DE102020106020A1 - Level measuring device - Google Patents

Abstract

The invention relates to a radar-based level measuring device (1) for measuring a level (L) in a container (3), the level measuring device (1) measuring from a lateral container wall (31). For this purpose, the filling level measuring device (1) comprises an antenna arrangement (13) by means of which the radar signal (SHF) can be transmitted perpendicular to the filling material (2) and can be received as a corresponding reception signal (EHF) after reflection on the filling material surface. The antenna arrangement (13) is characterized by an asymmetrical aperture (131) by means of which the radar signal (SHF) is transmitted with a main radiation lobe flattened towards the container wall (31). As a result, the antenna arrangement (13) can advantageously be designed in such a way that it only projects not far into the container (3) and the radar signal (SHF) is nevertheless not inadvertently reflected on the container wall (31). The level measuring device (1) therefore does not form a disruptive installation inside the container (3) due to the narrow side mounting. Nevertheless, the asymmetry ensures that the main radiation lobe is wide enough so that the radar signal (EHF) is reflected towards the level measuring device (1) even when the product surface is rough.

Description

The invention relates to a level measuring device which is used when it is attached to the side of the container.

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

Radar-based measurement methods have become established for measuring the level of products in containers, as they are robust and require little maintenance. A key advantage of radar-based measurement methods is the ability to measure the level almost continuously. In the context of this patent application, the term “radar” refers to radar signals with frequencies between 0.03 GHz and 300 GHz. Usual frequency bands in which level measurement is carried out are 2 GHz, 26 GHz, 79 GHz, or 120 GHz. The two common measuring principles are the pulse-transit time principle (also known under the term “pulse radar”) and the FMCW principle (“Frequency Modulated Continuous Wave”). A fill level measuring device that works according to the pulse transit time method is, for example, in the laid-open specification DE 10 2012 104 858 A1 described. With regard to a typical structure of FMCW-based level measuring devices, reference is made to the laid-open specification as an example DE 10 2013 108 490 A1 referenced.

The measuring principles of FMCW and pulse radar also in "Radar Level Detection, Peter Devine, 2000" .

Since radar-based level gauges determine the level indirectly by measuring the distance to the product surface from above, level gauges according to the state of the art are designed in such a way that they are attached to the top of the container. For this purpose, the respective containers must be equipped with a corresponding connection such as a flange connection on the top. Often, however, such connections have to be retrofitted separately, whereas side connections on the container are often present per se, for example as unused inflows or outflows, or as connections for pressure or temperature measurement. A lateral attachment to a container wall can also involve the risk that the container wall will be detected by the main radiation lobe of the transmitted radar signal, which can generate interfering reflections that lead to an incorrect level measurement.

The invention is therefore based on the object of providing a level measuring device by means of which the level can be reliably determined via a lateral connection of the container.

• - Ein Befestigungsmittel, wie beispielsweise einem Flanschanschluss, mittels dem das Füllstandsmessgerät an einer seitlichen Behälterwand befestigbar ist,
• - eine Signalerzeugungs-Einheit, die ausgelegt ist, ein Radar-Signal zu erzeugen,
• - eine Antennen-Anordnung, mittels der das Radar-Signal im befestigten Zustand in etwa senkrecht gen Füllgut aussendbar und nach Reflektion an der Oberfläche des Füllgutes als entsprechendes Empfangssignal empfangbar ist, mit
  • o einer derart asymmetrischen Apertur, mittels der das Radar-Signal mit einer zur Behälterwand hin abgeflachten Hauptabstrahlkeule ausgesendet wird, und
• - eine Auswertungs-Einheit, die ausgelegt ist, um anhand des Empfangssignals den Füllstand zu bestimmen.

The invention solves this problem by means of a radar-based level measuring device for measuring the level of a product in a container. For this purpose, the level measuring device comprises the following components:

• - A fastening means, such as a flange connection, by means of which the level measuring device can be fastened to a lateral container wall,
• - a signal generation unit which is designed to generate a radar signal,
• - An antenna arrangement by means of which the radar signal can be transmitted approximately perpendicular to the filling material in the attached state and can be received as a corresponding received signal after reflection on the surface of the filling material
  • o such an asymmetrical aperture by means of which the radar signal is emitted with a main radiation lobe flattened towards the container wall, and
• - An evaluation unit which is designed to determine the fill level on the basis of the received signal.

The technical implementation of the asymmetrical aperture is not restricted to a special embodiment variant within the scope of the invention. The asymmetrical aperture can therefore be implemented, for example, in the form of a quasi-optical lens, in particular a planar group antenna, or as a correspondingly asymmetrical, quasi-optical mirror. In the context of the present patent application, the term "main radiation lobe" refers to the area of those solid angles at which, starting from the main radiation direction (i.e. the vector of the maximum power of the transmitted radar signal), the power is reduced to 50%. or reduced by -3 dB, is included.

