Filling level measuring device and method for online calibration and / or verification of a filling level measuring device

Abstract

The invention relates to a fill level measuring device for determining a fill level (L) of a filling material (1) in a container (2) on the basis of microwaves. The invention is characterized in that the fill level measuring device has at least one reflection point (61,...) arranged outside the container (2), wherein the reflection point generates a reflection point echo signal (RE) by reflection of an emitted signal, wherein an electronic unit (3) calibrates and / or verifies a filling material echo signal (FE) on the basis of at least one reflection point echo signal (RE). The invention also relates to a method for calibrating and / or verifying a fill level measuring device on-line.

Description

Technical Field

[0001] This invention relates to a filling level measuring device for determining the filling level of a container based on microwaves. Furthermore, this invention relates to a method for online calibration and / or verification of the filling level measuring device. Background Technology

[0002] Microwave-based filling level measurement devices are used in many applications, especially where high accuracy is required to determine the filling level of filling materials. For example, in the food processing, pharmaceutical, and / or chemical industries, it is essential to accurately determine the quantity involved in a reaction process.

[0003] Similarly, in the oil and gas industry, it is necessary to precisely determine the filling material in containers, for example, when the payment amount in a commercial transaction is determined based on a precise quantity. Depending on the application in the aforementioned industries, the filling material can be, for example, a liquid, but it can also consist of solid particles, i.e., substantially granular.

[0004] Microwave-based liquid level measurement devices typically include an electronics unit and a transmitter / receiver unit. The electronics unit generates transmitted signals and processes echo signals, while the transmitter / receiver unit is connected to the electronics unit and transmits these signals and receives the echo signals in the direction of the filling material in the container. Depending on the embodiment, the transmitter / receiver unit and the electronics unit are designed as spatially separate units, for example, interconnected by cables.

[0005] (So-called "long-range" variant), or formed as spatially adjacent units (so-called "compact" variant). The present invention relates to both long-range and compact variants.

[0006] In measurement mode, the transmitter / receiver unit emits a transmission signal at a frequency in the microwave range or higher in the direction of the filling material. An echo signal is generated by the reflection of the transmitted signal at the surface of the filling material. This echo signal is transmitted back to the electronics unit, which then determines the filling level of the filling material based on the echo signal, for example, the time difference between the emission of the transmitted signal and the reception of the reflected echo signal. The FMCW (Frequency Modulated Continuous Wave) method is also used in microwave-based filling level measurement devices. This method varies the frequency range of the continuously transmitted signal and measures the distance by the frequency difference between the transmitted signal and the reflected echo signal. Besides filling level, microwave-based filling level measurement devices can also be used to determine the position of the boundary layer in the filling material and the dielectric constant (also known as the DC value) of the filling material as additional process variables.

[0007] Microwave-based fill level measuring devices have many variants, which can basically be divided into two groups, referred to as "free-space" or "guided-wave". Guided-wave microwave-based fill level measuring devices differ from free-space devices in that they comprise a conductive probe connected to the transmitter / receiver unit. The probe extends into the fill material and is used to forward the transmitted signals and the echo signals.

[0008] The present application relates to such guided-wave microwave-based fill level measuring devices with a probe, as described for example in DE 102 014 112 453 A1. The applicant manufactures and sells a guided-wave microwave-based fill level measuring device under the name "Levelflex".

[0009] In the patent specification DE 44 19 462 C2 a device and a method for calibrating and / or verifying a free-space microwave-based fill level measuring device using a reflection point arranged inside the container are disclosed.

[0010] It is desirable to be able to perform a calibration and / or verification of the fill level measuring device while the system is essentially in a running state. In this case, the calibration and / or verification is performed on a container filled with fill material; this is also referred to as wet calibration or online calibration. The fill level measuring device is thus kept in the installed state in and / or on a container which can be filled with fill material. SUMMARY

[0011] It is therefore an object of the present application to provide a simple online calibration and / or verification scheme for guided-wave microwave-based fill level measuring devices.

[0012] The object of the present application is achieved by a fill level measuring device and a method for online calibration and / or verification.

