WO2016026541A1

WO2016026541A1 - Pressure-measuring cell

Info

Publication number: WO2016026541A1
Application number: PCT/EP2014/078600
Authority: WO
Inventors: Andreas Rossberg; Elke Schmidt; Andrea Berlinger
Original assignee: Endress+Hauser Gmbh+Co. Kg
Priority date: 2014-08-20
Filing date: 2014-12-18
Publication date: 2016-02-25
Also published as: DE102014119111A1

Abstract

A pressure-measuring cell (3) is described, with a basic body (7) and a ceramic measuring membrane (11), which is arranged on the basic body (7) enclosing a pressure-measuring chamber (9) and can be subjected from the outside to a pressure (p) to be measured, which pressure-measuring cell can be inserted without the use of seals into a metallic housing (1, 39) or into a metallic housing section (53) by the basic body (7) being composed of metal, and basic body (7) and measuring membrane (11) are connected to each other via an adaptation body (15) which surrounds the pressure-measuring chamber (9) laterally on the outside and has a thermal coefficient of expansion which, along the adaptation body (15) in a direction running from the basic body (7) to the measuring membrane (11), drops from a coefficient of expansion corresponding to a thermal coefficient of expansion (OM) of the basic body (7) to a coefficient of expansion corresponding to a thermal coefficient of expansion (ακ) of the measuring membrane (11).

Description

Pressure measuring cell

The present invention relates to a pressure measuring cell with a base body and arranged on the base body with the inclusion of a pressure measuring chamber, externally acted upon by a pressure to be measured, ceramic

Measuring membrane.

Pressure measuring cells are widely used in almost all areas of industrial metrology.

There, among other ceramic pressure cells are used.

An example of a ceramic pressure measuring cell is described in EP 0 995 979 A1. This includes:

- A ceramic body, and

- One on the ceramic base body including a pressure measuring chamber arranged, externally acted upon by a pressure to be measured, ceramic measuring membrane.

Ceramic pressure cells offer the advantage that the ceramic

Measuring membrane can be exposed directly to the medium whose pressure is to be measured. Ceramics points to the extent for the application in the

Pressure measurement particularly advantageous chemical and mechanical

Properties on. Diaphragm seals, which transmit the pressure to be measured by means of a pressure-transmitting liquid to the pressure measuring cell, are therefore not required.

However, ceramic pressure cells must be mounted on site. For this they are regularly in a equipped with a process connection

metallic housing used, which has a measuring membrane free opening. In the housing, an outer edge of the pressure measuring cell in the axial direction

- So parallel to a surface normal to the measuring diaphragm - under

Interposition of a gasket clamped. The seal serves to the

To seal the interior of the housing from the environment. Elastomers, e.g. Acrylonitrile butadiene rubber or acrylate rubber used.

However, organic seals have a significantly lower chemical

Resistance to as ceramic pressure cells and must be replaced at the end of their service life. By replacing the seal can the Einspannverhaltnisse the pressure measuring cell in the housing and thus possibly. Also change their measurement properties.

It is an object of the invention to provide a pressure measuring cell with a ceramic measuring membrane, which can be used without the use of seals in a metallic housing.

For this purpose, the invention comprises a pressure measuring cell, with

- a basic body, and

- One on the body including a pressure measuring chamber

arranged, externally charged with a pressure to be measured, ceramic measuring membrane,

which is characterized by the fact that

- The base body consists of metal, and

- The base body and measuring diaphragm are connected to each other via a pressure measuring chamber enclosing the outside fitting body having a coefficient of thermal expansion along the fitting body extending from the base body to the measuring diaphragm direction of a thermal expansion coefficient of the body corresponding expansion coefficient to a coefficient of thermal expansion of the diaphragm corresponding expansion coefficient drops.

According to one embodiment of the invention, the adaptation body is connected to the base body by a first joining, in particular a welding, in particular an electron beam welding or a laser welding, and to an outer edge of the measuring membrane by a second joint.

A first further training provides that

the second joining is active brazing, in particular active brazing carried out by means of a ternary Zr-Ni alloy and titanium, active brazing solder, or

the fitting body is a sintered body made up of layers, and the second joint is one by sintering, esp. by laser sintering, one of

Measuring membrane facing outermost layer of the adapter body formed on the measuring membrane Füge is.

A second development consists in that a coating of a corrosion-resistant material, in particular of ceramic or of tantalum, is provided on an outer circumferential surface of the adaptation body. A further embodiment is characterized in that a capacitive electromechanical transducer is provided which comprises at least one capacitor,

- The one electrically isolated from the base body on one of

Measuring membrane-facing end face of the body, esp. An end face of a projecting in the direction of the measuring diaphragm, outside on all sides surrounded by the adjustment body and on all sides of the fitting body

spaced heel, arranged, spaced from the fitting body electrode comprises, and

- Which comprises a arranged on a side facing the base body side of the measuring membrane counter electrode.

A third development of the latter embodiment provides that

- Provided through the main body leading to the electrode electrical feedthrough, esp. A glass feedthrough, is provided, via which the electrode is electrically connected, and / or

an electrically conductive coating is provided, different from the

Counter electrode extends over an inner circumferential surface of the adapter body to the base body, so that the counter electrode is electrically connected via the base body.

