Patent Application
20250155395
This nonprovisional application claims priority under 35 U.S.C. § 119(a) to German Patent Application No. 10 2023 131 085.2, which was filed in Germany on Nov. 9, 2023, and which is herein incorporated by reference.
The invention is based on a method for operating a TDR level measuring device, wherein the TDR level measuring device comprises at least one probe for guiding an electromagnetic signal and a measuring transducer, wherein the measuring transducer comprises an electronic unit for generating a measuring signal and for evaluating a reflected measuring signal, and a process connection element, wherein the measuring transducer is connected to a container via the process connection element, wherein process medium to be measured is arranged in the container, and wherein a gaseous medium is arranged above the process medium, wherein the relative permittivity εr of the gaseous medium is determined by means of capturing and evaluating the amplitude AS of a measuring signal emitted by the electronic unit and the amplitude AR of a measuring signal reflected at the interface of the process connection element and the container.
Furthermore, the invention relates to a TDR level measuring device with at least one probe for guiding an electromagnetic signal and with a measuring transducer, wherein the measuring transducer comprises an electronic unit for generating a measuring signal and for evaluating a reflected measuring signal, and a process connection element, wherein the measuring transducer can be connected to a container via the process connection element.
TDR level measuring devices for measuring the fill level of a process medium arranged in a vessel are known from the prior art.
Known TDR level measuring devices are based on the transit time measurement of a measuring signal, which is guided via the probe in the direction of the process medium and reflected at the interface to the process medium. From the transit time, the distance between the process connection, which is usually designed as a flange, and the process medium surface, and thus the fill level in the container, can be determined.
To improve the accuracy of the transit time measurement and in this respect to optimize level determination, the knowledge of the propagation speed of the measuring signal moving along the probe is of crucial im-portance. If the gaseous medium arranged above the process medium is different from air, this also influences the propagation speed of the measuring signal moving along the probe through the gaseous medium.
It is known from the prior art DE 10 2017 108 702 A1, which corresponds to US 2018/0306632, which is incorporated herein by reference, to determine the relative permittivity εr of a gaseous medium arranged above the process medium.
It is therefore an object of the invention to provide a method for operating a TDR level measuring device that improves transit time determination. In addition, it is an object of the invention to disclose a corresponding TDR level measuring device for performing the method according to the invention.
According to an example of the present invention, the aforementioned object is achieved by a method described, in that for determining the relative permittivity εr, the attenuation α0 of the emitted measuring signal by the measuring transducer is taken into account, wherein for determining the attenuation α0, the attenuation de by the electronic unit and the mechanical attenuation am by the process connection element are determined, and/or that the impedance ratio IFR0=Z0_probe/ZMU is taken into account for determining the relative permittivity εr, wherein Z0_probe is the impedance of the probe in vacuum and ZMU is the impedance of the measuring transducer, and wherein the impedance ratio IFR0 is determined in a reference gas with known permittivity εr.
The determination of the attenuation α0 of the measuring signal in the measuring transducer is divided into the determination of the attenuation αe by the electronic unit and the mechanical attenuation αm by the process connection element.
This procedure represents a simple way of determining the total attenuation α0 of the measuring signal by the measuring transducer.
The attenuation αe is measured, wherein a reflector element, for example a resistor, a short circuit or an open end, can be placed at the output of the electronic unit to measure the attenuation αe, and wherein αe is determined by comparing the amplitude of a measuring signal AeS emitted by the electronic unit and a measuring signal AeR reflected at the reflector element. It is important for determining the attenuation of the measuring signal that the reflection coefficient of the reflector element is known.
The signal line of the electronic unit via which the generated measuring signal is transmitted can be elongated with a cable, for example with a coaxial cable, for determining αe. The attenuation αe is determined taking into account the influence of the additional cable on the measuring signal.
In particular, the resistance of the reflector element and/or the impedance of the additional cable and/or the attenuation due to the additional cable is also taken into account.
