EP3332246A1

EP3332246A1 - Measuring device for measuring the dielectric and/or magnetic properties of a sample by means of a microwave transmission measurement, apparatus using such a measuring device, and method using such an apparatus

Info

Publication number: EP3332246A1
Application number: EP16753274.6A
Authority: EP
Inventors: Albert Klein
Original assignee: Individual
Current assignee: Individual
Priority date: 2015-08-07
Filing date: 2016-07-28
Publication date: 2018-06-13
Also published as: AU2016307138A1; CA2994484A1; WO2017025340A1; DE102016113917A1; US10247681B2; US20180231476A1

Abstract

A microwave measuring device having a transmitting module (SM) and a receiving module (EM) and an apparatus having these modules are described. The two modules (SM, EM) are accommodated either in a common housing (G) or in separate housings. The transmitting module (SM) can be coupled to a transmitting antenna (10) and the receiving module (EM) can be coupled to a receiving antenna (20). In order to compensate for measurement errors, in particular temperature-related measurement errors, at least one RF bypass cable (61) runs outside the housing (G)/the housings and can be used to couple the transmitting module (SM) and the receiving module (EM) while bridging the measuring section defined by the two antennas (10, 20).

Description

Measuring device for measuring the dielectric and / or magnetic properties of a sample by means of a microwave transmission measurement, device using such a measuring device and method using such a device

description

The invention relates to a fair device for measuring the dielectric and / or magnetic properties of a sample by means of a microwave transmission measurement according to the preamble of claim 1, a device using such a measuring device according to claim 10 and a measuring method using such a device.

Various possibilities are known in the art for measuring the dielectric properties of a sample, for example moisture, without contact. For example, it is possible to irradiate the sample with microwaves and the desired information by comparing the radiated microwave or a derived Signa! with the transmitted microwave or a signal derived therefrom. In this case, both the absorption and the phase shift can be determined so that the complete information about the complex epsilon of the sample can be obtained from the corresponding measurement. A device suitable for this purpose has a transmitting module and a receiving module, which are usually accommodated in a common housing made of metal. In this case, the transmission module has at least one high-frequency generator (usually called a synthesizer, also called a synthesizer) for generating a high-frequency signal which is coupled into an RF coupling unit (transmitting antenna) connected to the synthesis generator, for which a transmitting is provided riger HF connection cable. The synthesis generator is clocked by a so-called frequency standard, which emits a low-frequency signal with a frequency of, for example, 10 MHz. The high-frequency signal generated by the at least one synthesis generator is also fed to the reception module which is connected to an RF decoupling unit (receiving antenna) and mixed there with the microwave received by the receiving antenna in a mixer. For the connection between the RF output unit and the receiving module, a receiving-side RF connecting cable is provided. RF injection unit (transmitting antenna) and RF decoupling unit (receiving antenna) define a measuring path in which a sample is arranged during measuring operation. Furthermore, an evaluation unit is provided, which can be designed as a separate module. This evaluation unit is supplied with the mixed signal. A distinction is basically made between two types of measuring systems, namely so-called homodyne systems, which operate at one time with only one frequency and have only one high-frequency generator, and so-called heterodyne systems which operate with two closely adjacent frequencies and have two synthesis generators. Both systems are equal in that they operate by comparing two microwave signals, one passing through the sample, thereby experiencing attenuation and / or phase shift while the other microwave signal does not pass through the sample and serve as a reference. This makes it necessary to provide a high frequency reference line (Lo line) between the transmitting module and the receiving module (this applies to both homodyne systems and heterodyne systems). In the case where the transceiver module is housed in a housing, the radiofrequency reference line may extend within the housing, in the case where the transceiver module is housed in spaced apart housings, an RF interface extending between the housings is provided. Reference cable provided, which forms part of the RF reference line. However, the measurement setup does not directly provide the insertion loss and phase shift of the sample, but the transfer function of the measurement system including the sample. Therefore, an empty measurement is additionally required, which provides the transfer function of the measuring system without the sample. Only the computation of the two transfer functions then supplies the vectorial transfer function (S21) of the sample, ie damping and phase shift.

Under laboratory conditions, the provision of the above-mentioned high-frequency reference line is usually unproblematic, since on the one hand no large local distances must be overcome, and on the other hand constant laboratory conditions, in particular a substantially constant temperature prevail.

If such a device is used in the industrial sector, the following problem arises: The temperature dependence of the wave propagation speed in a coaxial cable has an increasing effect on the phase shift with increasing frequency of the shaft. This means that in non-constant environmental conditions, in particular temperatures, significant phase shifts in the antenna feed lines (transmitting side RF connection cable and receiving HF connection cable) and - if present - in the RF reference cable can occur, which distort the measurement result, in industrial Applications, however, often fail to avoid that at least one of the RF cables is made relatively long (a few meters), which of course exacerbates this problem, especially if such a device is installed outdoors, so that it is completely or partially exposed to sunlight.

