DE102010000915A1 - Capacitive ceramic pressure sensor i.e. absolute pressure sensor, for container opening to measure absolute pressure on measuring membrane, has electrode and counter electrode between which space is formed and smaller than joint thickness - Google Patents

Abstract

The sensor has a metallic joint (7) that connects an outer rim of a measuring membrane (5) with an outer rim of a base body (1). A capacitor is formed by an electrode (9) and a counter electrode (11), where capacitance of the capacitor is provided as a measure for pressure-dependent deformation of the membrane. The body is projected inside a measuring chamber (3). A space between the electrode applied on a surface area of the body and the counter electrode applied on the membrane is smaller than thickness (d) of the joint. The body and the membrane consist of ceramic.

Description

The invention relates to a capacitive ceramic pressure sensor with a ceramic base body, a measuring diaphragm connected pressure-tight to the base body by means of a metal joint, and a capacitive electromechanical transducer which converts a pressure-dependent deformation of the measuring diaphragm into an electrical primary signal an electrode applied to a surface of the base body pointing into the measuring chamber and a counter electrode applied to a surface of the measuring diaphragm facing the measuring chamber, in which the electrodes form a measuring capacitor whose capacitance is a measure of the pressure-dependent deformation of the measuring diaphragm.

Pressure sensors in the sense used here include absolute pressure sensors, which measure the absolute, acting on the measuring diaphragm pressure against vacuum, relative pressure sensors, the pressure acting on the measuring membrane relative to a reference chamber supplied to the reference pressure, such. As the current atmospheric pressure, and differential pressure sensors that detect a pressure difference between a force acting on the diaphragm first pressure and the measuring chamber supplied second pressure.

Today you will find a wide range of applications in almost all areas of industrial metrology. Capacitive ceramic pressure sensors are manufactured and marketed by the Applicant under the name Cerabar.

There are a variety of applications in which preferably the smallest possible pressure sensors are used. This is the case, for example, in applications in which very little space is available for installing the pressure sensors. Another example is applications where the pressure sensors are inserted into container openings. Here one often strives to keep the required container openings as small as possible. This is the case, for example, with pressure-resistant containers for reasons of stability. Another example is containers in which space-saving manner many openings for receiving a variety of different sensors or measuring instruments must be accommodated.

However, the capacitive ceramic pressure sensors mentioned above have a significantly lower measuring accuracy with small dimensions.

One reason for this is that metallic joints have a minimum thickness due to the joining technique that can not be undercut. An example of this is the minimum thickness of a joint produced in a brazing process by means of a solder strip, which has an order of magnitude of 20 μm.

This has the consequence that a reduction in the base area of the pressure sensors leads to a significant reduction in the capacitance of the measuring capacitor while maintaining the minimum distance between the measuring electrodes that is constant, given the minimum thickness of the joint. The smaller the base area of the pressure sensors is formed, the lower the electrode area available in the pressure sensor. Correspondingly, the ratio of the electrode area to the electrode spacing, which is decisive for the capacitance to be measured, decreases with increasing miniaturization.

The smaller the capacitance of the measuring capacitor, the lower are also the pressure-dependent changes, which must be measured to measure a pressure acting on the measuring diaphragm. Accordingly, a reduction in the dimensions of the pressure sensors inevitably leads to a significant deterioration of the achievable accuracy of measurement with a constant, predetermined by the minimum thickness of the joint electrode spacing.

Another problem of miniaturization is that the membrane thickness must be reduced in order to ensure a pressure-dependent diaphragm stroke which is sufficient for the measurement with a smaller diaphragm surface area. However, this reduces the overload resistance of the pressure sensors.

It is an object of the invention to provide a capacitive ceramic pressure sensor with small dimensions and high accuracy.

