DE102020100861A1 - Measuring device for determining a dielectric value - Google Patents

Abstract

The invention relates to a measuring device (1) for determining the dielectric value of a medium (2), in which none of the components have to protrude into the medium (2). For this purpose, the measuring device (1) is based on an antenna arrangement (11) which comprises at least two specially arranged coil cores (111, 111 ') of different lengths. A coil (113, 113 ') is wound onto at least one of the coil cores (111, 111') to impress a high-frequency signal (SHF). The dielectric value is determined by tapping off a corresponding received signal rHFan the coil or coils (113, 113 '). This arrangement according to the invention of the magnets (111, 111 ') or the coils (113, 113') allows the antenna arrangement (11) to be implemented flat towards the medium (2), with the near field of the high-frequency signal (SHF ) can nevertheless penetrate sufficiently deep into the medium (2) to determine the dielectric value.

Description

The invention relates to a measuring device for determining a dielectric value of a medium.

In automation technology, in particular for process automation, field devices are often used that are used to record various measured variables. The measured variable to be recorded can be, for example, a level, a flow rate, a pressure, the temperature, the pH value, the redox potential, a conductivity or the dielectric value of a medium in a process plant. To acquire the corresponding measured values, the field devices each include suitable sensors or are based on suitable measurement methods. A large number of different types of field devices are manufactured and sold by the Endress + Hauser group of companies.

The determination of the dielectric value (also known as "dielectric constant" or "relative permittivity") of various media is of great interest for solids as well as for liquid and gaseous filling goods such as fuels, waste water, gases or chemicals, as this value is a reliable one Indicator for impurities, the moisture content, the substance concentration or the substance composition can represent. Possible measuring principles for determining the dielectric value are to measure the amplitude, the phase shift or the signal transit time of high-frequency signals. Here, a high-frequency signal with a defined frequency or within a defined frequency band is coupled into the medium and a corresponding received signal is evaluated with regard to its amplitude, phase position or signal propagation time in relation to the transmitted high-frequency signal. The term “high frequency signal” or “radar” in the context of this patent application refers to corresponding signals with frequencies between 0.1 GHz and 30 GHz.

A phase-based dielectric value measuring device is described, for example, in the publication DE 10 2017 130728 A1 . This makes use of the effect that the signal speed and thus the phase position along a measuring probe depends on the dielectric value of the medium that prevails along the measuring probe. In principle, a distinction is made here between a relative and an absolute phase measurement, with what is known as a quadrant correction being carried out in the case of an absolute phase measurement.

For example, the TDR principle (TDR is an acronym for “Time Domain Reflectometry”) can be used to determine the dielectric value by means of signal propagation time measurement. With this measuring principle, the sensor sends a pulse-shaped high-frequency signal with a frequency between 0.1 GHz and 150 GHz along an electrically conductive measuring probe and measures the duration of the pulse until the reflected high-frequency signal is received. This makes use of the effect that the pulse transit time is dependent on the dielectric value of the substance that surrounds the measuring probe. The functional principle of TDR sensors is described, for example, in the publication EP 0622 628 A2 . TDR sensors are sold in numerous embodiments, for example by the company IMKO Mikromodultechnik GmbH. Another advantage of TDR sensors is that, in addition to the dielectric value, the dielectric loss factor of the material can potentially also be determined.

Regardless of the measuring principle, the measuring probe of the measuring device must protrude into the medium in the common implementation variants so that the medium or its dielectric value has an influence on the phase or transit time measurement. In particular, if the dielectric value is to be measured in narrow pipes or in containers with agitators or something similar, it may not be possible to mount the measuring device appropriately on the container. The invention is therefore based on the object of providing a measuring device for determining the dielectric value of a device in which none of the components have to protrude into the medium.