[0013] With regard to the fill level measuring device, the object is achieved by a fill level measuring device for determining a fill level of a fill material in a container based on microwaves, the fill level measuring device having:

[0014] - an electronic unit designed to generate transmitted signals and to process echo signals;

[0015] - a transmitter / receiver unit connected to the electronic unit and designed to transmit the transmitted signals and to receive the echo signals in the direction of the fill material in the container; and

[0016] - a conductive probe connected to the transmitter / receiver unit, the conductive probe extending into the fill material and being used to forward the transmitted signals and the echo signals,

[0017] wherein the transmitter / receiver unit emits a transmission signal in the direction of the filling material along the probe in a measurement mode,

[0018] wherein a filling material echo signal is generated by a reflection of the transmission signal at the surface of the filling material, which signal returns along the probe to the transmitter / receiver unit and to the electronic unit to enable a determination of the filling level of the filling material by the electronic unit from the filling material echo signal, characterized in that

[0019] the filling level measuring device has at least one reflection point arranged outside the container, which reflection point generates a reflection point echo signal by a reflection of the transmission signal,

[0020] and wherein the electronic unit calibrates and / or verifies the filling material echo signal on the basis of the at least one reflection point echo signal.

[0021] The transmission signal is, for example, a high-frequency transmission signal, i.e. a high-frequency transmission signal from high-frequency measurement technology, which has a frequency of from 3 MHz to approximately 30 THz or more. The reflection point is characterized in that a partial reflection of the transmission signal occurs at the reflection point due to an impedance jump. If the position of the reflection point is fixed and known, a calibration and / or verification of the filling level measuring device can be carried out on the basis of the reflection point.

[0022] In the context of the present application, the at least one reflection point is now arranged outside the container, the filling level of the filling material of which can be determined with the filling level measuring device. The reflection for generating the reflection point echo signal used in the calibration therefore preferably does not take place completely at a reflection point arranged inside the (for example, closed) container.

[0023] In one embodiment, the filling level measuring device has at least two reflection points.

[0024] In one embodiment of the filling level measuring device, the at least one reflection point is arranged inside the container.

[0025] In one embodiment of the filling level measuring device, the probe has an end-of-probe (EOP) reflection point inside the container, which end-of-probe (EOP) reflection point is formed by the end of the probe facing away from the external transmitter / receiver unit.

[0026] In one embodiment of the fill level measuring device, the device includes a cable, wherein the electronic unit is connected to a transmitter / receiver unit via the cable, and the cable is used to relay transmitted and echo signals, and wherein the cable includes at least one reflection point. The cable is disposed outside the container. Therefore, it is advantageous that the cable itself is used to generate an impedance jump, through which the reflection point disposed outside the container is formed. This also has the positive effect that the cable is generally easy to replace, making it particularly easy to add the reflection point outside the container to the prior art fill level measuring device for calibration purposes (or, if necessary, remove the reflection point afterwards for measurement).

[0027] In one embodiment of the filling level measuring device, the cable is coiled and arranged in a housing, wherein the electronic unit is substantially directly adjacent to the housing, and the housing is substantially directly adjacent to the transmitter / receiver unit.

[0028] In the case of the aforementioned compact variant of the filling level measuring device without cables, for example, for calibration purposes, it is possible to add coiled cables to the compact variant via corresponding branches.

[0029] In a further improvement to the filling level measuring device, the cable is a coaxial cable having a first coaxial cable segment and a second coaxial cable segment adjacent to the first coaxial cable segment, wherein the reflection point is formed by the transition point between the first and second coaxial cable segments.

[0030] In the aforementioned further improved first embodiment, the first insulating layer of the first coaxial cable segment and the second insulating layer of the second coaxial cable segment have different dielectric constants.

[0031] Therefore, the dielectric constants of the first and second coaxial cable segments in their respective insulation layers are different. This causes an impedance jump at the transition point in the coaxial cable, thus creating a reflection point at the transition point between the two coaxial cable segments.

[0032] In the aforementioned further improved second embodiment, the first inner conductor and the first outer conductor of the first coaxial cable segment, and the second inner conductor and the second outer conductor of the second coaxial cable segment are sized such that a first quotient formed by dividing the diameter of the first inner conductor by the diameter of the first outer conductor is different from a second quotient formed by dividing the diameter of the second inner conductor by the diameter of the second outer conductor.

