring device (1) according to any one of claims 1 to 4, characterized in that the position of the at least two reference reflectors (7) on the waveguide (6) is determined depending on the dimensions of the waveguide (6) and the measuring environment and / or on the temperature distribution to be expected in the container during operation.

6. TDR fill level measuring device (1) according to any one of claims 1 to 5, characterized in that the at least two reference reflectors (7) are arranged at regular intervals along the waveguide (6).

7. TDR fill level measuring device (1) according to any one of claims 1 to 6, characterized in that at least the transition between the functional waveguide cross-sectional faces (8) that form the references reflector (7) is designed as one piece.

8. TDR fill level measuring device (1) according to any one of claims 1 to 7, characterized in that the waveguide (6) is designed as a coaxial conductor comprising at least one inner conductor (16) and at least one outer conductor (17), wherein the reference reflectors (7) are formed by the at least one inner conductor (16).

9. TDR fill level measuring device (1) according to anyone of claims 1 to 8, characterized in that the waveguide (6) is designed as a coaxial conductor comprising at least one inner conductor (16) and at least one outer conductor (17), wherein the reference reflectors (7) are formed by the at least one outer conductor (17).

10. Method (2) for operating a TDR fill level measuring device (1) for measuring the fill level of a medium in a container, wherein the TDR fill level measuring device (1) has at least one transmitting unit (3) for transmitting a pulse-shaped electromagnetic measuring signal, at least one receiving unit (4) for receiving at least one reflected reflection signal, at least one evaluation unit (5) for evaluating the at least one reflection signal and has at least one waveguide (6) wherein the waveguide (6) has at least one conductor for guiding the measuring signal and the reflection signal, wherein the waveguide has at least two waveguide sections, wherein each waveguide section has at least one functional waveguide cross-sectional face (8), wherein the functional waveguide cross-sectional face (8) corresponds to the cross-sectional face of the at least one conductor, wherein at least one reference reflector (7) is present, and wherein the reference reflector (7) is designed and arranged in such a manner that at least a part of the measuring signal is reflected at least once on the at least one reference reflector (7) during operation, wherein the at least one reference reflector (7) is formed by a transition between two waveguide sections having different shapes and / or different sizes of the functional waveguide cross-sectional faces (8), wherein the method (2) comprises the following steps: - transmitting (9) a measuring signal along the waveguide (6) by the transmitting unit (3), - receiving (10) at least one reflection signal by the receiving unit (4), wherein the reflection signal is at least a reflection of the measuring signal on the at least one reference reflector (7), - receiving (11) at least one further reflection signal by the receiving unit (4), wherein the further reflection signal is a reflection of the measuring signal on the surface of the medium to be measured, - determining (12) at least one permittivity ε of a medium surrounding a waveguide section from the transit time of the at least one reflection signal by the evaluation unit (5), wherein the reflection signal is a reflection of the measuring signal on the at least one reference reflector (7), - determining (13) a correction factor of the propagation speed of the measuring signal along the waveguide (6) based on the at least one permittivity ε and - determining (14) the fill level of the medium located in the container from the transit time and the corrected propagation speed of the at least one further reflection signal, wherein the further reflection signal is a reflection of the measuring signal on the surface of the medium to be measured; wherein at least two reference reflectors (7) are present, characterized in that the at least two reference reflectors (7) are designed as successive tapers of the at least one conductor of the waveguide (6) used for guiding the measuring signal, so that the functional waveguide cross-sectional area of the second waveguide section is smaller than the functional cross-sectional area of the first waveguide section and so that the functional waveguide cross-sectional area of the third waveguide section is smaller than the waveguide cross-sectional area of the second waveguide section.

11. Method according to claim 10, characterized in that the TDR fill level measuring device is designed according to any one of claims 2 to 9.