Method for operating a TDR fill level measuring device and TDR fill level measuring device

Abstract

The invention relates to a method for operating a TDR fill level measuring device, comprising at least one probe for guiding an electromagnetic signal and a measuring transducer, the measuring transducer having an electronic unit for generating a measuring signal and evaluating a reflected measuring signal and a process connection element, the measuring transducer being connected to a container via the process connection element, the process medium to be measured is arranged in the container, the gaseous medium is arranged above the process medium, and the relative dielectric constant [epsilon] r of the gaseous medium is determined by detecting and evaluating the amplitude AS of the measurement signal and the amplitude AR of the measurement signal reflected at the interface of the container and the process connection element, wherein an attenuation [alpha] 0 of the measurement signal through the measurement transducer, an attenuation [alpha] e through the electronic unit and a mechanical attenuation [alpha] m through the process connection element are determined for determining [alpha] 0, and / or an impedance ratio IFR0 = Z0Son / ZMU, where Z0Son is the impedance of the probe in the vacuum and ZMU is the impedance of the measurement transducer, is determined in a reference gas having a known [epsilon] r.

Description

Technical Field

[0001] The invention is based on a method for operating a TDR level measuring device, wherein the TDR level measuring device has at least one probe for guiding an electromagnetic signal and a measuring transducer, wherein the measuring transducer has an electronics unit and a process connection element for generating a measuring signal and for evaluating a reflected measuring signal,

[0002] wherein the measuring transducer is connected to the container via a process connecting element, wherein the process medium to be determined is arranged in the container, and wherein the gaseous medium is arranged above the process medium,

[0003] In this case, the amplitude A of the measurement signal emitted by the electronics unit is detected and evaluated. S and the amplitude A of the measurement signal reflected at the interface between the vessel and the process connection element R To determine the relative dielectric constant ε of the gaseous medium r .

[0004] Furthermore, the invention relates to a TDR level measuring device having at least one probe for guiding an electromagnetic signal and having a measuring transducer.

[0005] The measuring transducer has an electronic unit and a process connection element for generating a measuring signal and for evaluating a reflected measuring signal,

[0006] In this case, the measuring transducer can be connected to the container via the process connecting element. Background Art

[0007] TDR level measuring devices for measuring the fill level of a process medium arranged in a container are known from the prior art.

[0008] Known TDR level measuring devices are based on the measurement of the transit time of a measuring signal which is guided via a probe in the direction of the process medium and reflected at the interface with the process medium. From the transit time, the distance between the process connection, which is usually designed as a flange, and the surface of the process medium and thus the level in the container can be determined.

[0009] In order to improve the accuracy of the transit time measurement and in this respect to optimize the level determination, it is essential to know the propagation speed of the measurement signal moving along the probe. If the gaseous medium arranged above the process medium is different from air, this also affects the propagation speed of the measurement signal moving along the probe through the gaseous medium.

[0010] From the prior art DE 10 2017 108 702 A1 it is known to determine the relative dielectric constant ε of a gaseous medium arranged above a process medium.r . Summary of the invention

[0011] Based on the described prior art, the object of the present invention is to specify a method for operating a TDR level measuring device which improves the transit time determination. Furthermore, the object of the present invention is to specify a corresponding TDR level measuring device for carrying out the method according to the invention.

[0012] According to a first teaching of the invention, the aforementioned object is achieved by the method described at the outset in the following manner:

[0013] In order to determine the relative dielectric constant ε r , taking into account the attenuation α0 of the emitted measurement signal through the measuring transducer, wherein to determine the attenuation α0, the attenuation α through the electronics unit is determined e and mechanical attenuation α through process connection elements m ,

[0014] and / or

[0015] In order to determine the relative dielectric constant ε r , considering the impedance ratio IFR0=Z 0_Sonde / Z MU , where Z 0_Sonde is the impedance of the probe in vacuum, and Z MU is the impedance of the measuring transducer, and where in the r The impedance ratio IFR0 is determined in the reference gas.