Furthermore, (even here in particular in industrial use) measuring accuracies can occur if strong reflections occur in the region of the measuring path. In particular, in open measuring systems in which the sample is non-contact in a free-space measuring section, measurement errors occur, the caused by reflections on the sample or on reflectors in the environment.

In order to be able to achieve consistently good measuring results even under fluctuating environmental conditions, DE 10 2012 010 255 B3 proposes to provide at least one synthesis generator for generating a high-frequency signal both on the transmitting side and on the receiving side and to couple these two synthesis generators in a phase-stable reproducible manner, for which a common frequency standard is provided, which activates the two synthesis generators via at least one low-frequency signal line, which is referred to here as a low-frequency synchronization signal line. The provision of a receiving-side synthesis generator makes the use of the above-mentioned problematic high-frequency reference line superfluous in many applications, so that even if the transmitter module and the receiving module are spatially separated, no temperature-sensitive high-frequency reference cable is necessary. Due to the fact that transmitter module and receiver module are separated locally, the possibility is created to keep the antenna cables relatively short. If necessary, only one low-frequency line (in the form of a low-frequency cable) of great length may be provided which connects the two modules to one another. Such low-frequency signal lines are almost insensitive to the above-mentioned environmental influences even at great length, so that no recalibration is necessary even under strongly fluctuating environmental influences, in particular a strongly changing temperature. Such a device can basically be designed both as a homodyne system and as a heterodyne system.

The proposed system works well in principle, but it has the disadvantage that it works ideally only if it is operated permanently with a constant frequency or with two constant frequencies. However, working with multiple frequencies can be problematic, especially if a frequency band is "driven through", that is, if the synthesizers change their frequencies at certain time intervals have to. Since the locally spaced synthesis generators are coupled by a common low-frequency signal whose frequency is typically smaller by a factor of 100 to 500 than the frequency of the synthesis generators, it can not be guaranteed that both synthesis generators "lock in" on the same wave flank, which in turn can lead to inconsistent phase errors.

On this basis, the object of the invention is to provide an improved measuring device or device for measuring the dielectric and / or magnetic properties of a sample by means of a microwave transmission measurement.

This object is achieved by a measuring device having the features of claim 1 and by a device having the features of claim 9.

According to the invention, at least one HF bypass signal line is provided in measuring operation, the input of which can be coupled into the signal path between the first HF synthesis generator and the H F coupling unit and whose output can be coupled into the signal path between the HF output unit and mixer, so that when coupled HF bypass signal line, the RF signal is redirected from the measuring path in the first RF bypass signal line. A portion of this RF bypass signal line is formed as outside of the housing / housing extending RF bypass cable.

This means that it is possible to switch over between the measuring path and the RF bypass signal line during the measuring operation, so that the first input of the mixer either the RF signal which has passed through the measuring path, or the RF signal, which means the measuring path has bypassed at least one RF bypass signal line, is supplied, so that in addition to the measurements on the sample calibration measurements can be performed Due to the possibility of calibration measurements, the following improvements can be achieved:

In a first embodiment of the invention, the provision of an RF bypass cable serves to compensate for measurement errors caused by changes in temperature in the RF connecting cables to the antennas. For this purpose, the RF bypass cable is preferably designed such that it has the same thermal and electrical properties as the RF connection cable to the antennas and that its length of the total length of the RF connecting cable has up. In this case, the HF bypass cable is preferably laid so that it has the same temperature as the RF connection cable. If additionally a second HF bypass cable with a different length is used, the measurement error caused by a drift of the electronics can be compensated.

In a second embodiment, in which the device is designed in accordance with the principle described in DE 10 2012 010 255 B3, the calibration measurement serves to mathematically (that is, by the .DELTA.), The error, which results from different "snapping" of the synthesis generators during frequency change Evaluation unit).

In order not to again "deal with" errors due to fluctuating environmental conditions, such as, in particular, fluctuating temperatures, it is also preferable in this case to provide two HF bypass signal lines which differ in their length, the two HF bypass signal lines have the same electrical and thermal properties, and can be switched between the two RF bypass Signalle ^{'Maintenance,} so that the possibility of a double calibration measurement is provided. Finally, the calibration measurement can be used to the influence of the disturbing reflections at to at a blank measurement So far, an empty measurement is made as a comparative measurement with an empty measuring section, so that the influence of the sample on the microwave can be true. However, the disturbing reflections occur mainly when the measuring path is empty. Therefore, this measurement is replaced by the calibration measurement, which is a bypass measurement. In addition, then in a second measurement, the difference of the transfer function of the empty measurement path in relation to the RF bypass signal line must be determined, from which then the average value of the attenuation and phase shift is determined.

