DE102021131498A1 - level gauge - Google Patents

Abstract

The invention relates to explosion-proof fill level measuring device types which can be certified with less effort and have a reduced explosion pressure in their housing (11). For this purpose, the filling level measuring device (1) according to the invention comprises: a housing (11) with an interior (111); A transmitting/receiving unit (12) arranged there for generating radar signals (SHF) in order to determine the fill level (L) on the basis of corresponding received signals (RHF); An antenna (13) for transmitting and receiving the radar signals (RHF, SHF); A measuring device neck (14) arranged between the antenna (13) and the housing (11) for thermal insulation; And an inside (141) of the measuring device neck (14) arranged waveguide (15) for radar signal transmission. According to the invention, the filling level measuring device (1) has a filling body (16) which fills the interior (141) between the measuring device neck (14) and the waveguide (15). As a result, the volume inside (141) of the neck (14) of the measuring device is no longer considered potentially inflammable by the transmitter/receiver unit (12). Thus, the fill level measuring device type according to the invention can be certified with regard to explosion protection independently of the length of the measuring device neck (14).

Description

The invention relates to explosion-proof fill-level measuring device types that can be certified with reduced effort and have a reduced, ignitable gas volume.

Appropriate field devices are used in process automation technology to record relevant process parameters. For the purpose of recording the respective process parameters, suitable measurement principles are implemented in the corresponding field devices in order to record a fill level, a flow rate, a pressure, a temperature, a pH value, a redox potential or a 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). In principle, the higher the frequency, the higher the measurement resolution that can be achieved. 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. Depending on the application, however, high temperatures, high pressure or dangerous gases prevail inside the container. Therefore, if required, the transmitter/receiver unit is thermally encapsulated by a measuring device neck from the antenna. The measuring device neck is designed with different lengths depending on how high the heat resistance of the respective level measuring device type must be. The longer the gauge neck, the higher the heat resistance. Particularly in the case of radar-based fill level measuring device types, in whose transmitter/receiver unit radar frequencies of 60 GHz or higher are implemented, the radar signal is routed to the antenna via a waveguide running centrally in the measuring device neck.

On the other hand, the neck of the measuring device must separate the transmitter/receiver unit from the inside of the container in such a way that explosion protection is maintained. In this case, the corresponding level measuring device type is often to be designed in compliance with the international standard IEC 60079-1-1:2014 for explosion protection. Among other things, this standard takes into account the size of the gas volume surrounding the transmitter/receiver unit with regard to potential ignition. On the one hand, this includes the interior volume of the housing in which the transmitter/receiver unit is arranged. However, the inside of the neck of the measuring device also counts as a relevant volume, as this usually borders on the interior of the housing without any structural separation.

As a result, each type of level gauge that has its own gauge neck length must undergo a separate certification process with regard to the explosion protection standard, even if the remaining structure or the remaining components correspond to types of level gauges that have already been certified. In addition, the ignitable gas volume inside the device housing should be as small as possible in order to achieve the lowest possible explosion pressure with the ignition allowed by the standard. The invention is therefore based on the object of simplifying the certification process of fill level measuring device types, which differ only in the length of their measuring device neck, with regard to explosion protection specifications.

• - Ein Gehäuse mit einem Innenraum,
• - eine im Innenraum angeordnete Sende-/Empfangs-Einheit, die ausgelegt ist, Radar-Signale zu erzeugen und anhand entsprechender Empfangs-Signale den Füllstand zu bestimmen,
• - eine Antenne zum Aussenden der Radar-Signale gen Füllgut und/oder zum Empfang der Empfangs-Signale nach Reflektion an der Füllgut-Oberfläche,
• - einen zwischen der Antenne und dem Gehäuse angeordneten Messgeräte-Hals,
• - einen im Inneren des Messgeräte-Halses angeordneten Wellenleiter, über welchen die Signale zwischen der Sende-/Empfangs-Einheit und der Antenne geführt werden.

The invention solves this problem with a fill level measuring device for determining fill levels of filling goods in containers, which includes the following components:

• - A housing with an interior,
• - a transmitter/receiver unit arranged in the interior, which is designed to generate radar signals and to determine the fill level based on corresponding received signals,
• - an antenna for emitting the radar signals towards the filling material and/or for receiving the received signals after reflection on the filling material surface,
• - a gauge neck located between the antenna and the housing,
• - A waveguide arranged inside the neck of the measuring device, via which the signals between the transmitter/receiver unit and the antenna are routed.

