PRESSURE MEASURING CELL

Abstract

The invention relates to a pressure measuring cell with a base body including an internal space, which base body comprises a first opening. A pressure sensor is arranged in the internal space of the base body and the internal space is filled with a pressure transfer medium. The pressure measuring cell further comprises an uneven membrane made from plastic. The membrane fully covers the first opening of the base body and is metallically coated at least on one of its two sides.

Claims

1. Pressure measuring cell comprising a base body comprising an internal space, said base body having a first opening, a pressure sensor arranged in the internal space of the base body, a pressure transfer medium arranged in the internal space of the base body, said pressure transfer medium being a liquid, a gel, an oil or a hardened elastomer, a plastic membrane attached in such a way to the base body that the first opening is fully covered, wherein the membrane comprises an uneven form, and wherein the membrane comprises a metallic coating on at least one side.

2. Pressure measuring cell according to claim 1, wherein the base body comprises a second opening opposite to the first opening, and wherein a covering element is hermetically attached to the base body, so that the covering element fully covers the second opening, and so that the internal space is included by the base body and by the covering element.

3. Pressure measuring cell according to claim 1, wherein the base body (4) is at least partly composed of polyether ether ketone (PEEK) or of a PEEK composite material.

4. Pressure measuring cell according to claim 2, wherein the covering element is a circuit board.

5. Pressure measuring cell according to claim 1, wherein the pressure sensor is a piezo-resistive pressure sensor, in particular a micro-electromechanical (MEMS) pressure sensor.

6. Pressure measuring cell according to claim 2, wherein the pressure sensor is a piezo-resistive pressure sensor, in particular a micro-electromechanical (MEMS) pressure sensor.

7. Pressure measuring cell according to claim 1, wherein the membrane is composed of polyether ether ketone (PEEK) or of a PEEK composite material.

8. Pressure measuring cell according to claim 1, wherein the maximum transversal dimension of the first opening is less than 6 millimetres, preferably between 2 millimetres and 4 millimetres.

9. Pressure measuring cell according to claim 2, wherein the maximum transversal dimension of the first opening is less than 6 millimetres, preferably between 2 millimetres and 4 millimetres.

10. Pressure measuring cell according to claim 1, wherein the uneven membrane is thermically preformed.

11. Pressure measuring cell according to claim 2, wherein the uneven membrane is thermically preformed.

12. Pressure measuring cell according to claim 1, wherein both surfaces of the membrane are uneven and wherein the membrane has a waved form, wherein the waves are preferably arranged concentrically.

13. Pressure measuring cell according to claim 2, wherein both surfaces of the membrane are uneven and wherein the membrane has a waved form, wherein the waves are preferably arranged concentrically.

14. Pressure measuring cell according to claim 1, wherein the membrane comprises a metallic coating only on its side facing the internal space.

15. Pressure measuring cell according to claim 2, wherein the membrane comprises a metallic coating only on its side facing the internal space.

16. Pressure measuring cell according to claim 15, wherein the metallic coating of the membrane comprises a coating thickness of 100 nanometres to 600 nanometres, preferably a coating thickness between 300 nanometres and 500 nanometres.

17. Pressure measuring cell according to claim 1, wherein the membrane comprises a thickness of less than 50 micrometres, preferably from 10 micrometres to 20 micrometres.

18. Pressure measuring cell according to claim 2, wherein the membrane comprises a thickness of less than 50 micrometres, preferably from 10 micrometres to 20 micrometres.

19. Pressure measuring cell according to claim 1, wherein the membrane is attached to the base body by laser welding.

20. Pressure measuring cell according to claim 2, wherein the membrane is attached to the base body by laser welding.

21. Pressure measuring cell according to claim 2, wherein the pressure sensor is connected to the covering element, which preferably is a circuit board, by means of conductive elements, preferably by means of bonding wires.

22. Method for fabrication of a pressure measuring cell, comprising the following steps: positioning of a preformed metal-coated or uncoated membrane at a base body comprising an internal space and a first opening, so that the membrane fully covers the first opening of the base body; laser welding the membrane along the perimeter of the first opening, respectively a suitable distance to the perimeter of the first opening, for hermetically attaching the membrane to the base body; optionally, if the membrane is uncoated, coating, preferably through sputtering, the side of the membrane facing the internal space with a metal alloy, preferably with a nickel alloy; filling the internal space of the base body with a pressure transfer medium; hermetically fixating a covering element to which a pressure sensor is attached to the base body, preferably under negative pressure or vacuum conditions, so that the pressure sensor extends into the internal space and so that the pressure transfer medium fully fills the internal space delimited by the covering element, the base body and the membrane.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0060] Exemplary embodiments of the invention are disclosed in the description and illustrated by the drawings in which:

[0061] FIG. 1 shows a schematic sectional view of a possible embodiment;

[0062] FIG. 2A bis 2D show steps of a fabrication method of the embodiment shown in FIG. 1, wherein

[0063] FIG. 2A shows inserting of the waved plastic membrane into the base body of the pressure measuring cell,

[0064] FIG. 2B shows coating of the membrane attached to the inner side of the base body with a metal alloy,

[0065] FIG. 2C shows filling up of the internal space with pressure transfer medium,

[0066] FIG. 2D shows attaching of the covering element with pressure sensor to the base body.