• – einem Grundkörper,
• – einer scheibenförmigen Messmembran,
• – einer metallischen Fügestelle, die einen äußeren Rand der Messmembran mit einem äußeren Rand des Grundkörpers verbindet,
• – einer unter der Messmembran eingeschlossenen, durch die Fügestelle und den Grundkörper nach außen abgeschlossenen Messkammer, und
• – einem kapazitiven elektromechanischen Wandler,
• – der dazu dient, eine druckabhängige Verformung der Messmembran in ein elektrisches Primärsignal umzuwandeln,
• – der eine auf einer der Messmembran zugewandten Oberfläche des Grundkörpers flächig aufgebrachte Elektrode und eine auf einer dem Grundkörper zugewandten Oberfläche der Messmembran flächig aufgebrachte Gegenelektrode aufweist,
• – bei dem die Elektrode und die Gegenelektrode einen Kondensator bilden, dessen Kapazität ein Maß für die druckabhängige Verformung der Messmembran ist,

dadurch gekennzeichnet, dass
der Grundkörper in der Mitte des Drucksensors in die Messkammer hinein ragt, und ein Abstand zwischen der flächig auf die Oberfläche des Grundkörpers aufgebrachten Elektrode und der flächig auf die Messmembran aufgebrachten Gegenelektrode in der Mitte des Drucksensors geringer als eine Dicke der Fügestelle ist.For this purpose, the invention consists in a pressure sensor

• A basic body,
• A disk-shaped measuring membrane,
• A metallic joint connecting an outer edge of the measuring membrane to an outer edge of the body,
• - An enclosed under the measuring diaphragm, completed by the joint and the body to the outside measuring chamber, and
• A capacitive electromechanical transducer,
• - which serves to convert a pressure-dependent deformation of the measuring diaphragm into a primary electrical signal,
• - One on a measuring membrane facing surface of the body surface applied electrode and one on the base body facing surface of the Measuring membrane has a flat applied counter electrode,
• In which the electrode and the counterelectrode form a capacitor whose capacitance is a measure of the pressure-dependent deformation of the measuring diaphragm,

characterized in that
the base body protrudes into the measuring chamber in the middle of the pressure sensor, and a distance between the electrode applied flatly to the surface of the base body and the counterelectrode applied flatly to the measuring diaphragm in the middle of the pressure sensor is less than a thickness of the joint.

According to a first embodiment of the invention, the surface of the base body and the surface applied electrode is convex, esp. Ball or ellipsensegmentförmig.

According to a second embodiment of the invention, the surface of the base body is step-shaped and the surface applied electrode covers at least one arranged in the middle of the surface level.

The pressure sensor according to the invention has the advantage that the decisive for the achievable accuracy of measurement electrode spacing in the middle of the pressure sensor is no longer limited by the minimum thickness of the joint due to the inventive design of the base body down. The smaller electrode distance causes a significant increase in the measured pressure-dependent capacity or their changes. Accordingly, the pressure sensors according to the invention have a high measurement accuracy even in very small designs.

Another advantage is that the pressure sensors according to the invention have a high overload resistance even when using adapted to the reduced sensor dimensions thin measuring membranes. In this case, the portion of the base body pointing into the middle of the pressure sensor forms a bearing surface on which the measuring diaphragm comes to rest in the event of an overload. As a result, the diaphragm is protected in case of overload from further deformations and / or mechanical damage.

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

1 shows a section through a pressure sensor according to the invention with a convex body surface;

2 shows a section through a pressure sensor according to the invention with a one-step having body surface; and

3 shows a section through a pressure sensor according to the invention with a three-level body surface.

1 shows a section through a pressure sensor according to the invention with a substantially cylindrical body 1 and one with the main body 1 forming a measuring chamber 3 pressure-tight connected disk-shaped measuring diaphragm 5 ,

The pressure sensor may be designed, for example, as an absolute pressure sensor. In that case it is under the measuring membrane 5 enclosed measuring chamber 3 evacuated. Alternatively, the pressure sensor may be formed as a relative or differential pressure sensor, in which the measuring chamber 3 about one through the main body 1 guided through, in 1 indicated by dashed lines pressure supply line, a reference pressure p _R , z. B. an ambient pressure, or a second pressure p _{2 is} supplied.

body 1 and measuring membrane 5 consist of ceramic, esp. Of corundum. Ceramic has for application in pressure measurement particularly advantageous thermal, chemical and mechanical properties, including high long-term stability of the achievable measurement results and within relatively wide temperature ranges relatively stress-free installation of the pressure sensor in not shown here, usually metallic sensor housing and / or Allow process connections.

