DE102017109183A1 - Pressure measuring device - Google Patents

Abstract

The invention relates to a capacitive, membrane-based pressure measuring device (1) for process automation, by means of which, in particular, the provisions relating to explosion protection and heat resistance can be met. It is characterized by: an electrical coupler structure (6) which is in contact with the pressure-dependent capacitor (5); At least one first transmitting / receiving antenna (81) for emitting an electromagnetic signal (S) in the direction of the coupler structure (6), and for receiving an electromagnetic signal (E) reflected by the coupler structure (6); A waveguide (9) arranged between the at least first transmitting / receiving antenna (81) and the coupler structure (6). This makes it possible according to the invention to read the pressure (p) wirelessly by means of an electronic unit (7). This wireless form of pressure value transmission makes it possible to ensure that no active, live components are attached directly to the measuring diaphragm (3). In this case, the spacing of the transmitting / receiving antenna (81, 82) towards the measuring diaphragm (3) by means of the waveguide (9) forms the necessary distance in order to be able to fulfill the requirements applicable in process automation technology.

Description

The invention relates to a pressure measuring device and a corresponding method for determining the pressure by means of the pressure measuring device according to the invention.

In automation technology, in particular in process automation technology, field devices are often used which serve for detecting and / or influencing process variables of corresponding process media. For the detection of process variables, sensors are used which are used, for example, in level gauges, flowmeters, pressure and temperature measuring devices, pH redox potential measuring devices, conductivity meters, etc. They record the corresponding process variables, such as level, flow, pressure, temperature, pH, redox potential or conductivity. A large number of these field devices are manufactured and sold by Endress + Hauser.

In the case of pressure measurement, the pressure is often measured by the deformation of a measuring membrane under one-sided supply of pressure. In this case, the measuring diaphragm can be formed as an integrated part of a semiconductor structure. Such a sensor is for example in the publication WO 03/106952 A2 described. In addition, it is also possible to use ceramics (for example Al ₂ O ₃ ) or corrosion-resistant metals as membrane materials. The pressure chamber, the principle has to be formed on the back side between the membrane and a non-deformable body, is designed depending on whether the pressure sensor is used to determine a relative, differential or absolute pressure. In the case of relative or differential pressure measurement, the pressure chamber is completely closed and subjected to a vacuum or a constant reference pressure. In differential pressure measurement, the pressure chamber is open to that pressure system to whose pressure the differential pressure is to be determined (ie, for example, to the ambient atmosphere).

The mechanical deformation of the measuring diaphragm is converted into an electrical measuring signal by means of the (piezo) resistive or by means of the capacitive principle. This means that one or more resistive or capacitive elements are arranged on the measuring diaphragm whose resistance or capacity changes with the deformation.

In the field of process automation technology, various pressure-measuring devices are already known from the state of the art: In the Utility Model DE 20 2016 101 491 U1 For example, a temperature compensation of the pressure measurement in a ceramic-based pressure measuring device for process automation technology is described. In this case, the temperature is measured at the membrane by an infrared sensor.

However, the use of pressure measuring devices in process automation technology is problematic because of the generally higher requirements with regard to heat resistance and explosion protection. This is due to the often high process temperatures, for example in reactors, as well as the often explosive process atmospheres. However, compliance with these requirements (as defined, for example, in the case of explosion protection in the IEC 60079 series of standards) is only possible to a limited extent in membrane-based pressure measuring devices. A part of the electronic unit for reading out the pressure must be attached directly to the membrane or to the adjoining main body in order to prevent parasitic conduction capacitances and thus measurement errors. However, an electronic unit mounted close to the measuring diaphragm is directly exposed to the process temperature influences. This is on the one hand disadvantageous, as that above a temperature of about 150 ° C, the electronic unit can be irreversibly damaged. On the other hand, the electronic unit with respect to explosion protection aspects because of their electrical energy supply is a potential source of danger.

The publication font EP 1 806 569 A1 describes a capacitive pressure measuring device in which the electronic unit does not have to be arranged directly on the membrane. The capacity is read out by inductive sensors.

Nevertheless, in the case of inductive readout, it is necessary to attach at least the inductive sensor close to the diaphragm so as not to leave the magnetic near field. In addition, the energy consumption is higher due to the high induction currents required than with wired connection of the capacitance, so that here too the explosion protection is reduced. Because of these relationships, it is therefore difficult even in this type of pressure measuring devices to meet the above requirements.

The invention is therefore based on the object to provide a pressure measuring device that meets the requirements in process automation technology.

• - Einen Grundkörper,
• - eine Messmembran, die derart ausgestaltet und auf dem Grundkörper angeordnet ist, dass die Messmembran zum Grundkörper hin eine Druckkammer einschließt, und dass die Messmembran in Abhängigkeit eines zu messenden Druckes, der von einer dem Grundkörper abgewandten Fläche auf die Messmembran wirkt, verformbar ist,
• - einen Kondensator, mit
  • • einer ersten Elektrode, die in der Druckkammer am Grundkörper angeordnet ist, und
  • • einer zweiten Elektrode, die derart an der Messmembran in der Druckkammer angeordnet ist, dass die Kapazität des Kondensators vom Druck abhängig ist.

The invention achieves this object by a pressure measuring device which comprises at least the following components:

• - a basic body,
• a measuring diaphragm which is designed and arranged on the base body such that the measuring diaphragm encloses a pressure chamber towards the base body, and that the measuring diaphragm is deformable in dependence on a pressure to be measured acting on the measuring diaphragm from a surface facing away from the base body,
• - a capacitor, with
  • A first electrode, which is arranged in the pressure chamber on the base body, and
  • • A second electrode, which is arranged on the measuring diaphragm in the pressure chamber such that the capacitance of the capacitor is dependent on the pressure.

• - Eine am Grundkörper angeordnete elektrische Koppler-Struktur, die mit dem Kondensator kontaktiert ist,
• - zumindest eine erste Sende-/Empfangs-Antenne zum Aussenden eines elektromagnetischen Signals in Richtung des Grundkörpers bzw. der Koppler-Struktur, und zum Empfang eines vom Grundkörper und/oder von der Koppler-Struktur reflektierten elektromagnetischen Signals (erfindungsgemäß wäre ebenso der Einsatz einer reinen Sende-Antenne und einer separaten Empfangs-Antenne denkbar),
• - einen zwischen der zumindest ersten Sende-/Empfangs-Antenne und der Koppler-Struktur angeordneten Hohlleiter,
• - eine elektronische Einheit, die zumindest mit der ersten Sende-/Empfangs-Antenne kontaktiert ist. Dabei ist die elektronische Einheit ausgestaltet, um das elektromagnetische Signal zu erzeugen und den Druck anhand des reflektierten, elektromagnetischen Signals zu bestimmen.

In this case, the pressure measuring device according to the invention is characterized by the following components:

• An electrical coupler structure arranged on the main body, which is contacted with the capacitor,
• At least one first transmitting / receiving antenna for emitting an electromagnetic signal in the direction of the base body or the coupler structure, and for receiving an electromagnetic signal reflected from the base body and / or from the coupler structure (according to the invention would also be the use of a pure transmitting antenna and a separate receiving antenna conceivable),
• a waveguide arranged between the at least first transmitting / receiving antenna and the coupler structure,
• - An electronic unit which is contacted at least with the first transmitting / receiving antenna. In this case, the electronic unit is designed to generate the electromagnetic signal and to determine the pressure based on the reflected electromagnetic signal.

