ELECTRONIC UNIT FOR A LEVEL SENSOR

Description

Reference to related applications

[0001] This application claims priority from German patent application No. 10 2020 200 879.5, filed on January 24, 2020, as well as priority from German patent application No. 10 2020 200 866.3, filed on January 24, 2020. Field of the invention

[0002] The present invention relates to an electronic unit for a level measuring probe, a level measuring probe with such an electronic unit and the use of an electronic unit in a level measuring probe. background

[0003] A fill level or limit level can be monitored, for example, using a conductive measuring method. For this purpose, conductivity measurements are taken in the filling medium. The fill level or limit level can also be monitored using a capacitive measuring method. In this case, the fill level is determined from the capacitance formed by a measuring electrode and, for example, the container wall or a reference electrode.

[0004] The areas of application for these two measurement methods can vary. For example, for the conductive measurement method, it is crucial that the filling medium has a certain minimum conductivity. However, very high conductivity can lead to problems with capacitive level measurement, for example, if the electrodes of the level measuring probe are bare. Deposits on the probe can also have different effects.

[0005] It has now become apparent that there is a further need to provide an improved electronics unit for a level measuring probe.

[0006] It is therefore an object of the present invention to provide an improved electronics unit for a level measuring probe. These and other objects, which will become apparent upon reading the following description or may be recognized by a person skilled in the art, are achieved by the subject matter of the independent claims. The dependent claims develop the central idea of ​​the present invention in a particularly advantageous manner.

[0007] DE 10 2014 107927 A1, EP 3 165 883 A1 show measuring probes from the state of the art. Summary of the invention

[0008] The present invention provides an electronic unit for a level measuring probe for measuring a level of a medium, comprising: at least one first excitation electronic unit configured to emit a first excitation signal; at least one second excitation electronic unit configured to emit a second excitation signal; wherein the first excitation signal and the second excitation signal are different; and wherein the electronic unit is configured to emit the first excitation signal and the second excitation signal simultaneously to a level measuring probe.

[0009] In other words, the present invention proposes providing an electronic unit with which two measurement methods can be performed simultaneously. The excitation signals can be transmitted to a level measuring probe as individual excitation signals or as a combined excitation signal.

[0010] Preferably, the at least first excitation electronics unit is configured to output the first excitation signal for a conductive level measurement, and the at least second excitation electronics unit is preferably configured to output the second excitation signal for a capacitive level measurement. In this context, it should be noted that the present invention is not limited to a combination of a conductive and a capacitive measurement, although such a combination is particularly preferred. Rather, identical or different measurement principles can be used in the present invention.

[0011] Advantageously, the first excitation signal and the second excitation signal have different frequencies. Furthermore, it is preferred that the first excitation electronics unit is configured to output a square-wave signal and / or a sine signal as the first excitation signal, preferably for a conductive fill level measurement, wherein the square-wave signal and / or the sine signal is / are preferably output at a frequency of 5 kHz. Furthermore, it is preferred that the second excitation electronics unit is configured to output a triangular signal and / or a sine signal and / or a square-wave signal as the second excitation signal, preferably for a capacitive fill level measurement, wherein the triangular signal and / or the sine signal and / or the square-wave signal is / are preferably output at a frequency of 355 kHz.

[0012] Preferably, the first excitation electronics unit and / or the second excitation electronics unit comprises at least one Direct Digital Synthesis (DDS) unit to provide the first excitation signal and / or the second excitation signal.

[0013] Advantageously, the first excitation electronics unit and the second excitation electronics unit are configured to output the first excitation signal and the second excitation signal such that the first excitation signal and the second excitation signal have the same arithmetic mean. This allows offset differences, for example, to be avoided within the excitation electronics, so that they advantageously do not need to be taken into account by the evaluation electronics.

[0014] Preferably, the electronics unit further comprises at least one first evaluation electronics unit for evaluating a conductive fill level measurement and / or at least one second evaluation electronics unit for evaluating a capacitive fill level measurement, wherein a combined output signal of the fill level measuring probe is present as the input signal of the first evaluation electronics unit and / or the second evaluation electronics unit.