A preferred embodiment provides that

- The matching body to each other arranged layers of different

Composition, in particular by laser sintering of metallic and / or ceramic portions containing powder layers applied to one another layers, and

- The layers have a ceramic content that is greater than or equal to 0% and less than 100%, and have a metal content greater than or equal to 0% and less than 100%, wherein

- The proportion of ceramics increases in the running from the main body to the measuring diaphragm direction from layer to layer, and

- The metal content decreases in the running from the main body to the measuring diaphragm direction from layer to layer. A further preferred embodiment provides that

the adaptation body is a fitting body made up of layers,

a number of layers greater than or equal to a difference between the thermal expansion coefficient of the base body and the thermal one

Coefficient of expansion of the measuring membrane divided by 2 ppm / K, in particular greater than or equal to the difference divided by 1 ppm / K, in particular greater than or equal to twice the difference divided by

1 ppm / K. A further preferred embodiment provides that

the fitting body is a fitting body made up of layers, and

the layers have a layer thickness of not less than 10 μm, in particular not less than 20 μm, in particular not less than 40 μm, and of not more than 400 μm, in particular not more than 200 μm, in particular not more than 100 μm exhibit.

A further preferred embodiment provides that

- The adjustment body extending from the main body to the measuring diaphragm

Direction a height, and perpendicular to a width, and

a product of a ratio of the width of the fitting body to the height of the fitting body and the amount of the difference of the thermal

Coefficient of expansion of diaphragm and body is smaller than a constant of dimension 1 / K, where

the constant is less than 0.1% / K, in particular less than 500 ppm / K, in particular less than 250 ppm / K, in particular less than 125 ppm / K, in particular less than 60 ppm / K, and / or

- the constant is equal to a quotient of a dimensionless one

Deformation parameters and a temperature difference between a maximum and a minimum temperature at which the pressure cell is to be used is, and the deformation parameter is less than 4%, esp. Less than 2%, esp. Less than 1%.

A further preferred embodiment provides that

the adaptation body is a fitting body made up of layers arranged on one another,

- The individual layers each one parallel to the surface normal to the

Have layer extending layer thickness and perpendicular to the surface normal to the layer extending width, and

- The product of the ratio of the width of each layer to their

Layer thickness and the amount of difference of the thermal

Expansion coefficient of the layers adjacent to this layer is smaller than a constant with the dimension 1 / K, where

the constant is less than 0.1% / K, in particular less than 500 ppm / K, in particular less than 250 ppm / K, in particular less than 125 ppm / K, in particular less than 60 ppm / K, and / or - the constant is equal to a quotient of a dimensionless one

Deformation parameters and a temperature difference between a maximum and a minimum temperature at which the pressure measuring cell (3) is to be used, is, and the deformation parameter is less than 4%, esp. Less than 2%, esp. Less than 1%.

Furthermore, the invention comprises a pressure measuring cell according to the invention, which is characterized in that the adaptation body

a sintered body produced by sintering a blank produced in a screen printing process, and

consisting of layers arranged on one another, in particular layers having a layer thickness of the order of a few micrometers,

have either a rising from layer to layer in the base body to the measuring membrane direction of ceramic component and a running in the base body to the measuring membrane direction from layer to layer decreasing metal content, or

arranged in successive layer sequences of mutually superimposed layers, each consisting either exclusively of metal or exclusively of ceramic, a number of the layers consisting exclusively of ceramic and a number of layers contained in the individual layer sequences, consisting exclusively of metal layers is specified such that a ceramic component of the layer sequences in the base body to

Measuring membrane extending direction increases from layer sequence to layer sequence and decreases a metal content of the layer sequences in the running from the base body to the measuring membrane direction from layer to layer.

A development of the latter pressure measuring cell provides that

- The adjustment body is connected by a first joint with the base body and by a second joint with an outer edge of the measuring membrane, wherein

- the first and the second addition esp. by the sintering of the between the

Base body and the measuring diaphragm arranged blanks are produced joints.

Furthermore, the invention comprises a differential pressure measuring cell with a

Pressure measuring cell according to the invention, which is characterized in that

a second pressure measuring cell, in particular an identically designed second pressure measuring cell, on a rear side of the pressure measuring cell facing away from the measuring diaphragm, is arranged such that the measuring membranes of the two pressure measuring cells facing outward, and

- The pressure measuring chambers of the two pressure measuring cells via a

Pressure transmission line are connected together.

Furthermore, the invention comprises a differential pressure measuring cell according to the invention with two pressure measuring cells according to the third development, which is characterized in that on the side facing away from the measuring membrane back of each pressure measuring cell is provided in each case to the further through passage extending through the respective body through, the laterally out the differential pressure cell out.

A development of the two differential pressure measuring cells according to the invention provides that

- On the remote from the respective measuring membrane backs of the

Basic body is provided in each case an insulating layer, in particular a glass layer,

- On the surface facing away from the respective body of the

Isolation layers each have a conductor track, esp. Along the surface of a contact pin of the implementation to an outer surface of the

Differential pressure measuring cell extending conductor track, is provided, and

- Between the two interconnects another, the two interconnects electrically against each insulating insulating layer, esp. One the two

Pressure measuring cells mechanically interconnecting insulation layer is provided.

Furthermore, the invention comprises a pressure sensor with a

- The body in a recess of a housing or a

Housing section, esp. A used equipped with a process connection housing or housing section, in particular welded, is, or

- The base body and a body containing the housing portion, esp. A housing equipped with a process connection housing portion are formed as a one-piece component. The connection according to the invention of base body and measuring diaphragm via the adapter body makes it possible to place the ceramic measuring diaphragm on a

To arrange body made of metal. The different coefficients of thermal expansion of the base body and the measuring diaphragm are gradually transferred into one another via the adapter body. This is due to the different expansion coefficients of the base body and Measured membrane conditioned temperature-dependent voltages in terms of amount significantly reduced and shifted into the adjustment body, distributed over the entire height, they are then gradually absorbed. Since basic body and measuring diaphragm each at one end of the

Adjacent adjustment body, the one thermal

Expansion coefficient of the respective component corresponding thermal expansion coefficient, connect the

Arrangements between the fitting body and the basic body, as well as between

Adaptation body and measuring membrane each interfaces with the same or at least very similar thermal expansion coefficient.