Brief description of the drawings

1 shows the circuit diagram of a device of a first embodiment of a first embodiment of the invention,

FIG. 2 is a circuit diagram of a device of a second embodiment of the first embodiment of the invention,

FIG. 3 shows a circuit diagram of a device of a first exemplary embodiment of a second embodiment of the invention, FIG. 4 shows a circuit diagram of a device of a second exemplary embodiment of the second embodiment of the invention,

FIG. 5 is a circuit diagram of a device of a third embodiment of the second embodiment of the invention,

6 is a circuit diagram of a device of a fourth embodiment of the second embodiment of the invention, FIG.

7 shows a circuit diagram of a device according to the prior art,

Figure 8 shows a first preferred application of the invention and Figure 9 shows a second preferred application of the invention.

The following definitions and conventions apply to the following:

As "high-frequency signal" or "microwave" electromagnetic waves are called, which propagate in a conductor or free, and have a frequency between 800 MHz and 30 GHz. High frequency (microwave) signal lines suitable for such frequencies are known in the art. The sections of a high-frequency signal line running between a housing and an antenna (RF coupling unit and RF decoupling unit) are designed as coaxial cables and are referred to as RF cables. In the figures, the high-frequency Signalle ^' ments are shown in phantom.

By "low frequency" is meant here all electromagnetic waves or signals having a frequency below 200 MHz Signal lines for transmitting such low frequency signals are referred to herein as low frequency signal lines and are shown in the drawings as solid lines (control and bus lines ) or with the pattern dash-dot-dot-dash.

Not all signal lines (whether high-frequency signal lines or low-frequency signal lines) have been given their own name / reference in the description and drawings for the sake of clarity.

At least outside the housing, the high-frequency Signalteitungen are usually designed as coaxial cable. The low-frequency lines can be realized both with coaxial lines and with other cables. For cost reasons, higher quality coaxial cables are typically used for the high frequency signal lines than for the low frequency signal lines; This is however, not necessarily, it would also be possible to use, for example, sufficiently high-quality coaxial cables for all signal lines. In this respect, the terms "high-frequency signal line", "RF cable" and "low-frequency signal line" are primarily functional.

For a better understanding, reference is first made to the prior art with reference to FIG. FIG. 7 shows a classic heterodyne device, in which the measuring device consisting of the transmitter module SM and the receiver module EM is enclosed in a common metal housing G (usually of aluminum).

The transmission module SM has two transmission-side synthesis generators 12 and 14, two power dividers 18a, 18b, a transmission-side mixer 16 and a frequency normal 82. The receiving module EM has only one receiver-side mixer 26. The evaluation unit consists of a first microcontroller 40 (in the embodiment shown the only microcontroller). Transmitter module SM and receiving module EM are connected to each other by means of a high-frequency reference line (F2). The transmission module SM and the reception module EM are connected to the evaluation unit (ie to the first microcontroller) in each case by means of a low-frequency signal line (IF1, IF2). Furthermore, the transmission module SM is connected by means of a transmission-side RF connecting cable 58 to an RF coupling unit 10 (hereinafter usually referred to as transmitting antenna), the receiving module EM is by means of a receiving side RF connecting cable 59 with an RF decoupling unit 20 (hereinafter usually as Receiving antenna), for which the housing has a first RF signal output 31 a and a first RF signal input 51a. Transmitting antenna 10 and receiving antenna 20 define a measuring path in which a sample can be arranged. The operation is as follows: The frequency normal 82 clocks the two transmit-side synthesis generators 12, 14, wherein the clock frequency may be for example 10 MHz. The first transmission-side synthesis generator 12 generates a first high-frequency signal F1 a first high frequency of, for example, 3 GHz, and the second transmitting side synthesis generator 14 generates a second high frequency signal F2 having a high frequency slightly different therefrom, for example 3.001 GHz. The first high-frequency signal F1 of the first transmitting-side synthesis generator 12 is supplied to a first power divider 18a, whose first output is connected to the transmitting antenna 10 and whose second output is connected to the transmitting-side mixer 26. The second transmission-side synthesis generator 14 is connected to the second power divider 18b, the outputs of which are connected to the transmission-side mixer 16 and to the reception-side mixer 26 via the high-frequency reference line 50. The second input of the receiving-side mixer 22 is connected to the receiving antenna 20.

