Antenna for measuring dielectric values

Abstract

The invention relates to an antenna (10, 10') for a high-frequency-based measuring device (1) for determining dielectric values of a medium (2). For transmitting and / or receiving corresponding high-frequency signals (S HF , E HF ), the antenna (10, 10') is based on a high-frequency waveguide (100). The high-frequency signals (S HF , E HF ) are coupled in or out by means of a coaxial conductor (101) which extends orthogonally to the axis (a) of the high-frequency waveguide (100) for this purpose. In this case, the conductor end (1012) of the coaxial conductor (101) protrudes (1) beyond the high-frequency waveguide (100) so that the coaxial conductor (101) creates a defined capacitance (C) in this region. In this way, the coaxial conductor (101) is optimally matched to the high-frequency waveguide (100) without having to integrate additional electrical components for this purpose. This results in an efficient high-frequency antenna (10, 10') which is easy to produce due to its few components (100, 101).

Description

Technical Field

[0001] This invention relates to an antenna for measuring dielectric values ​​based on high frequencies. Background Technology

[0002] In automation technology, particularly in process automation, field devices are frequently used to detect various measurable variables. These measurable variables can be, for example, the fill level, flow rate, pressure, temperature, pH value, redox potential, conductivity, or dielectric value of a medium in a processing plant. To detect the corresponding measured values, field devices either incorporate suitable sensors or are based on appropriate measurement methods. Endress+Hauser Group manufactures and sells a wide variety of field devices.

[0003] From the complex-valued dielectric value (also known as the "dielectric constant" or "relative dielectric constant"), various measurement variables of the current medium can be derived, such as moisture content, material composition, or any impurities. Therefore, the determination of the dielectric value is important for both solid media (such as cement or grain) and liquid and gaseous media (such as fuels, wastewater, gases, or chemicals). In this case, the dielectric value can, in principle, be determined for both the stored and flowing media. Therefore, the term "container" in the context of this invention is defined, for example, as a tank, silo, pool, or section of pipeline.

[0004] Besides the inductance and capacitance measurement principles used to determine dielectric values, high-frequency measurement principles are primarily employed. In this context, the term "high frequency" refers to signals with frequencies between 0.03 GHz and 300 GHz. In addition to the TDR principle ("time domain reflectometer"), dielectric values ​​can also be determined by means of transmission or reflection high-frequency measurements. In the case of a transmission measurement principle, a high-frequency signal with a defined frequency or frequency variation is coupled into a measurement path that guides through the medium inside a container containing the medium to be examined. In this case, amplitude / amplitude variation and / or phase / phase shift are measured after passing through the measurement path to determine, for example, a possible complex dielectric value based on the corresponding calibration measurement. A transmission-operated dielectric value measuring device is described in more detail, for example, in German publication DE 10 2017 130 728 A1.

[0005] Depending on the manufacturer, various design requirements are imposed on the antennas of high-frequency dielectric value measuring instruments because the antenna may be the only component in direct contact with the medium: for example, the antenna must withstand corrosive media, high pressure, and high temperature. Furthermore, if possible, the antenna should not extend into the container. On the other hand, the antenna must exhibit efficient high-frequency signal transmission behavior.

[0006] British Patent GB 2 293 014 describes a waveguide-based antenna for high-frequency dielectric value determination. In this case, the waveguide is formed from a stainless steel body in which a glass-ceramic filler is fused. The glass filler gives the antenna high resistance to conditions within the container. However, the glass filler is associated with complex manufacturing. Furthermore, the antenna inevitably has a large volume because glass-ceramic has a low dielectric constant. Summary of the Invention

[0007] Therefore, the object of the present invention is to provide a high-efficiency antenna that is resistant to high voltage and high temperature, compact in construction, and easy to manufacture for high-frequency dielectric value measurement.

[0008] This invention achieves this objective by providing an antenna for transmitting and / or receiving high-frequency signals, the antenna comprising at least the following components:

[0009] - A high-frequency waveguide, by means of which high-frequency signals can be transmitted along a particularly straight waveguide axis, the high-frequency waveguide having

[0010] The first end face is oriented approximately orthogonal to the waveguide axis to transmit or receive high-frequency signals, and has...

[0011] The feedthrough element, which extends approximately perpendicular to the waveguide axis, is used for...