By the pressure measuring device according to the invention, the capacity (and concomitantly the pressure) can be read wirelessly by means of electromagnetic signals. A wired or inductive readout is therefore not necessary. This form of wireless transmission allows the sensing diaphragm to be galvanically isolated from any actively powered components (such as the electronic unit) since the sensing diaphragm is the closest electrical component to the process space in which the pressure is being measured.

In this case, the spacing of the transmitting / receiving antenna towards the measuring diaphragm by means of the waveguide forms the necessary distance in order to be able to comply with the regulations regarding explosion protection and heat resistance valid in process automation technology.

• - Einen Hochfrequenz-Generator zur Erzeugung eines elektrischen Hochfrequenz-Signals (beispielsweise als spannungsgesteuerter Oszillator realisiert, der durch einen entsprechenden Spannungsgenerator gesteuert ist),
• - zumindest eine erste Sende-/Empfangsweiche, die derart mit der ersten Sende-/Empfangs-Antenne verschaltet ist, um das elektrische Hochfrequenz-Signal als elektromagnetisches Signal auszusenden, und das reflektierte elektromagnetische Signal einzukoppeln, und
• - einen Microcontroller oder eine entsprechend geeignete elektrische Vorrichtung, der mittels des reflektierten, eingekoppelten Signals den Druck ermittelt.

In a first, very simple implementation variant of the pressure measuring device according to the invention, the electronic unit thereof comprises the following components:

• A high-frequency generator for generating a high-frequency electrical signal (realized, for example, as a voltage-controlled oscillator, which is controlled by a corresponding voltage generator),
• - At least a first transmitting / receiving switch, which is so connected to the first transmitting / receiving antenna to emit the high-frequency electrical signal as an electromagnetic signal, and couple the reflected electromagnetic signal, and
• - A microcontroller or a correspondingly suitable electrical device which detects the pressure by means of the reflected, coupled signal.

• - innerhalb des Frequenzbandes zumindest ein Amplituden-Minimum des reflektierten hochfrequenten elektromagnetischen Signals in Abhängigkeit der Frequenz ermittelt,
• - eine korrespondierende Frequenz des Amplituden-Minimums ermittelt, und
• - den Druck anhand der Frequenz des zumindest einen Amplituden-Minimums bestimmt.

In particular, in this simple implementation variant of the pressure measuring device, it is possible to determine the capacity (and thus the pressure) by the high-frequency generator is designed analogous to the FMCW radar-based distance measurement method so that it generates the electrical high-frequency signal at a frequency , which changes in time within a frequency band, in particular linear. This is used the effect that the coupler structure in conjunction with the capacitor forms a resonant circuit with a pressure-dependent natural frequency. By determining the intrinsic frequency can be inferred accordingly to the pressure. The natural frequency can in turn be determined if it is in the frequency band of the emitted electromagnetic signal, since due to the natural frequency of the resonant circuit, a frequency-dependent amplitude minimum of the reflected high-frequency electromagnetic signal is formed. Accordingly, the microcontroller in this case is preferably configured such that it

• at least one amplitude minimum of the reflected high-frequency electromagnetic signal as a function of the frequency is determined within the frequency band,
• - Finds a corresponding frequency of the amplitude minimum, and
• - Determines the pressure based on the frequency of the at least one amplitude minimum.

• - einen Signalteiler, der verschaltet ist, um das elektrische Hochfrequenz-Signal in einen ersten Signalpfad und einen zweiten Signalpfad aufzuteilen, wobei die erste Sende-/Empfangsweiche im ersten Signalpfad angeordnet ist,
• - eine zweite Sende-/Empfangsweiche, die im zweiten Signalpfad verschaltet ist (beide Sende-/Empfangsweichen können bspw. als Zirkulator oder als Koppler, insbesondere als Richtkoppler, realisiert sein),
• - eine zweite Sende-/Empfangs-Antenne, die an die zweite Sende-/Empfangsweiche angeschlossen ist, wobei die zweite Sende-/Empfangsweiche ausgestaltet ist, um das das von der zweiten Sende-/Empfangs-Antenne empfangene, reflektierte Signal in den zweiten Signalpfad einzukoppeln, und
• - einen Mischer, der mit der ersten Sende-/Empfangsweiche und der zweiten Sende-/Empfangsweiche verschaltet ist, um das in den ersten Signalpfad eingekoppelte, reflektierte Signal mit dem reflektierten

In an expanded implementation of the pressure measuring device according to the invention, the electronic unit additionally comprises the following components:

• a signal divider which is connected in order to divide the high-frequency electrical signal into a first signal path and a second signal path, wherein the first transceiver is arranged in the first signal path,
• a second transmitting / receiving diplexer which is connected in the second signal path (both transmitting / receiving switches can be realized, for example, as a circulator or as a coupler, in particular as a directional coupler),
• a second transceiver antenna connected to the second transceiver, the second transceiver being configured to transfer the reflected signal received from the second transceiver antenna to the second transceiver Coupling signal path, and
• - A mixer, which is connected to the first transmitting / receiving switch and the second transmitting / receiving switch to the coupled in the first signal path, the reflected signal with the reflected

Signal, which is coupled into the second signal path to mix. In this case, the microcontroller determines the pressure at least in this implementation variant by means of the mixed signal.

On the one hand, this extension offers the advantage that the frequency of the mixed signal, with a corresponding design of the electromagnetic signal to be transmitted, changes linearly with the capacitance of the capacitor or the pressure. A determination of the frequency of the mixed signal is in turn technically very easy to implement. On the other hand, the use of two transmit / receive antennas makes it possible to compensate for the temperature-related errors by thermal expansion of the waveguide. However, in this case the second transmitting / receiving antenna is preferably to be controlled such that the electromagnetic signal emitted by it is reflected by the coupler structure unaffected on the base body or at the transition between the base body and the waveguide. As a result, the reflected signal is altogether composed of a component independent of the coupler structure and a component dependent on the coupler structure.

For this purpose, suitable options for driving are that the first transmitting / receiving antenna and the second transmitting / receiving antenna are connected in such a way with the electronic unit to the electromagnetic signal to the second transmitting / receiving antenna with respect to first transmitting / receiving antenna with a predefined phase shift (in particular 90 °) emit. Additionally or alternatively, the first transmit / receive antenna and the second transmit / receive antenna can also be connected to the electronic unit in such a way that the electromagnetic signal at the second transmit / receive antenna is related to the first transmit and receive antenna. / Receiving antenna is emitted with a different mode. Accordingly, it is necessary for the thermal decoupling in both cases, so in deviating mode or shifted polarization between the first transmitting / receiving antenna and the second transmitting / receiving antenna, the coupler structure so that they are of the Mode or the polarization of the emitted by the second transmitting / receiving antenna signal is not excited.