• - Eine Antennen-Anordnung, bestehend aus:
  • ◯ Zumindest zwei Spulenkernen mit
    • • einer überwiegend geraden Achse, die jeweils eine unterschiedliche Achslänge und einen entsprechenden Achs-Mittelpunkt aufweisen, und mit
    • • endseitigen Abwinklungen an den Achs-Enden,
    wobei die zumindest zwei Spulenkerne derart angeordnet sind,
    • • dass die Achs-Mittelpunkte auf einem gemeinsamen Normalenvektor liegen,
    • • dass die Achsen der Spulenkerne in jeweils einer Ebene, welche jeweils orthogonal zum Normalenvektor verläuft, ausgerichtet sind, und
    • • dass die Abwinklungen in etwa parallel zum Normalenvektor verlaufen, und
    • • dass, sofern das Messgerät mit gen Medium gerichtetem Normalenvektor angeordnet ist, die Spulenkerne mit zunehmender Achslänge weiter vom Medium entfernt sind, und
  • ◯ zumindest einer Spule, die auf einen der Spulenkerne aufgewickelt ist,
• - eine Signalerzeugungs-Einheit, die ausgelegt ist, um in zumindest eine der zumindest einen Spule ein Hochfrequenz-Signal einzukoppeln, und
• - eine Auswertungs-Einheit, die ausgelegt ist, um
  • ◯ aus zumindest einer der zumindest einen Spule ein Empfangssignal auszukoppeln, und um
  • ◯ anhand des Empfangssignals, insbesondere einer Phasenlage oder einer Amplitude des Empfangssignals, den Dielektrizitätswert zu bestimmen.

The invention solves this problem with a measuring device for determining the dielectric value of a medium. For this purpose, the measuring device comprises at least the following components:

• - An antenna arrangement consisting of:
  • ◯ At least two coil cores with
    • • a predominantly straight axis, each with a different axis length and a corresponding axis center point, and with
    • • end bends at the axle ends,
    wherein the at least two coil cores are arranged in such a way
    • • that the center points of the axes lie on a common normal vector,
    • • that the axes of the coil cores are each aligned in a plane which is orthogonal to the normal vector, and
    • • that the bends run roughly parallel to the normal vector, and
    • • that, if the measuring device is arranged with a normal vector directed towards the medium, the coil cores are further away from the medium with increasing axial length, and
  • ◯ at least one coil that is wound onto one of the coil cores,
• a signal generation unit which is designed to couple a high-frequency signal into at least one of the at least one coil, and
• - An evaluation unit which is designed to
  • ◯ to decouple a received signal from at least one of the at least one coil, and to
  • ◯ to determine the dielectric value on the basis of the received signal, in particular a phase position or an amplitude of the received signal.

Either a coil can be wound onto each of the coil cores, or at least that / those coil cores / cores on which no coil is / are wound is / are designed as a permanent magnet. This inventive arrangement of the magnets or the coils allows an antenna arrangement to be realized that closes flatly towards the medium and with which the near field of the high-frequency signal can penetrate the medium sufficiently deep to determine the dielectric value.

In the context of the invention, the term “unit” is understood to mean in principle any electronic circuit that is designed to be suitable for the intended use. Depending on the requirements, it can therefore be an analog circuit for generating or processing corresponding analog signals. However, it can also be a digital circuit such as an FPGA or a storage medium in conjunction with a program. The program is designed to carry out the corresponding process steps or to apply the necessary arithmetic operations of the respective unit. In this context, different electronic units of the dielectric value measuring device in the sense of the invention can potentially also access a common physical memory or be operated by means of the same physical digital circuit.

So that the near field of the high-frequency signal penetrates sufficiently deeply into the medium, it is advantageous if the measuring device comprises four or more coil cores. For the same purpose it is also advantageous if the at least two coil cores are arranged in relation to the normal vector at a distance of at most 1/2 of the respective shorter axial length from one another. In addition, it is advantageous if the at least two coil cores are rotated with respect to the normal vector, in particular by a defined angle to one another. This increases the volume of the penetrated medium. It is advantageous for a symmetrical field distribution if the respective angle is 360 ° divided by twice the number of coil cores, or if the rotation per coil core is monotonous with increasing axis length or with increasing distance from the medium clockwise or counterclockwise increases.

If a coil is wound onto more than one coil core, the measuring device can also include a correspondingly designed phase delay unit by means of which the high-frequency signal can be coupled into the coils with a defined phase shift. The phase delay unit should preferably be designed in such a way that the respective phase shift between the individual coils is 360 ° divided by the number of coils, or that the absolute phase shift in relation to the phase position of the high-frequency signal on the shortest coil core per coil core with increasing axis length increases monotonically. This also causes the high-frequency signal to penetrate deeper into the medium. To achieve this effect, the signal generation unit can also be designed in such a way that the high-frequency signal is coupled into the coil of the coil core with the greatest axial length in relation to the amplitudes of the high-frequency signal at the other coils with the greatest amplitude , or that the high-frequency signal is coupled into the coil of the coil core that has the smallest axial length in relation to the amplitudes of the high-frequency signal at the other coils with the lowest amplitude. It goes without saying that the measuring device must include several coils in such a design.