Thus, the transmitting side mixer 16 generates a first intermediate frequency signal IF1 having a first intermediate frequency, which is the difference between the first high frequency (that is, the frequency of the transmitted microwave) and the second high frequency, that is, 1 MHz in the selected embodiment. The receiver-side mixer 26 in turn generates a second intermediate frequency signal SF2 which is the difference of the received microwave (this signal is referred to here as F1 ') and the second high-frequency signal of the second transmitter-side synthesis generator 14. The frequency of F1 and F is the same here, since the transmission through the sample P changes phase and amplitude, but not the frequency. For this reason, the two intermediate frequency signals IF1 and IF2 also have the same frequency, namely 1 MHz. From the comparison of the first intermediate frequency signal IF1 with the second intermediate frequency signal! F2, it is possible to deduce in a known manner both the phase shift and the attenuation which the microwave emitted by the transmitting antenna 10 undergoes when the sample P is irradiated in turn can be concluded on the dielectric properties of the sample. The corresponding calculations are carried out by the evaluation unit, namely the first microcontroller 40. In industrial applications, the transmitting-side RF connecting cable 58 and / or the receiving-side RF connecting cable 59 may be relatively long and unprotected, so that their temperature (for example, due to solar radiation) may change relatively rapidly over time. However, this leads to a change in the wave propagation speed, which in turn leads to a phase shift, which then - if no countermeasures are taken - leads to a measurement error.

1 shows a first embodiment of a first embodiment of a device with which the error just described is corrected. The basic structure of this device is identical to what has just been described, with the following elements being additionally provided:

Connected downstream of the first power divider 18a is a HF disconnecting device 30 (changeover switch), whose first output 31 is connected to the first RF signal output 31a and whose second output 32 is connected to a second RF signal output 32a of the housing. Similarly, the receiver-side mixer 26 is preceded by a switchable RF merge unit 50, the first input 51 is connected to the first RF signal input 51 and the second input 52 is connected to a second RF signal input 52a of the housing. Between the second RF signal output 32a and the second RF signal input 52a extends a first RF bypass cable 61. Thus, by means of the RF splitter 30 and the RF merger unit 30 can be switched such that the first RF signal F1 either the RF connection cable 58, 59 and the through the antennas 10, 20 defined measuring path passes through and thus to the high frequency signal F ', or that it passes through the first RF bypass cable 61 and thus to the high frequency signal F "H F-orders no Richtu ng 30 and RF merge unit 50 are driven by the microcontroller 40.

This first RF bypass cable 61 (in this embodiment the only RF bypass cable) preferably has the following properties: It has the same characteristics electrical and thermal properties such as the transmitting side RF connecting cable 58 and the receiving side RF connecting cable 59 {that is, all three cables are identical), it has a length which is the sum of the lengths of the transmitting side RF connecting cable 58 and the receiving end RF connection cable 59 corresponds and it is laid so that it has the same temperature as the two RF connecting cables 58, 59. The latter feature can be achieved, for example, by laying the RF bypass cable in sections parallel to these cables. On initial calibration of the device, in addition to the usual calibration, the HF bypass cable 61 is switched so that the signal F "arrives at the receiver-side mixer 26, which the receiver-side mixer 26 mixes with the second high-frequency signal F2 second intermediate frequency signal IF2 and the first intermediate frequency signal IF1 is stored as a reference value (reference attenuation and phase shift).

During normal operation (ie during the measurement on a sample located in the measuring section), the microcontroller 40 periodically switches over from the measuring section to the HF bypass cable. If there is a change in the phase shift between the currently measured phase shift between the second intermediate frequency signal IF2 and the first intermediate frequency signal IF1 and the stored reference phase shift, this can be attributed to a phase shift in the signal FT ^* and thus to a temperature change in the HF Close bypass cable 58, assuming that the electronics of transmitting and receiving module stable and drift-free works.

In the case of a symmetrical arrangement, because of the above-described properties of the HF bypass cable with respect to the connection cables 58, 59, it follows that the signal FT has the same phase shift due to the temperature change of the HF connection cables 58, 59. At unsymmet- rischer cable length, the change in the electrical properties of the cable can be calculated and transferred accordingly to the antenna cables 58 and 59 computationally. Without correction, the evaluation unit (in this case the first microcontroller 40) would "miscalculate" this phase shift of the sample, which would lead to a corresponding measurement error. in the simplest mathematical case, simply by subtracting the temperature-induced phase shift measured at the HF bypass cable from the phase shift measured in the measuring path.

FIG. 2 shows a second embodiment, which is very similar to the first embodiment. The difference is that two RF bypass cables are provided, namely the first RF bypass cable 61 and the second RF bypass cable 62. Again, all cables 58, 59, 61, 62 extending outside the housing are preferably identical. The first HF bypass cable 61 can here also have a length which corresponds to the sum of the length of the two connection cables. The second RF bypass cable must have a length different from the length of the first H F bypass cable. In order to be able to connect two RF bypass cables, a third RF signal output 33a and a third RF signal input are additionally provided. Accordingly, the RF splitter 30 has three outputs 31, 32, 33, and the RF splitter unit 50 accordingly has three inputs 51, 52, 53. All cables can be laid very close to each other, since they are never operated simultaneously and are extremely decoupled via the switch so that there is no danger of cross-talkers (this also applies to the first embodiment).