In particular, for the expression of the desired mode (s) of the emitted electromagnetic signal, it is of further advantage if the waveguide has a round cross-section with a defined inner diameter. The further influencing factor on the inner diameter forms the frequency of the electromagnetic signal to be emitted: the higher the frequency, the smaller the inner diameter is to be dimensioned. For the sake of compact dimensions of the Holleiters, it is therefore advantageous if the emitted electromagnetic signal has a frequency of at least 100 MHz, in particular greater than 1 GHz. In order to make the waveguide compact even with respect to its length, it is additionally useful according to the invention if a material with a dielectric constant greater than 1, in particular PE, PP, Teflon or glass, is introduced into the waveguide (corresponding to the increased propagation velocity of the emitted and reflected light Signal decreases the necessary length of the waveguide for coupling between the first transmitting / receiving antenna and the coupler structure). In addition, the incorporation of such a material, of course, potentially increases the explosion protection, as the material acts accordingly as a barrier to the process space in which the pressure is to be measured. To reduce transmission losses, it is also expedient to dimension the waveguide so that it has a length which is at most four times the inner diameter and / or at least a quarter of a wavelength of the electromagnetic signal.

For the desired coupling between the coupler structure and the first transmitting / receiving antenna with the coupler structure, it may also be advantageous if the coupler structure is mounted approximately centrally with respect to the cross section of the waveguide. For this purpose, the cross section, in particular the inner diameter of the waveguide with respect to the frequency of the electromagnetic signal to be dimensioned so that the electromagnetic signal is transmitted at least in the TE ₀₁ mode, the TE ₁₁ mode or the TM ₁₁ mode. This is because the intensity maximum of the electromagnetic signal is approximately centered when emitted in the TE ₀₁ mode, the TE ₁₁ mode or the TM ₁₁ mode (in relation to the inner diameter of the waveguide), so that an efficient coupling to the coupler structure ensues , Alternatively to a (partial) annular structure, an embodiment as a fractal structure would also be conceivable.

Above all, in order to dimension the pressure measuring device according to the invention as compact as possible, it is further preferable, the first transmitting / receiving antenna, the second transmitting / receiving antenna, and / or the coupler structure as a planar array consisting of a first ring segment and an approximately opposite arranged, second ring segment to design.

According to the inventive approach, at least that electrode of the capacitor which is connected to the coupler structure, galvanically separated from the transmitting / receiving antennas, so that the purely electromagnetic coupling to the coupler structure is possible. In addition, however, it is also advantageous if, in addition, the second electrode of the capacitor is also galvanically isolated from the first transmitting antenna or the electronic unit (and also in the presence of the second transmitting / receiving antenna). As a result, in particular the electromagnetic compatibility of the pressure measuring device can be reduced with respect to parallary electromagnetic interference signals.

• - Erzeugung eines elektrischen Hochfrequenz-Signals durch einen Hochfrequenz-Generator, wobei die Frequenz des elektrischen Hochfrequenz-Signals innerhalb eines Frequenzbandes, insbesondere linear, geändert wird,
• - Aussenden des elektrischen Hochfrequenz-Signals über zumindest eine erste Sende-/Empfangs-Antenne als hochfrequentes elektromagnetisches Signal,
• - Empfang des hochfrequenten elektromagnetischen Signals nach Reflektion an einer Koppler-Struktur und/oder einem Grundkörper durch zumindest die erste Sende-/Empfangs-Antenne,
• - Erfassung von zumindest einem Amplituden-Minimum des reflektierten hochfrequenten elektromagnetischen Signals in Abhängigkeit der Frequenz mittels eines Mikrocontrollers,
• - Bestimmung der Frequenz des zumindest einen Amplituden-Minimums, und
• - Bestimmung des Druckes anhand der Frequenz des zumindest einen Amplituden-Minimums.

According to the embodiment of the pressure measuring device according to the invention with only one required transmitting-receiving antenna, a method according to the invention for determining the pressure consists of at least the following method steps:

• - Generation of a high-frequency electrical signal by a high-frequency generator, wherein the frequency of the electrical high-frequency signal within a frequency band, in particular linear, is changed,
• Transmitting the high-frequency electrical signal via at least one first transmitting / receiving antenna as a high-frequency electromagnetic signal,
• Reception of the high-frequency electromagnetic signal after reflection at a coupler structure and / or a base body by at least the first transmitting / receiving antenna,
• Detecting at least one amplitude minimum of the reflected high-frequency electromagnetic signal as a function of the frequency by means of a microcontroller,
• Determining the frequency of the at least one amplitude minimum, and
• - Determining the pressure based on the frequency of the at least one amplitude minimum.

• - Erzeugung eines elektrischen Hochfrequenz-Signals durch einen Hochfrequenz-Generator, wobei die Frequenz des elektrischen Hochfrequenz-Signals innerhalb eines Frequenzbandes, insbesondere linear, geändert wird,
• - Aufteilen des elektrischen Hochfrequenz-Signals in einen ersten Signalpfad und einen zweiten Signalpfad,
• - Aussenden des elektrischen Hochfrequenz-Signals über eine erste Sende-/Empfangs-Antenne als hochfrequentes elektromagnetisches Signal, wobei das elektrische Hochfrequenz-Signal über eine im ersten Signalpfad angeordnete Sende-/Empfangsweiche in die erste Sende-/Empfangs-Antenne eingekoppelt wird,
• - Aussenden des elektrischen Hochfrequenz-Signals über eine zweite Sende-/Empfangs-Antenne als hochfrequentes elektromagnetisches Signal, wobei das elektrische Hochfrequenz-Signal über eine im zweiten Signalpfad angeordnete Sende-/Empfangsweiche in die zweite Sende-/Empfangs-Antenne eingekoppelt wird,
• - Empfang des hochfrequenten elektromagnetischen Signals nach Reflektion an der Koppler-Struktur und/oder dem Grundkörper durch die erste Sende-/Empfangs-Antenne und die zweite Sende-/Empfangs-Antenne,
• - Mischen des von der ersten Sende-/Empfangs-Antenne empfangenen, reflektierten Signals mit dem von der zweiten Sende-/Empfangs-Antenne empfangenen, reflektierten Signals mittels des Mischers, und
• - Bestimmung des Druckes anhand der Differenzfrequenz s_p des gemischten Signals.

When using the pressure measuring device according to the invention in an embodiment with two transmitting / receiving antennas, a corresponding method according to the invention for determining the pressure comprises at least the following method steps:

• Generating a high-frequency electrical signal by a high-frequency generator, the frequency of the high-frequency electrical signal being changed within a frequency band, in particular linearly,
• Splitting the high-frequency electrical signal into a first signal path and a second signal path,
• Transmitting the electrical high-frequency signal via a first transmitting / receiving antenna as a high-frequency electromagnetic signal, wherein the electrical high-frequency signal is coupled into the first transmitting / receiving antenna via a transmitting / receiving switch arranged in the first signal path,
• Emitting the electrical high-frequency signal via a second transmitting / receiving antenna as a high-frequency electromagnetic signal, wherein the electrical high-frequency signal is coupled via a arranged in the second signal path transmitting / receiving switch in the second transceiver antenna,
• Reception of the high-frequency electromagnetic signal after reflection at the coupler structure and / or the base body by the first transmitting / receiving antenna and the second transmitting / receiving antenna,
• Mixing the reflected signal received from the first transmitting / receiving antenna with the reflected signal received from the second transmitting / receiving antenna by means of the mixer, and
• - Determining the pressure based on the difference frequency s _{p of} the mixed signal.

