DE20023063U1 - Fill level and pressure measurement sensor has surface protrusions of liquid-repellent material at suitable distances so that liquid can run off surface without leaving residues - Google Patents

Abstract

The device has protrusions on at least some of its surface consisting of a liquid-repellent material, whereby the protrusions are arranged at suitable distances from each other on the surface so that liquid can run off the surface without leaving residues. Any part of the surface in more or less direct contact with the measurement medium has the protrusions. Independent claims are also included for the following: a horn antenna for a fill level sensor, a rod antenna for a fill level sensor, a device for sending and/or receiving sound waves for a fill level sensor, a chord, cable or rod for a fill level sensor, a vibrating rod for a fill level sensor, a vibrating fork for a fill level sensor, a device for measuring pressure, a display and the use of a component with surface protrusions of liquid repelling material for a level or pressure sensor.

Description

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Munich ■ Hamburg ■ Dusseldorf New York

Patent attorneys

Dr. Walter Maiwald (Munich) Dr. Volker Hamm (Hamburg) Dr. Stefan Michalski (Düsseldorf) Dr. Regina Neuefeind (Munich) Dipl.-Ing. Udo Preuss (Munich) Dipl.-Ing. Korbinian Kopf, M.A. (Munich) Dr. Norbert Hansen (Munich) Dipl.-Ing. Lutz Kietzmann LLM (Düsseldorf) Dr. Martin Huenges (Munich) Dr. Holger Glas (Munich)

Lawyer

Stephan N. Schneller (Munich)

In co-operation with:
Maiwald Inc.,

European IP Services, New York Dipl.-Ing. Korbinian Kopf, M.A. U.S. Patent Agent

Reference number Our reference

200 23 063.8 V 7422/UP

VEGA GRIESHABER KG

Munich,

14 April 2003

VEGA GRIESHABER KG

Main Street 1-5

77709 Wolfach

Level or pressure sensor or individual components thereof with dirt-repellent

and/or self-cleaning properties

TECHNICAL AREA

The present invention relates to level or pressure measuring sensors as well as individual
Components thereof with dirt-repellent and/or self-cleaning properties, which

UP.UP

PO Box 330523 ■ 80065 Munich ■ Elisenhof ■ Elisenstrasse 3 ■ 80335 Munich

Tel. +49 (0)89 74 72 660 ■ Fax +49 (0)89 77 64 24 ■ http://www.maiwald.de ■ info@maiwald.de

Managing Director: Dr. Walter M®fc*alel«©r. Vojxej· HaiTirjr-*pr. SteipftTiSchöTsi« ..Df. Re'gliia Nku(3fei«&l ■ HRB No. 111307

Cooperation with: Dr. Schmidt-Fj3lzinjirfn & Kozi^TnJa iJ^hfcanwiJlte fl-«anr5bu5gV*· *· · j ·

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prevent contamination and deposits of, for example, condensate on components at risk of contamination. In the context of the present invention, these level or pressure measuring sensors are also referred to as sensors for short.

Sensors of the type mentioned, which are used in particular in process measurement technology, are often used in environments in which dirt or condensate deposits form on individual surfaces or components due to vapors, moisture, dust or contact with media involved in the process. These dirt or condensate deposits can impair the functional reliability, measurement accuracy or even cause the sensor to fail. Examples of this are radar or ultrasonic sensors that are used to measure distances or fill levels. In these cases, dirt and condensate on the transducer or antenna lead to interference with the emission and reception of sound or microwaves. If such contamination or condensate deposits are to be expected, the sensors must be cleaned at regular intervals in order to permanently guarantee the measurement accuracy and functional reliability of the sensors used. This leads to a not inconsiderable amount of warning and control effort. In extreme cases, the impairment of measurement accuracy due to dirt or condensate deposits on parts of the sensor can even lead to such standard sensors not being able to be used in this medium or in its environment.