[0012] - A coaxial conductor, used to couple the high-frequency signal to be transmitted into the high-frequency waveguide, or to tap the received high-frequency signal, having...

[0013] an external conductor electrically connected to a high-frequency waveguide.

[0014] The conductor end is designed such that the high-frequency signal to be coupled or tapped is reflected at the conductor end, and

[0015] o Connecting device, which is opposite to the end of the conductor for high-frequency contact with the antenna.

[0016] According to the invention, the coaxial conductor extends far beyond the feedthrough, such that the coaxial conductor forms a defined capacitance between the feedthrough and the conductor end.

[0017] In this way, the coaxial conductor is optimally matched with the high-frequency waveguide in terms of high-frequency technology, without the need to integrate additional electrical components for this purpose. This results in highly efficient high-frequency antennas that can be easily manufactured due to their few components.

[0018] If the high-frequency waveguide and coaxial conductor are structurally surrounded by a carrier body, at least between the feedthrough and the conductor end, the high-frequency waveguide can be designed as an all-conductor by designing the carrier body as a negative shape of the high-frequency waveguide. In this case, the carrier body must be designed to be conductive at least on the surface of the negative shape, assuming that the carrier body is not entirely made of a conductive material such as steel. As an alternative to waveguide design, designing the high-frequency waveguide as a dielectric waveguide can also be considered.

[0019] Even when high-frequency waveguides are designed as waveguides, it is advantageous if they are filled with a dielectric material, such as titanium oxide, aluminum oxide, or zirconium oxide, which has a dielectric constant of at least 2 at the corresponding frequency of the high-frequency signal. As a result, the size of high-frequency waveguides can be significantly reduced compared to gas-filled waveguides. Furthermore, these materials are chemically and physically robust, allowing the antenna to have strong pressure and temperature resistance.

[0020] From a high-frequency perspective, it is also advantageous to reflect high-frequency signals with a 180° phase jump at the second end face of the high-frequency waveguide, which is opposite to the first end face relative to the waveguide axis. If the high-frequency waveguide is made of a dielectric material, a corresponding phase jump can be achieved at the second end face, for example, when a metallization layer is provided on the second end face. When the high-frequency waveguide is designed as a hollow conductor, a corresponding phase jump can be achieved through the conductive design of the second end face.

[0021] Assuming optimal coupling of high-frequency signals between the antenna and the dielectric, this maximizes the sensitivity of dielectric value measurements. Therefore, it is advantageous for the antenna to have a cutoff frequency at least 10% lower than the (lowest) frequency of the high-frequency signal. The primary parameter to optimize in this regard is the cross-section of the high-frequency waveguide. The distance between the feedthrough element and the second end face in the high-frequency waveguide should preferably be chosen to correspond to one-quarter of the high-frequency signal wavelength. Combined with a 180° phase jump at the second end face of the high-frequency waveguide, this results in positive interference from the high-frequency signal within the waveguide, maximizing the coupling of the high-frequency signal into or out of the waveguide.

[0022] The capacitance of the coaxial conductor between the feedthrough element and the conductor end in a high-frequency waveguide is optimized to compensate for the parasitic capacitance of the high-frequency waveguide. In this regard, it is advantageous if the conductor end of the coaxial conductor is designed such that the high-frequency signal to be coupled or tapped is reflected at the conductor end without a phase jump (e.g., by means of a cavity between the coaxial conductor and the carrier body).

[0023] The antenna according to the invention can be easily manufactured, particularly if the high-frequency waveguide is fixed in the carrier body by means of a threaded insert, which can be screwed into the carrier body in the direction of the coaxial conductor via the conductor end. A corresponding simple method for manufacturing the antenna includes the following steps:

[0024] -Provides high-frequency waveguides, coaxial conductors, and carrier bodies.

[0025] - The high-frequency waveguide is inserted into the carrier body through the corresponding opening in the carrier body for the first end face of the high-frequency waveguide.

[0026] - Insert the coaxial conductor into the feedthrough for the high-frequency waveguide, and

[0027] - The high-frequency waveguide and / or coaxial conductor are secured by screwing the threaded insert into the carrier body.