• 1: Eine Schnittansicht einer erfindungsgemäßen Druckmesseinrichtung,
• 2a: ein Diagramm zur Veranschaulichung eines möglichen Verfahrens zur Druck-Bestimmung mittels der erfindungsgemäßen Druckmesseinrichtung.
• 2b: eine vorteilhafte Anordnung einer Koppler-Struktur zu zwei Sende-/Empfangs-Antennen,
• 2c: eine Detailansicht zur Koppler-Struktur,
• 3: eine vorteilhafte Realisierung einer elektronischen Einheit der Druckmesseinrichtung.

The invention will be explained with reference to the following figures. It shows:

• 1 : A sectional view of a pressure measuring device according to the invention,
• 2a : a diagram for illustrating a possible method for pressure determination by means of the pressure measuring device according to the invention.
• 2 B : an advantageous arrangement of a coupler structure to two transmitting / receiving antennas,
• 2c : a detailed view of the coupler structure,
• 3 an advantageous realization of an electronic unit of the pressure measuring device.

1 shows a pressure measuring device according to the invention 1 for measuring a pressure p in the field of process automation technology. In this application, the pressure to be measured extends p potentially over a very wide range from 1 mbar up to 40 bar. As is customary in state-of-the-art capacitive or resistive pressure measurement, the pressure measuring device is based 1 on a base body 2 to which a measuring diaphragm 3 is appropriate. The main body 2 is designed so that between it and the measuring membrane 3 a cavity 4 is included. This measuring principle becomes the pressure to be measured p the surface of the measuring membrane 3 fed to the cavity 4 or the main body 2 turned away. Accordingly, this area is the measuring diaphragm 3 after installation in the process plant a process room in which the pressure p to be determined, facing. In this case, the process space can not only be a container or a chamber, but, for example, also a pipe of a process plant.

Depending on whether the pressure measuring device 1 is used for absolute or relative pressure measurement, is the cavity 4 either with vacuum or with a constant reference pressure applied. Not shown is a possible interpretation of the pressure measuring device 1 for differential pressure measurement, where the cavity 4 an opening for connection to a corresponding differential pressure system (for example, the ambient atmosphere).

As is already known in capacitive pressure measurement, is located in the cavity 4 a capacitor 5 , This is the capacitor 5 from a first electrode 5a on the main body 2 is arranged, and a second electrode 5b that of the first electrode 5a in the cavity 4 approximately opposite to the membrane 3 is arranged, formed. The capacitance C of the capacitor 5 can be approximately described by the formula for plate capacitors: $$\text{C}=\frac{{\epsilon }_0{\epsilon }_r{r}^2}{l}$$

In relation to the pressure measuring device 1 l corresponds to the distance between the two electrodes 5a . 5b of the capacitor 5 , or the height of the cavity 4 , In the case of a silicon-based measuring membrane 5 in the undeflected state, a distance l of at least approx. 1 μm is selected by default, while the distance l when using ceramic is dimensioned with at least approx. 20 μm. For r it is in the case of round design of the electrodes 5a . b around its radius. By the in 1 As shown arrangement, the capacitor undergoes 5 a capacity change when the pressure p that changes to the area of the membrane 3 that the cavity 4 or the main body 2 turned away, acts. As from the formula to the capacitance C of the capacitor 5 is suggested, it is to increase the capacity change given a change in pressure p also known as the cavity 4 with a dielectric material (for example corresponding oils or comparable fluids) having a dielectric value ε _r greater than 1 to fill. Typically, the capacitor becomes 5 designed so that its capacity C is in the range of a few pF up to about 100 nF.

zunutze gemacht werden. Entsprechend der Formel hat unter anderem das Elastizitätsmodul E des verwendeten Messmembranmaterials (vorwiegend Silizium oder eine Keramik, insbesondere Al₂O₃) Einfluss auf die Membranauslenkung Δl. Außerdem liegt der Formel die Annahme zugrunde, dass die Messmembran 3 kreisrund mit einem definierten Durchmesser d ausgelegt ist. Bei dem in 1 dargestellten Aufbau entspricht Δl der maximalen Änderung des Abstandes l zwischen den Elektroden 5a,b in der Mitte der Messmembran 3. Außerdem kann zur Bemaßung der Dicke t der Messmembran kann die Formel $$\mathrm{\Delta }{\text{l}}_{max}=\frac{1}{2}\text{l@}{p}_{max}$$

als Bemessungsgrundlage verwendet werden.Thus, the capacitance C of the capacitor 5 a decided pressure value p be assigned, for example, after appropriate calibration of the pressure measuring device 1 , The measuring range of the deliverable pressure depends on this p in addition to the dimensioning of the capacitance C of the capacitor 5 essentially from the design of the Meßmembrangeometrie (for example, a Unterdimensionierung the thickness t the measuring membrane 3 at too high pressure p lead to a membrane rupture; When oversizing the thickness t is the deflection Δl of the measuring diaphragm 3 too small to change the capacitance of the capacitor 5 to effect). In the case of silicon, the diameter becomes d the measuring membrane 3 in practice, it measures approx. 1.5 mm, in the case of ceramics the diameter becomes d 1 cm slightly higher. For a suitable design of the geometry of the measuring diaphragm 3 depending on the pressure p can also derive from the static derivable relationship $$\mathrm{\Delta }\text{l}\left(\text{p}\right)=\text{p}*\frac{{\mathrm{<figure-callout\; id="4"\; label="d"\; filenames="DE102017109183A1\_0007.png"\; state="\{\{state\}\}">d</figure-callout>}}^4}{6\mathrm{<figure-callout\; id="3"\; label="e\; t"\; filenames="DE102017109183A1\_0007.png"\; state="\{\{state\}\}">e\; </figure-callout>}{t}^{}{}^3}$$

be exploited. According to the formula, among other things, the elastic modulus E of the measuring membrane material used (predominantly silicon or a ceramic, in particular Al ₂ O ₃ ) has an influence on the membrane deflection Δl. In addition, the formula is based on the assumption that the measuring membrane 3 circular with a defined diameter d is designed. At the in 1 shown construction corresponds to .DELTA.l the maximum change of the distance l between the electrodes 5a , b in the middle of the measuring membrane 3 , In addition, for dimensioning the thickness t the measuring membrane can be the formula $$\mathrm{\Delta }{\text{l}}_{max}=\frac{1}{2}\text{l @}{p}_{max}$$

be used as the basis of assessment.

According to the invention, the capacitor 5 , as in 1 shown, for the transmission of its capacity neither conducted nor inductive with an electrical unit 7 connected. The transmission of the capacitance value to the electrical unit 7 takes place in the meaning of the invention by means of appropriate signals S _HF . E _HF in the form of electromagnetic waves. This type of transmission offers the advantage that the electronic unit 7 does not have to be arranged directly on the capacitor, but only at a distance at which a sufficient electromagnetic coupling is ensured. Thus, the field of application of the pressure measuring device according to the invention is not limited to otherwise usual process temperatures of 150 ° C.