Particularly preferably, αe is determined according to the following formula:
wherein AeR is the amplitude of the reflected signal, wherein AeS is the amplitude of the emitted measuring signal, and wherein αcable is the attenuation caused by the cable.
This design has the advantage that the transit time of the reflected pulse can be extended, so that the reflected pulse can be well distinguished from the measuring signal emitted by the electronic unit and, in particular, does not overlap with it.
The attenuation de can be measured during the manufacture or assembly of the measuring transducer. The measured value de is characteristic for the individual measuring transducer and is preferably stored in the electronics unit. According to a next advantageous design, the electronic unit comprises a temperature sensor that captures the temperature of the electronic unit. During the determination of the attenuation of the signal by the electronic unit, the temperature dependence of the attenuation can also be determined.
The mechanical attenuation αm corresponds to an average value for the process connection element used.
Such an average value can, for example, be determined in advance for a large number of different process connection elements.
The mechanical attenuation can be determined as follows:
Assuming that the attenuation by the electronic unit generating the signal is known, the process connection element can be short-circuited either in front of or behind the flange in the direction of propagation of the signal. The flange can be a part of the process connection element or can be arranged between the process connection element and the container.
If the process connection element is short-circuited in front of the flange, the attenuation by the process connection element can be determined by capturing a reflected pulse.
If the process connection element is short-circuited behind the flange, the reflection at the interface of the process connection element to the flange is also taken into account. In this case, the mechanical attenuation can be determined according to the following formula:
wherein AmR is the amplitude of the signal reflected at the termination element, wherein Apar is the amplitude of the signal reflected at the interface to the flange, and wherein AmS is the amplitude of the transmitted signal, and wherein αe is the known attenuation due to the electronic unit.
A plurality of process interface elements with the same characteristics can be measured and the average value for the signal attenuation αm is formed. This average value can be stored in the electronics unit.
Since the attenuation αm for different measuring transducers is subject to only minor fluctuations, it is not necessary to determine αm individually for each measuring transducer if the mean value of the attenuation αm is known.
Further, the following procedure can also be used to determine the attenuation αm:
With known αe, known process conditions, in particular known fill level and known process temperature, an expected value for αm can first be assumed, wherein this expected value is varied during the measurement of the fill level until the actual fill level is measured.
A temperature sensor can be provided which captures the temperature of the process connection element. When determining the mean value for αm, the temperature dependence for the attenuation αm can then also be determined.
It is also conceivable to use an extension element, for example an extension cable, to determine the mean value αm in the same way as the electronic unit determines the attenuation. In this way, the emitted pulse and the reflected pulse can be distinguished particularly well in terms of time.
For example, the process connection element can be designed as a coaxial conductor or a waveguide. Depending on the application, the coaxial conductor can have different dielectrics. The process connection element ensures, in particular thermal, insulation of the electronics unit from the process environment.
For the connection to the container, the process connection element can have a flange.
Thus, a stored value can be used as mechanical attenuation αm for different measuring transducers. It is not necessary to measure the value of the mechanical attenuation αm separately for individual measuring transducers. The actual deviations from an average value determined for the type of process connection element are so small that they can be neglected.
According to a next advantageous design, the impedance ratio IFR0=Z0_probe/ZMU is also taken into account for determining the relative permittivity εr of the gaseous medium, wherein Z0_probe is the impedance of the probe in a vacuum and ZMU is the impedance of the measuring transducer.
The impedance ratio IFR0 can be determined in a reference gas, especially in air. The impedance ratio is also a quantity that is measured individually for each measuring transducer at least once.
If the reference gas is air, the impedance ratio can be determined according to the following relationship:
where εr,air is approximately 1, where α0 is the attenuation by the measuring transducer, and where R is the reflection coefficient, which is the ratio of the amplitudes of a measuring signal AS emitted by the electronic unit and the amplitude AR of a measuring signal reflected at the interface of the process connection element and the container, i.e.