[0016] According to an advantageous embodiment of the invention, the determination of the attenuation α0 of the measurement signal in the measuring transducer is divided into the determination of the attenuation α0 by the electronics unit. e and determine the mechanical attenuation α through the process connection element m .

[0017] This action represents a simple way of determining the total attenuation α0 of the measurement signal through the measurement transducer.

[0018] According to a preferred design, the attenuation α is measured e , wherein a reflective element, such as a resistor, a short circuit or an open circuit end is placed at the output of the electronic unit for measuring the attenuation α e , and wherein by comparing the amplitude A of the measurement signal emitted by the electronic unit eS The amplitude A of the measured signal reflected at the reflective element eR To determine α e For the determination of the attenuation of the measurement signal it is important that the reflection coefficient of the reflective element is known.

[0019] According to a particularly preferred design, the signal line of the electronic unit is extended by a cable, for example, a coaxial cable, for determining α e The attenuation α is determined by taking into account the influence of the additional cable on the measurement signal. e .

[0020] In particular, the resistance of the reflective element and / or the impedance of the additional cable and / or the attenuation by the additional cable are also taken into account.

[0021] It is particularly preferred to determine α according to the following formula e :

[0022]

[0023] Among them A eR is the amplitude of the reflected signal, where A eS is the amplitude of the emitted measurement signal, and where α Kabel It is the attenuation caused by the cable.

[0024] This refinement has the advantage overall that the transit time of the reflected pulse can be prolonged, so that the reflected pulse can be distinguished well from the measurement signal emitted by the electronics unit and in particular does not overlap with the measurement signal.

[0025] The attenuation α is preferably measured during the manufacture or assembly of the measuring transducer. e The measured value α e The individual measuring transducers are characterized and preferably stored in the electronics unit. According to a further advantageous embodiment, the electronics unit has a temperature sensor which detects the temperature of the electronics unit. During the determination of the attenuation of the signal through the electronics unit, according to a particularly preferred embodiment, the temperature dependency of the attenuation is also determined.

[0026] According to one design of the method, the mechanical attenuation α m Corresponds to the mean value for the process connection element used.

[0027] Such a mean value can be determined in advance, for example, for a large number of different process connection elements.

[0028] According to one embodiment, the following actions can be taken when determining the mechanical attenuation:

[0029] Assuming that the attenuation by the electronic unit generating the signal is known, the process connection element is short-circuited in the propagation direction of the signal before or after the flange.The flange may be part of the process connection element or may be arranged between the process connection element and the container.

[0030] If the process connection element is short-circuited in front of the flange, the attenuation through the process connection element can be determined by detecting the reflected pulse.

[0031] If the process connection element is short-circuited behind the flange, the reflection at the interface of the process connection element and the flange is also taken into account. In this case, the mechanical attenuation can be determined according to the following formula:

[0032]

[0033] Among them A mR is the amplitude of the signal reflected at the termination element, where A par is the amplitude of the signal reflected at the interface with the flange, and where A mS is the amplitude of the emitted signal, and where α e is the known attenuation across the electronic unit.

[0034] Particularly preferably, a plurality of process connection elements having the same properties are measured and the signal attenuation α is formed. m The mean value is preferably stored in the electronic unit.

[0035] Due to the attenuation α m For different measuring devices, only small fluctuations are experienced, so knowing the attenuation α m In the case of a mean value of α, it is possible to dispense with the separate redetermination of α for each measuring transducer. m .

[0036] Alternatively, to determine the attenuation α m , or you can take action as follows:

[0037] In the known α e and known process conditions, especially known material level and known process temperature, it can be first assumed that for α m The expected value is then changed during the fill level measurement until the actual fill level is measured.

[0038] Particularly preferably, a temperature sensor is provided to detect the temperature of the process connection element. m When the mean of α is taken as the value, then we can also determine the attenuation α m temperature dependence.

[0039] It is also conceivable that in order to determine the mean α m , similarly to the use of extension elements, such as extension cables, for determining the attenuation through the electronics unit. In this way, the emitted pulses and the reflected pulses can be distinguished particularly well in time.