To implement the idea according to the invention is the capacitor 5 , as in 1 shown to a passive coupler structure 6 contacted. For transmission by means of electromagnetic signals S _HF . E _HF uses the pressure measuring device 1 According to the invention, the effect that the impedance and thus the natural frequency of the coupler structure 6 from the capacitance of the capacitor 5 depends (according to the invention, the coupler structure is different 6 to inductive transmission coils basically in that by means of the coupler structure 6 analogous to single-pole antennas no closed DC circuit is formed, since the coupler structure 6 represents only one electrical pole, or an arrangement of several poles. As a result, unlike coils, not only an electromagnetic near but also a corresponding far field is coupled out.

The natural frequency or the capacity (and thus the pressure p ) of this passive coupler structure 6 can be read in a very simple implementation of the inventive idea, for example, by an electromagnetic signal S _HF with changing frequency f (Analogous to the "FMCW" radar based distance measuring method preferably with an approximately linear frequency ramp within a predetermined frequency range f ₁ - f ₂ ) of at least one transmitting / receiving antenna 81 . 82 in the direction of the coupler structure 6 is sent out. As in 2a can be represented by the coupler structure 6 reflected (or the corresponding, absorbed) portion E _HF from corresponding transmit / receive antennas 81 . 82 be received and in and in relation to the frequency f of the transmitted signal S _HF be set. In this case, the frequency is the same f _min in which a minimum share E _HF the electromagnetic signal S _HF is reflected (or the frequency of the maximum absorption) of the natural frequency of the coupler structure 6 , As in 2a is shown, this frequency decreases f _min with increasing pressure p ,

At the in 1 The embodiment shown is the coupler structure 6 planar on a surface of the main body 2 arranged, that of the first electrode 51 of the capacitor 5 turned away. The planar arrangement makes it possible, for example, the coupler structure 6 as a track or to use microstructuring metallization technologies, such as sputtering or CVD ("Chemical Vapor Deposition") to use.

Adjacent to that surface of the main body 2 at the coupler structure 6 is disposed, closes a first end portion of a waveguide 9 at. In this case, the longitudinal axis of the waveguide extends 9 approximately orthogonal to this surface. At the second, opposite end region of the waveguide 9 are a first transmit / receive antenna 81 and a second transceiver antenna 81 appropriate. Corresponding to the coupler structure 6 is the waveguide 9 also orthogonal to two planar configured transmit / receive antennas 81 . 82 aligned. As a result, an effective electromagnetic coupling of the electromagnetic signals S _HF . E _HF between the two transmit / receive antennas 81 . 82 and the coupler structure 6 favors.

As the detection and transmission of the pressure p According to the invention on the basis of an electromagnetic signal S _HF takes only a comparatively low signal transmission power of less than 1mW, preferably in the range of less than about 100 uW are applied compared to inductive readout. As a result, the pressure measuring device 1 For example, it can be supplied and read out via a power-limited 4-20 mA interface. Accordingly, to set the above-mentioned 100 μW transmission power at a transmission / reception efficiency of the entire high-frequency electronics (that is, the two transmission / reception antennas 81 . 82 with an efficiency of up to 95% and the electronic unit 7 with correspondingly lower efficiency about 10%) of about 20% a momentary power input by the electronic unit 7 of 0.5mW (which is within the range of the 4-20mA transmittable power). The mean required power input can be further reduced if it is not measured continuously, but only cyclically during a limited measurement time t _mess and at a predetermined measurement rate R ,

The minimum required measurement time t _{mess, min} then results according to the Abtatst theorem by means of the relationship: $$t_{mess.min}=\frac{2*Q}{f}=R_{ma\mathrm{<figure-callout\; id="1"\; label="x"\; filenames="DE102017109183A1\_0007.png,DE102017109183A1\_0009.png"\; state="\{\{state\}\}">x</figure-callout>}}^1$$

As can also be seen from the formula, the minimum required measuring time t _{mess, min} also results directly in the measuring rate R in which the pressure value in the case of the pressure measuring device according to the invention 1 maximum can be determined or updated: If the quality Q the coupler structure 6 Thus, for example, Q = 4 * 10 ³ (an embodiment of the coupler structure with a quality of minimal Q = 5 * 10 ³ would be advantageous according to the invention) and the frequency f the emitted electromagnetic signal S _HF is in the range of 10 GHz, results in a maximum settable measuring rate R of 1.25 MHz or a minimum measuring time t _{mess, min} of 80 μs (finally high signal propagation times in the electronic unit and further parasitic effects are disregarded here). Within the scope of the invention, however, it would also be conceivable for the purpose of further power reduction, with a significantly lower measurement rate R for example, only 1 Hz (or possibly even lower) to work.

beträgt. Diese Länge verkürzt sich entsprechend durch Füllung des Hohlleiters 9 mit einem dielektrischen Material (bedingt durch die Änderung der Ausbreitungsgeschwindigkeit c), das einen Dielektrizitätswert größer 1 aufweist. Zur Verringerung von Übertragungsverlusten ist die Länge des Hohlleiters 9 außerdem vorzugsweise mit maximal dem Vierfachen des Innendurchmessers d des Hohlleiters 9 zu bemessen. Die Bemaßung dieser Länge bewirkt im Sinne der Erfindung die thermische Entkopplung der elektronischen Einheit 7 von der Temperatur, die am Ort des zu messenden Druckes p herrscht. Ein dielektrisches Material, welches in den Hohlleiter 9 eingebracht ist und zudem thermisch isolierend wirkt, würde also im Sinne der Erfindung die thermische Entkopplung weiter fördern.For the purpose of effective electromagnetic coupling is also the length of the waveguide 9 preferably in dependence of the frequency f the emitted electromagnetic signal S _HF to measure. It is favorable if the length along the longitudinal axis of the waveguide 9 almost a quarter of the wavelength λ (or an integer multiple n thereof) according to $$\mathrm{\lambda }=\frac{c}{f}$$

is. This length is shortened accordingly by filling the waveguide 9 with a dielectric material (due to the change of the propagation velocity c ) having a dielectric value greater than 1. To reduce transmission losses is the length of the waveguide 9 in addition, preferably at most four times the inner diameter d of the waveguide 9 to measure. The dimensioning of this length causes the purposes of the invention, the thermal decoupling of the electronic unit 7 from the temperature at the location of the pressure to be measured p prevails. A dielectric material, which in the waveguide 9 is introduced and also acts thermally insulating, so would further promote thermal decoupling in the context of the invention.