The filling level measuring device is characterized by a packing which fills the interior between the measuring device neck and the waveguide as completely as possible, ie preferably at least fills at least 90% to 95%. As a result, the volume inside the neck of the measuring device no longer counts as potentially ignitable by the transmitter/receiver unit, but only the volume of the interior of the housing. This means that the corresponding type of level gauge can be certified with regard to explosion protection within a single certification process, regardless of the length of the neck of the gauge. In addition, the explosion pressure and thus the housing wall thickness are reduced in accordance with the reduced volume.

In the context of the invention, it is not strictly prescribed how the filling body is realized: The filling body can be introduced into the neck of the measuring device, for example, in the form of a rigid foam, in particular PVC, PS or PU. Alternatively, the filling body can also be designed as a ceramic molded part or as a plastic molded part, which is made in particular of PP, PE or PC. Another advantage of the filling body according to the invention is that the thermal insulation between the antenna or the interior of the container and the transmitter/receiver unit can be further improved.

If the waveguide is designed as a waveguide, it must be encapsulated in a puncture-resistant manner using a radar-permeable seal to separate the interior of the housing. Such a seal can be designed as a glass seal, for example. The position of the seal in the waveguide is not fixed here. For example, the seal can be arranged on an end region of the waveguide that faces the antenna.

The design according to the invention is particularly advantageous for radar-based level measuring device types whose transmitter/receiver unit emits or receives the radar signal at frequencies of 60 GHz or higher, since the radar signal in this case has a center in the Meters-neck running waveguide is guided to the antenna. In this context, the term “unit” within the scope of the invention is in principle understood 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 module are arranged on a common printed circuit board or on several connected printed circuit boards.

• 1: Ein Radar-basiertes Füllstandsmessgerät an einem Behälter,
• 2: eine Querschnittsansicht des erfindungsgemäßen Füllstandsmessgerätes, und
• 3 ein vergrößerter Ausschnitt im Bereich des Messgeräte-Halses.

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,
• 2 : a cross-sectional view of the filling level measuring device according to the invention, and
• 3 an enlarged section in the area of the measuring device neck.

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.

As a rule, the fill level measuring device 1 has a separate interface unit, such as "4-20 mA", "PROFIBUS", "HART", or "Ethernet" with a higher-level unit 4, such. 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 if necessary. However, other information about the general operating status of the fill-level measuring device 1 can also be communicated.

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 only the antenna 13 of the fill level measuring device 1 is directed into the container 3 vertically downwards towards the filling material 2, while the other components 11, 14 of the fill level measuring device 1 are arranged outside of the container 3 .

proportional zum Abstand d zwischen dem Füllstandsmessgerät 1 und dem Füllgut 2, wobei c die Radar-Ausbreitungsgeschwindigkeit der Lichtgeschwindigkeit entspricht. 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. Zur Bestimmung der Signallaufzeit t bzw. des Füllstandes L anhand des eingehenden Empfangs-Signals R_HF dient eine entsprechend ausgelegte Sende-/Empfangs-Einheit 12 des Füllstandsmessgerätes 1, in welcher beispielsweise das FMCW- oder Pulslaufzeit-Messprinzip implementiert ist. Außerdem dient die Sende-/Empfangs-Einheit 12 zur Erzeugung des auszusendenden Radar-Signals S_HF. Bei der in 2 bzw. 3 gezeigten Ausführungsvariante ist die Sende-/Empfangs-Einheit 12 innerhalb des Geräte-Gehäuses 11 bspw. als monolithisch gekapseltes SMD-Bauteil auf einer der Antenne 13 zugewandten Seite einer Leiterplatte angeordnet.Radar signals S _HF are emitted in the direction of the surface of the filling material 2 via the antenna 13 . 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 13. 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 corresponds to the radar propagation speed of 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 . A correspondingly designed transmitter/receiver unit 12 of the level measuring device 1, in which the FMCW or pulse transit time measuring principle is implemented, is used to determine the signal propagation time t or the filling level L 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. At the in 2 or. 3 In the embodiment variant shown, the transmitter/receiver unit 12 is arranged within the device housing 11, for example as a monolithically encapsulated SMD component on a side of a printed circuit board facing the antenna 13.

1 1 shows that the housing 11 of the fill level measuring device 1 is spaced apart from the antenna 13 or from the container 3 via a measuring device neck 14 in order to thermally decouple the transmitter/receiver unit 12 housed there from the container interior. The length l of the measuring device neck 14 varies depending on the level measuring device type, depending on how high the potential thermal load from the inside of the container is. The higher the thermal load, the longer the measuring device neck 14 must be designed.