The asymmetrical emission of the radar signal according to the invention has a positive effect in several respects: On the one hand, the antenna arrangement can be designed in such a way that it protrudes only not far from the container and the radar signal is still not inadvertently reflected on the container wall. In this regard, the asymmetrical aperture can be designed, for example, or the frequency of the radar signal can be adapted to the aperture so that the main radiation lobe of the radar signal theoretically only touches the container wall at a distance from the level measuring device of at least 25 m. This means that the level measuring device can be safely used at least on containers up to 25 m high. For this purpose, the signal generation unit is to be designed in such a way that the electrical high-frequency signal is generated with a correspondingly tuned frequency, or the aperture is to be designed accordingly. In addition, the level measuring device does not form a disruptive installation inside the container due to the narrow side mounting. Nevertheless, the asymmetry ensures that the main radiation lobe is wide enough so that the reflected radar signal can be received by the level measuring device even when the product surface is rough.

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

The formulation "Such asymmetrical dimensioning of the aperture, so that the radar signal is emitted with a main radiation lobe flattened towards the container wall" is defined in connection with the invention, for example, in such a way that in the attached state a horizontal cross-section of the main radiation lobe is a maximum in relation to the container wall has parallel expansion that is greater than the maximum orthogonal expansion of the horizontal cross-section in relation to the container wall. In this case it is advantageous to dimension the aperture in such a way that the expansion parallel to the container wall is at least twice as large as the expansion of the cross section orthogonal to the container wall. A ratio of up to 4: 1 between the parallel expansion and the orthogonal expansion of the cross-section is also conceivable. In the context of the invention, it is not firmly specified which cross-sectional shape the horizontal cross-section of the main radiation lobe has. In order to achieve the desired ratio between the parallel propagation and the orthogonal propagation, the aperture can be designed, for example, in such a way that the horizontal cross section of the main radiation lobe of the emitted radar signal has an approximately elliptical or rectangular shape in the attached state. An approximately semicircular, horizontal cross section is also conceivable.

Due to the asymmetrical aperture, the antenna arrangement can be designed to be comparatively narrow without the main radiation lobe becoming too narrow overall and without the risk that the reflected radar signal will not be received. For this purpose, the antenna arrangement can be designed in the form of a rod, in particular, and the aperture can be designed in such a way that the maximum orthogonal spread of the cross section of the main radiation lobe to the container wall runs parallel to the rod axis. As a result, the fill level measuring device according to the invention can also be arranged on correspondingly narrow, lateral container connections.

Depending on the technical design of the asymmetrical aperture, for example in the case of a group antenna, this can be designed as part of the signal generation unit in such a way that the radar signal is generated in a focal point of the aperture. The advantage here is that the radar signal does not have to be routed separately along the antenna arrangement, as a result of which signal losses are avoided. If the signal generation unit is otherwise arranged in a housing area which is located outside the container wall in the fastened state, or if the signal generation unit is arranged within the antenna arrangement away from the aperture, the radar signal can, for example, by means of a waveguide or a dielectric waveguide to be guided towards the aperture.

To protect the aperture from contamination by the filling material, the fill level measuring device according to the invention can be extended to the effect that the antenna arrangement comprises a radome which is transparent to the radar signals and which covers at least the aperture or the entire antenna arrangement.

• - Erzeugen eines elektrischen Hochfrequenz-Signals,
• - In etwa senkrechtes Aussenden des elektrischen Hochfrequenz-Signals als Radar-Signal gen Füllgut, wobei das Radar-Signal mit einer zur Behälterwand hin abgeflachten Hauptabstrahlkeule ausgesendet wird, und
• - Empfang eines entsprechenden Empfangssignals nach Reflektion des Radar-Signals an der Füllgut-Oberfläche, und
• - Bestimmung des Füllstandes anhand zumindest des Empfangssignals.

Analogously to the fill level measuring device according to the invention, the object on which the invention is based is also achieved by a corresponding measuring method. The process includes the following process steps:

• - Generating a high-frequency electrical signal,
• - Approximately vertical transmission of the electrical high-frequency signal as a radar signal towards the product, the radar signal being transmitted with a main radiation lobe flattened towards the container wall, and
• - Reception of a corresponding received signal after reflection of the radar signal on the product surface, and
• - Determination of the fill level using at least the received signal.

• 1: Eine schematische Anordnung eines radar-basierten Füllstandsmessgerätes nach dem Stand der Technik an der Oberseite eines Behälters,
• 2: eine schematische Anordnung eines erfindungsgemäßen radar-basierten Füllstandsmessgerätes an der seitlichen Behälterwand, und
• 3: eine Detailansicht des erfindungsgemäßen Füllstandsmessgerätes.