The required coupling between the two transmit / receive antennas 81 . 82 and the coupler structure 6 has the hollow body 9 in addition to have at least one conductive inner wall. In the context of the invention, the cross-sectional shape of the waveguide per se is not predetermined. The cross section may for example be designed rectangular. Due to the simple manufacturability and a round cross-section with a defined diameter D preferable. The diameter can be D especially so on the frequency f the electromagnetic signal S _HF be tuned that the electromagnetic signal S _HF in defined modes, preferably in the TE ₀₁ mode, the TE ₁₁ mode or the TM ₁₁ mode, is transmitted. Above all, the expression of these three modes lends itself to, since their intensity maximum in relation to the cross section of the waveguide 9 formed in the middle when the two transmit / receive antennas 81 . 82 are arranged symmetrically to the center of the waveguide cross-section. Therefore it is, as in 1 illustrated, advantageous that the coupler structure 6 in relation to the cross section of the waveguide 9 is centrally located approximately.

gegeben. Dabei ist k_m eine von der jeweils gewählten Mode abhängige Konstante, die sich aus entsprechender Lösung der allgemein bekannten Bessel-Funktion ergibt. Im Falle der TE₁₁-Mode beträgt k_M = 1.841 (k_M = 2.405 bei TM₀₁; k_M = 3.054 bei TE₂₁, k_M = 3.83171 bei TM₁₁; k_M = 4.2012 bei TE₃₁; k_M = 5.136 bei TM₂₁; k_M = 5.317 bei TE₄₁; k_M = 5.331 bei TE₁₂; und k_M = 5.52 bei TM₀₂).The choice of the diameter D in relation to the frequency f the electromagnetic signal S _HF and the fashion to be imprinted is by context $$D=\frac{k_M*c}{\pi *f}$$

given. Here, k _{m is} a dependent of the selected mode constant, resulting from a corresponding solution to the well-known Bessel function. In the case of the TE ₁₁ mode, k _M = 1.841 (k _M = 2.405 for TM ₀₁ , k _M = 3.054 for TE ₂₁ , k _M = 3.83171 for TM ₁₁ , k _M = 4.2012 for TE ₃₁ , k _M = 5.136 TM ₂₁ , k _M = 5,317 for TE ₄₁ , k _M = 5,331 for TE ₁₂ , and k _M = 5:52 for TM ₀₂ ).

From the above formula it follows that the diameter to be selected D with increasing frequency f the electromagnetic signal S _HF decreases and increases with increasing fashion. Thus, the pressure measuring device 1 be made more compact overall. Therefore, it is obvious, the frequency f the electromagnetic signal S _HF as high frequency as possible, so interpreted for example with at least 100 MHz. Technically feasible is also a frequency in the radar range with more than 1 GHz, so for example 26 GHz. Also more than 100 GHz are conceivable. At a frequency of 26 GHz, the TE ₁₁ mode has a compact diameter d of 14 mm.

At the in 1 Shown embodiment serve both transmit / receive antennas 81 . 82 for emitting the electromagnetic signal S _HF and for receiving the reflected electromagnetic signal E _HF (According to the invention, the use of only a single transmitting / receiving antenna would already be used 81 auseichend; Alternatively, it would also be conceivable to use a pure transmitting antenna and a separate receiving antenna).

The use of two transmit / receive antennas 81 . 82 allows decoupling of the reflected electromagnetic signal E _HF contained pressure value p from the thermal expansion of the pressure measuring device 1 , or in particular of the thermal expansion of the waveguide 9 , In this case, the second transmitting / receiving antenna is used 82 to that, the electromagnetic signal S _HF send out so that it from the coupler structure 6 unaffected (at the base body 2 or at the transition between the base body 2 and the waveguide 9 ) is reflected. This sets the reflected signal E _HF from one of the coupler structure 6 independent and one of the coupler structure 6 dependent share together and can be adjusted accordingly by the electronic unit 7 are processed.

The sending out of the coupler structure 6 unaffected electromagnetic signal S _HF through the second transceiver antenna 82 can be carried out according to the invention in two different ways:

The second transmit / receive antenna 82 can be controlled so that the signal emitted by it S _HF is transmitted either in a different mode and / or in (preferably 90 °) twisted polarization (with respect to that of the first transceiver antenna 81 emitted electromagnetic signal S _HF ). The following combinations of different transmission through the two transmit / receive antennas 81 . 82 are advantageous in this case: First transmission / reception antenna 81 Second transmission / reception antenna 82 TE ₀₁ Fashion TE ₄₁ fashion TE ₁₁ fashion TM ₁₁ Mode, rotated by 90 ° TE ₁₁ fashion TE ₁₁ Mode, rotated by 90 ° TE ₄₁ fashion TM ₀₂ Mode TE ₂₁ fashion TE ₂₂ Fashion TE ₃₁ Fashion TE ₃₁ mode, rotated by 30 ° TE ₂₁ fashion TE21 ₂₁ Mode, twisted 90 °

As in 2 B is shown, it is also advantageous, the reflection of the second transmitting / receiving antenna 82 emitted electromagnetic signal S _HF amplify by the coupler structure 6 on the body 2 around a (galvanic isolated) reference structure 6c is extended. Here is the reference structure 6c preferably to be designed so that they in particular the mode of the second transmitting / receiving antenna 82 emitted signal S _HF is stimulated.

For reading the reflected signal E _HF and for subsequent determination of the pressure p can when emitting the electromagnetic signal S _HF in turn, the effect can be used in two different modes or with different polarization, that the first transmitting / receiving antenna 81 only the reflected signal E _HF in that mode and / or with that polarization receives whose mode and / or polarization emitted by it electromagnetic signal S _HF (The same applies to the second transmitting / receiving antenna 82 ).

To an electromagnetic signal S _HF that through the second transmit / receive antenna 82 By 90 ° twisted polarized is emitted to cause this electromagnetic signal S _HF unaffected by the coupler structure 6 must reflect the coupler structure 6 accordingly (to the second transmitting / receiving antenna 82 ) can be arranged. A suitable design variant is in 2 B shown:

As in 1 already indicated, illustrated 2 B a concrete embodiment of the pressure measuring device 1 with two transmitting / receiving antennas 81,82 and a coordinated design of the coupler structure 6 , For all three components 6 . 81 . 82 a planar arrangement is proposed, each consisting of a first ring segment 81a . 82a . 6a and an approximately oppositely disposed second ring segment 81b . 82b . 6b are / is. Here are the two transmit / receive antennas 81 . 82 designed as a quasi-closed ring. These are the two opposite ring segments 81a, b . 82a, b of the two transmit / receive antennas 81 . 82 arranged such that in each case alternately a ring segment 81a, b of the first transmitting / receiving antenna 81 to a ring segment 82a, b of the second transceiver antenna 82 connected to each other, and vice versa. By this arrangement of the two transmitting / receiving antennas 81 . 82 to each other is rotated by 90 ° polarization of the emitted electromagnetic signal S _HF between the two transmit / receive antennas 81 . 82 reached. For sufficient coupling to the coupler structure 6 are the two transmit / receive antennas 81 . 82 or their ring segments 81a, b ; 82a, b be interpreted as having a sufficient transmission / reception efficiency of more than 15% in particular.