Accordingly, the joints are exposed to only very small temperature-dependent loads. The pressure sensors according to the invention offer the advantage that housing and

Base body made of metal and thus directly, i. without the interposition of seals, connected to each other, especially welded, can be.

In addition, base body and housing have comparable, preferably even identical thermal expansion coefficients. This offers the advantage that no temperature-dependent stresses develop between the base body and the housing, which affect the measuring diaphragm and thus the

Could affect measurement accuracy. The invention and its advantages will now be explained in more detail with reference to the figures of the drawing, in which two embodiments are shown. Identical elements are provided in the figures with the same reference numerals.

Fig. 1 shows: a pressure sensor with a pressure measuring cell according to the invention;

and

Fig. 2 shows: a pressure sensor with an inventive

Differential pressure measuring cell. 1 shows an embodiment of a pressure sensor according to the invention with a pressure measuring cell 3 according to the invention inserted in a housing 1. The housing 1 consists of a metal, eg a stainless steel, and preferably has a process connection 5 via which the pressure sensor at the place of use is complementary to one Counterpart can be mounted. The process connection 5 is eg - as shown here - a flange, with which the pressure sensor on a corresponding counterflange can be mounted on site. Alternatively, other used in industrial metrology

Process connection variants, such as External thread or

Milk tube fittings are used.

The pressure measuring cell 3 comprises a metallic base body 7 and a ceramic measuring membrane 1 1 arranged on the base body 7, including a pressure measuring chamber 9. The main body 7 is preferably made of the same metal as the housing 1, in which the pressure measuring cell 3 is to be used. The metallic base body 7 offers the advantage that it can be connected directly to the housing 1 without the interposition of seals. In the illustrated embodiment, the base body 7 is arranged for this purpose in a form-identical recess in the housing 1, and connected via a - symbolized here by a triangle - welding with the housing 1.

Alternatively, the base body 7 and at least one housing section containing the main body 7 of the housing 1 may be formed as a one-piece component.

The base body 7 and the housing 1 have at least very similar, preferably identical, thermal expansion coefficients. This offers the advantage that no temperature-dependent voltages occur in the transition region of the housing 1 and the main body 7, which could adversely affect the pressure measuring cell 3, in particular its measuring accuracy.

The measuring membrane 1 1 consists for example of alumina (Al ₂ 0 ₃ ). Alternatively, it may also consist of another ceramic material, such as silicon carbide ceramic (SiC) or spinel.

In measuring operation, the side facing away from the base body 7 side of the measuring diaphragm 1 1 is acted upon from the outside with a pressure to be measured p, which causes a dependent of the pressure to be measured p deflection of the measuring diaphragm 1 1.

The pressure measuring cell 3 shown in FIG. 1 is designed as a relative pressure measuring cell. For this purpose, in the main body 7 a through the base body 7 extending through in the pressure measuring chamber 9 opening bore 13 is provided, via which the

Pressure measuring chamber 9, a reference pressure p _ref , for example, the atmospheric pressure to which the pressure to be measured is to be supplied is supplied. Alternatively, the Pressure measuring cell be designed as absolute pressure measuring cell. In the case eliminates the bore 13, and enclosed under the measuring membrane 1 1

Pressure measuring chamber 9 is evacuated. The metallic main body 7 is connected to the ceramic measuring membrane 1 1 via a pressure measuring chamber 9 on the outside enclosing fitting body 15. The adaptation body 15 is for this purpose preferably designed as a ring, esp. To a circular ring, closed web. The adaptation body 15 has a coefficient of thermal expansion which decreases along the adaptation body 15 in the direction from the base body 7 to the measuring membrane 1 1 direction of a thermal expansion coefficient a _{M of} the base body 7 corresponding expansion coefficient to the thermal expansion coefficient ακ of the measuring diaphragm 1 1 corresponding expansion coefficient.

For this purpose, the adaptation body 15 preferably consists of a number N of layers S arranged on top of one another, of different composition. The individual layers S, parallel to each other and parallel to the measuring membrane 1 1. The composition of the individual layers S, is set such that the adjoining the base body 7 outermost layer Si has a thermal expansion coefficient a _S i, the coefficient of expansion a _M of Base body 7 corresponds, and starting from this outermost layer Si from layer to layer gradually in such a way to the thermal

Expansion coefficient ακ of the measuring membrane 1 1 drops that to the

Measuring membrane 1 1 adjacent outermost layer S _N a thermal

Expansion coefficient OSN, the thermal

Expansion coefficient α _{κ of} the measuring membrane 1 1 corresponds. For this purpose, the layers S, each having a ceramic fraction which is greater than or equal to 0% and less than or equal to 100%, and a metal content which is greater than or equal to 0% and less than or equal to 100%. The proportions are preferably predetermined in such a way that the ceramic proportion of the layers S increases from layer to layer in the direction extending from the main body 7 to the measuring membrane 11, while the metal portion of the layers S, in the direction extending from the main body 7 to the measuring membrane 11, extends from layer to layer Layer decreases. Assigning the main body 7 facing outermost layer Si of the matching body 15, the coordinate z = 0, and the measuring membrane 1 1 facing outermost layer SN the coordinate z = h, where h is equal to the height of the matching body 15, the ceramic component of a For example, layer Si having the central axial coordinate z is 100% × (z / h), and the metal content of this layer Si is 100% × (1-z / h).