In addition to the sensor components, which are in more or less direct contact with the medium to be measured, most sensors also have measurement displays, which generally do not come into direct contact with the medium to be measured. However, these measurement displays also become dirty due to dust and weathering depending on the external environmental conditions and are usually no longer readable without cleaning after a long period of use.

When using standard materials and coatings for level or pressure sensors and their measured value displays, selected for example based on aspects such as chemical resistance, temperature behavior, electrical and mechanical properties or ease of manufacture, attempts have usually been made to reduce the amount of work required for cleaning by making surfaces as smooth as possible and assemblies without corners or recesses, and by making the sensors easy to dismantle or replace. In some cases, expensive materials also had to be used to make it easier to clean components that are at risk of contamination when dirt or condensate deposits are particularly stubborn.

STATE OF THE ART

EP 0 658 525 B1 discloses a multi-layered, water-repellent film in general terms. However, this does not contain any reference to the specific application area of the invention. The subsequently published EP 1 055 924 A2 also only discloses a window of an optical measuring device with a special surface structure. Furthermore, the website "www-du-mich-auch.de/sonde/archiv/04-12-99/kompakt.html" describes the "lotus effect" named after the leaves of the lotus flower in general terms and explains its possible application for house facade paints. Finally, EP 772 514 describes self-cleaning surfaces through the action, sprinkling or presence of water, which have an artificial surface structure with hydrophobic elevations at a distance of 5 - 200 μm and a height of 5-100 μm. The self-cleaning property of such surface structures is based on the fact that dirt particles lying on the surface are absorbed by water droplets and removed without leaving any residue. To clean the surfaces in accordance with EP 772 514, the use of moving water is required, which absorbs dirt particles from the surface and removes them. The use of corresponding self-cleaning surfaces

-A-

in components of level or pressure measuring sensors to prevent dirt or condensate deposits or to increase the measuring accuracy and/or functional reliability of such sensors is not described in EP 772 514.

DESCRIPTION OF THE INVENTION

Level or pressure measuring sensors according to the invention with dirt-repellent and/or self-cleaning properties have, at least in part, elevations made of wetting-repellent material on the part of the outer surface which is in more or less direct contact with the medium to be measured, wherein the elevations are arranged at regular intervals from one another on the surface and liquid runs off the surface essentially without leaving residue.

Surprisingly, it has been shown that the use of analog surface structures, as described in EP 772 514 for water exposure, can lead to an increase in the measurement accuracy and functionality of level or pressure measuring sensors. In particular, if, for example, parts of a component at risk of contamination are at least temporarily immersed in the medium to be measured or are in direct contact with it, significant improvements in the measurement accuracy and functional reliability of the sensors used could be determined with level or pressure measuring sensors designed according to the invention. In particular, with aggressive, highly adhesive media, the use of corresponding sensors with dirt-repellent or self-cleaning properties is made possible in this way.

Level or pressure sensors according to the invention now have dirt-repellent and/or self-cleaning properties for the first time. In particular,

The novel design of certain surface areas also enables increased measurement accuracy and/or functional reliability and/or readability in the presence of dirt, dust or condensate-forming media. According to the invention, it is also possible for the first time to provide dirt-repellent and/or self-cleaning level or pressure measuring sensors, each of which can be adapted so that it has self-cleaning properties in the presence of a specific liquid. In addition, sensitive components of level or pressure measuring sensors can be designed to be insensitive to the effects of dirt or condensate. Furthermore, level or pressure measuring sensors can also be made available with significantly reduced monitoring, warning or cleaning requirements. Finally, it is now also possible to avoid residues on wetted components of level or pressure measuring sensors if parts of the sensors are temporarily immersed in a medium or are in direct contact with it. As can be seen from the above explanations, level or pressure measuring sensors according to the invention and their displays can be less sensitive to weather influences, in particular their functional reliability and readability can be permanently maintained even without cleaning.