The frequency with which the high-frequency signal is generated is to be selected in principle depending on the dielectric value measuring range. With a measuring range of the dielectric value between 2 and 140 (in addition to aqueous media, it includes gases with 1 to 1.5 and oily media with 2 to 20), the signal generation unit must be designed accordingly to generate the electrical high-frequency signal with a frequency between 0.1 GHz and 30 GHz. In the case of aqueous media, the dielectric value of which is approximately 80 to 100, the high-frequency signal should preferably be generated at a frequency between 5 GHz and 8 GHz. The axis length of the coil cores is also to be selected depending on the dielectric value measuring range, among other things. Is advantageous in this Relationship when the axis lengths differ by a length difference between 1/5 and 2/5, in particular between 3/10 and 4/10.

• - Einkoppeln des Hochfrequenz-Signals in zumindest eine der zumindest einen Spule,
• - Auskoppeln eines entsprechenden Empfangssignals aus zumindest einer der zumindest einen Spule, und
• - Bestimmung des Dielektrizitätswertes anhand des Empfangssignals.

Corresponding to the dielectric value measuring device according to the invention according to one of the embodiment variants described above, the object on which the invention is based is also achieved by a corresponding method for operating the measuring device. Accordingly, the process comprises at least the following process steps:

• - Coupling of the high-frequency signal into at least one of the at least one coil,
• Decoupling of a corresponding received signal from at least one of the at least one coil, and
• - Determination of the dielectric value based on the received signal.

• 1: Ein erfindungsgemäßes Dielektrizitätswert-Messgerät an einem Behälter,
• 2: einen schematischen Aufbau des erfindungsgemäßen Messgerätes, und
• 3: eine Draufsicht auf die erfindungsgemäße Antennen-Anordnung.

The invention is explained in more detail with the aid of the following figures. It shows:

• 1 : A dielectric value measuring device according to the invention on a container,
• 2 : a schematic structure of the measuring device according to the invention, and
• 3 : a plan view of the antenna arrangement according to the invention.

For a general understanding of the dielectric value measuring device according to the invention 1 is in 1 a schematic arrangement of the measuring device 1 on a container 3 that with a medium 2 is filled, shown: To determine the dielectric value of the medium 2 is the measuring device 1 on the side of a connection on the container 3 , e.g. attached to a flange connection. With the medium 2 it can be liquids such as beverages, paints, cement or fuels such as liquefied gases or mineral oils. However, it is also conceivable to use the measuring device 1 for media in bulk 2 such as grain.

The measuring device 1 can optionally with a parent unit 4th , such as a process control system. "PROFIBUS", "HART", "Wireless HART" or "Ethernet" can be implemented as the interface. This can be used to transmit the dielectric value as an amount or as a complex value with real part and imaginary part. However, other information about the general operating status of the measuring device can also be provided 1 communicated.

As in 1 is shown schematically, comprises the measuring device 1 an antenna arrangement to determine the dielectric value 11 . The antenna arrangement 11 from a wall permeable to electromagnetic high-frequency signals _{SHF in} such a way from the medium 2 disconnected that the meter 1 after installation, closes with a form fit to the inner wall of the container, so that no components of the measuring device 1 inside the container 3 extend.

The antenna arrangement 11 is designed according to the invention in such a way that it sends the high-frequency signal _SHF required to determine the dielectric value into the medium as an electromagnetic near field 2 radiates. As in 2 is based on the antenna arrangement 11 for this on two spools 113 , 113 ' , each on a bobbin 111 , 111 ' are wound up. The coils point 113 , 113 ' or their coil cores 111 , 111 ' a straight axis, the axis lengths I ₁₁₁ , I ₁₁₁ , are each different. How out 2 can be seen, the corresponding axis centers are located m ₁₁₁ , m ₁₁₁ , the axes on a common normal vector ň , the two coil cores 111 , 111 ' are arranged in parallel such that the axes of the coils 113 , 113 ' in parallel planes, which are each orthogonal to the normal vector ň run, are aligned.

At both ends of the axles, the two coil cores comprise 111 , 111 ' end bends 112 , 112 ' by 90 ° each time. The coil cores are accordingly 111 , 111 ' again arranged so that the bends 112 , 112 ' parallel to the normal vector ň run away. In contrast to the in 2 The illustration shown can be the bends 112 , 112 ' also have a rounded transition towards the respective end of the axle.