[0015] In this context, it is preferred that the first evaluation electronics unit is assigned a first filter unit that is configured to filter a first output signal for a conductive level measurement from the combined output signal; and / or wherein the second evaluation electronics unit is assigned a second filter unit that is configured to filter a second output signal for a capacitive level measurement from the combined output signal. In this context, it is further preferred that the first filter unit is provided as a digital filter unit that comprises at least one bandpass filter unit whose center frequency corresponds to the first excitation signal; and / or wherein the second filter unit is provided as a digital filter unit that comprises at least one bandpass filter unit whose center frequency corresponds to the second excitation signal.With such an evaluation, no switching arrangement is necessary in the receiving branch that switches back and forth between a conductive and a capacitive signal. However, the evaluation is not limited to such a configuration; it can, for example, be carried out via a processor unit and / or an analog evaluation electronics unit. Furthermore, alternatively or additionally, units for performing a continuous Fourier transformation for an analog combined output signal of a level measuring probe and / or for performing a discrete Fourier transformation for a digital combined output signal can be provided. Advantageously, the electronics unit comprises at least one first digital-to-analog converter unit, which is configured to convert at least one digital excitation signal from the electronics unit into an analog excitation signal that can be output to the level measuring probe as an analog excitation signal.Depending on the design of a level measuring probe, two independent excitation signals or a single combined excitation signal can be transmitted to the level measuring probe. In this context, it should be noted that the present invention is not limited to a specific analog-digital design. Rather, the entire signaling can be implemented in analog or digital form. Analog-digital combinations can also be used using appropriate analog-digital converter units. Such converter units can typically convert signals from analog to digital and vice versa, so that the terms "analog-to-digital converter unit" and "digital-to-analog converter unit" are used below, without excluding a specific conversion direction.

[0016] Preferably, the electronics unit comprises at least one second analog-digital converter unit which is configured to convert at least one combined analog output signal of the level measuring probe into a digital combined output signal which can be output as a digital combined output signal to the two evaluation electronics units.

[0017] The electronics unit preferably comprises a weighting unit configured to weight the measurement results of a conductive level measurement and a capacitive level measurement depending on a media-specific property of the medium whose level is being detected, wherein the media-specific property is preferably the electrical conductivity and / or the dielectric constant of the medium whose level is being detected. This makes it possible to adapt the measurement results of the electronics unit to such an extent that a measurement method better suited to a specific medium and / or specific ambient conditions has a greater influence on the measurement result. In this context, it is particularly preferred that the one or more media-specific properties are determined from a test and / or a calibration signal.For example, it is possible to emit and evaluate such a test and / or calibration signal at regular intervals so that the electronics unit can automatically adapt to potentially changing ambient conditions and / or different media. Such a test signal can also be provided by a regular measurement. It is also possible to deactivate one of the two excitation signals and, if necessary, also deactivate the corresponding components of the electronics unit required for such a measuring method if an evaluation of the test and / or calibration signal shows that one of the two measuring methods is not producing meaningful measurement results, for example because the conductivity of the filling medium is too low or too high, so that either the conductive or the capacitive measurement cannot produce meaningful results.In this case, it can also be provided that a deactivated measuring method is reactivated (on a trial basis) under certain circumstances or after a certain period of time, in order to subsequently determine whether conditions have changed and this measuring method can be used effectively again. This can save energy and time, as both measuring methods do not have to be evaluated if one of the two measuring methods cannot provide meaningful measurement results. In this context, it is also possible for an operator to manually deactivate one of the two measuring methods, so that in this case the electronics unit only measures according to one measuring method.

[0018] Furthermore, the present invention relates to a level measuring sensor or a level measuring device for measuring a fill level, comprising at least one electronic unit as described above. The term "level measuring sensor" is to be understood broadly in this context and encompasses all devices with which a fill level and / or a limit level of a medium in a container, a pipe, a basin, or the like can be detected.

[0019] Finally, the present invention relates to the use of an electronic unit described above in a level measuring sensor or level measuring device for measuring a level. Description of a preferred embodiment

[0020] Below is a detailed description of the figures, showing Figure 1 a schematic view of a preferred embodiment of an electronic unit according to the invention for a level measuring sensor; and Figure 2a schematic view of another preferred embodiment of an electronic unit according to the invention.

[0021] Figure 1 shows a schematic view of a preferred embodiment of an electronic unit 10 according to the invention for a level measuring sensor or a level measuring device.

[0022] The electronics unit 10 comprises a first excitation electronics unit 11 for generating a first excitation signal for a conductive fill level measurement. In the preferred embodiment, the first excitation signal is a digital square-wave signal or a digital sine signal with a frequency of 5 kHz. Furthermore, the electronics unit comprises a second excitation electronics unit 12 for generating a second excitation signal for a capacitive fill level measurement. In the preferred embodiment, the second excitation signal is a digital triangular, sine, or square-wave signal with a frequency of 355 kHz. The excitation signals can, for example, be emitted by the electronic units in such a way that the first excitation signal and the second excitation signal have the same arithmetic mean value, wherein such averaging can also be achieved by corresponding capacitors, for example those in Figure 1 capacitors 13, 14 shown or those in Figure 2shown capacitors 20, 21. This is particularly preferred if both excitation signals are output as a combined excitation signal, since this can avoid large offset differences.

