EP2758752A1

EP2758752A1 - Measuring device

Info

Publication number: EP2758752A1
Application number: EP12756140.5A
Authority: EP
Inventors: Sergej Lopatin; Ralf Leisinger; Ralf Reimelt; Peter KLÖFER
Original assignee: Endress and Hauser SE and Co KG
Current assignee: Endress and Hauser SE and Co KG
Priority date: 2011-09-23
Filing date: 2012-08-23
Publication date: 2014-07-30
Also published as: WO2013041321A1; US20140242328A1; DE102011083333A1; CN103857992A

Abstract

The invention describes a measuring device having at least one corrosion-resistant process-oriented surface, wherein at least one joint between a component (1) which is composed of an electrically conductive material and a component (2) which is composed of an electrically insulating material is sealed by a sealing means (2), and wherein the process-oriented surface is provided with a coating (4) in such a way that at least the sealing means (3), a transition region between the conductive component (1) and the sealing means (3), and a transition region between the insulating component (2) and the sealing means (3) are covered by the coating (4).

Description

gauge

The present invention relates to a measuring device whose process-oriented

Surface sections of an electrically conductive material and

partially made of an electrically insulating material. In which

Measuring device is, for example, a pressure sensor, a capacitive or conductive level gauge, a microwave barrier for detecting a limit level or a radar level gauge.

For monitoring processes, a large variety of measuring instruments is available for determining different process variables. Often, gauges are subjected to harsh conditions during use, such as large temperature fluctuations or aggressive media. At the same time, high demands are frequently placed on the reliability of measured value determination, material resistance and hygiene. Various measuring devices are made up of a large number of different components. Also, the portion of the measuring device, which may be in contact with the process medium, may be composed of several components. For example, a measuring device for capacitive level measurement has a probe which can be introduced into a container with a sensor

metallic housing, at least one electrode, and at least one insulation for galvanic separation of electrode and housing. Here, a tight connection between the individual components is important in order to prevent ingress of moisture or liquid and thus the occurrence of corrosion. As insulation material, various materials are used, such as plastic, glass or ceramic. A disadvantage of plastic insulation is the plastic deformation of plastic at high temperatures and the large difference in thermal expansion coefficients of the metal and plastic. This can cause gaps between metal parts and plastic parts into which process medium can penetrate and lead to corrosion. In the case of a measuring device introduced into a container, this leakage can cause a leakage, since the process medium can escape through the measuring device into the environment outside the container. In addition, there is the possibility that bacteria settle in the gap, which is especially at

Hygiene applications should be avoided. By contrast, glass insulation is susceptible to glass corrosion, especially on contact with liquids which have a high pH.

Due to its high resistance, ceramics are particularly suitable as insulation material. Furthermore, the expansion behavior of ceramic and metal by appropriate choice of dimensions taking into account the respective

coefficients of thermal expansion well adaptable to each other. Such a temperature-compensated coaxial structure is disclosed in DE-OS

102010001273 A1.

In most cases ceramic parts and metal parts are connected to each other via an active solder. However, if the surface of such a structure is in contact with an electrolyte, corrosion effects may also occur since the solder and the metal parts may cause the occurrence of electrolysis (battery effect).

The object of the invention is to specify a corrosion-resistant connection between a part consisting of an electrically conductive material and one of an electrically insulating part of a measuring device.

The problem is solved by a measuring device with at least one

corrosion-resistant process facing surface, wherein at least one joint between a component consisting of an electrically conductive material and a component consisting of an electrically insulating material is sealed with a sealant, and wherein the process-facing surface is provided with a coating such that at least the sealant, a

Transition region between the conductive member and the sealant and a transition region between the insulating member and the sealant are covered by the coating. In one embodiment, the coating comprises a transition metal, in particular tantalum, gold, platinum, zirconium, titanium, as well as compounds of the transition metals, in particular oxides, nitrides, fluorides.

The coating covers the critical points of the connection between conductive component and sealant, as well as insulating component and sealant. The

The sealant itself is also coated so that the process fluid does not come into contact with the sealant. Due to the coating, the

Process medium does not penetrate into the joint between the conductive and insulating component. For example, an accumulation of moisture or an ingress of air is avoided.

Tantalum e.g. has a particularly high resistance to corrosion.

In addition, tantalum is well reducible on a hot surface and therefore suitable for coating.

In another embodiment, the coating comprises an element of

Carbon group, in particular carbon, silicon, diamond-like carbon (DLC), as well as compounds of the carbon group, in particular silicon carbide SiC. An advantage of SiC is its polymorphism, in particular its tetrahedral structure. Furthermore, SiC is oxidation resistant by forming a passive layer of SiO 2 SiO 2 and exhibits relatively high hardness and good adhesion. Because SiC is structurally and crystallographically similar to diamond, it is well combinable with diamond and diamond-like carbon compounds for coating.