When calibrating the device, one now obtains two reference phase shifts with respect to IF1, namely the first reference phase shift obtained by mixing F '(first RF bypass cable) with F2 and the second reference phase shift which one obtains By measuring Ff "(second RF bypass cable) with F2 Obtained in the measurement operation, of course, according to a first phase difference and a second phase difference (in each case based on IF1), so that the evaluation unit in addition to the temperature compensation drift error of the electronics (transmission module and receiving module), as shown in the following consideration:

Due to the longer length of the second RF bypass cable, the second phase shift is greater than the first phase shift, and as the temperature of the cable increases, the electrical length changes. If one notes (that is to say the evaluation unit) that the first and second phase shifts have changed with the same amount with respect to their respective reference phase shift, this can not be due to a temperature change of the cables, but is a phase shift which occurs in one Drift of electronics is justified. This phase error can then also be taken into account in the correction of the phase shift when measuring on the sample.

More mathematically speaking, a system has two independent sources of error (temperature change of the cables and drift of the electronics) and two measurements are made, with the RF cables used having the same temperature coefficient so that the size of both errors can be determined.

The presence of a bypass has another advantage: you can use the bypass as an empty measurement. Since the electrical length of the bypass is not adjusted to the electrical length of the measuring path, however, an offset will result for both the attenuation D in dB and for the phase shift Phi in 7 GHz, which must be taken into account in the calibration.

Starting from the calibration equation in the simplest form W = A * Phi / m ^u + B * D / m "+ E Now, taking into account the offset D ₀ and Phi ₀ , one obtains for D or Phi:

W = A * (Phi + Phi ₀ ) / m ^u + B ^* (D + D ₀ ) m + E

= A * (Phi) / m ^u + B * (D) m "+ C / m" + E with:

W water content

m "basis weight of the sample,

A, B, C, coefficients which are determined during the calibration by means of regression.

The second task of the blank measurement is to determine the frequency response of the measurement with the sample despite nonlinear frequency response, e.g. caused by the dispersion of the antennas, to linearize. Therefore, in addition, a measurement is carried out which is similar in frequency response to the measurement with the sample, whereby both the frequency response and the mean value of the measurement is determined and calculated so that only frequency response affects the measurement, but not the absolute value of the Measurement.

With reference to Figure 3, a second embodiment of the device according to the invention will now be described, which is also designed as a heterodyne system.

The device is basically constructed as is known from DE 10 2012 010 255 B3, two additional HF bypass cables 61, 62 being provided, as described above. Just as in the embodiment described above, it is possible to switch between the measuring path and the two HF bypass cables 61, 62, but this achieves a different goal, as will be described in more detail later. The two modules SM and EM are spatially separated and housed in separate metal housings G1 and G2. introduced. In the second housing G2 and the evaluation unit in the form of a first microcontroller 40 and a frequency normal 82 is integrated. However, these components could equally well be housed in the first case G1 or in a separate case.

The transmission module SM has two transmission-side synthesis generators 12 and 14, which each generate a high-frequency signal F1 or F2, wherein the high frequencies are slightly different from each other, for example, the first high frequency in a switching state 3 GHz and the second high frequency 3.001 GHz. The two transmitter-side synthesis generators 12, 14 are controlled by a second microcontroller 42, which is controlled by the first microcontroller 40. The two microcontrollers 40, 42 are connected by means of a bus line 80. The first synthesizer 12 feeds its high-frequency signal F1 into a power divider 18, which in turn is connected to a transmitting-side mixer 16 and the input 35 of a HF designed as a crossover. Separating device 30 is connected. As in the previously described embodiment, the first output 31 of this RF splitter 30 is connected to the RF injection unit 10 via a first RF signal output 31a of the housing and the transmit-side RF interconnect cable 58. Again, the RF splitter 30 has two further outputs 32, 33, which are each connected to an RF signal output 32a, 33a of the housing, from each of which an RF bypass signal cable 61, 62 extends. These two RF bypass signal cables 61, 62 also here have the same electrical and thermal properties, but the second RF bypass signal line 62 has a greater length than the first RF bypass signal line 61 (as in the second embodiment). In the exemplary embodiment shown, the RF splitter 30 is constructed from two switches connected in series, which are controlled by the second microcontroller 42. The second transmission-side synthesis generator 14 feeds the second high-frequency signal F2 generated by it directly into the transmission side Mixer 16, which is connected to the evaluation unit, namely with the microprocessor 40 and this the first intermediate frequency signal IF1 supplies.