[0040] For example, the process connection element is configured as a coaxial conductor or a waveguide. Depending on the application, the coaxial conductor can have different dielectrics. The process connection element ensures the isolation, in particular the thermal isolation, of the electronic unit from the process environment.

[0041] For connection to the container, the process connection element particularly preferably has a flange.

[0042] Thus, the stored value can be used as the mechanical attenuation α for different measuring transducers. m It is not necessary to measure the mechanical attenuation α separately for each measuring transducer. m The actual deviation from the mean value determined for a process connection element of this type is so small that it can be neglected.

[0043] According to a further advantageous embodiment, in order to determine the relative dielectric constant ε of the gaseous medium r , also consider the impedance ratio IFR0 = Z 0_Sonde / Z MU , where Z 0_Sonde is the impedance of the probe in vacuum, and Z MU is the impedance of the measuring transformer.

[0044] The impedance ratio IFR0 is preferably determined in a reference gas, in particular air. The impedance ratio is also a variable that is measured at least once individually for each measuring transducer.

[0045] If the reference gas is air, the impedance ratio can be determined according to the following relationship:

[0046]

[0047] where ε r,Luft is approximately 1, where α0 is the attenuation through the measuring transducer, and where R is the reflection coefficient resulting from the amplitude A of the measuring signal emitted by the electronic unit S The amplitude A of the measurement signal reflected at the interface between the container and the process connection element R The ratio of

[0048] Measurement amplitude A S and A R Used to determine impedance ratios in air.

[0049] Alternatively, the impedance ratio IFR0 can also be determined in a medium different from air, where the relative permittivity ε of the medium is r is known, and the impedance ratio IFR0 is inferred from the impedance ratio determined in this way by a corresponding correction.

[0050] The impedance ratio IFR0 is preferably stored in the electronic unit and used to determine the relative dielectric constant ε of the gaseous medium. r According to this design, it is not necessary to determine the individual impedance Z anew for each measuring transducer. 0_Sonde and Z MU Only the impedance ratio IFR0 is important.

[0051] According to another preferred embodiment of the method according to the invention, the relative dielectric constant of the gaseous medium arranged above the process medium in the container is determined by the following formula:

[0052]

[0053] Here, preferably α0=α e α m .

[0054] According to another embodiment of the method according to the invention, the value α e and α m or α0 and IFR0 are stored in the electronics unit so that the relative permittivity ε of the gaseous medium above the process medium can be determined or monitored at regular or irregular intervals even during measurement operation. r .

[0055] Relative dielectric constant ε r Particularly preferably, it is determined permanently and taken into account when measuring the fill level.

[0056] If the relative dielectric constant ε r If changes occur during operation of the TDR fill level measuring device, the propagation speed of the measurement signal moving through the gaseous medium can be adapted.

[0057] According to another embodiment of the method, there are other sensors, in particular temperature sensors, which measure process parameters, in particular the temperature, in the container. Particularly preferably, if the value of the process parameter, in particular the temperature, in the container exceeds a predetermined tolerance range, the relative permittivity ε is re-determined. r .

[0058] The method thus has the advantage that the determination of the transit time of the measurement signal can be adapted to changes in process parameters such as temperature or the composition of the gaseous medium, so that the fill level of the process medium to be monitored can be determined particularly precisely.

[0059] According to a further advantageous embodiment, at least one temperature sensor is present, which determines the temperature of the electronics unit and / or the process connection element. For example, there may be one temperature sensor, which determines both the temperature of the electronics unit and the temperature of the process connection element. However, there may also be two temperature sensors, one of which determines the temperature of the electronics unit and one of which determines the temperature of the process connection element.

[0060] If at least one such temperature sensor is present, it is particularly advantageous if the temperature of the electronics unit and / or the process connection element is detected during operation. In the event of a change in the temperature of the electronics unit and / or the process connection element, the α is corrected according to the stored temperature change characteristic. e or α m The value of .

[0061] In this context, the total attenuation α0 also changes in the event of a temperature drift. By adapting the value of the attenuation α0 to the temperature change, the relative dielectric constant ε can be determined particularly accurately. r and thus determine the propagation speed of the measurement signal through the medium.