[0028] A high-frequency measuring device for determining the dielectric value of a medium can be realized based on the antenna according to the present invention. For this purpose, the measuring device includes the following components:

[0029] - At least one antenna according to one of the foregoing variants, for transmitting high-frequency signals toward the medium, and / or receiving high-frequency signals after interacting with the medium.

[0030] - A signal generation unit, connected to the transmitting antenna, generates a high-frequency signal to be transmitted, via a transmit / receive switch if necessary.

[0031] - An evaluation unit, which may again be connected via a transmit / receive switch to a connection device for receiving an antenna, in order to determine the dielectric value based on the received high-frequency signal.

[0032] In the context of this invention, the term "interaction" refers to transmission through a medium along a defined measurement path (i.e., between the transmitting and receiving antennas), or reflection from a medium.

[0033] At least under the principle of transmission measurement, the evaluation unit can determine the dielectric value of the medium as a complex value based on the amplitude, phase, or signal propagation time of the received high-frequency signal. In this context, the term "unit" within the scope of this invention is understood to mean any electronic circuit suitably designed for its intended use. Depending on the requirements, it can therefore be an analog circuit for generating or processing a corresponding analog signal. However, it can also be a digital circuit, such as an FPGA or a storage medium that works with a program designed to perform corresponding method steps or apply necessary computational operations to the corresponding unit. In this context, different electronic units of the measuring device for the purposes of this invention can also potentially access a common physical memory or operate by means of the same physical digital circuitry. Attached Figure Description

[0034] The invention will be explained in more detail with reference to the following figures. They are shown below:

[0035] Figure 1 High-frequency dielectric measurement equipment on pipeline sections, and

[0036] Figure 2 Cross-sectional view of an antenna for measuring dielectric value based on high frequency according to the present invention. Detailed Implementation

[0037] exist Figure 2 The diagram illustrates a cross-sectional view of pipeline section 3 for general understanding of dielectric value measurement. A gaseous medium 2, such as propane or nitrogen, or a liquid medium 2, such as fuel, beverage, or wastewater with solid deposits, flows through pipeline section 3. In this case, the dielectric value DK of medium 2 needs to be determined. For this purpose, transmitting antenna 10 and receiving antenna 10' are arranged opposite each other on the inner wall of pipeline section 3 and aligned with each other. Transmitting antenna 10 is used to transmit a high-frequency signal S to medium 2. HF The receiving antenna 10' receives the high-frequency signal E after passing through the obtained measurement path. HF .

[0038] High-frequency signal S HF The signal is generated by a correspondingly designed signal generation unit 11, which is connected to the transmitting antenna 10 for this purpose. Based on the received signal E... HF The dielectric value measuring device 1 then determines the dielectric value DK of the medium 2. For this purpose, the evaluation unit 12 of the dielectric value measuring device 1 is sequentially connected to the receiving antenna 10' to detect the received signal E. HF The phase, signal propagation time, and / or amplitude. Based on this, the evaluation unit 12 can, for example, determine the dielectric value DK of the medium 2 based on corresponding calibration data. Therefore, it can also determine the dielectric value DK relative to the high-frequency signal S to be transmitted. HFDetermining the phase or amplitude, the evaluation unit 12 is connected to the signal generation unit 11 accordingly when needed, such as... Figure 1 As shown. In this case, Figure 1 The signal generation unit 11 in the dielectric value measurement device 1 shown can be based on a PLL (“phase-locked loop”). In this context, the signal generation unit 11 and the evaluation unit 12 can be designed together as a network analyzer, for example.

[0039] As Figure 1 In an alternative embodiment of the dielectric value measuring device 1 shown, one of the antennas 10 and 10' of the dielectric value measuring device 1 can also be designed as a combined transmit / receive antenna for high-frequency signal S. HF E HF The reflector is attached to the location of another antenna 10, 10'. In this case, the signal generation unit 11 and the evaluation unit 12 are respectively connected to the transmit / receive antenna via transmit / receive switches. In another variation, the reflector can also be omitted, such that the evaluation unit 12 determines not the transmitted component E via the combined transmit / receive antenna. HF Instead, it is the high-frequency signal S generated by reflection at the transmitting / receiving antenna. HF The component. Similar to the transmission method, in this reflection method, the dielectric value of medium 2 can be transmitted via the generated high-frequency signal S. HF The reflection component is used to determine this.