[0033] Therefore, in this embodiment, the impedance jump at the transition point is caused by the different quotients or ratios of the diameters in the first and second coaxial cable segments.

[0034] In a further improvement to the filling level measuring device, the cable is a coaxial cable, and the reflection point of the cable is formed by a stub circuit, wherein the stub circuit is connected to at least one conductor of the coaxial cable, i.e., connected to the inner conductor and / or outer conductor of the coaxial cable, by means of a stub arranged at a fixed position on the cable.

[0035] In a further embodiment of the latter, the stub circuit includes a switch.

[0036] Specifically, the stub circuit also includes other circuit components. For example, the position of the switch can be used to determine whether different circuit components (e.g., resistors, inductors, capacitors, etc.) are connected in the stub circuit, or, for example, whether the outer conductor is short-circuited to the inner conductor via the stub circuit at the stub.

[0037] Therefore, the amplitude ratio between the reflection point echo signal and the filling material echo signal can be specifically set by the position of the switch. For example, the switch can be used to switch between operation utilizing the minimum possible amplitude of the reflection point echo signal and operation utilizing the maximum possible amplitude of the reflection point echo signal.

[0038] In one embodiment of the filling level measuring device, the connection point between the transmitter / receiver unit and the probe forms a coupling-in reflection point, at which the transmitted signal is coupled into the probe.

[0039] In a further improvement to the filling level measuring device, the probe has at least one additional reflection point that generates echo signals from other reflection points, wherein the additional reflection point is arranged between the end of the probe away from the external transmitter / receiver unit and the connection point.

[0040] In a further embodiment of the latter, the additional reflection point of the probe is formed by the transition between the first probe segment and the second probe segment.

[0041] For example, the probe includes a first probe segment made of a first material and a second probe segment made of a second material adjacent to the first probe segment, wherein the first material and the second material have different RF (radio frequency) characteristics from each other.

[0042] Alternatively, the two probe segments are made of the same material, but a different material with different RF properties is inserted between the probe segments, and is in the form of a needle-shaped element (such as a "needle") between the two probe segments, for example.

[0043] In one embodiment of the filling level measuring device, the additional reflection point of the probe is formed by a local modification of the probe shape.

[0044] The local modification is specifically selected from the group consisting of: protrusions, indentations, grooves, and holes.

[0045] If necessary, additional reflective points can be formed by components within the container, such as vibratory filling level limit switches, stirrers, or other lateral components.

[0046] Regarding this method, this objective is achieved by a method for online calibration and / or verification using a microwave-based filling level measuring device according to at least one of the preceding claims when determining the filling level of the filling material in the container.

[0047] In this system, the transmitted signal is emitted along the probe in the direction of the filling material by an external transmitter / receiver unit in measurement mode. The echo signal from the filling material is generated by the reflection of the transmitted signal at the surface of the filling material. This echo signal returns along the probe to the transmitter / receiver unit and is then transmitted to the electronic unit, so that the filling level of the filling material is determined by the electronic unit based on the echo signal.

[0048] Its features

[0049] The method includes the following steps:

[0050] - Generate at least one reflection point echo signal, which is generated by the reflection of the transmitted signal at the reflection point, wherein the at least one reflection point is arranged outside the container.

[0051] - Perform online calibration and / or verification of the echo signal of the filling material based on the echo signal of at least one reflection point.

[0052] In one embodiment of the method, deposits and / or corrosion at the connection point are detected based on the reflected echo signal coupled into the reflection point.

[0053] Typically, deposits produce reflected echo signals with a 180° phase shift from the emitted signal. On the other hand, corrosion often produces reflected echo signals without a significant phase shift. Therefore, considering the phase shift, it is possible to conclude whether deposits or corrosion exist. Attached Figure Description

[0054] The invention and further advantageous embodiments will now be explained in more detail with reference to exemplary embodiments. In all the drawings, the same parts are labeled with the same reference numerals; reference numerals previously used will not be repeated in subsequent drawings for clarity, or if it seems reasonable for other reasons.