The level or pressure measuring sensors according to the invention comprise at least one component whose outer surface at least partially has elevations made of wetting-repellent material, the elevations being arranged at regular intervals from one another on the surface, and liquid running off the surface essentially without leaving any residue. The choice of the material from which the surface and/or the elevations on it are made, as well as the height of the elevations and their distances from one another on the surface play an important role. By suitable selection and dimensioning, the wetting properties of devices according to the invention or of parts on their surface are designed in such a way that a suitable liquid medium runs off this surface almost without leaving any residue.

In particular, it is preferred to design the wetting properties in such a way that the liquid medium with which the device or parts thereof come into contact, for example the filling material in a container or condensate forming therefrom, runs off essentially without leaving residues.

Depending on the wetting properties of the liquid, its surface tension, polarity, viscosity, etc., the person skilled in the art will select a suitable material and suitable dimensions of the elevations on the device surface or parts thereof so that the liquid runs off essentially without leaving residue.

In the case of water and water mixtures, aqueous solutions and the like, as well as polar alcohols and ethers with similar wetting properties, the elevations are made of hydrophobic or permanently hydrophobized material, so that the surface has completely or at least partially hydrophobic or permanently hydrophobized elevations, the distance between which is in the range between 5 - 200 μηη and the height of which is in the range of 5-100 μηι.

Suitable materials include, for example, hydrophobic plastics such as polytetrafluoroethylene (Teflon®, also usable as an oleophobic agent), Kevlar®, polysilanes and surface-silanized materials, polysiloxanes, polyethylene, polypropylene, paraffins, waxes, metal soaps, etc. with additions of aluminum or zirconium salts, quaternary organic compounds, urea derivatives, fatty acid-modified melamine resins, chromium complex salts, silicones, tin organic compounds, glutaraldehyde, etc.

The wetting-repellent surface according to the invention means that any liquid that hits it runs off without leaving any residue. The liquid drops collect any particles that may be on the surface and/or in the interstices between the raised areas.

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(Dirt) particles and remove them from the surface, resulting in the dirt-repellent or self-cleaning effect.

If the devices according to the invention only come into contact with solids, such as powders, dusts and the like, it is preferable to remove contaminants resulting therefrom by making the surface self-cleaning in the presence of water, so that simple cleaning of the contaminated surfaces by exposure to water is possible.

For devices used in the presence of non-aqueous media, the material and dimensions of the elevations are adapted to the wetting properties of the liquid so that it runs off with almost no residue. For non-polar liquids such as oils, hydrocarbons, concentrated sulfuric acid and the like, the use of perfluorinated hydrocarbons is preferred. However, the self-cleaning effect of such surfaces, i.e. the ability to drain solid particles, is, as described by Barthlott et al. for water, solely a result of the combination of material properties and the distance and height of the elevations.

In particular, it is also preferred if only those components that are in direct contact with the medium to be measured or involved in the process are provided with a corresponding surface. Examples of this are antennas, sound transducers, electrodes or membranes of microwave or ultrasonic, capacitive or pressure sensors for level measurement technology or process pressure measurement technology.

The application of the self-cleaning structured surfaces can be achieved by a coating as well as by applying a film or the use of varnishes, or also by using materials such as metals, ceramics or plastics, the surface of which has the properties claimed according to the invention.

The corresponding surface structures can be embossed or etched. The application of powder structure paints, dispersions of powder particles in corresponding hydrophobic binders and the like can also be used in principle to produce the surface structures desired according to the invention on level or pressure measuring sensors.

Level or pressure measuring sensors according to the invention comprise devices for transmitting and receiving electromagnetic waves, devices for generating and receiving sound waves, devices for measuring electrical resistance or electrical conductivity, devices for detecting a limit level by means of a vibrating rod or a vibrating fork, devices for measuring a capacitance, devices for measuring pressure, devices for displaying a measured value and devices for measuring a distance.

In devices according to the invention for transmitting and receiving electromagnetic waves, it is preferred to provide at least the matching cone, a funnel or a reflection surface, preferably a parabolically curved reflection surface and/or a rod antenna with a surface structure according to the invention.