In another embodiment, the coating may be polycrystalline, amorphous, semi-crystalline, or textured.

In a first embodiment, the electrically conductive component is made of a metal, a metal alloy or a conductive ceramic. For example, the electrically conductive component made of stainless steel, titanium, Invar or Kovar. The electrically conductive component of the measuring device is, for example, an electrode or a housing. In a further embodiment, the insulating component consists of a ceramic material. Preferably, the ceramic material is a

Aluminum oxide ceramic. The component made of the insulating material is, for example, an insulation for the galvanic separation of two conductive components, e.g. two electrodes. However, it can also be a component with a measuring function, for example a diaphragm of a pressure sensor.

In one embodiment, the sealant is a solder or a glass. The invention is further achieved by a method for producing a corrosion-resistant process-facing surface of a measuring device, wherein at least one joint between a component consisting of an electrically conductive material and a component consisting of an electrically insulating material is sealed with a sealant, and wherein the process-facing surface is provided with a coating such that at least the sealant, a transition region between the conductive member and the sealant and a transition region between the insulating member and the sealant are covered by the coating. The method according to the invention not only enables the production of a corrosion-resistant connection between two components separated by a sealed joint, but also the production of a vacuum-tight connection of the same. In a first embodiment of the method, the process-facing

Surface completely coated in a first step and the coating removed in sections in a second step, so that the insulating member is at least partially free of the coating. The insulating component is therefore completely or partially not coated with the coating. About the coating conductive interconnected and separated by the insulating component of an electrically conductive material components are separated by the partial removal of the coating galvanic. According to one embodiment, the coating is removed in sections by removing material from the coated insulating component. For this purpose, the insulating component is already produced with Opfererhöhungen, which are then removed after the coating, including the coating. For example, sacrificial heights are abraded or removed by another mechanical method.

In one embodiment, the coating is removed in sections by etching. In this embodiment, no material is removed from the insulating component, but only the coating selectively removed.

According to another embodiment of the method, only the process-facing surface of the sealant, the transition region between the conductive component and the sealant and the transition region between the insulating component and the sealant are selectively coated. For example, the selective coating is carried out by applying a mask to the process-facing surface and thus only coating the mask

uncovered surfaces are coated. An embodiment provides that a between 5 and 100 microns thick coating is generated. Preferably, the thickness of the coating is between 30 and 50, in particular about 40 microns when deposited from a gas phase. According to a further embodiment of the method, the coating comprises a transition metal, in particular tantalum, gold, platinum, zirconium, titanium, as well as

Compounds of the transition metals, in particular oxides, nitrides, fluorides ,.

The coating with tantalum is preferably carried out by depositing tantalum from a gas phase by a thermal decomposition of tantalum halides.

According to one embodiment, the coating comprises an element of

Carbon group, in particular carbon, silicon, diamond-like carbon, DLC and compounds of the carbon group, in particular silicon carbide SiC. SiC coatings increase chemical resistance and impact strength and are also hydrophobic, making them useful as a non-stick coating and having low surface energy. Furthermore, SiC and DLC can be combined in a single layer, whereby the physical

Properties such as surface energy and water repellency or water diffusion can be optimized even more advantageously depending on the composition.

An advantage of carbon and carbon compounds is the maximum hardness and the maximum wear resistance and the low coefficient of friction.

According to another embodiment, the coating is polycrystalline, amorphous, semi-crystalline, or textured.

According to another embodiment of the method, the coating is produced by the CVD (chemical vapor deposition) and / or PVD (physical vapor deposition) method.

The invention will be explained in more detail with reference to the following figures. In each case show in schematic representations:

1 shows a probe of a capacitive / conductive level measuring device.

FIG. 2 is a sectional view of the part of a probe close to the process of FIG. 1; FIG. Fig. 3 shows the sectional view of the process-related part of the probe of FIG. 1 with

Coating the process-facing surface;

FIG. 4 shows a detail from the sectional view with the surface coated in sections; FIG.

5 shows a pressure sensor;

6 shows a radar measuring device for filling level measurement; 7 shows a measuring device with a guided radar.

In Fig. 1, a longitudinal and a cross section through a probe 10 for capacitive or conductive level measurement are shown schematically. Such a probe 10 is front flush on the level to be monitored in the wall of the container in which the filling is located, can be introduced. The probe 10 has a coaxial structure consisting of probe electrode 6, insulation 9, guard electrode 7, further insulation 9 and housing 8. For capacitive measurement, the

Probe electrode 6 is supplied with an AC electrical signal and the capacitance between the probe electrode 6 and housing 8 or

Container wall measured. The guard electrode 7 is supplied with the same signal as the probe electrode 6 and serves the more reliable measurement at formation of deposits. However, it is also probes 10 without guard electrode 7, and probes 10 of greater length, which protrude into the container known.