The adaptation body 15 is preferably a sintered body whose layers S are produced, for example, by laser sintering of powder layers corresponding from layer to layer of different composition. For this purpose, for example, in the IMW Industry Communication No. 29 (2004) by Trenke entitled "Selective laser sintering of metallic / ceramic layer structures"

described laser sintering method can be used.

For this purpose, the components can be provided in the form of microscale granules whose grain size is preferably not more than 20 μm and more preferably not more than 10 μm. For preparing a layer, the coordinate-dependent mixture of

Granules applied to the already solidified layers and solidified by laser sintering. The desired composition of the respective layer S, can be produced by applying a metal powder and ceramic powder in the desired mixing ratio in powdery layer containing mixed form and solidified by laser sintering. Alternatively, the composition can be achieved by applying the appropriate amount of metal powder and the corresponding amount of ceramic powder in each case as a powder layer of appropriate thickness, and the two powder layers are mixed and solidified by laser sintering.

Possibly. can the sintered body after preparation under pressure at high

Temperature are kept to compact the structure.

The differences of the thermal expansion coefficients asi, asi + i of adjacent layers S ,, S _{i + of} the matching body 15 are the lower, the larger the number N of the layers S is. The smaller these differences are, the lower are the differences due to the different thermal properties

Expansion coefficients forming temperarturabhängigen voltages. The number N of layers is therefore a function of the difference Δα = OM - ακ the stepwise each other to be fitted over the fitting body 15 thermal expansion coefficient _α Μ, ακ of base body 7 and

Measuring diaphragm 1 1 preferably specified such that the number N not less than (Δα) / (2 ppm / K), in particular not less than

(Δα) / (1 ppm / K) and preferably not less than (2Δα) / (1 ppm / K). The adaptation body 15 has a height h in cross-section in a direction parallel to the surface normal to the layers S, from the base body 7 to the measuring membrane 1 1 extending direction and in a direction perpendicular to the surface normal to the layers Si direction extending to a width d. These dimensions of the

Adaptation body 15 are preferably set such that the product of the ratio of its width d to its height h and the amount of the difference Δα of the thermal expansion coefficient α _κ , α _Μ of the base body 7 and diaphragm 1 1, smaller than a predetermined constant ξ with the dimension

1 / K, for which the following applies: ξ <0.1% / K, in particular <500 ppm / K, preferably <250 ppm / K, more preferably <125 ppm / K and particularly preferably <60 ppm / K:

- · \ Αα \ <ξ,

h ^{1 1}

The constant ξ is preferably a quotient of a dimensionless deformation parameter C and a temperature difference ΔΤ according to:

determined, where

- The temperature difference ΔΤ equal to the difference T _max - T _{min of} the maximum and the minimum temperature T _max , T _min , at which the pressure measuring cell 3 is to be used, and

C is a dimensionless deformation parameter for which C <4%, in particular C <2% and preferably C <1%.

In this case, the individual layers S, of the adaptation body 15 are preferably dimensioned such that the product of the ratio of the width d _{s of} the respective layer S, to the layer thickness s and the amount of the difference Δα _{5 of} the thermal expansion coefficients asi-i, asi + i the to this layer S, adjacent

Layers SM, S _{i +} also smaller than the above preferably as a quotient of the dimensionless deformation parameter C and the

Temperature difference ΔΤ specific constant ξ is. D. h .:

The individual layers S, preferably have a layer thickness s of not less than 10 μm, in particular not less than 20 μm, and preferably not less than 40 μm, and of not more than 400 μm, in particular not more than 200 μm, and preferably no longer as 100 μιη on. Taking as an example a metallic base body 7 made of stainless steel with a thermal expansion coefficient a _M of 16 ppm / K and a measuring membrane 1 1 of alumina ceramic with a thermal expansion coefficient ακ of 8 ppm / K, then the difference Δα is the thermal

Expansion coefficient 8 ppm / K. This results in a preferred

Minimum number N> 2 Δα / (1 ppm / K) of

16 layers. In the above-mentioned particularly preferred layer thicknesses of 40 μm to 100 μm, this results in a preferred minimum height h of

Adaptation body 15 from 640 μιη to 1, 6 mm. If one goes from one

Temperature range from - 40 ° C to + 130 ° C, in which the pressure sensor is to be used, is obtained using the most preferred

Deformation parameter C of 1% for the constant ξ according to ξ = C / ΔΤ a value of 58.88 ppm / K. Thus, the width d of the adaptation body 15, which can be calculated via the above-mentioned design rule d / h ΙΔαΙ <ξ, is preferably below 4.8 mm at a height h of 640 μm.

The adaptation body 15 has an end face facing the base body 7, which is connected in a pressure-tight manner via a first joint 17 to an end face of the base body 7 facing the measuring membrane 1 1. This first joint 17 is preferably a weld, e.g. an electron beam welding or a laser welding.

The opposite, the measuring diaphragm 1 1 facing end face is connected via a second joint 19 with an outer edge of the main body 7 facing side of the measuring diaphragm 19 pressure-tight. This second joining 19 is preferably realized in that the adaptation body 15 is built up in layers on the edge of the measuring membrane 1 1. In this case, the second joining 19 forms during sintering of the outermost layer SN on the edge of the measuring membrane 1 1.