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

• 1 : A schematic arrangement of a radar-based level measuring device according to the state of the art on the top of a container,
• 2 : a schematic arrangement of a radar-based fill level measuring device according to the invention on the side container wall, and
• 3 : a detailed view of the fill level measuring device according to the invention.

For a basic understanding of the invention is in 1 a freely radiating, radar-based level measuring device 1' shown the prior art at the top of a container 3 is arranged. It is in the container 3 a filling good 2 , its level L. through the level measuring device 1' is to be determined.

Usually the level gauge is 1' via a bus system such as "Ethernet", "PROFIBUS", "HART" or "Wireless HART" with a higher-level unit 4th , for example connected to a process control system or a decentralized database. On the one hand, this can be used to provide information about the operating status of the level measuring device 1' communicated. However, information about the fill level can also be sent via the bus system L. be transmitted to the container if necessary 3 to control existing inflows or outflows.

To determine the fill level L. is the level measuring device 1' above the container 3 attached to a flange connection provided for this purpose. A corresponding signal generation unit is independent of the measuring principle implemented 12th of the level measuring device 1' designed so that z. B. according to the FMCW principle or the pulse delay principle, a corresponding radar signal S _HF vertically in the direction of the product 2 is sent out. On the surface of the product 2 becomes the radar signal S _HF reflected and after a corresponding signal delay from the level measuring device 1' accordingly as a received signal E _HF receive. The signal propagation time of the radar signal depends on this S _HF , E _HF from the distance d = h - L of the level measuring device 1' towards the product surface. A corresponding evaluation unit 14th of the level measuring device 1' can based on the received signal E _HF the signal propagation time and, based on this, the level L. determine.

Also the fill level measuring device according to the invention 1 works according to the in connection with 1 described radar principle. According to the invention, the level L. but from a side wall 31 of the container 3 can be determined from. As in 2 is shown is the level measuring device according to the invention 1 therefore on a side flange connection 11 of the container 3 attached, with a rod-shaped antenna arrangement 13th of the level measuring device 1 for this purpose protrudes into the interior of the container, while a housing area with any interfaces and electronic components outside the container 3 remains.

Based on the antenna arrangement 11 that are orthogonal to the container wall 31 protrudes inwards and is thus aligned horizontally, the axis of the main radiation lobe of the radar signal runs S _HF perpendicular to the product 2 . As from the comparison of the front view and the side view of the level measuring device 1 in 2 As can be seen, the main radiation lobe is asymmetrical: that to the container wall 31 maximum parallel propagation a _p of the horizontal cross-section of the main radiation lobe is approx. 3 times as large as that of the container wall 31 maximum orthogonal spread a _o of the beam cross-section, so that the main radiation lobe of the radar signal S _HF to the container wall 31 is flattened out accordingly.

The asymmetrical main radiation lobe is through a corresponding aperture 131 causes within the antenna arrangement 13th is arranged. This is shown in more detail in 3 : The rod-shaped antenna arrangement 13th of the fill level measuring device according to the invention there 1 shows schematically two design variants of the aperture 131 , one elliptical and one rectangular. The aperture stands out 131 in both cases by a defined aperture length a ' _o , which is parallel to the rod axis 132 and an aperture width a ' _p which is orthogonal to the rod axis 132 runs out. Thus the relationship between the axis and the member corresponds to 132 parallel aperture length a ' _o and the aperture width a' _p orthogonal to the rod axis is the ratio between that to the container wall 31 maximum parallel propagation a _p and the one to the container wall 31 maximum orthogonal propagation a ' _{o of} the horizontal cross section of the main radiation lobe according to $$\frac{a_O}{a_p}=\frac{a{\text{'}}_O}{a{\text{'}}_p}$$

In the exemplary embodiment shown, this ratio corresponds to approximately 3 to 1. The aperture can be implemented 131 For example in the form of an appropriately designed quasi-optical lens, an in particular planar group antenna, or as a correspondingly asymmetrical quasi-optical mirror. Due to the rod-shaped design of the antenna unit 13th it is possible to arrange the antenna 13th given the quasi-optical properties of the aperture 131 to realize with minimal dimensions, so that the level meter 1 can also be mounted on the smallest possible side container openings. In this context, in contrast to the variant embodiment shown, it is also possible to use the antenna arrangement 13th for example by means of a corresponding ball joint in relation to the container wall 31 designed to be movable in such a way that the main radiation lobe of the radar signal S _HF is pivotable in a certain angular range. This ensures that the radar signal S _HF even with a slightly inclined container wall 31 perpendicular to the product 2 is sent out.