Between the electrodes 6, 7 and the insulation, as well as between the housing 8 and the insulation 9, there is a gap in each case. This joint 1 1 is sealed with a sealant 3. This is shown in more detail in FIG. In the prior art, each joint 1 1 is a problem, since it depends on the design of the

Grouting or sealing can lead to deformation and / or corrosion. The invention solves this problem with a coating 4.

An advantageous embodiment of the inventive method for producing the corrosion-resistant process-facing surface of a measuring device will be explained with reference to FIGS. 2-4 using the example of the probe 10 of FIG.

Fig. 2 discloses schematically a section through the process-side portion of a probe 10 of FIG. 1 prior to the application of the coating 4 on the

process-facing surface. Electrically conductive components 1 and electrically insulating components 2 alternate in this structure. The joints 1 1 between a conductive component 1 and an insulating member 2 are each filled by a sealant 3. By way of example, the sealing means 3 is a glass seal or an electrically conductive solder. By the sealant 3 are the Components 1, 2 connected to each other such that a dense process-facing surface is formed. The cavity formed in the housing 8 is closed by the dense process-facing surface in particular vacuum-tight with respect to the process.

The insulating members 2 are made with protrusions facing the process and serving as the sacrificial material 5, i. in a later one

Step removed. FIG. 3 shows the process-facing surface after coating with tantalum. The coating 4 is applied so that they

process-facing surface completely covered. The thickness of the coating 4 is for example between 5 and 100 micrometers, the achievable thickness depending on the method with which the tantalum coating 4 on the

process-facing surface is deposited. In a coating by deposition from a gas phase, for example TaBr ₅ , a thickness of about 40 micrometers has proven to be advantageous.

A section of the structure according to FIG. 3 after a further method step is shown in FIG. 4. After application of the coating 4, this becomes

partially removed again. For this purpose, the sacrificial material 5 of the insulating components 2 is removed; for example, by grinding. The deposited on the sacrificial material 5 part of the coating 4 is removed together with the sacrificial material 5, so that the insulating member 2 only in its edge region

is coated. The edge region forms the transition region to the sealant 3.

The process-facing surface of the sealant 3 is further completely coated, so that the sealant 3 does not come into contact with the process medium.

The conductive component 1 can remain completely coated; However, the coating 4 can also be partially removed. In the latter case, the coating 4 remains at least in the edge regions, so that the transition region between electrically conductive component 1 and sealing means 3 of the

Tantalum coating 4 is covered.

However, a coating pattern as shown in Fig. 4 may be made in an alternative manner. One possibility is to make a matching mask and on the process facing surface

is positioned so that on subsequent deposition of the tantalum only those areas of the surface are coated, which are free of the mask. The production of the insulating components 2 with removable sacrificial material 5 is then unnecessary. Another possibility, in which likewise no sacrificial material 5 is provided, consists in first fully coating the process-facing surface and then selectively removing the coating 4 in a further step, for example in an etching process. The coating 4 according to the invention is not based on capacitive or conductive

Level gauges limited. It is applicable everywhere where a gap 1 1 between an electrically conductive component 1 and an insulating member 2 occurs, which must remain sealed, so that no medium can penetrate into the joint 1 1. Some application examples are shown in FIGS. 4-6.

5, a section of a pressure sensor 20 is sketched. In the metallic housing 23, a ceramic capacitive pressure measuring cell 22 is arranged. The pressure measuring cell 22 is introduced into the housing 23 such that the process pressure can act on the membrane 21 and the pressure measuring cell 22 is vacuum-tightly connected to the housing 23. The connection is made by the solder 24. The coating 4 according to the invention is applied to the process-facing surface of the pressure sensor 20, so that a part of the housing 23 and the

Membrane 21 are completely coated and thus the junction between these two parts and the solder 24 are covered by a tantalum layer. The membrane 21 may also be recessed from the coating 4 or the

Coating 4 can be removed again in the area of the membrane. However, at least a narrow transition region to the solder 24 is covered by the coating 4. Fig. 6 shows a wheel arm essgerät 30 for continuous level measurement with waveguide feedthrough. In the partially filled with a dielectric 34th

Waveguides 32 are irradiated via the feed element 33 microwaves. About the horn antenna 31, the waves are radiated into the container 36, where they meet as incoming wave S on the medium 37, are reflected by this, and are detected as the outgoing wave R from the meter 30. The fill level can be determined from the runtime. Between horn antenna 31 and dielectric 34 there is a sealed joint, for example with a glass seal as sealing means 3. According to the invention, this is coated with a tantalum layer 35.