An outer edge of the measuring membrane 5 is with an outer edge of the main body 1 by means of a metallic joint 7 pressure-tight and gas-tight connected. For this joint 7 Preferably, an active brazing material is used. Especially suitable for this purpose are ternary active hard solders which have a Zr-Ni alloy and titanium. An example of this is in the EP 0 490 807 B1 described. The joint 7 is manufactured, for example, by the active brazing material as a ring-shaped solder preform between the edges of the measuring membrane 5 and basic body 1 is introduced and soldered there.

The joint 7 has a thickness d, which is the distance between the measuring diaphragm 5 and the body 1 determined at the outer edge of the pressure sensor. In this case, a minimum thickness of the joint 7 in the order of 20 microns with today technical possibilities are not undershot. This minimum thickness is predefined in particular by the minimum thickness in which solder preforms can be manufactured and processed.

The measuring membrane 5 is pressure-sensitive, ie a pressure p acting on it from outside causes a deflection of the measuring diaphragm 5 from their rest position. The pressure sensor has a capacitive electromechanical transducer, which serves to a pressure-dependent deformation of the measuring diaphragm 5 to convert into a primary electrical signal. The transducer comprises one on one of the measuring membrane 5 facing surface of the body 1 flat electrode applied 9 and one on one of the main body 1 facing inside of the measuring diaphragm 5 flat counter electrode 11 ,

The electrode 9 gets over one through the main body 1 electrically outwardly guided primary signal path. This is in the main body 1 a cylindrical, through the main body 1 through bore provided, into which a metal pin 13 is used. The metal pin 13 is preferably made of the same material as the electrode 9 , preferably tantalum. The counter electrode 11 is preferably with the Fügstelle 7 in electrical contact and is over the Fügstelle 7 electrically contacted.

electrode 9 and counter electrode 11 form a capacitor whose capacity depends on the pressure-induced deflection of the measuring diaphragm 5 changes. The pressure-dependent capacity or its changes are via a to the electrode 9 and the counter electrode 11 connected, not shown here measuring circuit detected and converted into a pressure-dependent measurement signal, which is then available for display, for further processing and / or evaluation.

According to the invention, the main body protrudes 1 in the middle of the pressure sensor in through the thickness d of the outer edge of the measuring diaphragm 5 with the outer edge of the body 1 connecting joint 7 and the disk-shaped measuring membrane 5 clamped cylindrical measuring chamber 3 into it. As a result, the distance between the surface on the surface of the body 1 applied electrode 9 and the surface on the measuring membrane 5 applied counter electrode 11 in the middle of the pressure sensor less than the thickness d of the joint 7 , Thus, in the middle of the pressure sensor electrode distances can be realized, which is smaller than the minimum thickness of the joint 7 are.

For this purpose, a variety of different configurations of the shape of the surface of the body 1 be used.

In the in 1 illustrated embodiment, the surface of the body 1 and thus also the surface of the surface applied electrode 9 convex. This convex surface 15 is, for example, spherical segment-shaped or elliptical segment-shaped. Accordingly, the distance between the electrode 9 and the counter electrode 11 in the middle of the pressure sensor to a minimum, and rises to the edge of the measuring chamber 3 towards the outside continuously.

2 and 3 show two alternative embodiments in which the surface of the main body 1a . 1b is stepped and the surface applied electrode 9a . 9b at least one step located in the middle of the surface 17 . 19 . 21 . 23 covered.

In the in 2 illustrated embodiment, the surface of the body 1a a single step 17 on, one parallel to the measuring diaphragm 5 running, into the measuring chamber 3 pointing in step surface, which completely from the electrode 9a is covered. The stage 17 Here is a cylindrical, in the measuring chamber 3 projecting heel over the height of the electrode spacing over the entire surface of the electrode 9a is set.

In the in 3 illustrated embodiment, the surface of the body 1b three steps rising towards the center of the pressure sensor 19 . 21 . 23 on whose stepped surfaces also parallel to the measuring diaphragm 5 are aligned. The electrode 9b covers all three levels 19 . 21 . 23 , For this purpose, it is applied to the associated step surfaces and to the cylindrical connecting surfaces running perpendicular to the step surfaces between the adjacent step surfaces.