The RF decoupling unit 20 is connected via the receiving-side RF connecting cable 59 and the first RF signal input 51 a to an input 51 of a symmetrical to RF separation device 30 formed RF merge device 50. The two further inputs 52, 53 of the RF convergence device 50 are each connected via the further RF signal inputs 52a, 53a, each with an RF bypass cable. The RF merger 50 is driven via the first microcontroller.

In the reception module EM, a reception-side synthesis generator 22 is provided, which in each case generates the same high frequency as the second transmission-side synthesis generator 14, ie, 3.001 GHz in the selected embodiment. This receiving-side synthesis generator 22 is connected to the frequency standard 82 and is controlled by the microcontroller 40. The receiving-side synthesis generator 22 feeds the third high-frequency signal F3 which it generates into the receiver-side mixer 26, whose second input is connected to the output 55 of the HF converger 50, so that it is at the appropriate switching state of RF splitter 30 and RF merger 50 the received by the sample P transmitted first high-frequency signal F1 'receives.

The transmitter-side mixer 16 generates a first intermediate-frequency signal IF1, likewise the receiver-side mixer 26 generates a second intermediate frequency signal IF2, the two intermediate frequencies being equal, namely 1 MHz in the described embodiment. These intermediate frequency signals are thus low frequency signals (low frequency signals). These two intermediate frequency signals 1F1 and IF2 are fed to the evaluation unit, ie the first microprocessor 40. In order to obtain from the phase shift between the first intermediate frequency signal IF1 and the second intermediate frequency signal IF2 a relevant statement about the phase shift which the first radio frequency quency signal F1 when passing through the sample P learns, can derive, all synthesis generators 12, 14 and 22 must be synchronized with each other. This synchronization is provided by the frequency standard 82, which is connected to the receive-side synthesis generator 22 by a send-side low-frequency synchronization signal line 84a with the two transmit-side synthesis generators 12, 14 and with a receive-side low-frequency synchronization signal line 84b a clock signal TS emits, with the synthesis generators are coupled in a phase-stable reproducible. The "heart" of such a frequency standard is usually a crystal whose resonant frequency is used as the normal frequency, typically this normal frequency is between 1 and 30 MHz, in particular 10 MHz, as selected in this embodiment Both low-frequency synchronization signal lines 84a , 84b, are low-frequency signal lines, which are preferably physically identical, in particular of the same length (not shown) and of identical construction.Owing to the local separation of transmitter module SM and receiver module EM, transmitter-side RF connection cable 58 and receiver-side RF connection cable 59 can be very be made short, so that any temperature fluctuations lead to only small errors.The switchover to the RF bypass cable 61, 62 is therefore used for something else:

As described above, in an initial calibration, reference phase differences between IF1 and the mixture of FT and F3, between IF1 and the mixture of F 'and F3 and between IF1 and the mixture of FT "and F3, where F2 and F3 have the same frequency This process must be carried out for each high-frequency pair to be used during a measurement process In the measurement state, the input 35 of the RF splitter is connected to its first output 31 and the first one Input 51 of the RF merger 50 is connected to its output 55, so that the Device operates as described above and the two RF bypass cables are inoperative (as described above with reference to Figure 2).

If a frequency change is now carried out by the system (ie the sendesei- term synthesis generators 12, 14 are controlled accordingly by the second microcontroller 42 and the receiving-side synthesis generator 22 is controlled accordingly by the first microcontroller 40), the phase position of the receiving-side synthesis generator 22 with respect to transmit side synthesis generators 12, 14 are no longer known because the system does not "know" how the synthesis generators "lock in". Therefore, after a frequency change (for example from 3.000 GHz, or 3.001 GHz to 4.000 GHz or 4.001 GHz), a calibration measurement is first performed by means of the first RF bypass signal line 61, that is, the currently measured phase difference between the mixture For this purpose, the RF splitter 30 is switched to the second output 32 and the RF merger 50 to the second input 52, and a calibration measurement is performed based on the performed initial calibration, at which a corresponding reference phase shift has been measured, the evaluation unit can calculate the phase error possibly occurred by the frequency switching and perform a corresponding correction after switching back to the first output 31 and the first input 51 when measuring the sample P.

However, in industrial applications where fluctuating temperatures are to be expected, the electrical properties of the first HF bypass cable 61 change with temperature, which can be relatively long depending on local conditions. In order to be able to compensate for this, the second HF bypass signal line 62 is provided, which has the same properties as the first HF bypass signal line 61 up to the length. The two RF bypass cables 61, 62 are preferably laid parallel to one another, so that they can be assumed to have the same temperature. Thus, a "double calibration measurement" can be carried out at certain time intervals. be performed, in which the two RF bypass signal lines are connected in succession between the transmission module SM and the receiving module, so that due to the different lengths of the two RF bypass signal lines, the temperature effect can be computationally eliminated, as described above.