The two coil cores 111 , 111 ' are within the antenna arrangement 11 according to the invention arranged so that when the measuring device 1 with gene medium 2 directed normal vector ň on the container 3 attached (as it is in 2 is symbolized), the coil cores 111 , 111 ' with increasing axis length I ₁₁₁ < I ₁₁₁ , further from the medium 2 are away. Unless the measuring device 1 is oriented so that the normal vector ň gen medium 2 shows, the bends are accordingly 112 , 112 ' the coil cores 111 , 111 ' gen medium 2 aligned. This inventive design of the antenna arrangement 11 enables the high-frequency signal _SHF to penetrate sufficiently deep into the medium to determine the dielectric value 2 can penetrate without any component of the measuring device 1 in the medium 2 must protrude.

The two coils are controlled 113 , 113 ' at the in 2 shown embodiment of the antenna arrangement 11 from a signal generation unit 11 that generates the high-frequency signal _SHF. The signal generation unit can do this 11 for example on a corresponding High frequency oscillator, such as a voltage controlled oscillator based.

Due to the design of the coils according to the invention 113 , 113 ' their impedances are dependent on the dielectric value of the medium 2 . A received signal r _HF that by the high frequency signal _SHF in the coils 113 , 113 ' is induced, can accordingly be used to determine the dielectric value. At the in 2 The embodiment variant shown is the receive signal r _HF only on the rear, longer spool 113 tapped. This is what this coil is for 113 via a send / receive switch 14th with an evaluation unit 13th connected. In the context of the invention, however, it is also conceivable that the received signal r _HF additionally or alternatively also on the front spool 113 ' to tap. The evaluation unit 13th the real part of the dielectric value based on the phase or the transit time of the received signal r _HF determine. The imaginary part of the dielectric value can be determined via the amplitude or the attenuation of the received signal.

At the in 2 The embodiment variant shown, the high-frequency signal _{SHF is} not in phase in the two coils 113 , 113 ' fed in, but with a defined phase shift φ of preferably 180 °, i.e. 360 ° divided by the number of coils 113 , 113 ' per antenna arrangement. For this purpose is between the signal generation unit 12th and the coils 113 , 113 ' a phase delay unit 15th interposed. The phase delay unit can be implemented 15th for example on the basis of a line branching with signal path lengths of different lengths. The advantage of a phase-shifted control is that the magnetic field of the coils 113 , 113 ' thereby deeper into the medium 2 penetrates and thus the resolution of the dielectric value measurement is increased.

Another way to increase the resolution in this way is in contrast to that in 2 shown embodiment of the antenna arrangement 11 in it, more than two coil cores 111 , 111 ' to use. In this regard, at least four coil cores are ideal 111 , 111 ' which in turn increases with the axis length in relation to the medium 2 are arranged accordingly one behind the other. In this context, it is not essential in the context of the invention that all coil cores 111 , 111 ' a coil 113 , 113 ' is wound up. Rather, only those coil cores need 111 , 111 ' who have no coil 113 , 113 ' include, be designed as permanent magnets. All coil cores 113 , 113 ' on the one reel 113 , 113 ' are wound, can for example also be made of a para- or diamagnetic material.

In 3 is a further embodiment of the antenna arrangement according to the invention 11 shown. The axes of the two coil cores run here 111 , 111 ' not parallel to each other, but the axes of the two coil cores 111 , 111 ' are in relation to the normal vector ň at a defined angle α rotated by 90 ° to each other. This increases the volume of the medium 2 that of the near field of the coils 113 , 113 ' is penetrated, increases. If there are more than two coil cores 111 , 111 ' can the angle α between the individual cores in principle corresponding to 360 °, divided by twice the number of coil cores 113 , 113 ' be designed, for example α = 45 ° with four coils 113 , 113 ' per antenna arrangement. This in turn ensures a field distribution that is as homogeneous as possible.

List of reference symbols

1

Measuring device

2

medium

3

container

4th

Parent unit

11

Antenna arrangement

12th

Signal generation unit

13th

Evaluation unit

14th

Transmit / receive switch

15th

Phase delay unit

111, 111 '

Coil core

112, 112 '

Angulation

113, 113 '

Kitchen sink

I111, I111

Axle length

m111, m111,

Axis center point

rHF

Received signal

SHF

High frequency signal

ň

Normal vector

α

angle

φ

Phase shift

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 102017130728 A1 [0004]
• EP 0622628 A2 [0005]

Claims (15)