[0055] In the attached image:

[0056] Figure 1 An embodiment of the filling liquid level measuring device according to the present invention is shown;

[0057] Figure 2 A further embodiment of the filling liquid level measuring device according to the present invention is shown;

[0058] Figure 3 An embodiment of the cable of the filling liquid level measuring device according to the present invention is shown;

[0059] Figure 4 A further embodiment of the cable of the filling liquid level measuring device according to the present invention is shown;

[0060] Figure 5a , Figure 5b Various embodiments of the probe of the filling liquid level measuring device according to the present invention are shown. Detailed Implementation

[0061] Figure 1 An embodiment of the filling level measuring device according to the present invention is shown. The filling level measuring device includes a probe 5 that extends into a container 2 containing filling material 1. A transmission signal from an external transmitter / receiver unit 4 is transmitted via the probe 5 in the direction of the filling material 1, reflected at the surface of the filling material 1, and then transmitted back via the probe 5 to the external transmitter / receiver unit 4, which is located at the upper seal of the container 2. The transmitter / receiver unit 4 is connected via a cable 7 to an electronic unit 3, which is designed to generate the transmission signal and process the echo signal.

[0062] Figure 1 The illustrated embodiment is a remote variant of the filling level measuring device mentioned above, wherein the transmitter / receiver unit 4 is spatially separated from the electronic unit 3. According to the invention, at least one reflective point 61 is provided arranged outside the container 2. This at least one reflective point is inserted into… Figure 1 Cable 7. See also [reference needed]. Figure 3 and Figure 4 The reflection point 61 is arranged between the first coaxial cable segment 71 and the second coaxial cable segment 72.

[0063] In addition, zero-point reflection 65 exists at the attachment point between electronic unit 3 and cable 7.

[0064] In addition, the filling level measuring device also includes other reflection points 62, 63, and 64, including:

[0065] -EOP reflection point 62, which is located at the end (EOP) of the probe 5 away from the transmitter / receiver unit 4.

[0066] - Coupled-in reflection point 64, which is arranged at the connection point 16 between the transmitter / receiver unit 4 and the probe 5, and

[0067] - Additional probe reflection point 63, which is arranged between EOP reflection point 62 and connection point 16.

[0068] The echo signal recorded by the filling level measuring device according to the present invention and processed by the electronic unit 3 is plotted as a function of transmission time in the form of a function amplitude. Figure 1 On the left edge. The amplitude is plotted along the horizontal axis (from left to right in the image plane), while the transmission time, which can be converted into distance, is plotted along the vertical axis (from top to bottom in the image plane). If necessary, the electronic unit 3 of the filling level measuring device still includes corresponding components and / or algorithms for amplifying various echo signals FE, RE.

[0069] The echo signals FE and RE include, on the one hand, the filler material echo signal FE, which is used to determine the filler level L (for example, the distance can be determined from the transmission time of the filler material echo signal FE, and thus the filler level L), and on the other hand, a number of reflection point echo signals RE. The latter are generated by a single reflection of the transmitted signal at reflection points 61, 62, 63, 64, and 65 according to the invention. Of course, multiple reflections may also occur; these typically only manifest as background noise in the amplitude.

[0070] Calibration and / or verification can be performed using the reflected point echo signal RE. For example, during calibration, a constant coefficient is determined based on the known and fixed locations of reflection points 61, 62, 63, 64, and 65 and the recorded transmission time of the reflected point echo signal RE to convert the transmission time of the reflected point echo signal RE into a path distance. This coefficient can then be compared with a coefficient stored in the fill level measuring device, for example, in its electronic unit 3, during calibration and / or verification.

[0071] Calibration is generally understood as the detection of deviation; in this case, the deviation is the difference between the coefficient determined (and assumed to be correct) via the reflected point echo signal RE and the stored coefficient. Verification additionally includes determining the accurate value of the deviation and its evaluation value. Adjustment refers to adjusting the fill level measuring device so that the detected deviation is compensated for by adjustment. If necessary, adjustment may also be performed, wherein the stored coefficient is adjusted based on the reflected point echo signal RE.

[0072] When using echo signals (REs) from several reflection points, multi-point calibration can be performed. For example, at least two-point calibration can be performed using reflection point 61 and EOP reflection point 62 of cable 7, taking into account... Figure 1 All reflection points 61, 62, 63, 64, and 65 shown are used to perform at least a 5-point calibration.