[0062] According to a second teaching of the invention, the object set out at the outset is achieved by the TDR level measuring device described at the outset in that the electronics unit is designed and configured to carry out one of the previously described methods. With regard to the embodiment of the TDR level measuring device, all previously described embodiments also apply.

[0063] There are now numerous possibilities for designing and improving the method according to the invention and the TDR fill-level measuring device according to the invention. To this end, reference is made to the patent claims that are dependent on the independent patent claims and to the exemplary embodiments described below in conjunction with the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] In the attached figure

[0065] Figure 1 An embodiment of a TDR level measuring device is shown,

[0066] Figure 2 The method for determining the attenuation α is shown e An example of a structure,

[0067] Figure 3 An embodiment of a method for determining the relative dielectric constant of a gaseous medium is shown,

[0068] Figure 4 An exemplary embodiment of a method for determining the fill level of a process medium in a container is shown. DETAILED DESCRIPTION

[0069] Figure 1 An exemplary embodiment of a TDR fill-level measuring device 1 is shown, which has a probe 2 for guiding electromagnetic signals and has a measuring transducer 3 .

[0070] The measuring transducer 3 comprises an electronics unit 4 for generating a measuring signal and for evaluating a reflected measuring signal, and a process connection element 5 , wherein the measuring transducer 3 is connected to a container 7 via the process connection element 5 having a flange 6 .

[0071] In the exemplary embodiment shown, the process connection element 5 is designed as a waveguide. It is also conceivable that the process connection element 5 is designed as a coaxial conductor.

[0072] A process medium 8 is arranged in the container 7, the fill level of which can be determined and / or monitored by the fill level measuring device 1. To determine the fill level, the fill level measuring device 1 emits a measurement signal which moves along the probe 2 in the direction of the process medium 8 and is reflected at the interface with the process medium.

[0073] The distance between flange 6 and process medium surface and thus the level of process medium 8 in container 7 is determined from the transit time of the reflected measurement signal. In this connection, it is relevant to know the exact propagation speed of the measurement signal moving along probe 2 .

[0074] If the gaseous medium 9 above the process medium 8 is different from the air or if the temperature in the container 7 changes, that is, if the relative permittivity ε r If it is greater than 1, the propagation speed of the measurement signal decreases.

[0075] The electronics unit 4 is therefore designed and configured such that it determines the relative dielectric constant ε of the gaseous medium arranged above the process medium in the container 7. r .

[0076] In operation, the electronics unit 4 detects the amplitude A of the measurement signal emitted by the electronics unit 4. S The amplitude A of the measurement signal reflected at the interface between the container and the process connection element R The relative dielectric constant ε is determined by the measured ratio r .

[0077] Furthermore, the electronics unit 4 takes into account the attenuation α0 of the measurement signal in the region of the measuring transducer 3 and the impedance Z 0_Sonde The impedance Z of the measuring transformer MU The impedance ratio IFR0.

[0078] The impedance ratio IFR0 is determined for the TDR level measuring device shown in an empty container 7 , ie in air, and is stored in the electronics unit 4 .

[0079] The attenuation α0 is determined by the attenuation α through the electronic unit 4. e and mechanical attenuation α through the process connection element 5 m composition.

[0080] In order to determine the attenuation α0, the attenuation α by the electronics unit 4 is already measured during the production, ie, assembly, of the measuring transducer 3. e Mechanical attenuation α m The values ​​of are known for the process connection elements 5 used and correspond to average values ​​for process connection elements of the type shown.

[0081] In the exemplary embodiment shown, the value of the attenuation α0 determined in this way is stored in the electronics unit 4 .

[0082] In this connection, the TDR level measuring device 1 shown can determine the current dielectric constant ε permanently or at regular or irregular intervals during operation. r , and the current dielectric constant is taken into account in the level calculation.

[0083] The TDR level measuring device therefore has a particularly high precision.

[0084] Figure 2 The attenuation α for measuring the electronic unit 4 is shown. e The electronic unit 4 is connected to a cable 10 for extending the measuring section. A reflective element 11 with a known reflection coefficient is arranged at the end of the cable 10. Such an extension has the advantage that the reflected pulses can be better distinguished from the emitted measurement signal due to the longer transit time.