The amplitudes AS and AR can be measured to determine the impedance ratio in air.
Alternatively, the impedance ratio IFR0 can be determined in a medium other than air, wherein the relative permittivity εr of the medium is known, and wherein the impedance ratio IFR0 is inferred from the impedance ratio thus determined by appropriate correction.
The impedance ratio IFR0 can be stored in the electronic unit and used to determine the relative permittivity εr of the gaseous medium. According to this design, it is not necessary to determine the values of the individual impedances Z0_probe and ZMU. Only the impedance ratio IFR0 is relevant.
According to another preferred design of the method according to the invention, the relative permittivity of the gaseous medium arranged above the process medium in the container is determined by the following formula:
Here, preferably α0=αe·αm.
The values αe and αm or α0 and IFR0 can be stored in the electronic unit, so that the relative permittivity εr of the gaseous medium above the process medium can be determined or monitored at regular or irregular intervals, even during measurement operation.
The relative permittivity εr can be determined permanently and taken into account in the level measurement.
If the relative permittivity εr changes during operation of the TDR level measuring device, the propagation speed of the measuring signal moving through the gaseous medium can be adjusted.
Also, another sensor, for example, a temperature sensor, can be provided to measure a process parameter, for example, the temperature, in the container. The relative permittivity εr can be redetermined when the value of the process parameter, for example the temperature, in the container exceeds a predetermined tolerance range.
The method thus has the advantage that the determination of the transit time of the measuring signal can be adapted to changes in process parameters, such as the temperature or even the composition of the gaseous medium, so that the determination of the fill level of the process medium to be monitored is particularly accurate.
At least one temperature sensor can be provided that determines the temperature of the electronic unit and/or the process connection element. For example, one temperature sensor can be provided that determines both the temperature of the electronics unit and the temperature of the process connection element. However, two temperature sensors may also be provided, wherein one temperature sensor determines the temperature of the electronics unit and one temperature sensor determines the temperature of the process connection element.
If at least one such temperature sensor is provided, it is particularly advantageous if the temperature is captured by the electronics unit and/or the process connection element during operation. If the temperature of the electronic unit and/or the process connection element changes, the values for αe or αm are corrected according to the stored temperature behavior.
In this respect, the total attenuation α0 also changes in the case of a temperature drift. By adapting the value of the attenuation α0 to a temperature change, the value of the relative permittivity εr and thus the propagation speed of the measuring signal through the medium can be determined particularly accurately.
According to a second teaching of the present invention, the object set out at the beginning is achieved by a TDR level measuring device described at the beginning in that the electronics unit is designed and set up to perform one of the methods described above. In view of the design of the TDR level measuring device, reference is made to all designs described above.
There are now a large number of possibilities for designing and further developing the method according to the invention and the TDR level measuring device according to the invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes, combinations, and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:
The measuring transducer 3 comprises an electronic 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 with a flange 6.
In the example shown, the process connection element 5 is designed as a waveguide. It is also possible that the process connection element 5 is designed as coaxial conductor.
A process medium 8 is arranged in the container 7, the fill level of which can be determined and/or monitored by the level measuring device 1. To determine the fill level, the level measuring device 1 emits a measuring signal that moves along the probe 2 in the direction of the process medium 8 and is reflected at the interface with the process medium.
From the transit time of the reflected measuring signal, the distance between the flange 6 and the process medium surface and, from this, the fill level of the process medium 8 in the container 7 is determined. In this respect, it is relevant to know the exact propagation speed at which the measuring signal moves along the probe 2.
If the gaseous medium 9 above the process medium 8 is different from air or if the temperature in the container 7 changes, i.e. if the relative permittivity εr is greater than 1, the propagation speed of the measuring signal is reduced.
The electronics unit 4 is therefore designed and arranged to determine the relative permittivity εr of the gaseous medium arranged in the vessel 7 above the process medium.