[0073] Preferably, calibration and / or verification can be performed online, i.e., for the filling level measuring device installed in the processing plant and in the presence of filling material 1 in container 2.

[0074] Furthermore, based on the coupling-in reflection point 64, in one embodiment of the method according to the invention, it may be checked whether deposit 17 has formed on the transmitter / receiver unit 4, or more likely, whether corrosion is present. As described above, this is accomplished, for example, by considering the phase relationship between the emitted transmitted signal at the coupling-in reflection point 64 and the received reflected echo signal RE.

[0075] As mentioned at the beginning, the solution according to the invention is applicable to both Figure 1 The shown long-range variant also applies to the compact variant. The latter is... Figure 2 As shown in more detail, the electronic unit 3 of the filling level measuring device is located substantially directly adjacent to the transmitter / receiver unit 4 via the housing 8. The cable 7 is coiled within the housing 8, and a reflective point 61 is inserted into the cable. If necessary, this cable 7 with the reflective point 61 can also be added subsequently to a compact variant of the filling level measuring device without cables via corresponding branch connections.

[0076] Figure 3 One embodiment of providing a cable 7 with a reflective point 61 is shown. Figure 3 In the illustrated embodiment, a perspective view of a segment of cable 7 is shown in more detail. To relay signals between electronic unit 3 and transmitter / receiver unit 4, a coaxial cable is used, which in principle includes an inner conductor, an outer conductor, and an insulating layer disposed between the inner and outer conductors. According to the invention, Figure 3 The coaxial cable 7 of the illustrated embodiment now includes a first coaxial cable segment 71 and a second coaxial cable segment 72, which are adjacent to each other at a transition point 73 forming a reflection point 61.

[0077] The impedance jump at reflection point 61 is caused, for example, by the fact that the dielectric constant of the first insulating layer 91 in the first coaxial cable segment 71 is different from that of the second insulating layer 92 in the second coaxial cable segment 72. Otherwise, the cross-sections of the two coaxial cable segments 71, 72 could have substantially the same construction. The different dielectric constants of the insulating layers 91, 92 are set, for example, primarily by correspondingly selecting and / or adjusting the materials of the respective insulating layers 91, 92.

[0078] An alternative is to design the diameter ratios of the conductive layers 11a, 12a or 11b, 12b in the two coaxial cable segments 71, 72 to be different. This will also cause an impedance jump at the transition point 73, resulting in a reflection point 61. Specifically, the ratio (first quotient) of the diameter of the first inner conductor 11a to the diameter of the first outer conductor 12a in the first coaxial cable segment 71 is different from the ratio (second quotient) of the diameter of the second inner conductor 11b to the diameter of the second outer conductor 12b in the second coaxial cable segment 72. This can also be achieved, for example, by using uniform insulating layers 91, 92 and otherwise using the same material for the inner conductors 11a, 11b and the outer conductors 12a, 12b. Different diameter ratios in Figure 3 It is not explicitly shown to scale.

[0079] Figure 4 A further option for assembling the reflection point 61 with cable 7 is shown. In this embodiment, cable 7 is a monolithic coaxial cable, i.e., having a monolithic inner conductor 11, outer conductor 12, and insulation layer 9. The reflection point 61 of cable 7 is formed such that stub 14 connects to the inner conductor 11 and outer conductor 12 at this point. Stub 14 is integrated into stub circuit 13. Other circuit components, not shown in detail here, can also be integrated into stub circuit 13, which also determine the typical electronic circuit variables of stub circuit 13, i.e., resistance, capacitance, inductance, etc. In the simplest case, inner conductor 11 is short-circuited to outer conductor 12 via stub circuit 13. This short circuit of stub 14 causes a relatively strong reflection point echo signal RE at reflection point 61 compared to the fill material echo signal FE used for filling level determination. "Strong" here is characterized in relation to its corresponding amplitude.