[0085] The amplitude A of the emitted measurement signal can be calculated by taking into account the influence of the cable 10. S The measurement of the amplitude A of the measured signal reflected at the end of the cable 10 R The attenuation α is determined by measuring e .

[0086] Figure 3 An exemplary embodiment of a method 12 for operating a TDR fill-level measuring device 1 is shown.

[0087] In a first step 13, the attenuation α by the electronic unit 4 is determined as described above. e And stored in the electronic unit 4.

[0088] In a next step 14, the attenuation α caused by the process connection element 5 is determined. m . Decay α m The value of corresponds to the mean value recorded in a preparation step for a plurality of different process connection elements.

[0089] In step 15, the decay α e and α m The attenuation α0 in the measuring transducer is determined by multiplication from the value of .

[0090] After the measuring transducer 3 has been completely assembled and the fill level measuring device 1 has been arranged at the container 7 , the impedance ratio IFR0 is determined in a next step 16 , wherein the container 7 is empty and the gaseous medium 9 surrounding the probe 2 is a dielectric constant ε 0 . r About 1 air.

[0091] The impedance ratio IFR0 determined in this way is likewise stored in the electronics unit 4 .

[0092] During operation of the TDR level measuring device 1 , the relative permittivity ε of the gaseous medium 9 arranged above the process medium 8 can now be determined based on previously determined and stored values. r .

[0093] To this end, in step 17 the amplitude A of the measurement signal generated by the electronics unit 4 is detected. S and the amplitude A of the measurement signal reflected at the interface with the container 7 R .

[0094] In the next step 18, the stored attenuation α0, the stored impedance ratio IFR0 and the measured amplitude ratio A can be used to obtain the measured amplitude ratio A. R / A S To determine the relative dielectric constant ε of the gaseous medium 9 above the process medium 8 r .

[0095] The determined dielectric constant ε is taken into account when determining the transit time and, for that matter, when determining the fill level. r .

[0096] The method 12 shown in this regard has the advantage that changes in process conditions that influence the propagation speed of the measurement signal in the container 7 are taken into account, so that overall the accuracy of the fill level determination can be improved.

[0097] Figure 4 The relative dielectric constant ε is shown for r An embodiment of a method 12 for determining a filling level under the circumstances of determination.

[0098] In a first step 17, the amplitude ratio A of the measurement signal reflected at the transition to the container 7 to the measurement signal generated by the electronics unit 4 is determined. R / A S .

[0099] In a next step 18, the relative dielectric constant ε of the gaseous medium above the process medium is determined from the amplitude ratio and the stored value for the attenuation α0 in the measuring transducer and the impedance ratio IFR0. r The value of .

[0100] Subsequently, in step 19 , the transit time of the measurement signal reflected at the surface of the process medium is determined taking into account the determined relative permittivity of the gaseous medium.

[0101] In a next step 20 , the fill level of the process medium 8 is determined from the measured transit time.

[0102] Due to the consideration of the current relative permittivity ε of the gaseous medium above the process medium r , the method shown has a particularly high accuracy.

[0103] Reference numerals

[0104] 1Level measurement equipment

[0105] 2 Probe

[0106] 3 Measurement Transducer

[0107] 4 Electronic units

[0108] 5Process connection elements

[0109] 6 Flange

[0110] 7 Container

[0111] 8 Process media

[0112] 9 Gaseous medium

[0113] 10 Cables

[0114] 11Reflective element

[0115] 12 Methods for operating a TDR level measurement device

[0116] 13 Determine the attenuation α through the electronic unit e

[0117] 14 Determine the attenuation α caused by the process connection elements m

[0118] 15 Determine the attenuation α0

[0119] 16 Determine the impedance ratio

[0120] 17 Detection amplitude A S and A R

[0121] 18 Determine the relative dielectric constant ε of the gaseous medium r

[0122] 19 Considering the relative dielectric constant ε r Determine the transit time of the measurement signal in the case of

[0123] 20 Determine the level of the process medium.