During operation, the electronics unit 4 determines the relative permittivity εr from the measured ratio of the amplitude AS of a measuring signal emitted by the electronics unit 4 and the amplitude AR of a measuring signal reflected at the interface of the process connection element and the container 7.
Furthermore, the electronics unit 4 takes into account the attenuation α0 of the measuring signal in the area of the measuring transducer 3 and the impedance ratio IFR0 of the impedance of the probe Z0_probe and the impedance of the measuring transducer ZMU.
The impedance ratio IFR0 has been determined for the TDR level measuring device shown in an empty container 7, i.e. in air, and stored in the electronics unit 4.
The attenuation α0 is composed of the attenuation αe by the electronics unit 4 and the mechanical attenuation αm by the process connection element 5.
To determine the attenuation α0, the attenuation αe by the electronic unit 4 was measured during the manufacture, i.e. the assembly, of the measuring transducer 3. The value of the mechanical attenuation αm is well known for the process connection element 5 used and corresponds to an average value for the type of process connection element shown.
The value of the attenuation α0 determined in this way is stored in the electronics unit 4 in the example shown.
In this respect, the illustrated TDR level measuring device 1 can determine the current permittivity εr permanently or at regular or irregular intervals during operation and take it into account in the level calculation.
As a result, the TDR level measuring device thus exhibits particularly high accuracy.
From the measurement of the amplitude AS of the emitted measuring signal and the measurement of the amplitude AR of the measuring signal reflected at the end of the cable 10, the attenuation de can be determined, taking into account the influence of the cable 10.
In a first step 13, the attenuation de is determined by the electronic unit 4 as described above and stored in the electronic unit 4.
In a next step 14, the attenuation αm caused by the process connection element 5 is determined. The value of the attenuation αm corresponds to an average value recorded in preparatory steps for a plurality of different process connection elements.
The attenuation α0 in the measuring transducer is determined from the attenuation αe and αm values by multiplication in step 15.
After the transducer 3 is fully assembled and the level measuring device 1 is placed on a container 7, the impedance ratio IFR0 is determined in step 16, wherein the container 7 is empty and thus the gaseous medium 9 surrounding the probe 2 is air with a permittivity εr approximately 1.
The impedance ratio IFR0 determined in this manner is likewise stored in the electronics unit 4.
During operation of the TDR level measuring device 1, the relative permittivity εr of the gaseous medium 9 arranged above the process medium 8 can now be determined based on the previously determined and stored values.
For this, the amplitude AS of a measuring signal generated by the electronic unit 4 and the amplitude AR of a measuring signal reflected at the interface to the container 7 are captured in step 17.
From the stored attenuation α0, the stored impedance ratio IFR0 and the measured amplitude ratio AR/AS, the relative permittivity εr of the gaseous medium 9 above the process medium 8 can be determined in a next step 18.
The determined permittivity εr is taken into account in the transit time determination and to that extent in the level determination.
The method 12 shown has the advantage that changes in process conditions which affect the speed of propagation of the measuring signal in the container 7 are taken into account, so that the overall accuracy of the level determination can be improved.
In a first step 17, the amplitude ratio AR/AS of a measuring signal reflected at the transition to the container 7 and a measuring signal generated by the electronic unit 4 is determined.
From the amplitude ratio and the stored values for the attenuation α0 in the measuring transducer and the impedance ratio IFR0, the value of the relative permittivity εr of the gaseous medium above the process medium is determined in step 18.
Subsequently, the transit time of the measuring signal reflected at the surface of the process medium is determined in step 19 taking into account the determined relative permittivity of the gaseous medium.
From the measured transit time, the fill level of the process medium 8 is determined in a next step 20.
Due to the consideration of the current relative permittivity εr of the gaseous medium above the process medium, the method shown has a particularly high accuracy.
The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2023 131 085.2 | Nov 2023 | DE | national |
