DE102021131501A1 - level gauge - Google Patents

Abstract

The invention relates to a fill level measuring device (1) for determining fill levels (L) in containers (3), which has the following components: an antenna (11) for transmitting radar signals (SHF) towards the filling material (2) and/or for receiving them Corresponding received signals (RHF) after reflection on the product surface; And a transmitter/receiver unit (12), which is designed to generate the radar signals (SHF) and to determine the fill level (L) using the received signals (RHF), with a waveguide segment (121) , which is arranged in such a way that the radar signals (SHF, RHF) can be transmitted to or from the antenna (11). According to the invention, the fill-level measuring device (1) is characterized by a separating element (13) which electrically separates the waveguide segment (121) from the antenna (11) and also makes the waveguide segment (121) gen antenna (11) dustproof closes without absorbing the radar signals (SHF, RHF). The advantage here is that the separating element (13) has a fluid-sealing effect in addition to the galvanic isolation. This simplifies the structure of the fill level measuring device (1), since an additional glass seal can be dispensed with.

Description

The invention relates to a level gauge.

Appropriate field devices are used in process automation technology to record relevant process parameters. In order to record the respective process parameters, suitable measuring principles are implemented in the respective field device type in order to record a fill level, flow rate, pressure, temperature, pH value, redox potential or conductivity as process parameters. A wide variety of field device types are manufactured and sold by the Endress + Hauser group of companies.

Non-contact measuring methods have become established for level measurement of filling goods in containers, as they are robust and low-maintenance. Another advantage of non-contact measuring methods is the ability to measure the level almost continuously. In the field of continuous level measurement, radar-based measurement methods are therefore predominantly used (in the context of this patent application, the term “radar” refers to signals or electromagnetic waves with frequencies between 0.03 GHz and 300 GHz). The pulse propagation time method and FMCW (“Frequency Modulated Continuous Wave”) have established themselves as measuring methods. Radar-based level measurement is described in more detail, for example, in "Radar Level Detection, Peter Devine, 2000".

Due to the principle, the antenna of radar-based fill level measuring devices must be attached with direct contact to the inside of the container, since there must not be a barrier impermeable to radar signals between the antenna of the fill level measuring device and the filling. For explosion protection purposes in particular, however, a spatial separation between the active, i.e. power-supplied, transmitter/receiver unit for processing the radar signals and the passive antenna is often required. In addition, high temperatures, high pressure or dangerous gases prevail inside the container, depending on the application. Therefore, depending on the design, the transmitter/receiver unit is encapsulated at least dust-tight or even completely fluid-tight by the exposed antenna.

For reasons of explosion protection, the permissible voltages within the transmitter/receiver unit are also limited to a maximum value, in particular to prevent flashovers that could lead to ignition. In addition to dust-tight encapsulation, radar-based level gauges also require galvanic isolation of the transmitter/receiver unit from the antenna. This prevents corresponding voltage limit values from being exceeded if high voltages are suddenly present from the outside. Since the transmitter/receiver unit is designed as a monolithically integrated half-litre component, particularly at frequencies above 60 GHz, and is accordingly connected directly to the antenna via a waveguide segment, a galvanically isolating sleeve can be used between the antenna and the waveguide segment . Overall, however, it is clear that the design effort increases due to the increasing number of requirements.

The invention is therefore based on the object of providing a reliable filling level measuring device with a structurally reduced complexity.

• - Eine Antenne zum Aussenden von Radar-Signalen gen Füllgut und/oder zum Empfang entsprechender Empfangs-Signale nach Reflektion an der Füllgut-Oberfläche, und
• - Eine Sende-/Empfangs-Einheit, die ausgelegt ist, die Radar-Signale zu erzeugen und anhand der Empfangs-Signale den Füllstand zu bestimmen, mit
  • ◯ einem Hohlleiter-Segment, das derart angeordnet ist, so dass die Radar-Signale zur bzw. von der Antenne übertragbar sind.

The invention solves this problem with a fill level measuring device for determining a fill level of a filling material in a container, which comprises the following components:

• - An antenna for emitting radar signals towards the filling material and/or for receiving corresponding received signals after reflection on the filling material surface, and
• - A transmitter/receiver unit that is designed to generate the radar signals and to determine the fill level based on the received signals
  • ◯ a waveguide segment arranged in such a way that the radar signals can be transmitted to and from the antenna.