Similarly, the coupler structure 6 is in two parts with opposite ring segments 6a , b formed, wherein the ring segments 6a, b the coupler structure 6 in relation to the longitudinal axis of the waveguide 9 about 90 ° twisted to the two ring segments 82a, b the second transmitting / receiving antenna 81 are arranged (thus, the ring segments 6a , b of the coupler structure 6 in relation to the longitudinal axis of the waveguide 9 approximately congruent to the ring segments 81a, b the first transmitting / receiving antenna 81 ). The exact angle Orientation or position is, for example, by means of appropriate simulation of the modes used and the length of the waveguide 9 to make dependent. Corresponding to the two transmit / receive antennas 81 . 82 For reasons of good coupling, the coupler should be dimensioned such that it has a quality of at least 4000.

By 2 B it becomes clear that in the case of the coupler structure 6 the contacting of each of the two ring segments 6a , b to the condenser 5 at least partially via a likewise planar electrical line in the plane of the respective ring segment 6a , b must be done. In this case, it is preferable in accordance with the invention to provide the respective planar electrical line with a delay structure dL, in order to prevent the planar line from acting as a parasitic resonator which transmits the reflected signal E _HF falsified. A possible execution with delay structure is in 2c shown: The delay structure dL is for this, as in 2c imaged, at least partially meander-shaped. Here, at least one straight line segment of the meandering delay structure dL has a length corresponding to 1/8 of the wavelength of the electromagnetic signal S _HF to prevent the effect of the electrical conduction as a parasitic resonator. As in 2c in turn, the delay structure can turn over a via hole in the main body 2 from the plane of the coupler structure 6 be led out to the two ring segments 6a, b with the capacitor 5 to contact.

As in 1 shown, the generation of the electromagnetic signal takes place S _HF and the processing of it reflected signal E _HF through the electronic unit 7 By using the two transmit / receive antennas 81 . 82 is contacted.

3 shows a possible embodiment of the electronic unit 7 , by means of the use of two transmit / receive antennas 81 . 82 a very efficient determination of the pressure p is possible. Core of the electronic unit shown there 7 is a signal divider 72 , This shares a high frequency electrical signal S _HF that from a high frequency generator 71 is generated in a first signal path s _{HF, 1} and a second signal path S _{HF, 2} on. In this case, the high-frequency generator 71 in particular when generating the high-frequency electrical signal S _HF be implemented in the GHz range analogous to the radar measurement technology as a voltage-controlled oscillator, the oscillator is in turn controlled by a voltage generator.

Via a first transmitting / receiving switch 73a which is arranged in the first signal path s _{HF, 1} , becomes the high-frequency electrical signal S _HF in the first transmitting / receiving antenna 81 coupled and accordingly as an electromagnetic signal S _HF in the direction of the reflector structure 6a , b sent out. It is for coupling into the first transmitting / receiving antenna 81 between her and the transceiver 73a a first balun 74 interposed. At the same time, the first transceiver is used 73a that from the first transmit / receive antenna 81 received, reflected electromagnetic signal E _HF in the first signal path s _{HF, 1} coupled and a mixer 75 fed.

Analogously to the first signal path s _{HF, 1} is via a second transmitting / receiving switch 73b , which is arranged in the second signal path s _{HF, 2} , the high-frequency electrical signal s _HF via a second balun 74b in the second transmitting / receiving antenna 82 coupled to an electromagnetic signal S _HF in the direction of the main body r 6a , b to be sent out. Also the second transmitting / receiving switch 73a also couples that from the second transmit / receive antenna 82 received, reflected electromagnetic signal E _HF again in the second signal path s _{HF, 1} and leads it to the mixer 75 to.

In the mixer 75 thus becomes that of the first transmit / receive antenna 81 received signal E _HF with that of the second transceiver antenna 82 received signal E _HF mixed (where the reflected signal E _HF each case is received in a different mode and / or with different polarization). Unless the high frequency generator 71 So the send signal S _HF with a (linear) changing frequency f In this case, mixing allows a very simple determination of the pressure p : Because by the mixer 75 formed difference frequency s _p , which is the difference between the frequency of the first transmitter / receiver antenna 81 received received signal E _HF and the frequency of the second transceiver antenna 82 received received signal E _HF In this case, the pressure changes linearly with the pressure p , The difference frequency s _p again can be detected very technically easy. As in 3 is shown, this can after appropriate A / D conversion, for example by means of a microcontroller 76 respectively.

LIST OF REFERENCE NUMBERS

1

Pressure measuring device

2

body

3

measuring membrane

4

pressure chamber

5a, b

Capacitor / electrodes of the capacitor

6a, b, c

Coupler structure

7

Electronic unit

9

waveguide

71

High-frequency generator

72

signal splitter

73a, b

Transmit / receive switch

74a, b

baluns

75

mixer

76

microcontroller

81.82

Transmit / receive antennas

A _{E, HF}

Amplitude of the reflected electromagnetic signal

E _HF

Reflected electromagnetic signal

D

Diameter of the waveguide

d

Diameter of the measuring diaphragm

f

frequency

f _min

Frequency of the amplitude minimum

l

electrode distance

p

print

Q

Goodness of the coupler structure

R

measuring rate

r

Radius of the electrodes of the capacitor

S _HF

Electromagnetic signal

s _{HF, 1.2}

signal paths

s _p

difference frequency

t

Thickness of the measuring membrane

t _mess

Measuring Time

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been 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.

Cited patent literature

• WO 03/106952 A2 [0003]
• DE 202016101491 U1 [0005]
• EP 1806569 A1 [0007]

Claims (17)