[0040] Figure 2 An antenna structure according to the present invention is shown, which can be compactly designed, easy to manufacture, and allows for high voltage and temperature resistance. At the heart of the antenna structure shown here—which can serve as both a transmitting antenna 10 and a receiving antenna 10'—is a high-frequency waveguide 100, in which the high-frequency signal S to be transmitted... HF and the high-frequency signal E to be received HF It can transmit along the straight waveguide axis a. Facing medium 2, the high-frequency waveguide 100 terminates at the first end face 1001. Therefore, the high-frequency signal S to be transmitted... HF It can be coupled to the medium 2 with low loss via the first end face 1001, or make the high-frequency signal E to be received HF It can be coupled into the high-frequency waveguide 100 with low loss, and the orientation of the first end face 1001 is approximately orthogonal to the waveguide axis a. The cross-sectional shape (e.g., circular or rectangular) and cross-sectional dimensions of the high-frequency waveguide 100 along the waveguide axis a are specific to the high-frequency signal S. HF E HF The frequency is optimized.

[0041] exist Figure 2In the illustrated embodiment, the high-frequency waveguide 100 is made of a dielectric material. In this case, the smaller the size of the high-frequency waveguide 100 can be designed, the better the dielectric material reacts with the high-frequency signal S. HF E HF The higher the dielectric constant at the corresponding frequency, the better. Suitable materials for this purpose—those with a dielectric constant greater than two and additionally reliable pressure resistance and / or temperature resistance—are, for example, titanium oxide, alumina, or zirconium oxide. Optionally, in addition to the first end face 1001, the HF waveguide 100 can be externally metallized to further improve transmission within the high-frequency waveguide 100. In this context, if the second end face 1003 of the high-frequency waveguide 100, opposite the waveguide axis a of the first end face 1001, reflects the high-frequency signal S with a 180° phase jump... HF E HF That would be advantageous.

[0042] At high frequencies, the high-frequency waveguide 100 is driven by the signal generation unit 11 or the evaluation unit 12 via a coaxial conductor 101, such as a coaxial cable. Through this coaxial conductor 101, the signal generation unit 11 can transmit the high-frequency signal S to be transmitted. HF The high-frequency signal E is coupled into the high-frequency waveguide 100, or can be received by the evaluation unit 12 via the coaxial conductor 101. HF For this purpose, the continuous feedthrough 1002 enters the high-frequency waveguide 100 perpendicular to the waveguide axis a, and its diameter matches the outer diameter of the coaxial conductor 101. In this case, the outer conductor 1011 for the coaxial conductor 101 is electrically connected to the high-frequency waveguide 100. The inner conductor for the coaxial conductor 101 extends through the feedthrough 1002 to the conductor end 1012 of the coaxial conductor 101. In this case, the feedthrough 1002 is optimally attached such that the distance d from the second end face 1003 of the high-frequency waveguide 100 to the coaxial conductor 101 corresponds to the high-frequency signal S. HF E HF One-quarter of the wavelength. Combined with a 180° phase jump at the second end face 1003, this optimizes transmission in the high-frequency waveguide 100.

[0043] On the end side, the coaxial conductor 101 has a connection device 1013—such as a bayonet connection—for high-frequency connection to the coaxial conductor 101 or corresponding elements 11, 12 of the antennas 10, 10'. Opposite to the connection device 1013 on the coaxial conductor 101, the conductor end 1012 of the coaxial conductor 101 is designed such that the high-frequency signal S to be coupled or tapped... HF E HF There it is reflected without a phase jump. For this purpose, in Figure 2In the illustrated embodiment, the coaxial conductor 101 is designed with an open conductor end. Furthermore, the coaxial conductor 101 is guided through the feedthrough 1002 such that the conductor end 1012 does not terminate flush with the feedthrough 1002, but rather protrudes beyond the feedthrough 1002 with a defined excess length l. Therefore, a defined capacitance C can be allocated to the coaxial conductor 101 between the feedthrough 1002 and the conductor end 1012. In this case, the capacitance C is measured based on the parasitic capacitance of the high-frequency waveguide 100.