Claims

1. A method (12) for operating a TDR level measuring device (1), The TDR level measuring device (1) comprises at least one probe (2) for guiding electromagnetic signals and a measuring transducer (3). The measuring transducer (3) has an electronics unit (4) for generating a measuring signal and for evaluating a reflected measuring signal, as well as a process connection element (5), wherein the measuring transducer (3) is connected to the container (7) via the process connection element (5), wherein a process medium (8) to be determined is arranged in the container (7), and wherein a gaseous medium (9) is arranged above the process medium (8), In this case, by means of detecting (17) and evaluating the amplitude A of the measurement signal emitted by the electronic unit (4), S and the amplitude A of the measurement signal reflected at the interface between the container (7) and the process connection element (5) R Determine the relative dielectric constant ε of the gaseous medium (9) r , characterized in that, In order to determine the relative dielectric constant ε r , taking into account the attenuation α0 of the emitted measurement signal through the measuring transducer (3), wherein in order to determine the attenuation α0, the attenuation α e and the mechanical attenuation α through the process connection element (5) m , and / or In order to determine the relative dielectric constant ε r , considering the impedance ratio IFR0=Z 0_Sonde / Z MU , where Z 0_Sonde is the impedance of the probe (2) in vacuum, and Z MU is the impedance of the measuring transducer (3), and wherein in the case of a dielectric constant ε r The impedance ratio IFR0 is determined in the reference gas.

2. The method (12) according to claim 1, characterized in that: Measuring the attenuation α of the measuring transducer (3) e , wherein a reflector (11) is placed at the output end of the electronic unit (4) for measuring the attenuation α e , and wherein by comparing the amplitude A of the measurement signal emitted by the electronic unit (4) eS and the amplitude A of the measurement signal reflected at the reflector (11) eR To determine α e .

3. The method (12) according to claim 1 or 2, characterized in that: The signal line of the electronic unit is extended by a cable (10), for example a coaxial cable, for determining α e , transmitting the generated measurement signal via the signal line, and determining the attenuation α taking into account the attenuation of the measurement signal via the additional cable (10) e .

4. The method (12) according to any one of claims 1 to 3, characterized in that During assembly of the measuring transducer (3) α is determined e .

5. The method (12) according to any one of claims 1 to 4, characterized in that The attenuation α m Corresponds to the mean value for the process connection element used.

6. The method (12) according to any one of claims 1 to 5, characterized in that The impedance ratio IFR0 is determined in air.

7. The method (12) according to any one of claims 1 to 5, characterized in that The impedance ratio IFR0 is determined in a medium different from air, wherein the relative permittivity ε r is known, and the impedance ratio IFR0 is inferred from the impedance ratio determined in this way by a corresponding correction.

8. The method (12) according to any one of claims 1 to 7, characterized in that The relative dielectric constant ε of the gaseous medium (9) is determined according to the following formula: r :

9. The method (12) according to claim 8, wherein in the relative dielectric constant ε r In the determination of, the attenuation is α0 = α e α m .

10. The method (12) according to claim 1, wherein the determined relative permittivity ε is taken into account when evaluating the transit time of the measurement signal reflected at the surface of the process medium (8). r .

11. The method (12) according to any one of claims 1 to 10, characterized in that By measuring the amplitude ratio A R / A S Re-determine the relative permittivity ε at regular or irregular intervals r .

12. The method (12) according to any one of claims 1 to 11, characterized in that In determining the relative dielectric constant ε r When adjusting the temperature of the electronics unit and / or the process connection element, the temperature of the electronics unit and / or the process connection element is also taken into account and the value of the attenuation α0 is adapted when the temperature of the electronics unit and / or the process connection element changes.

13. A TDR level measuring device (1) comprising at least one probe (2) for guiding an electromagnetic signal and a measuring transducer (3), The measuring transducer (3) has an electronics unit (4) for generating a measuring signal and for evaluating a reflected measuring signal, as well as a process connection element (5), The measuring transducer (3) can be connected to a container (7) via the process connection element (5), characterized in that: The electronics unit (4) is designed and configured to carry out a method (12) according to any one of claims 1 to 12.

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