Pressure measuring device, comprising: - a base body (2), - a measuring diaphragm (3) which is designed and arranged on the base body (2) such that the measuring diaphragm (3) encloses a pressure chamber (4) towards the base body (2), and that the measuring diaphragm (3) is deformable as a function of a pressure (p) to be measured, which acts on the measuring diaphragm (3) from an area facing away from the main body (2), - a capacitor (5), with a • first electrode (5a), which is arranged in the pressure chamber (4) on the base body (2), and • a second electrode (5b) which is arranged on the measuring diaphragm (3) in the pressure chamber (4) such that the capacitance (C (p)) of the capacitor (5) is dependent on the pressure (p), characterized by - an electrical coupler structure (6) arranged on the main body (2) which is in contact with the capacitor (5), - at least one first transmitter - / Reception antenna (81) for emitting an electromagnetic signal (S _HF ) in the direction of the coupler Structure (6), and for receiving an electromagnetic signal (E _HF ) reflected by the base body (2) and / or by the coupler structure (6), - one between the at least first transmitting / receiving antenna (81) and waveguide (9) arranged in the coupler structure (6), - an electronic unit (7) which is contacted at least with the first transmitting / receiving antenna (81), wherein the electronic unit (7) is designed to accommodate the To generate electromagnetic signal (S _HF ) and to determine the pressure (p) based on the reflected electromagnetic signal (E _HF ). Pressure measuring device according to Claim 1 , characterized in that the electronic unit (7) comprises the following components: - a high-frequency generator (71) for generating a high-frequency electrical signal (s _HF ), - at least a first transmitting / receiving switch (73a), which with such the first transmitting / receiving antenna (81) is connected in order to emit the electrical high-frequency signal (s _HF ) as an electromagnetic signal (S _HF ), and to couple the reflected electromagnetic signal (E _HF ), and - a microcontroller (76 ), which determines the pressure (p) by means of the injected signal (s _p ). Pressure measuring device according to Claim 2 , characterized in that the high-frequency generator (71) is designed to - the high-frequency electrical signal (s _HF ) with a frequency (f), which varies in time within a frequency band (f ₁ -f ₂ ) in particular linear, to create. Pressure measuring device according to Claim 3 , characterized in that the microcontroller (76) is designed in order - within the frequency band (f ₁ -f ₂ ) to determine at least one amplitude minimum of the reflected high-frequency electromagnetic signal (E _HF ) as a function of the frequency (f), determine a corresponding frequency (f _min ) of the amplitude minimum, and - determine the pressure (p) based on the frequency (f _min ) of the at least one amplitude minimum. Pressure measuring device according to Claim 2 . 3 or 4 , characterized in that the electronic unit (7) comprises the following components: - a signal divider (72) which is connected to the high-frequency electrical signal (s _HF ) in a first signal path (s _{HF, 1} ) and a second signal path (s _{HF, 2} ) to be divided, wherein the first transmitting / receiving switch (73a) in the first signal path (s _{HF, 1} ) is arranged, - a second transmitting / receiving switch (73b) in the second signal path (s _{HF, 2} ), - a second transceiver antenna (82) connected to the second transceiver (73b), wherein the second transceiver (73b) is designed to be that of the second transceiver (73b) transmitting / receiving antenna (82) received, reflected signal (e _HF) in the second signal path (s _{HF, 2)} to couple, and - a mixer (75) connected to the first transmit / receive switch (73a) and the second transmitting / receiving switch (73b) is connected to the in the first signal path (s _{HF, 2} ) coupled, reflected signal (E _HF ) with the reflected signal (E _HF ), which is coupled into the second signal path (s _{HF, 2} ), wherein the microcontroller (76) determines the pressure by means of one of the mixed signal (s _p ) the pressure (p). Pressure measuring device according to Claim 5 , characterized in that the first transmit / receive antenna (81) and the second transmit / receive antenna (82) are connected in such a way to the electronic unit (7) in order to transmit the electromagnetic signal (S _HF ) to the second transmit / receive antenna Antenna (82) with respect to the first transmit / receive antenna (81) with a predefined phase shift, in particular 90 °, and / or wherein the first transmit / receive antenna (81) and the second transmit / receive antenna Antenna (82) are connected in such a way with the electronic unit (7) to the electromagnetic signal (S _HF ) at the second transmitting / receiving antenna (82) with respect to the first transmitting / receiving antenna (81) with a send out divergent fashion. Pressure measuring device according to one of Claims 2 to 6 , characterized in that the high-frequency generator (71) is realized as a voltage-controlled oscillator which is controlled by a voltage generator. Pressure measuring device according to at least one of Claims 2 to 7 , characterized in that the first transmitting / receiving switch (73a) and / or the second transmitting / receiving switch (73b) are designed as a circulator or as a coupler, in particular as a directional coupler / is. Pressure measuring device according to at least one of the preceding claims, characterized in that the emitted electromagnetic signal (S _HF ) has a frequency (f) of at least 100 MHz, in particular greater than 1 GHz. Pressure measuring device according to at least one of the preceding claims, characterized in that the waveguide (9) has a round cross section with a defined inner diameter (d). Pressure measuring device according to at least one of the preceding claims, characterized in that in the waveguide (9) a material having a dielectric constant of greater than 1, in particular PE, PP, Teflon or glass, is introduced. Pressure measuring device according to one of the preceding claims, characterized in that the coupler structure (6) with respect to the cross section of the waveguide (9) is mounted approximately centrally, wherein the cross section, in particular the inner diameter (d) of the waveguide (9) with respect to the frequency (f) of the electromagnetic signal (S _HF ) is dimensioned such that the electromagnetic signal (S _HF ) at least in the TE ₀₁ mode, the TE ₁₁ mode or the TM ₁₁ mode is transmitted. Pressure measuring device according to at least one of Claims 9 to 12 , characterized in that the waveguide (9) has a length which is at most four times the inner diameter (d) and / or at least a quarter of a wavelength of the electromagnetic signal (S _HF ). Pressure measuring device according to at least one of the preceding claims, characterized in that the first transmitting / receiving antenna (81), the second transmitting / receiving antenna (82), and / or the coupler structure (6) as a planar arrangement consisting of a first ring segment (81a, 82a, 6a) and an approximately opposite arranged second ring segment (81b, 82b, 6b), are configured / is. Pressure measuring device according to at least one of the preceding claims, characterized in that the second electrode (5b) of the capacitor (5) is electrically isolated at least from the first transmitting antenna (81). Method for determining the pressure (p) by means of a pressure measuring device according to one of Claims 2 to 14 , comprising the following method steps: - generating a high-frequency electrical signal (s _HF ) by a high-frequency generator (71), the frequency (f) of the high-frequency electrical signal (s _HF ) within a frequency band (f ₁ -f ₂ ) , in particular linear, is changed, - emitting the electrical high-frequency signal (s _HF ) via at least a first transmitting / receiving antenna (81) as a high-frequency electromagnetic signal (S _HF ), - receiving the high-frequency electromagnetic signal (E _HF ) after reflection at a coupler structure (6) and / or a base body (2) by at least the first transmitting / receiving antenna (81), - detecting at least one amplitude minimum of the reflected high-frequency electromagnetic signal (E _HF ) in Dependence of the frequency (f) by means of a microcontroller (76), - determination of the frequency (f _min ) of the at least one amplitude minimum, and Determining the pressure (p) based on the frequency (f _min ) of the at least one amplitude minimum. Method for determining the pressure (p) by means of a pressure measuring device according to one of Claims 5 to 15 , comprising the following method steps: - generating a high-frequency electrical signal (s _HF ) by a high-frequency generator (71), the frequency (f) of the high-frequency electrical signal (s _HF ) within a frequency band (f ₁ -f ₂ ) , in particular linear, is changed, - dividing the high frequency electrical signal (s _HF ) into a first signal path (s _{HF, 1} ) and a second signal path (s _{HF, 2} ), - transmitting the electrical high frequency signal (s _HF ) via a first transmitting / receiving antenna (81) as a high-frequency electromagnetic signal (S _HF ), wherein the electrical high-frequency signal (s _HF ) via a in the first signal path (s _{HF, 1} ) arranged transceiver (73a) is coupled into the first transmitting / receiving antenna (81), - emitting the electrical high-frequency signal (s _HF ) via a second transmitting / receiving antenna (82) as a high-frequency electromagnetic signal (s _HF ), wherein the electrical High frequency signal (s _HF ) over one in the second signal path (s _{HF, 1} ) arranged transceiver (73b) is coupled into the second transceiver antenna (82), - Reception of the high-frequency electromagnetic signal (E _HF ) after reflection at the coupler structure ( 6) and / or the base body (2) by the first transmitting / receiving antenna (81) and the second transmitting / receiving antenna (82), - mixing of the first transmitting / receiving antenna (81) received, reflected signal (E _HF ) with the received by the second transmitting / receiving antenna (82), reflected signal (E _HF ) by means of the mixer (75), and - determining the pressure (p) on the basis of the difference frequency s _p of the mixed signal.

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