DETAILED DESCRIPTION OF DRAWINGS

[0067] An embodiment according to the invention is shown in FIGS. 1 to 2D and described hereinafter.

[0068] FIG. 1 is a schematic sectional view of a possible embodiment of a pressure measuring cell with a base body 4 and a covering element 2. The covering element 2 can be screwed to the base body, wherein a sealing ring 10 is arranged to create a hermetical connection between covering element 2 and base body 4.

[0069] In the shown embodiment the covering element 2 is a circuit board. The pressure sensor 1, which is a piezo-resistive MEMS pressure sensor in the shown example, is attached to a glass substrate 12 and by means of the glass substrate 12 fixated to the covering element 2. In this embodiment pressure sensor 1 with glass substrate 12 are fixated by means of a glue 7 to the covering element 2.

[0070] The shown pressure sensor 1 is conductively connected via bonding wires 8 to the electronics of the covering element 2, in the current case a circuit board.

[0071] The base body includes together with the covering element 2 an internal space into which the pressure sensor 1 extends. The base body comprises on its side opposite to the covering element 2 a first opening 9. This first opening is the measurement opening for the pressure measurement.

[0072] The measurement opening 9 is fully covered by a plastic membrane 5. The plastic membrane is attached to the base body 4 around the first opening so that the membrane 5 hermetically closes the opening 9. Preferentially, the membrane 5 is fixated to the base body 4 by means of laser welding.

[0073] As shown in FIG. 1, the membrane has a wave form.

[0074] In the shown embodiment the membrane 5 comprises on its inner side facing the internal space a metallic coating 6. In this example, the coating is a nickel alloy.

[0075] For metallic coating of the membrane 5 commercially available alloys can be used. For example, the alloy can comprise the following elements: nickel up to a maximum of 63 percent by weight, molybdenum 15 percent by weight to 17 percent by weight, chromium 14.5 percent by weight to 16.5 percent by weight, iron 4 percent by weight to 7 percent by weight, tungsten 3 percent by weight to 4.5 percent by weight, cobalt up to a maximum of 2.5 percent by weight, and, optionally, further elements which respectively have a weight percentage part of less than 1 percent by weight. For example, alloys with material numbers 2.4819 or 1.4404 can be used for the coating.

[0076] The invention is, however, not limited to these alloys. Other metal coatings, for example made of nickel, or of chromium, or also of nickel and/or alloys comprising chromium can be used as well. Other chemically resistant metals or metal alloys are also suited for the coating.

[0077] To enable an efficient pressure transmission from the membrane 5 to the pressure sensor 1, the internal space of the base body is fully filled with a pressure transfer medium 3. In the shown embodiment the pressure transfer medium is a silicone gel. Other pressure transfer media are, however, also suitable, for example oils.

[0078] Under the influence of a pressure or in the case of a pressure change, the membrane deforms. In the case of a positive pressure, respectively a positive pressure change the membrane 5 curves in the direction of the internal space.

[0079] The direction and the extent of this form change of the membrane is transmitted via the pressure transfer medium to the pressure sensor. The coves, respectively form changes, are admittedly minimal, but since the internal space of the base body is fully filled with substantially incompressible pressure transfer medium, this minimal change leads to a change of the hydrostatic pressure in the internal space of the base body. This changed hydrostatic pressure acts on all surfaces contacting the pressure transfer medium, including the outer surface of the pressure sensor, and thereby the measurement surface of the pressure sensor. In the piezo-resistive pressure sensor the pressure sensor element is thereby deformed, leading to a change in the electric resistance of the measurement bridge arranged on the pressure sensor element. Signal amplification and digitisation and correction of the signal can proceed on the circuit board or also on an ASIC controller added to the pressure sensor element.

[0080] In a preferred embodiment the base body 4 is composed of PEEK or a PEEK composite material. Further, the membrane 5 is preferentially of PDDK or a PEEK composite material and its outer side facing away from the internal space is uncoated. The membrane 5 can, however, also be coated on its outer side. The outer surface of the pressure measuring cell is in this preferred embodiment thus made of PEEK or a PEEK composite material.

[0081] FIGS. 2a to 2d show in single steps the fabrication of the embodiment shown in FIG. 1.

[0082] As shown in FIG. 2a, in a first step the uncoated membrane 5 is inserted into the internal space of the base body 4 and positioned in such a way that its first opening is fully covered. Thereafter, the membrane is laser welded to the base body 4.

[0083] In a next step, FIG. 2b, the membrane 5 fixated to the base body 4 is coated with a metal alloy 6. Preferentially, the membrane is coated with the alloy with the PVD method, respectively sputtered.

[0084] Thereafter, as shown in FIG. 2c, the internal space of the base body is preferentially fully filled up with the pressure transfer medium 3.

[0085] As last step, FIG. 2d, the covering element with the pressure sensor is attached to the base body to hermetically close the filled internal space 3.

[0086] To enable an oozing out of the volume of the pressure transfer medium 3 displaced by the pressure sensor 1, the covering element preferentially comprises a small opening 13. This opening is hermetically closed after fixating the covering element, for example by soldering.

[0087] It is to be understood that different embodiments and modifications of the herein described, presently preferred embodiments are obvious to the skilled person. Insofar as these embodiments do not diverge from the scope of the claims, it is envisaged that they are also comprised by the herein disclosed invention.