[0023] The excitation electronics units 11, 12 can, for example, comprise a direct digital synthesis (DDS) unit to provide the digital excitation signals. However, the present invention is not limited to digital signal generation. Although the excitation electronics units 11, 12 are designed as separate units in the illustrated embodiment, they can also be combined into an integral unit. As shown in Figure 1 As shown, galvanic isolation in the form of capacitors 13, 14 can also be provided in the signal path.

[0024] The excitation signals can then be transmitted simultaneously to a level measuring probe 15, whereby the excitation signals can be transmitted to the level measuring probe 15 as a combined excitation signal or as separate excitation signals. The excitation signals can also be transmitted to the level measuring probe 15 in digital or analog form.

[0025] Finally, in the preferred embodiment shown, the electronics unit 10 also comprises a first evaluation electronics unit 16 for evaluating a conductive level measurement and a second evaluation electronics unit 17 for evaluating a capacitive level measurement, wherein a combined output signal of the level measuring probe 15 is present as the input signal of the first evaluation electronics unit 16 and the second evaluation electronics unit 18. The signals of the level measuring probe 15 are generally output in analog form by the level measuring probe 15. However, it is also possible to assign an analog-to-digital converter unit to the level measuring probe 15, so that the combined output signal can also be provided digitally. As shown in Figure 1As shown, the first evaluation electronics unit 16 is assigned a first filter unit 18, which is configured to filter a first output signal for a conductive level measurement from the combined output signal. The second evaluation electronics unit 17 is assigned a second filter unit 19, which is configured to filter a second output signal for a capacitive level measurement from the combined output signal.

[0026] The first filter unit 18 can, for example, be provided as a digital filter unit comprising at least one bandpass filter unit whose center frequency corresponds to the first excitation signal. The second filter unit 19 can also be provided as a digital filter unit comprising at least one bandpass filter unit whose center frequency corresponds to the second excitation signal. However, the evaluation of the output signals of the level measuring sensor 15 is not limited to such a configuration; it can also be carried out, for example, via a processor unit and / or via an analog evaluation electronics unit. Furthermore, alternatively or additionally, units for performing a continuous Fourier transformation for an analog combined output signal of a level measuring probe or for performing a discrete Fourier transformation for a digital combined output signal can also be provided.The signals of the evaluation electronics units 16, 18 can then be forwarded to an output unit 22 and / or a further processor unit, which derives, for example, a specific fill level of a container from the signals of the evaluation electronics units 16, 18.

[0027] Furthermore, it should be noted that more than two excitation signals and more than two evaluation electronics units with different filter units can also be provided. The present invention is therefore not limited to the two excitation signals and the two evaluation electronics units cited as examples.

[0028] Figure 2shows a second preferred embodiment of an electronic unit 30 according to the invention. In this embodiment, the electronic unit 30 is additionally assigned a first digital-to-analog converter 33, with which the two excitation signals 32 shown here, which are generated in an excitation and evaluation electronic unit 31, can be converted into a combined analog excitation signal and transmitted to a level measuring probe 34. The excitation and evaluation electronic unit 31 can, for example, comprise a microcontroller with corresponding peripherals and software. The excitation and evaluation electronic unit 31 can, for example, be as shown in Figure 1shown. Furthermore, the electronics unit 30 can be assigned, for example, a further electronics unit 35 for performing a Fourier transformation, which transforms the analog combined output signal of the level measuring probe 34 before it is subsequently fed, for example, to a second analog-to-digital converter 36 and then fed to the excitation and evaluation electronics unit 31 for further evaluation.

[0029] In this context, it should be noted that the present invention is not limited to a specific analog-digital configuration. Rather, the entire signaling can be implemented in analog or digital form. Analog-digital combinations can also be used using appropriate analog-digital converter units. It is also possible to use Figure 2shown predominantly digital design, either only the filtering of the output signal of the level measuring probe or only the formation of the excitation signal can be carried out digitally.

[0030] However, the present invention is not limited to the foregoing preferred embodiments, as long as it is encompassed by the subject matter of the following claims. It should also be noted that the terms "comprising" and "having" do not exclude other elements or steps, and the indefinite articles "a" or "an" do not exclude a plurality. Furthermore, the term "unit" is to be understood broadly; in particular, this term is not to be understood as requiring the respective units to be formed as integral components. Furthermore, the respective units can also be positioned differently. Finally, different units can also be combined in an assembly.Furthermore, it is pointed out that features or steps that have been described with reference to one of the above embodiments can also be used in combination with other features or steps of other embodiments described above. List of reference symbols

[0031] 10First embodiment of an electronic unit according to the invention 11First excitation electronic unit 12Second excitation electronic unit 13Capacitor 14Capacitor 15Level measuring probe 16First evaluation electronic unit 17Second evaluation electronic unit 18First filter unit 19Second filter unit 20Capacitor 21Capacitor 22Output unit 30Second embodiment of an electronic unit according to the invention 31Excitation and evaluation electronic unit 32Excitation signals 33Analog-to-digital converter unit / digital-to-analog converter unit 34Level measuring probe 35Electronic unit (Fourier transformation) 36Analog-to-digital converter unit / digital-to-analog converter unit

Claims

1. Electronic unit (10, 30) for a level measuring probe (15, 34) for measuring a level of a medium, comprising: at least one first excitation electronic unit (11), configured to emit a first excitation signal; at least one second excitation electronic unit (12), configured to emit a second excitation signal; wherein the first excitation signal and the second excitation signal are different; characterized in that the electronic unit (10, 30) is configured to emit the first excitation signal and the second excitation signal simultaneously to a level measuring probe (15, 34).