Alternatively, the adaptation body 15 can be prefabricated as a separate component. In the case, the second joint 19 between measuring diaphragm 1 1 and

Adaptation body 15 preferably an active brazing. The active brazing is preferably carried out with a Zr-Ni alloy and titanium ternary active brazing. Such active hard solders are known from EP 0 490 807 A2, and have the advantage of a thermal

Coefficient of expansion of ceramic matched thermal

Expansion coefficients on. Alternatively, the fitting body 15 may be made by sintering one in one

Be produced by screen printing process, made of superimposed printed layers existing blanks sintered body. The production of the blank takes place by the individual layers in successive executed

Printing processes are printed on each other, with the printed

Layers each, e.g. are solidified by drying before being overprinted with the next layer.

The adaptation body 15 produced by the screen printing method preferably has layers with a layer thickness of the order of a few micrometers.

By sintering produced by screen printing, built up from each other layers of different composition

Blanks produced three-dimensional sintered bodies are described for example in EP 0 627 983 B1. In addition, in a handout to a 9th seminar held in Dresden on July 2 and 3, 2014 for current trends in the construction and connection technology by Mr. Riecker lecture entitled "Fraunhofer Institute for Manufacturing Technology and Applied Materials" entitled : '3D screen printing - A process for component manufacturing' presented a three-dimensional graded structure of steel and ceramic, whose ceramic content decreases continuously in a spatial direction, and their steel content in the same

Spatial direction increases accordingly.

The adaptation body 15 produced in this way can, as in the previous exemplary embodiment, be constructed of layers of different compositions described in connection with the previous exemplary embodiment whose proportion of ceramics increases from layer to layer in the direction extending from the main body 7 to the measuring membrane 11, and the same Metal content decreases from the base body 7 to the measuring membrane 1 1 extending direction from layer to layer. For this embodiment, the design data given above for the number of layers N, the ratio of the width d of the adaptation body 15 to its height h, and the ratio of the width d _{s of} the individual layers to their layer thickness s apply

Accordingly, the design data refer here to the present after sintering of the blank dimensions.

Alternatively, the matching body 15 may have layer sequences arranged on each other, each consisting of layers arranged on one another, each consisting either exclusively of metal or exclusively of ceramic. Here, the number of contained in the individual layer sequences, consisting exclusively of ceramic layers and the number of contained in the individual Schichtfolgenden, consisting exclusively of metal layers specified such that the ceramic component of the layer sequences in the base body 7 to the measuring membrane 11 extending direction of layer sequence to layer sequence increases and the metal content of the layer sequences in from the body 7 to the measuring membrane 1 1 extending direction decreases from layer to layer.

In this case, the layers preferably have the smallest possible thickness, in particular a thickness of the order of magnitude of a few micrometers, in particular 2 μm to 3 μm. This embodiment offers the advantage that only two different printing pastes, namely a ceramic paste and a metal paste are needed to produce the blank. For imprinting ceramic and metallic

Layers thus only one sieve is needed in each case, which need not be cleaned between successive printing operations. In connection with a matching body 15 produced by the screen printing process, the first and the second joint 17, 19 can be produced by arranging the blank between the base body 7 and the measuring membrane 11 and sintering it there. For additional improvement of the corrosion resistance of the matching body 15 may on an outer circumferential surface of the adapter body 15 a

Coating 21 of a corrosion-resistant material, esp. Made of ceramic, preferably from the ceramic of the measuring membrane 1 1, or tantalum, are applied. The coating 21 may, depending on the choice of material, e.g. by

Plasma coating or be applied by sputtering.

About the adjustment body 15, the different thermal

Expansion coefficients of measuring diaphragm 1 1 and base body 7 gradually transferred into each other. Due to the different thermal

Expansibility coefficients thermomechanical stresses are thus distributed over the entire height h of the adjustment body 15, and degraded over this.

This causes a significant reduction in temperature-induced stresses in the region of the first and second joints 17, 19 and in the region of the measuring membrane 11.

This makes it possible, the metallic body 7 with the ceramic

To connect measuring diaphragm 1 1, without the risk that the joints 17, 19 are charged due to temperature-induced voltages over charge or even break, and without the measurement accuracy due to the Measuring membrane 1 1 impacting temperature-dependent tension is significantly impaired.

The pressure measuring cell 3 comprises an electromechanical transducer which serves to convert the deflection of the measuring diaphragm 1 1 dependent on the pressure to be measured into an electrical signal dependent on the pressure to be measured, and for display and / or further evaluation and / or processing To make available. As a possible embodiment of such an electromechanical transducer, a capacitive transducer is provided in Fig. 1, which has at least one capacitor with a dependent of the deflection of the measuring membrane 1 1 capacity. The capacitor comprises an electrode 23 arranged on an end face of the main body 7 facing the measuring diaphragm 11, and a side of the measuring diaphragm 7 arranged on the side of the main body 7

Counter electrode 25.

The electrode 23 is spaced from the matching body 15 and thus electrically insulated therefrom. For the electrical insulation of the electrode 23 with respect to the main body 7, an insulating layer 27, e.g. a glass layer or a silicon dioxide layer (S1O2), on which the electrode 23 is arranged.