A device according to the invention for generating and receiving sound waves with a self-cleaning surface comprises one or more piezoelectronic sound generators, wherein the emitted or received sound waves have a frequency of 10-100 kHz.

In devices according to the invention for measuring an electrical resistance or an electrical conductivity, it is preferred to use one or more rope or rod measuring probes which are equipped with the self-cleaning surface according to the invention.

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In the case of devices according to the invention for detecting a limit level in aqueous and/or similarly polar media, it is preferred to equip the vibrating rods or vibrating forks used with a surface that has hydrophobic elevations at a distance of 5 - 200 μηη and with a height of 5-100 μιγ. This also applies to devices according to the invention for measuring a capacitance. When used in the presence of non-aqueous media, the material and structure of the elevations are to be adapted to the wetting properties of the medium according to the invention.

In a preferred device for measuring a distance by means of an electromagnetic wave which is guided along a rope or a rod, the invention provides that the rope or the rod has a self-cleaning structured surface.

When used in or in the vicinity of liquid media, the dirt-repellent and/or self-cleaning devices according to the invention ensure that condensate that forms can slide off the component surfaces with a self-cleaning surface structure more easily, whereby dirt particles are optionally washed away and a self-cleaning effect is achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

This can be seen from the attached figures using the example of a horn antenna of a radar level measuring device.

Fig. 1 shows a horn antenna of a radar level gauge with a conventional surface,

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Fig. 2 shows a horn antenna of a radar level gauge with self-cleaning surface.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The horn antenna 1 of such a level sensor protrudes into the interior of a container (e.g. a liquid tank) when installed. A radar measurement pulse emitted by the horn antenna 1 is reflected on the surface of the filling material in the container. The antenna catches the reflected pulse. The distance of the reflecting surface from the antenna, which corresponds to the filling level, is determined from the total running time of the pulse.

In the case of liquid filling materials, contact between the antenna 1 and filling material vapor leads to surface deposits 4 and possibly to the formation of condensate 3, e.g. in gaps and other narrow cavities in the antenna structure 1. Particulate filling materials can also reach the antenna 1, e.g. when filling the container.

While with conventional surfaces such condensate 3 or such particles 4 adhere to the antenna 1 and cause corresponding distortions in the transmitted or received radar signal, with the inventive level or pressure measuring sensors with a self-cleaning surface 2, condensate portions easily run off the antenna 1; adhering dirt particles 4 are absorbed by condensate drops 3 during operation of the device and carried away from its surface 2. The permanent self-cleaning of the sensor caused by this prevents the permanent adhesion of dirt to its surface 2 and thus ensures consistent, distortion-free measurement accuracy and functional reliability.

Since level or pressure measuring sensors are often used in outdoor systems that are exposed to normal weather conditions, it is preferred according to the invention to also equip those parts or components of the sensors with a self-cleaning surface that do not come into direct contact with the medium to be measured. It is therefore sensible and preferred according to the invention to equip housing parts and measured value or parameter displays that are exposed to the weather with a self-cleaning surface. The corresponding housings or measured value display parts of sensors according to the invention are accordingly regularly freed of adhering dirt or dust by the action of rain, which means that both a clean external appearance and the readability of displays are permanently maintained even without special cleaning effort.

Fill level or pressure measuring sensors according to the invention also have the advantage that the required cleaning or maintenance intervals are significantly extended or even completely eliminated, which leads to a considerable reduction in effort. If the fill level or pressure measuring sensors according to the invention still have to be cleaned from time to time, it is possible to ensure sufficient removal of dirt particles simply by exposure to running water (or cleaning solution). The use of mechanical cleaning processes or chemical cleaning agents, the residues of which can lead to corresponding contamination in the media used, is no longer necessary.

