MEASURING DEVICE FOR DETERMINING A DIELECTRIC VALUE

Abstract

A measuring device for determining the dielectric value of a medium in a phase-based manner comprises a measurement section which can be brought into contact with the medium, a signal generation unit for injecting a high-frequency signal at a defined frequency into the measurement section, and an evaluation unit designed to receive a corresponding reception signal after said high-frequency signal passes through the measurement section, to determine a phase shift between the high-frequency signal and the reception signal, and to determine the dielectric value of the medium on the basis of the determined phase shift. The measuring device also comprises at least one filter which transmits the frequency of the high-frequency signal and is arranged such that the received reception signal and/or the generated high-frequency signal is/are filtered. This ensures that the determined dielectric value is not distorted by noise caused by components or the environment.

Claims

1-11. (canceled)

12. A measuring device for determining a dielectric value of a medium, comprising: a measurement section that can be brought into contact with the medium; a signal generation unit designed to inject a high-frequency signal having a defined frequency into the measurement section; an evaluation unit designed to: receive a corresponding reception signal after passage through the measurement section; determine a phase shift between the high-frequency signal and the reception signal; and on the basis of the determined phase shift, determine the dielectric value of the medium; and a first filter and a second filter, each filter permeable to the frequency of the high-frequency signal and arranged such that the received reception signal and the generated high-frequency signal are filtered.

13. The method according to claim 12, the first filter and the second filter are each designed as a high-pass filter.

14. The measuring device according to claim 13, wherein the high-pass filters are each designed as a filter of odd order such that the corresponding high-pass filter blocks below a lower cutoff frequency and passes above an upper cutoff frequency that is lower than the defined frequency of the high-frequency signal.

15. The measuring device according to claim 14, wherein the high-pass filters below the lower cutoff frequency have a constant phase delay.

16. The measuring device according to claim 12, wherein the evaluation unit includes a network analyzer or a phase detector for determining the phase shift.

17. The measuring device according to claim 12, wherein the signal generation unit is designed to generate the high-frequency electrical signal with a variable frequency between 0.1 GHz and 30 GHz, and wherein the evaluation unit is designed to detect the phase shift at the corresponding frequency.

18. The measuring device according to claim 12, wherein the measurement section is designed as an electrically- or dielectrically-conductive measuring probe that is contacted with the signal generation unit via a first probe end in order to inject the high-frequency signal.

19. The measuring device according to claim 17, wherein the measuring probe is contacted with the evaluation unit via the first probe end such that, at a second probe end opposite the first probe end, the high-frequency signal is reflected as a reception signal.

20. The measuring device according to claim 18, wherein the probe is contacted, via the second probe end, with the evaluation unit such that the high-frequency signal is transmitted as a reception signal to the second probe end.

21. The measuring device according to claim 12, wherein the signal generation unit includes a transmitting antenna designed to transmit the high-frequency signal as a radar signal, wherein the evaluation unit includes a receiving antenna, and wherein the antennas are arranged and aligned opposite to each other on the measurement section such that the receiving antenna correspondingly receives the radar signal, after passage through the medium, as the reception signal.

22. A method for determining a dielectric value of a medium, comprising: providing a measuring device for determining a dielectric value of a medium, including: a measurement section that can be brought into contact with the medium; a signal generation unit designed to inject a high-frequency signal having a defined frequency into the measurement section; an evaluation unit designed to: receive a corresponding reception signal after passage through the measurement section; determine a phase shift between the high-frequency signal and the reception signal; and on the basis of the determined phase shift, determine the dielectric value of the medium; and a first filter and a second filter, each filter permeable to the frequency of the high-frequency signal and arranged such that the received reception signal and the generated high-frequency signal are filtered; injecting the high-frequency signal into the measurement section at a defined frequency; receiving a corresponding reception signal after passage through the measurement section; filtering the reception signal and the high-frequency signal; determining a phase shift between the filtered reception signal and the filtered high-frequency signal; and determining the dielectric value on the basis of the phase shift.

Description

[0026] The invention is explained in more detail with reference to the following figures. The following are shown:

[0027] FIG. 1: a measuring device according to the invention for dielectric-value measurement of a medium in a container,

[0028] FIG. 2: a basic circuit diagram of the measuring device according to the invention,

[0029] FIG. 3: a graph of the amplitude and phase spectra of the filter, and

[0030] FIG. 4: a possible realization of the filter according to the invention.