According to the invention, the fill level measuring device is characterized by a separating element which on the one hand electrically separates the waveguide segment from the antenna and on the other hand seals the waveguide segment from the antenna (e.g. in accordance with guideline EN 60079-11) in a dust-tight manner. The separating element is designed in such a way that it is permeable to the radar signals despite the dust seal. In the case of guideline EN 60079 - 11, it is necessary for the separating element to have a wall thickness of at least 0.5 mm.

The advantage of the fill level measuring device according to the invention is that the separating element, in addition to the galvanic isolation, also provides protection against dust-related explosion. As a result, the structural complexity of the fill level measuring device can be reduced, since an additional glass separation can be dispensed with. In particular, fill level measuring devices whose transmission/reception unit generates the radar signals with a frequency of 60 GHz or more or processes corresponding reception signals benefit from the design according to the invention. Because because of Correspondingly small waveguide cross-section, a galvanic isolation or dust seal must generally be designed more filigree with increasing frequency.

Within the scope of the invention, the term “unit” is understood in principle to mean a separate arrangement or encapsulation of those electronic circuits that are provided for a specific application, for example for high-frequency signal processing or as an interface. Depending on the intended use, the corresponding module can therefore include corresponding analog circuits for generating or processing corresponding analog signals. However, the module can also include digital circuits such as FPGAs, microcontrollers or storage media in conjunction with appropriate programs. The program is designed to carry out the necessary procedural steps or to apply the necessary arithmetic operations. In this context, different electronic circuits of the module within the meaning of the invention can potentially also access a common physical memory or be operated using the same physical digital circuit. It is irrelevant whether different electronic circuits within the unit are arranged on a common printed circuit board or on several connected printed circuit boards.

The material of the separating element is not strictly specified within the scope of the invention. If the separating element is generally made of a dielectric material such as glass, ceramic or plastic (in particular PTFE or PFA), it is ensured that the radar signals are not completely absorbed or reflected by the separating element. In particular, a reflection can be effectively suppressed if the separating element has a wall thickness that corresponds to a whole multiple of half the wavelength of the radar signals. The dust-tight delimitation of the waveguide segment by the separating element can also be ensured in that the transmitter/receiver unit is fastened in the housing, for example via a spring, in such a way that the waveguide segment is pressed against the separating element with a defined force. element is pressed. It is also advantageous within the scope of the invention if the housing in which the transmitter/receiver unit is arranged is arranged electrically isolated from the transmitter/receiver unit, since the housing may have to be electrically connected to the antenna.

• 1: Ein Radar-basiertes Füllstandsmessgerät an einem Behälter, und
• 2: eine Querschnittsansicht des erfindungsgemäßen Füllstandsmessgerätes.

The invention is explained in more detail on the basis of the following figures. It shows:

• 1 : A radar-based level gauge on a tank, and
• 2 : a cross-sectional view of the filling level measuring device according to the invention.

For a basic understanding of the fill level measuring device 1 according to the invention, 1 a container 3 is shown with a filling material 2, the filling level L of which is to be determined. Depending on the type of filling material 2 and depending on the area of use, the container 3 can be up to more than 100 m high. The conditions in the container 3 also depend on the type of filling material 2 and the area of application. In the case of exothermic reactions, for example, high temperatures and pressures can occur. In the case of dusty or flammable substances, appropriate explosion protection conditions must be observed inside the container.