The signal generation unit 12th for generating the radar signal S _HF as well as the evaluation unit 14th based on the received signal E _HF the level L. are determined by the in 3 embodiment variant shown in the housing area of the level measuring device 1 arranged, which is after attachment of the level measuring device 1 outside the container 3 is located. Accordingly, these are electronic components 12th , 14th via a dielectric waveguide or a waveguide with the aperture 131 connect to. The advantage here is that the level measuring device 1 can more easily comply with any explosion protection requirements. A direct attachment of the signal generation unit 12th in the spotlight f the aperture 131 in contrast, offers the advantage of reduced signal loss.

List of reference symbols

1, 1 '

Level measuring device

2

Filling material

3

Container wall

4th

Parent unit

11

Fasteners

12th

Signal generation unit

13th

Antenna arrangement

14th

Evaluation unit

31

Container wall

131

Aperture

132

Bar axis

ap

The beam cross-section spreads parallel to the container wall

a'p

Aperture width

ao

The beam cross-section is orthogonal to the wall

a'o

Aperture length

d

distance

EHF

Received radar signal

f

Focus

H

Installation height

L.

Level

SHF

Radar signal

x

distance

QUOTES INCLUDED IN THE DESCRIPTION

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

Patent literature cited

• DE 102012104858 A1 [0003]
• DE 102013108490 A1 [0003]

Non-patent literature cited

• FMCW and pulse radar also in "Radar Level Detection, Peter Devine, 2000" [0004]

Claims (11)

Radar-based fill level measuring device for measuring a fill level (L) of a product (2) in a container (3), comprising: - a fastening means (11) by means of which the fill level measuring device (1) can be fastened to a lateral container wall (31), - A signal generation unit (12) which is designed _{to generate a radar signal (S HF} ), - an antenna arrangement (13), by means of which the radar signal (S _HF ) in the attached state is approximately perpendicular to the product (2) can be emitted and, after reflection on the surface of the filling material (2), can be received as a corresponding received signal (E _HF ), with o such an asymmetrical aperture (131), so that the radar signal (S _HF ) with a to the container wall ( 31) is emitted towards the flattened main radiation lobe, and - an evaluation unit (14) which is designed to determine the level (L) _{on the basis of the received signal (E HF).} Level measuring device according to Claim 1 , the aperture (131) being asymmetrically dimensioned in such a way that, in the fastened state, a horizontal cross section of the main radiation lobe has a maximum parallel spread (a _p ) in relation to the container wall (31) which is greater than that in relation to the container wall (31 ) maximum orthogonal expansion (a _o ) of the horizontal cross-section. Level measuring device according to Claim 2 , wherein the aperture (131) is dimensioned such that the maximum parallel expansion (a _p ) to the container wall (31) is at least twice as large as the maximum orthogonal expansion (a _o ) of the cross section to the container wall (31). Level measuring device according to Claim 2 or 3 , the aperture (131) being designed in such a way that, in the fastened state, the horizontal cross section of the main radiation lobe of the emitted radar signal (S _HF ) has an approximately elliptical or rectangular shape. Level measuring device according to one of the Claims 2 until 4th , the antenna arrangement (13) being designed in the shape of a rod, and the aperture (131) being designed in such a way that the maximum orthogonal spread (a _o ) of the cross-section of the main radiation lobe parallel to the rod axis (in relation to the container wall (31)) 132) runs. Filling level measuring device according to at least one of the preceding claims, wherein the antenna arrangement (13) _{comprises a radome which is transparent for the radar signals (S HF} , E _HF ) and which covers at least the aperture (131). Filling level measuring device according to one of the preceding claims, the asymmetrical aperture (131) being implemented in the form of a quasi-optical lens, in particular a planar group antenna, or as a correspondingly asymmetrical quasi-optical mirror. Filling level measuring device according to one of the preceding claims, wherein the signal generation unit (12) is designed _{to generate the radar signal (S HF} ) with such a tuned frequency, and wherein the aperture (131) is designed such that the main radiation lobe of the radar -Signal (S _HF ) touches the container wall (3) at a distance from the level measuring device (1) of at least 25 m. Filling level measuring device according to at least one of the preceding claims, wherein the signal generation unit (12) is designed _{to generate the radar signal (S HF} ) in a focal point (f) of the aperture (131). Level measuring device according to at least one of the Claims 1 until 8th , wherein the signal generating unit (12) is arranged in a housing area which is located outside the container wall (31) in the fastened state. Method for measuring the filling level of a filling material in a container by means of the filling level measuring device (1) according to one of the preceding claims, comprising the following method steps: - generating an electrical high-frequency signal, - approximately vertical transmission of the electrical high-frequency signal as a radar signal (p _HF ) to the filling material (2), the radar signal (S _HF ) being emitted with a main radiation lobe flattened towards the container wall (31), and - reception of a corresponding received signal (E _HF ) after reflection of the radar signal (S _HF ) on the product surface, and - Determination of the fill level (L) using at least the received signal (EHF).

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