[0044] In order to maximize the high-frequency signal S from antennas 10, 10' or entering antennas 10, 10' HF E HF The coupling out and coupling in are configured to set the cutoff frequencies of antennas 10 and 10', ensuring that the cutoff frequency is at least higher than that of the high-frequency signal S. HF E HF A 10% reduction in the (lowest) frequency is also advantageous. The key relevant parameter in this context is the cross-sectional geometry of the high-frequency waveguide 100 relative to the waveguide axis a. Furthermore, the entire length of the high-frequency waveguide 100 along axis a, i.e., the length between the first end face 1001 and the second end face 1003 of the high-frequency waveguide 100, must also be designed to maximize the high-frequency coupling between the coaxial conductor 101 and the high-frequency waveguide 100.

[0045] like Figure 2 As shown, except for the connecting device 1013 and the first end face 1001, the high-frequency waveguide 100 and the coaxial conductor 101 are surrounded by the carrier body 102. In this case, the carrier body 102 surrounds the HF waveguide 100 in a form-fit manner until the second end face 1003 of the high-frequency waveguide 100 forms a defined cavity. In this case, the cavity is used to permanently fix the high-frequency waveguide 100 by means of adhesive. The coaxial conductor 101 also surrounds the carrier body 102 in a form-fit manner until the length l between the feedthrough 1002 and the conductor end 1012. In principle, assuming the form-fit design of the carrier body 102, the antennas 10 and 10' can seal the corresponding openings of the conduit section 3, to which the antennas 10 and 10' are attached to resist overpressure.

[0046] With antennas 10 and 10' in their completed state, the high-frequency waveguide 100 is initially and exclusively secured to the carrier body 102 by means of a threaded insert 1021. From Figure 2As can be seen, for this purpose, a carrier body 102 and a threaded insert 1021 are provided by means of corresponding threads, such that the threaded insert 1021 can be screwed into the carrier body 102 via the conductor end 1012 in the direction of the coaxial conductor 101. As a result, when in the screwed-in state, the threaded insert 1021 presses the high-frequency waveguide 100 against the carrier body 102 via a spring element 1022 orthogonal to the waveguide axis a. Additional adhesive can be injected into the cavity behind the second end face 1003 to permanently fix the high-frequency waveguide 100. In this case, a sealing ring 1023 surrounding the coaxial conductor 101 is additionally arranged between the spring element 1022 and the high-frequency waveguide 100 for sealing the medium 2 or adhesive. However, in order to manufacture antennas 10 and 10', the high-frequency waveguide 100 must first be inserted through a corresponding opening in the carrier body 102 for the first end face 1001, which faces the dielectric 2 in the assembled state before screwing in. Furthermore, the coaxial conductor 101 must be inserted into the feedthrough 1002 of the high-frequency waveguide 100, which can be done before or after screwing in the threaded insert 1021. In general, antennas 10 and 10' can therefore be manufactured in several manufacturing steps.