FIG. 4 shows a further exemplary embodiment of the second embodiment. By means of the synthesis generators coupled in phase-locked reproducible manner, both intermediate frequencies IF1 and IF2 can also be generated on the receiver side, so that the connection cable for the signal of the first intermediate frequency IF1 between the transmitter module SM and the evaluation module AE can be dispensed with. A concrete exemplary embodiment is shown in FIG. 4: In this case, the transmission module SM has only one synthesis generator 11. All further components are integrated into the receiving module EM, which thus has a first and a second receiving-side synthesis generator 23, 24, the second synthesis generator 24 generating a second high-frequency signal F2 having the same high frequency as the first high-frequency signal F1 of the transmitting-side synthesis generator 11 (FIG. For example, again 3 GHz), while the first synthesis generator 23 (as in the embodiment described above) generates a third high frequency signal F3 with a slightly different high frequency (for example, again 3.001 GHz). The first intermediate-frequency signal IF1 is generated by mixing the second high-frequency signal F2 with the third high-frequency signal F3, to which the first receiver-side mixer 27 serves, one input via a power divider 29 to the first receiving-side synthesis generator 23 and the other input to the second receiving-side synthesis generator 24 is connected. The second intermediate frequency signal IF2 is generated as described above, for which the second receiver-side mixer 28 is used, which corresponds to the receiver-side mixer 26 of the first embodiment. As in the embodiment described above, all synthesis generators 11, 23, 24 are clocked in phase by the frequency normal 82. FIG. 5 shows a further exemplary embodiment in which only one transmitter-side frequency generator 11 is provided for generating a first high-frequency signal F1 and only one receiver-side frequency generator 22 for generating a further high-frequency signal, which for reasons of consistency is referred to here as the third high-frequency signal F3. Here serves as a reference signal (this is in the previous embodiments, the first intermediate frequency signal 1F1) directly the clock signal TS of the frequency normal 82 or optionally derived directly from this signal. If the clock signal TS is to serve directly as a reference signal, as shown in the embodiment of FIG. 5 and for which purpose a further low-frequency synchronization signal line 84c is provided which connects the frequency standard 82 to the first microprocessor 40, then the frequency of the second intermediate frequency signal IF2 (the mixed signal of F3 and FT) be equal to the frequency of the clock signal TS. If the frequency of the clock signal TS is also 10 MHz here, for example, the frequency of the first high-frequency signal F1 could be 3 GHz and the frequency of the third high-frequency signal F3 3.01 GHz. This embodiment leads to a simplification of the circuit, but is still not recommended because filtering the IF and the frequency normal can not be separated.

In applications in which fluctuating environmental influences, in particular fluctuating temperatures do not play a decisive role, optionally (as in the first embodiment of the first embodiment) can be dispensed with the second RF bypass cable. An embodiment of this is shown in FIG. The RF splitter (switch) 30 here has only two outputs 31, 32 and the H F-Zusammenfü hrein device 50 has only two inputs 51, 52 on. In this case, the only HF bypass cable 61 which can be switched parallel to the measuring path can be used in exactly the same way as described above (ie for correcting any latching fault), but not for temperature compensation. As already mentioned, the advantages of the improvement according to the invention are particularly evident in the industrial use of such a device, for example in the online measurement of bulk materials SG such as coal or ore conveyed on a conveyor, for example a conveyor belt 60 (FIG. 6) or in the online measurement of liquid flowing through a pipe (65) (FIG. 7). Also the measurement in a container is possible. Shown here are measuring devices according to the first two embodiments.

LIST OF REFERENCE NUMBERS

10 RF coupling unit

11 transmitter-side synthesis generator

12 first transmitter-side synthesis generator

14 second transmitter-side synthesis generator

16 transmitter-side mixer

18 power dividers

18a first power divider

18b second power divider

20 RF decoupling unit

22 receiving-side synthesis generator

23 first receiving-side synthesis generator

24 second receiver synthesizer

26 receiver-side mixer

27 first receiver-side mixer

28 second receiver-side mixer

29 power dividers

30 HF separating device

31 first output of the RF splitter

31a first RF signal output

32 second output of the RF splitter

32a second RF signal output

33 third output of the RF splitter

33a third RF signal output

35 entrance

40 first microcontroller

42 second microcontroller

50 RF merger unit

51 first entrance

51a first RF signal input 52 second entrance

52a second RF signal input

53 third entrance

53a third RF signal input

55 output

58 transmitting side RF connecting cable

59 receiving side RF connection cable

61 first RF bypass cable

62 second HF bypass cable

80 bus

82 frequency standard

90 conveyor belt

95 pipe

F1 first high frequency signal with first frequency

F2 second high frequency signal with second frequency

F3 third high frequency signal with third frequency

IF1 first intermediate frequency signal with first intermediate frequency

IF2 second frequency signal with second intermediate frequency

TS clock signal

SM transmitter module

EM reception module

G common housing

G1 first housing (transmitter-side housing)