The pressure dependent capacity of this capacitor is e.g. determined by means connected to the electrode 23 and the counter electrode 25 measuring electronics 29, and for example by means of a preliminary in the context of a

Calibration method determined characteristic assigned to a pressure on the measuring membrane 1 1 to be measured pressure p. The electrical connection of the electrode 23 to the measuring electronics 29 is preferably carried out via an electrical feedthrough 31 which extends through the main body 7 therethrough. The bushing 31 is e.g. a glass feedthrough with a contact pin 33 extending to the electrode 23, e.g. can be contacted via a arranged on the back of the pressure measuring cell 3 contact.

The electrical connection of the counterelectrode 25 to the measuring electronics 29 preferably takes place via an electrically conductive coating 35 connecting the counterelectrode 25 to the base body 7. This extends from the counterelectrode 25 via an inner circumferential surface of the matching body 15 to the base body 7 the counter electrode 25 at the same potential As the base body 7, so that the connection of the counter electrode 25 can be made via a arranged for example on the back of the body 7 contact.

The conductive coating 35 is preferably after sintering the

Adaptation body 15 on the measuring membrane 1 1 or after the addition of

Measuring diaphragm 1 1 and fitting body 15 applied before the composite of measuring diaphragm 1 1 and fitting body 15 is fixed by means of the first joint 17 on the base body 7. The conductive coating 35 is preferably a metallization, which is preferably applied in one operation together with the counterelectrode 25 likewise designed as a metallization, e.g. sputtered, will.

The measurement accuracy achievable with the capacitive electromechanical transducer is the greater, the larger the basic capacitance of the capacitor formed by the electrode 23 and the counter electrode 25. This basic capacity is in turn the greater, the smaller the electrode spacing between electrode 23 and

Counter electrode 25 is.

When equipped with a capacitive electromechanical transducer

According to the invention pressure measuring cells 3, the electrode 23 is therefore preferably arranged on a protruding in the direction of the measuring membrane 1 1 paragraph 37 of the base body 7. The shoulder 37 is on the outside surrounded on all sides by the adjustment body 15 and spaced from it on all sides. This has the advantage that a corresponding dimensioning of the height of the shoulder 37, a small electrode spacing can be achieved, and the electrode spacing co-determining height h of the matching body 15 at the same time according to the above-described design rules for an optimal adjustment of the thermal expansion coefficient ακ, OM of measuring diaphragm 1 1 and body 7 can be specified.

Fig. 2 shows a further embodiment of an inventive

Pressure sensor with a enclosed in a metallic housing 39

Differential pressure measuring cell 41 according to the invention. Due to the extensive agreement with the pressure sensor shown in Fig. 1, only the existing differences are explained in more detail below. Incidentally, reference is made to the description of FIG. 1.

The differential pressure measuring cell 41 is formed by the fact that on the side facing away from the measuring diaphragm 1 1 back of the pressure measuring cell according to the invention 3, for example, according to FIG. 1, a second, preferably identical pressure measuring cell 3 is arranged such that the measuring membranes 1 1 of the two pressure measuring cells 3 face outward. In addition, in the differential pressure measuring cell 41 a

Pressure transmission line 43 is provided, via which the two pressure measuring chambers 9 are interconnected. The pressure measuring chambers 9 and the

Pressure transmission line 43 are connected to a pressure transmitting liquid, e.g. Silicone oil, filled.

In measuring operation, one of the two measuring membranes 1 1 is applied with a first pressure pi, and the other measuring membrane 1 1 with a second pressure p ₂ . This pressurization causes the differential pressure to be measured Δρ between the first and the second pressure-p ι, p ₂ dependent deflection of the measuring membrane 1 1, which by means of an electromechanical transducer

measured and dependent on the differential pressure Δρ = pp ₂ dependent

Measuring signal is converted.

Again, for metrological detection of the deflections of the

Measuring membranes 1 1 each of the capacitive transducer already described with reference to FIG. 1 are provided. The differential pressure Δρ can be determined on the basis of the measured capacitance of each of the two capacitors, or on the basis of the differential change f of the capacitances C1, C2 of the two capacitors. The differential change f of the two capacitances C1, C2 is z. B. determined as the ratio of the difference between the two capacitances to their sum according to: f = (C1 - C2) / C1 + C2).

Here, too, the electrical connection of the two counterelectrodes 25 preferably takes place in each case via a contact arranged on an outer circumferential surface of the associated base body 7, which is in electrically conductive connection with the respective counterelectrode 25 via the respective base body 7 and the respective conductive coating 35.

The connection of the two electrodes 23 via the through the respective base body 7 extending therethrough 31 and a subsequent further forward implementation 45, via which the connection laterally from the

Differential pressure measuring cell 41 out is performed.

Each of these secondary bushings 45 has a on the of the

Measuring membrane 1 1 facing away from the back of the respective body 7 applied insulating layer 47, e.g. a layer of glass, through which the

Contact pin 33 of the bushing 31 passes therethrough. On the one of the respective Base body 7 facing away from the surface of the respective insulating layer 47, a conductor 49 is provided in each case, which extends along the surface of the contact pin 33 to an outer surface of the differential pressure measuring cell 41, where it can be contacted via a corresponding contact.

Between the two interconnects 49, a further insulating layer 51 is provided, via which the two interconnects 49 are electrically isolated from each other. This further insulation layer 51 is preferably at the same time for

mechanical connection of the two back each provided with the insulating layer 47 and the conductor 49 main body 7 used. For this purpose it may e.g. be formed as a glass layer of the base body 7 connecting glass soldering.