2. Electronic unit (10, 30) according to claim 1, wherein the at least first excitation electronic unit (11) is configured to emit the first excitation signal for a conductive level measurement; and wherein the at least second excitation electronic unit (12) is configured to emit the second excitation signal for a capacitive level measurement.

3. Electronic unit (10, 30) according to claim 1 or claim 2, wherein the first excitation signal and the second excitation signal have different frequencies.

4. Electronic unit (10, 30) according to any one of the preceding claims, wherein the first excitation electronic unit (11) is configured to emit a square wave signal and / or a sinusoidal signal as a first excitation signal, preferably for conductive level measurement, wherein the square wave signal and / or the sinusoidal signal is preferably emitted at a frequency of 5 kHz.

5. Electronic unit (10, 30) according to any one of the preceding claims, wherein the second excitation electronic unit (12) is configured to emit a triangular signal and / or a sinusoidal signal and / or a square-wave signal as a second excitation signal, preferably for a capacitive level measurement, wherein the triangular signal and / or the sinusoidal signal and / or the square-wave signal is preferably emitted with a frequency of 355 kHz.

6. Electronic unit (10, 30) according to any one of the preceding claims, wherein the first excitation electronic unit (11) and / or the second excitation electronic unit (12) comprises at least one Direct Digital Synthesis (DDS; "Direct Digital Synthesis") unit to provide the first excitation signal and / or the second excitation signal.

7. Electronic unit (10, 30) according to any one of the preceding claims, wherein the first excitation electronic unit (11, 31) and the second excitation electronic unit (12, 31) are configured to emit the first excitation signal and the second excitation signal such that the first excitation signal and the second excitation signal have the same arithmetic mean value.

8. Electronic unit (10, 30) according to any one of the preceding claims, wherein the electronic unit (10, 30) further comprises at least one first evaluation electronic unit (16) for evaluating a conductive level measurement and / or at least one second evaluation electronic unit (17) for evaluating a capacitive level measurement, wherein a combined output signal of the level measuring probe (15, 34) is present as input signal of the first evaluation electronic unit (16) and / or of the second evaluation electronic unit (17).

9. Electronic unit (10, 30) according to claim 8, wherein the first evaluation electronic unit (16) is assigned a first filter unit (18) which is configured to filter a first output signal for a conductive level measurement from the combined output signal; and / or wherein the second evaluation electronic unit (17) is assigned a second filter unit (19) which is configured to filter a second output signal for a capacitive level measurement from the combined output signal.

10. Electronic unit (10, 30) according to claim 8 or claim 9, wherein the first filter unit (18) is provided as a digital filter unit comprising at least one bandpass filter unit whose center frequency corresponds to the first excitation signal; and / or wherein the second filter unit (19) is provided as a digital filter unit comprising at least one bandpass filter unit whose center frequency corresponds to the second excitation signal.

11. Electronic unit (10, 30) according to any one of the preceding claims, wherein the electronic unit (10, 30) comprises at least a first digital-to-analog converter unit (33) configured to convert at least a digital excitation signal of the electronic unit (10, 30) into an analog excitation signal that can be emitted as an analog excitation signal to the level measuring probe (15, 34).

12. Electronic unit (10, 30) according to any one of the preceding claims, wherein the electronic unit (10, 30) comprises at least a second analog-to-digital converter unit (36) configured to convert an analog output signal of the level measuring probe (15, 34) into a digital output signal which can be emitted as a digital output signal to the evaluation electronic units (16, 17, 31).

13. Electronic unit (10, 30) according to any one of the preceding claims, wherein the electronic unit (10, 30) comprises a weighting unit which is configured to weight the measurement results of a conductive level measurement and a capacitive level measurement in dependence on a medium-specific property of the medium whose level is detected, wherein the medium-specific property is preferably the electrical conductivity and / or the dielectric constant of the medium whose level is detected, in particular wherein one or more media-specific properties are determined from a test signal and / or a calibration signal.

14. Level measuring probe (15, 34) for measuring a level, comprising at least one electronic unit (10, 30) according to any one of claims 1 to 13.

15. Use of an electronic unit (10, 30) according to any one of claims 1 to 13 in a level measurement sensor for measuring a level.