In order to be able to determine the fill level L independently of the prevailing conditions, the fill level measuring device 1 is fitted above the filling material 2 at a known installation height h above the brine of the container 3 . The fill level measuring device 1 is attached or aligned to a corresponding opening of the container 3 so that it is pressure and media-tight in such a way that an antenna 11 of the fill level measuring device 1 is directed vertically downwards towards the filling material 2 into the container 3 .

proportional zum Abstand d zwischen dem Füllstandsmessgerät 1 und dem Füllgut 2, wobei c die Radar-Ausbreitungsgeschwindigkeit entsprechend Lichtgeschwindigkeit ist. Die Signallaufzeit t kann vom Füllstandsmessgerät 1 beispielsweise mittels des FMCW- oder mittels des Pulslaufzeit-Verfahrens bestimmt werden. Hierdurch kann das Füllstandsmessgerät 1 beispielsweise auf Basis einer entsprechenden Kalibration die gemessene Laufzeit t dem jeweiligen Abstand d zuordnen. Hierüber kann das Füllstandsmessgerät 1 gemäß $$d=h-L$$

wiederum den Füllstand L bestimmen, sofern die Einbauhöhe h im Füllstandsmessgerät 1 hinterlegt wird.Radar signals S _HF are emitted in the direction of the surface of the filling material 2 via the antenna 11 . After reflection on the surface of the filling material, the level measuring device 1 receives the reflected radar signals R _HF again via the antenna 11. The signal propagation time t between transmission and reception of the respective radar signal S _HF , R _HF is according to $$t=\frac{2\ast \mathrm{i.e}}{c}$$

proportional to the distance d between the level gauge 1 and the filling material 2, where c is the radar propagation speed corresponding to the speed of light. The signal propagation time t can be determined by the fill level measuring device 1, for example using the FMCW method or using the pulse propagation time method. As a result, the fill-level measuring device 1 can assign the measured transit time t to the respective distance d, for example on the basis of a corresponding calibration. About this, the level gauge 1 according to $$\mathrm{i.e}=H-L$$

in turn determine the fill level L if the installation height h is stored in the fill level measuring device 1 .

As a rule, the fill level measuring device 1 is connected via a separate interface unit, such as "4-20 mA", "PROFIBUS", "HART", or "Ethernet". with a parent unit 4, such as. B. connected to a local process control system or a decentralized server system. The measured filling level value L can be transmitted via this, for example in order to control inflows or outflows of the container 3 . However, other information about the general operating status of the fill-level measuring device 1 can also be communicated. The separate accommodation of the interfaces as a separate module has the advantage that it can also be used in other modular field device types in addition to level measuring devices.

As in 2 is outlined, the antenna 11 within the level measuring device 1 is controlled in terms of high frequency by a transceiver unit 12, in which the FMCW or pulse propagation time measuring principle, for example, is implemented to determine the signal propagation time t based on the incoming reception signal R _HF . In addition, the transmission/reception unit 12 is used to generate the radar signal S _HF to be transmitted. For this purpose, the transmitter/receiver unit 11 in the embodiment variant shown is arranged within a device housing 14, for example as a monolithically encapsulated SMD component on a side of a printed circuit board facing the antenna 11.

The printed circuit board, together with the transmitter/receiver unit 12, is enclosed within the housing 14 by an encapsulation 15, which is made of a plastic such as PC, PE, PP or PA, for example. This makes it possible to additionally encapsulate the printed circuit board together with the transmitter/receiver unit 12 using a casting compound for explosion protection purposes (not explicitly mentioned in 2 shown). As a high-frequency coupling to the horn antenna of the antenna 11, the transmission/reception unit 12 includes a straight waveguide segment 121, which extends orthogonally from the transmission/reception unit 12 in relation to the printed circuit board. The waveguide segment 121 or the printed circuit board is fastened in the encapsulation 15 in such a way that the waveguide segment 121 is routed to the outside through a passage 141 in the housing 14, where the antenna 11 forms a galvanic contact on the housing 14 is attached. In terms of safety, it is not relevant whether a galvanic contact is formed between the antenna 11 and the housing 14 .

At the in 2 In the embodiment variant shown, the antenna 11 is fastened to the housing 14 at the level of a galvanic isolating element 13 by means of a screw thread, which is aligned along the axis of the waveguide segment 121 . A radially symmetrical step is formed below the separating element 13 at the interface between the antenna 11 and the housing, which serves as an end stop for the screw thread and thereby prevents any creepage distance via the antenna 11 into the interior of the housing 14 for explosion protection purposes prevents.