Also in this embodiment, the differential pressure measuring cell 41 is used without interposing seals in the housing 39 by the

Base 7 directly connected to the housing 39, esp. Welded, are. For this purpose, the housing 39 preferably has two interconnected housing sections 53, each having a recess for receiving one of the two interconnected main body 7. In this way, each housing section 53 can be pushed over the respective base body 7 from the outside over the respective measuring diaphragm 1 1 and welded there.

Alternatively, the base body 7 and the respective base body 7 containing housing sections can also be formed here as a one-piece component.

In addition, the housing 39 has a arranged on the outer surface of the differential pressure measuring cell 41 contacts for the connection of

Electrodes 23 and the counter electrodes 25 exposed recess 55, through which the electrodes 23 and the counter electrodes 25 are connected to a measuring electronics 57.

Each housing section 53 is equipped with a process connection 5, via which the differential pressure sensor 41 can be connected at the place of use with a counterpart complementary thereto via which the respective measuring diaphragm 11 in FIG

Measuring operation of the first and the second pressure pi, p _{2 is} supplied. 1 housing

3 pressure measuring cell

5 process connection

7 basic body

9 pressure measuring chamber

1 1 measuring diaphragm

13 hole

15 adaptation body

17 addition

19 coincidence

21 coating

23 electrode

25 counter electrode

27 insulation layer

29 Measuring electronics

31 implementation

33 contact pin

35 coating

37 paragraph

39 housing

41 pressure measuring cell

43 pressure transmission line

45 implementation

47 insulation layer

49 trace

51 insulation layer

53 housing section

55 recess

57 Measuring electronics

Claims

claims

1 . Pressure measuring cell, with

- A basic body (7), and

- One on the base body (7) including a pressure measuring chamber (9) arranged, from the outside with a pressure to be measured (p)

acted upon, ceramic measuring membrane (1 1),

characterized in that

- The base body (7) consists of metal, and

- Body (7) and measuring diaphragm (1 1) with each other via a

Pressure measuring chamber (9) on the outside enclosing fitting body (15) are connected, which has a thermal expansion coefficient along the adjustment body (15) in the base body (7)

Measuring diaphragm (1 1) extending direction of a thermal expansion coefficient (o _M ) of the base body (7) corresponding

Expansion coefficients on a thermal

Expansion coefficient (ακ) of the measuring diaphragm (1 1) corresponding expansion coefficient drops.

Pressure measuring cell according to claim 1, characterized in that

the adaptation body (15) by a first joint (17), esp. A weld, esp. An electron beam welding or a laser welding, with the base body (7) and by a second joint (19) with an outer edge of the measuring membrane (1 1) connected is.

Pressure measuring cell according to claim 1, characterized in that

the second joint (19) is an active brazing, in particular an active brazing, carried out by means of a ternary, Zr-Ni alloy and titanium, active brazing alloy, or

the adaptation body (15) is a sintered body constructed from layers, and the second joint (19) has an outermost layer (SN) of the. by sintering, in particular by laser sintering, of one of the measuring membrane (11)

Matching body (15) on the measuring diaphragm (7) formed Fufgung is.

4. Pressure measuring cell according to claim 1, characterized in that

on an outer circumferential surface of the adapter body (15) a coating (21) made of a corrosion-resistant material, esp. Made of ceramic or tantalum is provided.

5. Pressure measuring cell according to claim 1, characterized in that a capacitive electromechanical transducer is provided which comprises at least one capacitor,

- The one electrically isolated from the base body (7) on one of

Measuring membrane (11) facing the end face of the base body (7), esp. An end face of a in the direction of the measuring diaphragm (1 1) above,

on the outside on all sides of the fitting body (15) surrounded and on all sides by the adjustment body (15) spaced shoulder (37) arranged, from the adjustment body (15) spaced electrode (23) comprises, and

- Which on a the base body (7) facing side of the measuring diaphragm (1 1) arranged counter electrode (25).

6. Pressure measuring cell according to claim 5, characterized in that

- One through the base body (7) leading to the electrode (23) connected to the electrical feedthrough (31), esp. A glass feedthrough, is provided, via which the electrode (23) is electrically connected, and / or

- An electrically conductive coating (35) is provided which extends from the counter electrode (25) via an inner circumferential surface of the adapter body (15) to the base body (7), so that the counter electrode (25) via the main body (7) electrically is connectable.

7. Pressure measuring cell according to claim 1, characterized in that

- The adaptation body (15) arranged on each other layers (S,)

of different composition, in particular by laser sintering of metallic and / or ceramic portions containing powder layers applied to each other layers, and

- The layers (S,) have a ceramic content that is greater than or equal to 0% and less than 100%, and have a metal content greater than or equal to 0% and less than or equal to 100%, wherein

- The ceramic part in from the base body (7) to the measuring diaphragm (1 1) out

extending direction increases from layer to layer, and

- The metal content in from the base body (7) to the measuring diaphragm (1 1) out

extending direction decreases from layer to layer.

8. Pressure measuring cell according to claim 1, characterized in that

- The adaptation body (15) one of layers (S,) built

Fitting body is,

a number (N) of the layers (S,) greater than or equal to a difference (Δα) between the thermal expansion coefficient (OM) of the main body (7) and the thermal expansion coefficient (α _κ ) of the measuring diaphragm (1 1) divided by 2 ppm / K, in particular greater than or equal to the difference (Δα) divided by 1 greater than or equal to twice the difference (Δα) divided by 1 ppm / K.

9. Pressure measuring cell according to claim 1, characterized in that

- The adaptation body (15) one of layers (S,) built

Fitting body is, and

- The layers (S,) a layer thickness (s) of not less than 10 μιη,

in particular not less than 20 μm, in particular not less than 40 μm, and of not more than 400 μm, in particular not more than 200 μm, in particular not more than 100 μm.