[0080] In a preferred variant, switch 15 is also arranged in stub circuit 13 such that stub circuit 13 can be switched between an "open stub" variant and a "closed stub" variant, in which inner conductor 11 and outer conductor 12 are short-circuited to each other. For example, the "open stub" position is suitable for pure measurement mode, so that the filler material echo signal FE is not excessively interfered with by the reflection point echo signal RE, and the energy required to generate the reflection point echo signal RE is also reduced. On the other hand, the "closed stub" position is suitable when performing calibration and / or verification, so as to obtain a particularly prominent reflection point echo signal RE with the maximum possible amplitude in calibration mode.

[0081] Of course, by appropriately combining the preceding text... Figure 3 and Figure 4 By combining the embodiments mentioned above, cable 7 may also have several such reflection points 61, each of which is of the same kind and / or different from one another.

[0082] In addition, probe 5 itself may have several reflection points 62, 63; see also Figure 5a , Figure 5b Each probe 5 has an EOP reflection point 62 at its end away from the transmitter / receiver unit 4 (naturally).

[0083] exist Figure 5a In this design, probe 5 also has an additional probe reflection point 63, which is formed by using two adjacent probe segments 51 and 52 with different high-frequency characteristics. Therefore, an impedance jump occurs at the transition from the first probe segment 51 to the second probe segment 52. Alternatively, the two probe segments 51 and 52 are made of the same material, and a needle-shaped element (not shown) made of a different material, i.e., with different high-frequency characteristics, is inserted between these two probe segments.

[0084] exist Figure 5b On the other hand, a local modification portion 53 is introduced into the probe 5, which here takes the form of an indentation on the probe 5. This indentation also causes impedance jumps. The invention includes additional variations of the local geometric modification portion of the probe 5, such as one of the aforementioned variations including protrusions, grooves, holes, etc.

[0085] exist Figure 5a , 5b In this embodiment, the additional probe reflection point 63 is centrally arranged between the connection point 16 and the end of the probe 5 with the EOP reflection point 62. Of course, the present invention also includes probe 5 with a non-central arrangement or with several additional probe reflection points 63.