The antenna 13 is coupled to the transmitter/receiver unit 12 via a waveguide 15 acting as a waveguide, with the waveguide 15 emanating from the transmitter/receiver unit 12 orthogonally in relation to the printed circuit board and along the axis of the measuring device neck 14 runs. In this case, the waveguide 15 is preferably made of a metal, such as stainless steel, for the purpose of high-frequency conductivity and mechanical stability. Apart from its lower end area, the cross section of the waveguide 15 is dimensioned such that the waveguide 15 is spaced from the wall of the measuring device neck 14 by approximately twice its outer radius. As a result, a corresponding free space is formed without further measures, through which, on the one hand, the waveguide 15 is thermally insulated from the neck 14 of the measuring device. On the other hand, the spacing between the waveguide 15 and the measuring device neck 14 promotes the thermal insulation between the antenna 13 and the transmitter/receiver unit 12.

As in particular in the enlarged representation of 3 As can be seen, a filling body 16 is introduced between the waveguide 15 and the inner wall of the neck 14 of the measuring device, which fills the interior space 141 completely and at the same time has a thermally insulating effect. For this purpose, the filling body 16 can be introduced during the manufacture of the level measuring device 1, for example in the form of a hard foam. However, it is also conceivable to design the filling body 16 as a molded part, which is inserted into the neck 14 of the measuring device together with the waveguide 15, for example, during production. In order to have a thermally insulating effect, it is advantageous if it is made of a ceramic or a plastic such as PTFE, PVDF or PFA.

Due to the inventive design, the volume inside 141 of the measuring device neck 14 no longer counts as potentially ignitable by the transmitter/receiver unit 12, but only the volume in the interior 111 of the housing 11 Be certified as part of a single certification process, regardless of how long the neck of the measuring device is, provided that the remaining components, in particular the housing 11 and the transmitter/receiver unit 12, are otherwise structurally identical. This simplifies the certification of fill-level measuring device types with measuring device necks 14 that can be executed in different lengths with regard to explosion protection in accordance with the IEC 60079-1-1:2014 standard, since the respective fill-level measuring device type is not available separately for each available length l of the measuring device neck 14 must be certified. As a further aspect, this results in the fact that the interior 141 of the measuring device neck 14 no longer has to be taken into account with regard to explosion protection. As a result, the explosion pressure to be taken into account is reduced in terms of approval, as a result of which the housing 11 can be designed with a smaller wall thickness.

In contrast to the in 2 or. 3 In the embodiment variant shown, it is also conceivable not to attach the glass seal 17 to that end area of the waveguide 15 which faces the antenna 13, but rather to attach it to the opposite end area.

As an alternative to the in 2 or. 3 In the embodiment variant shown, instead of a waveguide 15, a waveguide made of a dielectric material such as PP, PE or PTFE can also be used. In this case, the glass seal 17 can be dispensed with, since such a waveguide has no cavity which can represent a connection between the interior 141 of the neck 14 of the measuring device and the interior 111 of the housing 11 .

Reference List

1

level gauge

2

contents

3

container

4

parent unit

11

Housing

12

Transmitting/receiving unit

13

antenna

14

gauges neck

15

waveguide

16

random packing

17

poetry

111

interior of the housing

141

Inside of the gauge neck

A

Enlarged section

i.e

distance

H

installation height

L

level

l

Gauge neck length

RHF

Reflected radar signal

SHF

radar signal

Claims (8)

Filling level measuring device for determining a filling level (L) of a filling (2) in a container (3), comprising the following components: - a housing (11) with an interior (111), - a transmitting/receiving device arranged in the interior (111) Unit (12) which is designed to generate radar signals (S _HF ) and to determine the fill level (L) on the basis of corresponding received signals (R _HF ), - an antenna (13) for emitting the radar signals (S _HF ) gene filling material (2) and/or for receiving the received signals (R _HF ) after reflection on the filling material surface, - a measuring device neck (14) arranged between the antenna (13) and the housing (11), - A waveguide (15) arranged inside (141) of the neck (14) of the measuring device, via which the signals (S _HF , R _HF ) are conducted between the transmitting/receiving unit (12) and the antenna (13). , characterized by - at least one filling body (16) which at least partially fills the interior (141) between the measuring device neck (14) and the waveguide (15). level gauge claim 1 , wherein the filling body (16) fills the interior (141) to at least 90%, in particular 95%. level gauge claim 1 or 2 , wherein the filling body (16) is introduced into the measuring device neck 14 in the form of a hard foam, in particular PVC, PS or PU. level gauge claim 1 or 2 , wherein the filling body (16) is designed as a plastic molded part, which is made in particular of PTFE, PVDF or PFA. level gauge claim 1 or 2 , wherein the filling body (16) is designed as a ceramic molded part. Level gauges according to one of the preceding claims, wherein the waveguide (15) is designed as a waveguide. level gauge claim 5 , wherein the waveguide (15) is encapsulated in an impact-resistant manner by means of a radar-permeable seal (17), the seal (17) being designed in particular as a glass seal. Filling 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 corresponding reception signals (R _HF ). process.

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