[0047] List of reference numerals

[0048] 1. Dielectric value measuring equipment

[0049] 2. Medium

[0050] 3. Pipeline Sections

[0051] 10 transmitting antennas

[0052] 10' receiving antenna

[0053] 11 Signal Generation Unit

[0054] 12 Evaluation Units

[0055] 100 high-frequency waveguide

[0056] 101 coaxial conductor

[0057] 102 Carrier Main Body

[0058] The first end face of the 1001 high-frequency waveguide

[0059] Feedthrough components in 1002 high-frequency waveguide

[0060] The second end face of the 1003 high-frequency waveguide

[0061] 1011 coaxial conductor's external conductor

[0062] The conductor end of a 1012 coaxial conductor

[0063] 1013 Connecting device

[0064] 1021 Threaded Insert

[0065] 1022 Spring Element

[0066] 1023 Sealing Ring

[0067] a waveguide axis

[0068] C. Capacitance of a coaxial conductor

[0069] DK dielectric value

[0070] d Distance from the second end face to the feeder

[0071] E HF Received high-frequency signals

[0072] l The length of the coaxial conductor behind the feeder

[0073] S HF High frequency signal

Claims

1. An antenna for transmitting and / or receiving high-frequency signals, comprising: - A high-frequency waveguide (100) through which a high-frequency signal can be transmitted along the waveguide axis (a), the high-frequency waveguide (100) having o A first end face (1001), the first end face (1001) being oriented approximately orthogonal to the waveguide axis (a) for transmitting the high-frequency signal into the medium (2) and receiving the high-frequency signal from the medium (2), and having o A feedthrough (1002) extending approximately orthogonal to the waveguide axis (a) is used for - A coaxial conductor (101), said coaxial conductor (101) being used to transmit the high-frequency signal S to be transmitted. HF Coupled to the high-frequency waveguide (100), or used to tap the received high-frequency signal E HF The coaxial conductor has o Electrically connected external conductor (1011), which is electrically connected to the high-frequency waveguide (100). o Conductor end (1012), said conductor end (1012) being designed such that the high-frequency signal to be coupled or tapped is reflected at said conductor end, and o A connecting device (1013), which is opposite to the conductor end (1012), for high-frequency contact of the antenna. The coaxial conductor (101) is guided beyond the feeder (1002) such that the coaxial conductor (101) forms a defined capacitance between the feeder (1002) and the conductor end (1012).

2. The antenna according to claim 1, comprising: - Carrier body (102) which surrounds the high-frequency waveguide (100) and the coaxial conductor (101) at least between the feedthrough (1002) and the conductor end (1012).

3. The antenna according to claim 1, wherein, The high-frequency waveguide (100) is designed as a dielectric waveguide.

4. The antenna according to claim 3, wherein, Provided that the high-frequency waveguide (100) is designed as a dielectric waveguide, the high-frequency waveguide (100) is made of a dielectric material having a dielectric constant of at least 2 at the corresponding frequency of the high-frequency signal.

5. The antenna according to claim 4, wherein, The high-frequency waveguide (100) is made of titanium oxide, aluminum oxide or zirconium oxide.

6. The antenna according to claim 3, wherein, Provided that the high-frequency waveguide (100) is designed as a dielectric waveguide, the high-frequency waveguide (100) is plated with an electroplated layer except for the first end face (1001).

7. The antenna according to any one of claims 1 to 6, wherein, The high-frequency waveguide (100) includes a second end face (1003) which is opposite to the first end face (1001) about the waveguide axis (a) and reflects the high-frequency signal with a 180° phase jump.

8. The antenna according to claim 7, wherein, The distance (d) between the feedthrough (1002) and the second end face (1003) is one-quarter of the wavelength of the high-frequency signal.

9. The antenna according to any one of claims 1 to 6, wherein, The cross-sectional dimensions of the high-frequency waveguide (100) are designed such that the cutoff frequency of the antenna is at least 10% lower than the frequency of the high-frequency signal.

10. The antenna according to any one of claims 1 to 6, wherein, The conductor end (1012) of the coaxial conductor (101) is designed such that a high-frequency signal to be coupled or tapped is reflected at the conductor end without a phase jump.

11. The antenna according to any one of claims 2 to 6, wherein, The high-frequency waveguide (100) is fixed in the carrier body (102) by means of a threaded insert (1021), which can be screwed into the carrier body (102) in the direction of the coaxial conductor (101) via the conductor end (1012).

12. A method for manufacturing an antenna according to any one of claims 1 to 11, comprising the following method steps: - Provides a high-frequency waveguide (100), a coaxial conductor (101), and a carrier body (102). - The high-frequency waveguide (100) is inserted into the carrier body (102) through a corresponding opening in the carrier body (102) for the first end face (1001) of the high-frequency waveguide (100). - Insert the coaxial conductor (101) into the feedthrough (1002) for the high-frequency waveguide (100), and - The high-frequency waveguide (100) and / or the coaxial conductor (101) are secured by screwing the threaded insert (1021) into the carrier body (102).

13. A high-frequency based measuring device for determining the dielectric value of a medium (2), comprising: - At least one antenna according to any one of claims 1 to 12, for transmitting a high-frequency signal S toward the medium (2). HF and / or receiving the high-frequency signal E after interacting with the medium (2). HF , - A signal generation unit (11), which is connected to a connection device (1013) for transmitting antenna (10) to generate a high-frequency signal S to be transmitted. HF ,as well as - Evaluation unit (12), which is connected to the connection device (1013) for receiving antenna (10') for use at least based on the received high-frequency signal E HF To determine the dielectric value.

14. The measuring device according to claim 13, wherein, The evaluation unit (12) is designed to be based on the received high-frequency signal E HF The dielectric value is determined by the amplitude, phase, or signal propagation time.

Images