[0031] For a general understanding of the dielectric-value measuring device 1 according to the invention, a schematic arrangement of the measuring device 1 on a container 3, which is filled with a medium 2, is shown in FIG. 1. To determine the dielectric value of the medium 2, the measuring device 1 is arranged laterally on a connector of the container 3, e.g., on a flange connector. For this purpose, the measuring device 1 is attached to the container inner wall in an approximately form-fitting manner. The material 2 can be liquids such as beverages, paints, cement, or propellants, such as liquid gases or mineral oils. However, the use of the measuring device 1 for bulk-material-type media 2, such as grain for example, is also conceivable.

[0032] The measuring device 1 can be connected to a higher-level unit 4, such as, for example, a process control system. As interface, “PROFIBUS,” “HART,” or “Wireless HART” can, for example, be implemented. The dielectric value can be transmitted via these as an absolute value, or complex-valued with a real part and an imaginary part. However, other information about the general operating state of the measuring device 1 can also be communicated.

[0033] As shown schematically in FIG. 1, the measuring device 1 comprises a measuring probe 11, which, after installation, extends into the interior of the container 3. In this way, the measuring probe 11 is in contact with the medium 2 at a corresponding minimum fill-level of the medium 2, so that the measuring device 1 can determine the dielectric value of the medium 2 via the measuring probe 11.

[0034] Basically, the measuring device 1 is based upon a high-frequency signal s.sub.HF which is injected into the measuring probe 11, whereby the electromagnetic near-field of the high-frequency signal s.sub.HF penetrates the medium 2. For this purpose, the measuring probe 11 is designed to be electrically- or dielectrically-conductive, so that a correspondingly-designed signal generation unit 12 of the measuring device 1 (see FIG. 2) can inject the high-frequency signal s.sub.HF into a first probe end 111. Here, the probe geometry or the length d must be adapted to the corresponding medium 2. The signal generation unit 12 can be based, for example, upon a controllable high-frequency oscillator, the frequency of which is regulated by a “phase-locked loop.” The frequency f.sub.HF or the frequency band of the high-frequency signal s.sub.HF is to be matched to the specific type of medium 2 or to the specific value range of the dielectric value to be measured. Accordingly, a frequency f.sub.HF between 0.433 GHz and 6 GHz is suitable for media 2 which have a high water content. The advantage of using several different individual frequencies or one frequency band is, for one, the possibility of additionally determining the density of the medium 2. On the other hand, in the case of negative interference at a specific individual frequency, it can be possible to switch over to alternative individual frequencies.

[0035] On the basis of a reception signal r.sub.HF correspondingly reflected at the opposite, second probe end 112 of the measurement probe 11, the dielectric value of the medium 2 can be determined by an evaluation unit 13, wherein the evaluation unit 13 in the exemplary embodiment shown in FIG. 2 is in turn connected for this purpose to the first probe end 111. To split the signals s.sub.HF, r.sub.HF, the signal generation unit 12 and the evaluation unit 13 are connected to the first probe end 111 via a transmitting/receiving switch. Instead of the evaluation unit 13 being contacted at the first probe end 111, as shown in FIG. 2, the evaluation unit 13 can in principle also be connected to the opposite, second probe end 112. In this case, the evaluation unit 13 receives as a reception signal r.sub.HF the transmitted portion of the injected high-frequency signal s.sub.HF, so that a transmitting/receiving switch 15 is not necessary at the first probe end 111.

[0036] Differing from the measuring probe 11 shown in FIG. 2, a probe range for the medium 2 can alternatively also be defined as a measurement section, as shown for example in the publication document DE 10 2017 130728 A1. Here, the measurement section is defined by a transmitting antenna for transmitting the high-frequency signal s.sub.HF as a radar signal, and by a receiving antenna for receiving the corresponding reception signal r.sub.HF. For this purpose, the antennas are arranged or aligned opposite one another at a corresponding distance d.

[0037] To determine the dielectric value of the medium 2, the evaluation unit 13 determines a phase shift φ between the injected high-frequency signal s.sub.HF and the reception signal r.sub.HF. In this case, the evaluation unit 13 can carry out an absolute phase measurement, i.e., between a phase shift of 0° and, theoretically, infinity. Alternatively, the phase measurement is carried out as a relative measurement between 0° and 360°, i.e., without additional quadrant correction. For the purpose of comparing the phase shift φ in relation to the phase angle of the high-frequency signal s.sub.HF, the evaluation unit 13, as shown in FIG. 2, can be coupled to the signal generation unit 12 via a signal divider 16. In this case, for measuring the phase shift φ, the evaluation unit 13 can comprise, for example, a network analyzer or a phase detector, such as a Gilbert cell. With the aid of the measured phase shift φ, the evaluation unit 13 can in turn determine the dielectric value of the medium 2, e.g., on the basis of a corresponding calibration measurement series.

[0038] The measurement principle of the phase-based measurement of dielectric value shown in FIG. 2 offers the advantage that the dielectric value can be determined with high sensitivity. However, this measuring principle is also susceptible to noise sources internal or external to components.