[0086] Appendix labels and symbols

[0087] 1. Filling material

[0088] 2 containers

[0089] 3 electronic units

[0090] 4 Transmitter / Receiver Units

[0091] 5 probes

[0092] 51, 52 First and second probe segments

[0093] 53 Local Shape Modification Section

[0094] 61. Reflection points outside the container

[0095] 62 EOP reflection points

[0096] 63 Additional reflection points of the probe

[0097] 64 Coupled into reflection point

[0098] 65 Zero-point reflection point

[0099] 7 Cables

[0100] 71, 72 First and second coaxial cable segments

[0101] 73 Transition Point

[0102] 8 boxes

[0103] 91, 92 First and second insulation layers

[0104] 9 insulation layers

[0105] 11a, 11b First and second inner conductors

[0106] 11 Inner Conductor

[0107] 12a, 12b First and second outer conductors

[0108] 12. Outer conductor

[0109] 13 Short-circuit circuit

[0110] 14 Short line

[0111] 15 Switches

[0112] 16 Connection Points

[0113] 17. Accumulations

[0114] L Fill level

[0115] EOP probe tip

[0116] FE filler material echo signal

[0117] RE Reflection Point Echo Signal

Claims

1. A filling liquid level measuring device, the filling liquid level measuring device being used to determine the filling liquid level (L) of filling material (1) in a container (2) based on microwaves, the filling liquid level measuring device having: - Electronic unit (3), the electronic unit is designed to generate the transmitted signal and process the echo signal; - A transmitter / receiver unit (4), connected to the electronic unit (3), and designed to transmit the transmitted signal and receive the echo signal in the direction of the filling material (1) in the container (2); and - A conductive probe (5), which is connected to the transmitter / receiver unit (4), extends into the filling material (1) and is used to relay the transmitted signal and the echo signal. in, In measurement mode, the transmitter / receiver unit (4) transmits a transmission signal along the conductive probe (5) in the direction of the filling material (1). The transmission signal is reflected at the surface of the filler material (1) to generate a filler material echo signal (FE). The filler material echo signal returns along the conductive probe (5) to the transmitter / receiver unit (4) and is transmitted to the electronic unit (3), so that the electronic unit (3) can determine the filling liquid level (L) of the filler material (1) based on the filler material echo signal (FE). Its features The filling level measuring device has at least one reflection point (61, ...) arranged outside the container (2), which generates a reflection point echo signal (RE) by reflecting the transmitted signal. Furthermore, the electronic unit (3) performs online calibration and / or verification of the filler material echo signal (FE) based on the at least one reflection point echo signal (RE). The filling level measuring device has a cable (7), wherein the electronic unit (3) is connected to the transmitter / receiver unit (4) via the cable (7), and the cable (7) is used to forward the transmitted signal and the echo signal, and wherein the cable (7) has the at least one reflection point (61). The cable (7) is a coaxial cable, which has a first coaxial cable segment (71) and a second coaxial cable segment (72) adjacent to the first coaxial cable segment. Furthermore, the reflection point (61) of the cable (7) is formed by the transition point (73) between the first coaxial cable segment (71) and the second coaxial cable segment (72). The cable (7) is a coaxial cable, and the reflection point (61) of the cable (7) is formed by a stub circuit (13), wherein the stub circuit (13) is connected to at least one conductor (11, 12) of the coaxial cable through a stub (14) arranged at a fixed position on the cable, i.e. connected to the inner conductor (11) and / or the outer conductor (12) of the coaxial cable.

2. The filling liquid level measuring device according to claim 1, It has at least two reflection points (61, 62, ...).

3. The filling liquid level measuring device according to claim 2, in, At least one reflection point (62, 63, ...) is arranged inside the container (2).

4. The filling liquid level measuring device according to claim 3, in, The conductive probe (5) has a probe end (EOP) reflection point (62) inside the container (2), which is formed by the end of the conductive probe (5) away from the transmitter / receiver unit (4).

5. The filling liquid level measuring device according to claim 1, in, The first insulating layer (91) of the first coaxial cable segment (71) and the second insulating layer (92) of the second coaxial cable segment (72) have different dielectric constants.

6. The filling liquid level measuring device according to claim 1, wherein, The stub circuit (13) includes a switch (15).

7. The filling liquid level measuring device according to any one of claims 1 to 6, in, The connection point (16) between the transmitter / receiver unit (4) and the conductive probe (5) forms a coupling-in reflection point (64), at which the transmitted signal is coupled into the conductive probe (5).

8. The filling liquid level measuring device according to claim 7, in, The conductive probe (5) has at least one additional reflection point (63), which generates an additional reflection point echo signal (RE). Furthermore, the additional reflection point (63) is arranged between the end of the conductive probe (5) facing away from the transmitter / receiver unit (4) and the connection point (16).

9. The filling liquid level measuring device according to claim 8, in, The additional reflection point (63) of the conductive probe (5) is formed by the transition between the first probe segment (51) and the second probe segment (52).

10. The filling liquid level measuring device according to claim 8 or 9, in, The additional reflection point (63) of the conductive probe (5) is formed by a partial modification (53) of the shape of the conductive probe (5).

11. The filling liquid level measuring device according to claim 10, in, The local modification is selected from the group consisting of: protrusions, indentations, grooves, and holes.

12. A method for online calibration and / or verification using a microwave-based filling level measuring device according to any one of claims 1 to 11 when determining the filling level (L) of filling material (1) in a container (2), in, The transmitter / receiver unit (4) transmits a signal along the conductive probe (5) in the direction of the filling material (1) in measurement mode. The filling material echo signal (FE) is generated by the reflection of the transmitted signal at the surface of the filling material (1). The filling material echo signal returns along the conductive probe (5) to the transmitter / receiver unit (4) and is transmitted to the electronic unit (3) so that the filling liquid level (L) of the filling material (1) is determined by the electronic unit (3) based on the filling material echo signal (FE). Its features The method includes the following steps: - Generate at least one reflection point echo signal (RE), said at least one reflection point echo signal being generated by reflection of the transmitted signal at reflection points (61, ...), wherein said at least one reflection point (61, ...) is arranged outside the container (2). - Perform online calibration and / or verification of the filler material echo signal (FE) based on the at least one reflection point echo signal (RE).

13. The method according to claim 12, in, Based on the echo signal (RE) of the reflection point coupled into the reflection point (64), deposits (17) at the connection point (16) and / or corrosion at the connection point (16) are detected.

Images