The inventive design of the body 1 . 1a . 1b , causes in the middle of the pressure sensor, a targeted reduction in the distance between the surface on the surface of the body 1 . 1a . 1b applied electrode 9 and the counter electrode 11 , This increases the capacitance of the measuring capacitor to be measured, and thus the achievable measuring accuracy. In this way it is despite the minimum thickness of the joint 7 predetermined distance between the outer edge of the measuring diaphragm 5 and the outer edge of the body 1 . 1a . 1b It is possible to manufacture extremely small, capacitive ceramic pressure sensors with high measuring accuracy.

In this case, the thickness of the measuring diaphragm 5 be easily reduced in adaptation to the small diameter of the pressure sensor to a measurable pressure-dependent diaphragm stroke guarantee. In conjunction with correspondingly thin measuring membranes 5 provides the inventive shape of the surface of the body 1 . 1a . 1b the advantage that they provide effective and stable overload protection for the diaphragm 5 offers. Acts on the measuring membrane 5 an overpressure, so comes the measuring diaphragm 5 due to the small electrode spacing in the middle of the main body 1 . 1a . 1b the pressure sensor to support and is thus mechanically protected.

The pressure sensors according to the invention can be manufactured without sacrificing the accuracy of measurement with extremely small dimensions. For example, a pressure sensor with a diameter of the order of 1.5 cm to 2 cm designed for an example measuring range of 100 mbar can be produced. In conjunction with this measuring range and this diameter, the thickness of the measuring diaphragm is preferably in the order of 100 microns, and by the inventive design of the body 1 . 1a respectively. 1b reduced electrode spacing in the middle of the pressure sensor is preferably in the order of 5 microns to 15 microns. This distance is significantly less than the minimum thickness of the joint 7 and causes a drastic increase in capacity. This in turn leads to a significant improvement in measurement accuracy. With the example sensor described here, pressure measurements can be carried out with a measurement accuracy of 0.1%.

LIST OF REFERENCE NUMBERS

1, 1a, 1b

body

3

measuring chamber

5

measuring membrane

7

metallic joint

9, 9a, 9b

electrode

11

counter electrode

13

metal pin

15

convex surface

17

step

19

step

21

step

23

step

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 0490807 B1 [0023]

Claims (3)

Pressure sensor with - a basic body ( 1 . 1a . 1b ), - a disc-shaped measuring membrane ( 5 ), - a metallic joint ( 7 ), which forms an outer edge of the measuring diaphragm ( 5 ) with an outer edge of the basic body ( 1 . 1a . 1b ), - one under the measuring membrane ( 5 ), through the joint ( 7 ) and the basic body ( 1 . 1a . 1b ) to the outside sealed measuring chamber ( 3 ), and - a capacitive electromechanical transducer, - which serves a pressure-dependent deformation of the measuring diaphragm ( 5 ) into an electrical primary signal, - one on one of the measuring membrane ( 5 ) facing surface of the body ( 1 . 1a . 1b ) surface applied electrode ( 9 . 9a . 9b ) and one on one of the main body ( 1 . 1a . 1b ) facing surface of the measuring membrane ( 5 ) surface-mounted counterelectrode ( 11 ), - in which the electrode ( 9 . 9a . 9b ) and the counterelectrode ( 11 ) form a capacitor whose capacity is a measure of the pressure-dependent deformation of the measuring diaphragm ( 5 ), characterized in that the basic body ( 1 . 1a . 1b ) in the middle of the pressure sensor into the measuring chamber ( 3 protrudes into it, and a distance between the surface on the surface of the body ( 1 . 1a . 1b ) applied electrode ( 9 . 9a . 9b ) and the flat on the measuring membrane ( 5 ) counter electrode ( 11 ) in the center of the pressure sensor is less than a thickness (d) of the joint. Pressure sensor according to claim 1, characterized in that the surface of the base body ( 1 ) and the surface applied electrode ( 9 ) is convex, in particular spherical segment-shaped or elliptical segment-shaped. Pressure sensor according to claim 1, characterized in that the surface of the base body ( 1a . 1b ) is step-shaped and the surface applied electrode ( 9a . 9b ) at least one stage located in the middle of the surface ( 17 . 19 . 21 . 23 ) covered.

Images