[0039] According to the invention, the measuring device 1 therefore comprises a first high-pass filter 14, permeable to the frequency f.sub.HF of the high-frequency signal s.sub.HF, which is arranged in the reception path upstream of the evaluation unit 13. For this purpose, the first high-pass filter 14 is tuned to the high-frequency signal s.sub.HF in such a way that, below a defined, lower cutoff frequency f.sub.g,l, the corresponding signal components of the high-frequency signal s.sub.HF are suppressed by at least −10 dB, and in particular at least −80 dB. Above a defined, upper cutoff frequency f.sub.g,h that is lower than the frequency f.sub.HF of the high-frequency signal s.sub.HF or of the reception signal r.sub.HF, the first high-pass filter 14 conducts the reception signal r.sub.HF with an attenuation as low as possible of at most −10 dB. This characteristic is shown schematically in the graph of FIG. 3. Any noise that can impair the determination of the dielectric value is thus suppressed by the first high-pass filter 14 in the reception signal r.sub.HF.

[0040] For the same reason, in the embodiment variant of the measuring device 1 shown in FIG. 2, a second high-pass filter 14′ is also arranged in the signal path of the high-frequency signal s.sub.HF between the signal generation unit 12 and the transmitting/receiving switch 15. Here, the second high-pass filter 14′ also preferably has the filter characteristics shown in FIG. 3. Instead of the two high-pass filters 14, 14′, it is also conceivable to arrange a corresponding filter between the transmitting/receiving switch 15 and the first probe end 111 of the measuring probe 11 (not shown in FIG. 2).

[0041] FIG. 3 also shows a further advantageous design of the two high-pass filters 14, 14′: Accordingly, below the lower cutoff frequency f.sub.g,l, corresponding signal components of the high-frequency signal s.sub.HF between input and output of the high-pass filter 14 are delayed with a phase delay σ between, in particular, 30° and 200°, which is approximately constant in relation to the frequency f.sub.HF. Above the lower cutoff frequency f.sub.g,l, the phase delay σ decreases linearly in the schematic representation, so that the high-pass filter 14 passes the reception signal r.sub.HF above the upper cutoff frequency f.sub.g,h without any significant phase delay σ, i.e., less than 10°. This frequency-dependent phase behavior results in the advantage that measurement of the dielectric value is more robust with respect to manufacturing tolerances of the electronic components of the measuring device and with respect to thermal influences.

[0042] A possible variant for implementing the high-pass filter 14, which has the properties shown in FIG. 3, is shown in FIG. 4. In this variant, the high-pass filter 14 is designed as a two-dimensional conductor track structure 141 on a printed circuit board substrate 142. For example, a structurable copper or silver layer can be used as the conductor track material. Characteristic of the conductor track structure 141 here is a serial arrangement of three rectangles, which are in principle of the same area and which, in comparison to external contact, are connected to one another by two conductor tracks which are tapered by approximately ⅔. In this case, the signal r.sub.HF, s.sub.HF to be filtered is supplied via one of the two external contacts and, after corresponding filtering, tapped via the other external contact. Due to the symmetrical design in the path direction of the high-pass filter 14, 14′ illustrated in FIG. 4, it is in principle irrelevant which of the two external contacts serves as input or as output.

[0043] As shown in FIG. 4, in contrast to the two outer rectangles, the middle rectangle has an asymmetry in the form of a supplementary structure at one end. As a result, the high-pass filter 14 forms corresponding properties of odd order, so that the frequency-dependent transmission behavior of signal amplitude A.sub.HF shown in FIG. 3 results. It goes without saying that the high-pass filter 14, 14′ can also be realized in hybrid fashion with a corresponding odd order instead of the embodiment variant shown in FIG. 4.

LIST OF REFERENCE SIGNS

[0044] 1 Measuring device [0045] 2 Medium [0046] 3 Container [0047] 4 Higher-level unit [0048] 11 Measurement probe [0049] 12 Signal generation unit [0050] 13 Evaluation unit [0051] 14, 14′ Filter [0052] 15 Transmitting/receiving switch [0053] 16 Signal divider [0054] 111 First probe end [0055] 112 Second probe end [0056] 141 Conductor track structure [0057] 142 Printed circuit board substrate [0058] A.sub.HF Signal strength at filter [0059] d Length of the measurement probe [0060] f.sub.HF Frequency of the high-frequency or reception signal [0061] f.sub.g,l Lower cutoff frequency [0062] f.sub.g,h Upper cutoff frequency [0063] r.sub.HF Reception signal [0064] s.sub.HF High-frequency signal [0065] φ Phase shift [0066] σ Phase delay