Measuring device for determining the dielectric value of a medium (2), comprising: - An antenna arrangement (11), consisting of: ◯ At least two coil cores (111, 111 ') with • a predominantly straight axis, each with a different axis length (I ₁₁₁ , I _{111 '} ) and a corresponding axis center point (m ₁₁₁ , m _111' ), • end bends (112, 112 ') at the axis ends, the at least two coil cores (111, 111') being arranged in this way , • that the axis centers (m ₁₁ , m _{11 '} ) lie on a common normal vector (ň), • that the axes of the coil cores (111, 111') are each in a plane which is orthogonal to the normal vector (ň) , are aligned, and • that the bends (112, 112 ') run approximately parallel to the normal vector (ň), and • that, provided that the measuring device (1) is arranged with the normal vector (ň) directed towards the medium (2), the Coil cores (111, 111 ') with increasing axial length (I ₁₁₁ <I _111' ) further away from the medium ( 2) are removed, and ◯ at least one coil (113, 113 '), which is wound onto one of the coil cores (111, 111'), - a signal generation unit (12) which is designed to be inserted into at least one of the at least a coil (113, 113 ') to couple a high-frequency signal (SHF), and - an evaluation unit (13) which is designed to ◯ from at least one of the at least one coil (113, 113') a received signal (r _HF ) and in order to determine the dielectric value on the basis of the received signal (r _HF ), in particular a phase position or an amplitude of the received signal (r _HF). Measuring device after Claim 1 , a coil (113, 113 ') being wound onto each of the coil cores (111, 111'). Measuring device after Claim 1 , wherein at least that / those coil cores (111, 111 ') on which no coil (113, 113') is / are designed as a permanent magnet, unless on each of the coil cores (111, 111 ') ) a spool (113, 113 ') is wound up. Measuring device according to one of the preceding claims, comprising at least four coil cores (111, 111 '). Measuring device according to one of the preceding claims, wherein the at least two coil cores (111, 111 ') are rotated with respect to the normal vector (ň), in particular by a defined angle (α) with respect to one another. Measuring device after Claim 5 , the respective angle (α) being 360 ° divided by twice the number of coil cores (111, 111 '). Measuring device after Claim 5 or 6th , the rotation per coil core (111, 111 ') increasing _{monotonically with increasing axis length (I 111} , I _111' ) clockwise or counterclockwise. Measuring device according to one of the preceding claims, comprising: - a phase delay unit (15) by means of which the high-frequency signal (S _HF ) can be coupled into the coils (113, 113 ') with a defined phase shift (φ), if more than one Coil core (111, 111 ') a coil (113, 113') is wound. Measuring device after Claim 8 , wherein the phase delay unit (15) is designed such that the respective phase shift (φ) between the individual coils (113, 113 ') is 360 °, divided by the number of coils (113, 113'). Measuring device after Claim 8 or 9 , the phase delay unit (15) being designed in such a way that the absolute phase shift in relation to the phase position of the high-frequency signal (S _HF ) on the shortest coil core (111) per coil core (111, 111 ') with increasing axis length (I ₁₁₁ , I _{111 '} ) increases monotonically. Measuring device according to one of the preceding claims, wherein the signal generation unit (12) is designed to feed the high-frequency signal (S _HF ) into the coil (112) of that coil core (111) which has the greatest axial length (I ₁₁₁ <I _{111 '} ) has, in relation to the amplitudes of the high-frequency signal (S _HF ) to the other coils (112 ') with the greatest amplitude, and / or wherein the signal generation unit (12) is designed to generate the high-frequency signal (S _HF ) into the coil (112 ') of that coil core (111') which has the smallest axial length (I ₁₁₁ <I _{111 '} ), in relation to the amplitudes of the high-frequency signal (S _HF ) at the other coils (112') to be coupled in with the lowest amplitude, provided that the measuring device (1) comprises several coils (112, 112 '). Measuring device according to one of the preceding claims, wherein the axis lengths (I ₁₁₁ , I _{111 '} ) differ by a length difference between 1/5 and 2/5, in particular between 3/10 and 4/10. Measuring device according to one of the preceding claims, wherein the at least two coil cores (111, 111 ') are arranged in relation to the normal vector (ň) at a distance of at most 1/2 of the respectively shorter axis length (I _111' ) from one another. Measuring device according to at least one of the preceding claims, wherein the signal generation unit (12) is designed _{to generate the electrical high-frequency signal (S HF} ) with a frequency between 0.1 GHz and 30 GHz, preferably between 5 GHz and 8 GHz . Method for determining the dielectric value of a medium (2) by means of the measuring device (1) according to one of the preceding claims, comprising the following method steps: coupling the high-frequency signal (S _HF ) into at least one of the at least one coil (111, 111 '), - decoupling a corresponding received signal (r _HF ) from at least one of the at least one coil (113, 113 '), and - determining the dielectric value on the basis of the received signal (r _HF ).

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