The galvanic isolation 13 is designed in such a way that the waveguide segment 121 and the antenna 11 are electrically insulated from one another when the level gauge 1 is in the installed state, with the waveguide segment 121 and the antenna 11 being connected to the galvanic isolation 13 from the other side without a gap adjoin. For this purpose, the galvanic isolation 13 is made of an electrically insulating material such as a plastic, a glass or a ceramic. Thus, any overvoltage at the transmitter/receiver unit 12 cannot be transmitted into the interior of the container 3, which ensures appropriate protection against explosion.

The encapsulation 15 is pressed against the galvanic isolation 13 with a defined force so that the waveguide segment 121 borders the galvanic isolation element 13 without a gap for optimal HF transmission. For this purpose, a spring element 16 is clamped inside the housing 14 on that outside of the encapsulation 15 which faces away from the waveguide segment 121 . The interior of the housing 14 serves as a guide for the encapsulation 15 or the waveguide segment 121.

How out 2 As becomes clear, the galvanic isolating element 13 according to the invention does not include a feedthrough between the waveguide segment 121 and the antenna 11. Rather, the isolating element 13 is designed in such a way that the waveguide segment 121 is sealed off from the antenna 11 in a dust-tight manner. A wall thickness of the separating element 13 of at least 0.5 mm is required so that the corresponding EN guideline with regard to dust tightness is observed. In order to still be able to determine the fill level L, the separating element 13 is made of a material that is transparent to the radar signals S _HF , R _HF . This can be achieved, for example, if PTFE or PFA is used as the plastic material for the separating element 13 and if the wall thickness of the separating element 13 is a whole multiple of half the wavelength of the radar signals S _HF , R _HF , so that any reflections of the radar signals S _HF , R _HF at the separating element 13 are avoided by negative interference. To ensure adequate fluid tightness, it is advantageous in the case of PTFE or PFA if the separating element 13 has a wall thickness of more than 0.5 mm. The advantage of the design of the galvanic isolating element according to the invention is that, in addition to the galvanic isolation, this also provides protection against dust conditional explosion is reached. Overall, the galvanic isolating element 13 reduces the design complexity of the fill level measuring device 1 since an additional glass separation can be dispensed with.

Reference List

1

level gauge

2

contents

3

container

4

parent unit

11

antenna

12

Transmitting/receiving unit

13

separator element

14

Housing

15

encapsulation

16

feather element

121

waveguide segment

141

execution

i.e

distance

H

installation height

L

level

RHF

Reflected radar signal

SHF

radar signal

Claims (8)

Level measuring device for determining a level (L) of a filling (2) in a container (3), comprising the following components: - An antenna (11) for emitting radar signals (S _HF ) towards the filling (2) and/or for receiving corresponding received signals (R _HF ) after reflection on the surface of the filling material, - a transmitter/receiver unit (12) which is designed to generate the radar signals (S _HF ) and based on the received signals (R _HF ) to determine the filling level (L), with o a waveguide segment (121), which is arranged in such a way that the radar signals (S _HF , R _HF ) can be transmitted to or from the antenna (11), and - a separating element (13) which o electrically separates the waveguide segment (121) from the antenna (11), o closes the waveguide segment (121) away from the antenna (11) in a dust-tight manner, and o is transparent to the radar signals (S _HF , R _HF ). level gauge claim 1 , comprising: - a housing (14) in which the transmitter/receiver unit (12) is arranged in a galvanically isolated manner. level gauge claim 2 , wherein the housing (14) is galvanically connected to the antenna (11). Level gauge according to one of claims 2 until 3 , The transmitter/receiver unit (12) being fastened in the housing (14) in such a way that the waveguide segment (121) is pressed against the separating element (13) with a defined force. Level gauge according to one of the preceding claims, wherein the separating element (13) has a wall thickness which corresponds to a whole multiple of half the wavelength of the radar signals (S _HF , R _HF ). Level gauge according to one of the preceding claims, wherein the separating element (13) is made of a dielectric material, in particular a glass, a ceramic or a plastic. level gauge claim 6 , wherein the separating element (13) has a wall thickness of at least 0.5 mm. Level measuring device according to one of the preceding claims, wherein the transmission/reception unit (12) is designed to generate the radar signals (S _HF ) with a frequency of at least 60 GHz or to process corresponding reception signals (R _HF ). .

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