Claims (19)

1. A level or pressure measuring sensor, the part ( 2 ) of the outer surface of which, which is in more or less direct contact with the medium to be measured, has at least partially elevations made of wetting-repellent material, wherein the elevations are arranged at suitable distances from one another on the surface ( 2 ) so that liquid can drain off the surface ( 2 ) without leaving residue. 2. Sensor according to claim 1, characterized in that the elevations consist of hydrophobic or permanently hydrophobicized material, and their distance from one another is in the range between 5-200 µm and their height is in the range between 5-100 µm, wherein the material, distance and dimensions of the elevations are adapted to the surrounding medium. 3. Sensor according to one of claims 1 and 2, characterized in that a device ( 1 ) for transmitting and/or receiving electromagnetic waves, in particular in the microwave range, is present. 4. Sensor according to claim 3, characterized in that an adaptation cone ( 5 ), a funnel ( 1 ), a reflection surface or a rod antenna is equipped with the elevations. 5. Sensor according to one of claims 1 and 2, characterized in that a device ( 1 ) for transmitting and/or receiving sound waves is present. 6. Sensor according to claim 5, characterized in that the sound waves are generated by one or more piezoelectronic sound generators which are equipped with the elevations. 7. Sensor according to claim 5 or 6, characterized in that the transmitted or received waves are in the frequency range of 10-100 kHz. 8. Sensor according to one of claims 1 and 2, characterized in that it comprises a rope, cable or rod along which electromagnetic waves are guided and on whose surface the elevations are present. 9. Sensor according to one of claims 1 and 2, characterized in that a vibrating rod or a vibrating fork is present, wherein the vibrating rod or the vibrating fork is equipped with the elevations on the surface. 10. Sensor according to one of claims 1 and 2, characterized in that a device for detecting pressures is present, which is equipped with the elevations. 11. Sensor according to one of claims 1 to 10, characterized in that the sensor part ( 2 ) which is exposed to external environmental conditions is at least partially equipped with the elevations. 12. Sensor according to claim 11, characterized in that the sensor part which is exposed to the external environmental conditions is a housing or a measured value or parameter display. 13. Horn antenna ( 1 ) for a level measuring sensor, in particular comprising an adaptation cone ( 5 ), a funnel and a reflection surface, the part ( 2 ) of the outer surface of which, which is in more or less direct contact with the medium to be measured, has at least partially elevations made of wetting-repellent material, wherein the elevations are arranged at suitable distances from one another on the surface so that liquid can drain off the surface without leaving residue. 14. Rod antenna for a level measuring sensor, the part of the outer surface of which, which is in more or less direct contact with the medium to be measured, has at least partially elevations made of wetting-repellent material, wherein the elevations are arranged at suitable distances from one another on the surface so that liquid can drain off the surface without leaving residue. 15. Device for transmitting and/or receiving sound waves for a level measuring sensor, the part of the outer surface of which which is in more or less direct contact with the medium to be measured has at least partially elevations made of wetting-repellent material, wherein the elevations are arranged at suitable distances from one another on the surface so that liquid can drain off the surface without leaving residue. 16. Rope, cable or rod for a level measuring sensor, the part of the outer surface of which which is in more or less direct contact with the medium to be measured has at least partially elevations made of wetting-repellent material, the elevations being arranged at suitable distances from one another on the surface so that liquid can drain off the surface without leaving residue. 17. Vibrating rod for a level measuring sensor, the part of the outer surface of which, which is in more or less direct contact with the medium to be measured, has at least partially elevations made of wetting-repellent material, the elevations being arranged at suitable distances from one another on the surface so that liquid can drain off the surface without leaving residue. 18. Vibrating fork for a level sensor, the part of the outer surface of which which is in more or less direct contact with the medium to be measured has at least partially elevations made of wetting-repellent material, the elevations being arranged at suitable distances from one another on the surface so that liquid can drain off the surface without leaving residue. 19. Device for measuring pressures for a pressure measuring sensor, the part of the outer surface of which which is in more or less direct contact with the medium to be measured has at least partially elevations made of wetting-repellent material, the elevations being arranged at suitable distances from one another on the surface so that liquid can drain off the surface without leaving residue.