10. Pressure measuring cell according to claim 1, characterized in that

- The adjustment body (15) extending from the base body (7) to the measuring diaphragm (1 1) extending direction a height (h), and perpendicular to a width (d), and

a product of a ratio of the width (d) of the fitting body (15) to the height (h) of the fitting body (15) and the amount of difference (Δα) of the thermal expansion coefficients (α _κ , α _Μ ) of the measuring diaphragm

(1 1) and basic body (7) is smaller than a constant (ξ) with the dimension 1 / K, where

the constant (ξ) is less than 0.1% / K, in particular less than 500 ppm / K, in particular less than 250 ppm / K, especially less than 125 ppm / K, in particular less than 60 ppm / K , and or

- the constant (ξ) is equal to a quotient of a dimensionless one

Deformation parameter (C) and a temperature difference (ΔΤ) between a maximum and a minimum temperature (T _max , T _min ) at which the

Pressure measuring cell (3) is to be used is, and the deformation parameter is less than 4%, esp. Less than 2%, esp. Less than 1%. 1 1. Pressure measuring cell according to claim 1, characterized in that

the adaptation body (15) is a fitting body made up of layers (S,) arranged on one another,

- The individual layers (S,) each have a parallel to the surface normal to the layer (S,) extending layer thickness (s) and perpendicular to the surface normal to the layer (S,) extending width (d _s ), and

the product of the ratio of the width (d _s ) of the respective layer (S,) to its layer thickness (s) and the amount of the difference (Δα ₅ ) of the thermal expansion coefficients of the layers (S,) adjoining this layer (S,) i, Sj ₊ i) is less than a constant (ξ) of dimension 1 / K, where the constant {ξ) is less than 0.1% / K, in particular less than 500 ppm / K, in particular less than 250 ppm / K, in particular less than 125 ppm / K, in particular less than 60 ppm / K, and or

- the constant (ξ) is equal to a quotient of a dimensionless one

Pressure measuring cell (3) is to be used is, and the

Deformation parameter is less than 4%, esp. Less than 2%, esp. Less than 1%.

12. Pressure measuring cell according to claim 1, 4, 5 or 6, characterized in that the adjustment body (15)

- Of layers arranged on each other, esp. Layers with a

Layer thickness of the order of a few microns, there is

either the one in the base body (7) to the measuring membrane (11)

extending direction from layer to layer rising ceramic portion and in the base body (7) to the measuring diaphragm (11) extending direction from layer to layer decreasing metal content, or

- Which are arranged in successive layer sequences of mutually arranged either exclusively made of metal or exclusively of ceramic layers to each other, wherein a number of contained in the individual Schichtfolgenden, consisting exclusively of ceramic layers and a number of in the individual

Layer following contained, consisting exclusively of metal

Layers is predetermined such that a ceramic portion of the layer sequences in the base body (7) to the measuring membrane (1 1) extending direction of layer sequence to layer sequence increases and a metal portion of the layer sequences in the base body (7) to the measuring membrane (1 1) extending direction of

Decreases layer to layer.

13. Pressure measuring cell according to claim 12, characterized in that

- The adjustment body (15) by a first joint (17) with the base body (7) and by a second joint (19) with an outer edge of the

Measuring diaphragm (1 1) is connected, wherein

- The first and the second joint (17, 19) esp. By the sintering of the between the main body (7) and the measuring diaphragm (1 1) arranged blankings produced (17, 19).

14. Differential pressure measuring cell with a pressure measuring cell (3) according to one of the preceding claims, characterized in that

- On one of the measuring diaphragm (11) facing away from the back

Pressure measuring cell (3) a second pressure measuring cell (3), esp. An identically formed second pressure measuring cell (3), is arranged such that the

Point the measuring diaphragms (1 1) of the two pressure measuring cells (3) outwards, and

- The pressure measuring chambers (9) of the two pressure measuring cells (3) via a

Pressure transmission line (43) are interconnected.

15. Differential pressure measuring cell according to claim 14 with two pressure measuring cells (3) according to claim 6, characterized in that on the of

Measuring diaphragm (11) facing away from the rear of each pressure measuring cell (3) each one to the through the respective base body (7) extending therethrough

Implementation (31) subsequent further implementation (45) is provided which leads laterally out of the differential pressure measuring cell (41) out.

16. Differential pressure measuring cell according to claim 14 or 15, characterized in that

- On the back of the main body (7) facing away from the respective measuring membrane (1 1) is provided in each case an insulating layer (47), in particular a glass layer,

- On the respective base body (7) facing away from the surfaces

Isolation layers (47) each have a conductor track (49), esp. Along the surface of a contact pin (33) of the passage (31) to an outer surface of the differential pressure measuring cell (41) extending conductor track (49) is provided, and

- Between the two interconnects (49) another, the two interconnects (49) electrically mutually insulating insulating layer (51), esp. One of the two pressure measuring cells (3) mechanically interconnecting

Insulation layer (51) is provided.

17. Pressure sensor with a pressure measuring cell (3) according to claim 1, characterized

marked that

- The main body (7) in a recess of a housing (1, 39) or a

Housing portion (53), esp. A used with a process connection (5) housing (1, 39) or housing portion (53) inserted, esp., Is welded, is, or - The main body (7) and a base body (7) containing

Housing section, in particular one equipped with a process connection (5) housing portion, are formed as a one-piece component.