FIG. 7 shows a guided radar measuring device 40 also used for continuous level measurement. The waves are over here

Stab probe 41 radiated into the container 36. In the area of the process connection there is a coaxial leadthrough 42 for the rod probe 41. This has a metallic frame 43, which also serves as a ground potential, and a dielectric 44. The joint between rod probe 41 and dielectric 44, as well as between socket 43 and dielectric 44, is sealed with a sealant 3 and coated according to the invention with tantalum. The sealant around the rod probe 41 around, as well as the coating are not shown for clarity. The coating is applied analogously to the exemplary embodiment illustrated in FIG. 4.

LIST OF REFERENCE NUMBERS

1 Electrically conductive component

2 Electrically insulating component

3 sealants

4 coating

5 sacrificial material

6 probe electrode

7 guard electrode

8 housing

9 insulation

10 Capacitive / conductive probe

1 1 joint

20 pressure sensor

21 membrane

22 pressure measuring cell

23 housing

24 lot

30 radar gauge

31 horn antenna

32 cavity

33 feed element

34 dielectric

35 Tantalum coating

36 containers

37 medium

40 meter with guided radar

41 rod probe

42 implementation

43 version

44 dielectric

Claims

claims

1 . Measuring device with at least one corrosion-resistant process-facing surface,

wherein at least one joint between one of an electrically conductive

Material existing component (1) and one consisting of an electrically insulating material component (2) with a sealing means (3) is closed, and

wherein the process-facing surface is provided with a coating (4) such that at least the sealing means (3), a transition region between the conductive component (1) and the sealing means (3) and a

Transition region between the insulating member (2) and the sealing means (3) of the coating (4) are covered.

2. Measuring device according to claim 1,

characterized,

the coating (4) comprises a transition metal, in particular tantalum, gold, platinum, zirconium, titanium, and also compounds of the transition metals, in particular oxides, nitrides, fluorides.

3. Measuring device according to claim 1 or 2,

characterized,

the coating (4) is an element of the carbon group, in particular carbon, silicon, diamond-like carbon (DLC), as well as

Compounds of the carbon group, in particular silicon carbide comprises.

4. Measuring device according to one of the preceding claims,

characterized,

the coating (4) is polycrystalline, amorphous, semi-crystalline or textured.

5. Measuring device according to one of the preceding claims,

characterized, in that the electrically conductive component (1) is made of a metal, a

Metal alloy or a conductive ceramic is made.

6. Measuring device according to one of the preceding claims,

characterized,

the insulating component (2) consists of a ceramic material.

7. Measuring device according to one of the preceding claims,

characterized,

in that the sealing means (3) is a solder or a glass.

8. Method for producing a corrosion-resistant, process-facing surface of a measuring device,

wherein at least one joint between a component (1) consisting of an electrically conductive material and a component (2) consisting of an electrically insulating material is sealed with a sealant (3), and

Transition region between the insulating member (2) and the sealant (3) are covered by the coating (4).

9. Method according to the preceding claim,

characterized,

that the process-facing surface is completely coated in a first step,

and that the coating (4) is removed in sections in a second step, so that the insulating component (2) is at least partially free of the coating (4).

10. The method according to claim 9,

characterized, in that the coating (4) is removed in sections by removing material from the coated insulating component (1).

1 1 .Method according to claim 9,

characterized,

that the coating (4) is removed in sections by etching.

12. The method according to claim 8,

characterized,

that selectively only the process-facing surface of the sealant (3), the

Transition region between the conductive member (1) and the sealing means (3) and the transition region between the insulating member (2) and the sealing means (3) are coated.

13. The method according to any one of claims 8 to 12,

characterized,

that a between 5 and 100 microns thick coating (4) is generated.

14. The method according to any one of the preceding claims,

characterized,

the coating (4) is a transition metal, in particular tantalum, gold, platinum, zirconium, titanium, as well as compounds of the transition metals,

in particular oxides, nitrides, fluorides.

15. The method according to any one of the preceding claims,

characterized,

the coating (4) comprises an element of the carbon group, in particular carbon, silicon, diamond-like carbon, and compounds of the carbon group, in particular silicon carbide.

16. The method according to any one of the preceding claims,

characterized, the coating (4) is polygonal, amorphous, semi-crystalline or textured.

17. The method according to any one of the preceding claims,

characterized,

the coating (4) is produced by the CVD (chemical vapor deposition) and / or PVD (physical vapor deposition) method.