G2 second housing (receiving-side housing)

SG bulk goods

Claims

claims

1. measuring device for measuring the dielectric and / or magnetic properties of a sample (P) by means of a microwave transmission measurement with

a transmission module (SM) having a first synthesis generator (11, 12) for generating a first high-frequency signal (F1) having a first frequency, and a first RF signal output (31a) connectable to the first synthesis generator (11, 12) to which a RF coupling unit (10) by means of a transmitting side RF connecting cable (58) can be coupled,

a receiving module (EM), with a first RF signal input (51a), to which an RF decoupling unit (20) by means of a receiving side RF connecting cable (59) can be coupled, and an RF mixer (26, 28) with a first A mixer input connectable to the first RF signal input (51a), a second mixer input connected to or connectable to the first RF synthesizer in a homodyne system or a second RF synthesizer in a heterodyne system, and a mixer output outputs a LF signal which is mixed from the two RF signals fed to the inputs,

wherein transmitter module (SM) and receiver module (EM) are arranged either in a common housing (G) or in separate housings (G1, G2),

an evaluation unit which is connected to the output of the mixer and thus processes the AF signal in a first state in a first operating state of the device, characterized

in that the transmission module additionally has at least one second HF signal output (32a) which can be connected to the first synthesis generator and the receiving module (EM) additionally has at least one second HF signal input (52a) which can be connected to the first mixer input of the mixer,

so that at least one out of the housing (G) / the housing (G1, G2) extending first RF bypass cable (61) can be connected, whose input into the signal path between the first RF synthesizer (11, 12) and the HF Coupling unit can be coupled in (10) and whose output can be coupled into the signal path between the RF decoupling unit (20) and mixer (26, 28), so that when the first RF bypass cable (61) is coupled in, the RF signal from the measuring path, which in the coupled sendeseiti- according RF connection cable (58) and the coupled empfangsse ^'RTI according RF connection cable (59) by the RF decoupling unit (10) and the RF coupling unit (10) is defined in the first RF bypass Cable (61) is redirected so that the device then assumes a second operating state in which the AF signal has a second state in which it contains no information about a sample (P) positioned in the measuring path

Measuring device according to claim 1, characterized

the transmission module furthermore has a third HF signal output (33a) which can be connected to the first synthesis generator, and in that the reception module additionally additionally has a third HF signal input (53a) which can be connected to the first mixer input of the mixer.

Measuring device according to claim 2, characterized in that

a first RF switching or splitting device (30) having an input (35) connected to the first RF synthesis generator, a first output (31) connected to the first RF signal output (31a), and one connected to the second RF signal output (32a) second output (32) and a third output (33a) connected to the third output (33) is provided, and

a second RF switching unit (50) having a first input (51) connected to the first RF signal input (51 a), an output (55) connected to the mixer, and a second one connected to the second RF signal input (52a) Input (52) and one connected to the third RF signal input (53 a) third input (53) is arranged.

4. Measuring device according to one of the preceding claims, characterized in that the first HF synthesis generator is a transmitting side HF synthesis generator (12), that the second HF synthesis generator is a receiving side HF synthesis generator (22) and that the HF synthesis generators ( 12, 22) in each case by means of a low-frequency Synch ron isations-Sig al leitu ng connected to a frequency normal and coupled to this phase-locked.

5. Measuring device according to claim 4, characterized in that two transmitting side HF synthesis generators (12, 14), and a receiving side HF synthesis generator (22) or a transmitting side (11) and two receiving side synthesis generators and a further mixer are provided.

6. Measuring device according to one of claims 4 to 5, characterized in that the at least one receiving side H F synthesis generator is part of a transmitting module, that the at least one receiving side HF synthesis generator is part of a receiving module, that transmission module and that the transmission module and receiving module locally from each other are spaced and that the at least one RF bypass signal line and the low-frequency synchronization signal line between the transmitter! and receiving module run.

1 1. Apparatus according to claim 10, characterized in that the sen- sided HF-connection cable, the receiving side RF connection cable and the RF bypass cable are constructed identically.

12. The device according to claim 11, characterized in that the sum of the lengths of the transmitting side RF connecting cable and the receiving side RF connecting cable corresponds to the length of the RF bypass cable.

13. The apparatus of claim 12 or claim 13, wherein the measuring unit is designed according to claim 2, and a second RF bypass cable connected to the third RF signal output and the third RF signal input, wherein the two RF bypass cables are identical are constructed and that second RF bypass cable has a greater length than the first RF bypass cable.

14. measuring method using a device according to one of claims 10 to 13, characterized in that the at least one RF bypass cable to compensate for temperature errors of the RF connecting cable, and / or the drift of the electronic components of the transmitting and receiving module and / or used to carry out empty measurements.