Pressure gauge for determining a first pressure of a medium

Abstract

The invention relates to a pressure gauge (1) for determining a first pressure (p1) of a medium (2), comprising - a pressure sensor (3) having a ceramic main part (4) and having a ceramic measurement diaphragm (6) connected to the ceramic main part by means of a joint (5), wherein the first pressure (p1) can be applied to the measurement diaphragm (6), - a housing sleeve (7) having an interior (8) and having a contact surface (9), the pressure sensor (3) being disposed in the interior (8) and being supported on the contact surface (9) in an edge region (6a) of the measurement diaphragm (6), and - a first sealing element (10) and a second sealing element (11) which are disposed between the contact surface (9) and the pressure sensor (3), the second sealing element (11) surrounding the first sealing element (10) so that an intermediate space (12) is formed between the first sealing element (10) and the second sealing element (11), and - at least one ventilation opening (13), which is designed and is disposed in the housing sleeve (7) such that a gas exchange occurs between the intermediate space (12) and surroundings (14) of the pressure gauge (1).

Description

[0001] Pressure sensor for determining a first pressure of a medium

[0002] The invention relates to a pressure sensor for determining a first pressure of a medium.

[0003] In pressure measurement technology, absolute pressure, differential pressure, and gauge pressure sensors are known. Absolute pressure sensors determine the prevailing pressure of a process medium absolutely, i.e., relative to a vacuum, while differential pressure sensors determine the difference between two different pressures of the process medium or media. With gauge pressure sensors, the pressure of the process medium to be measured is determined relative to a reference pressure, with the atmospheric pressure prevailing in the vicinity of the gauge pressure sensor serving as the reference pressure.

[0004] Pressure transducers have a pressure-sensitive measuring element, the so-called pressure sensor, with a pressure applied to its first and second surfaces. In the case of relative or absolute pressure transducers, the pressure of the process medium to be determined acts on the first surface of the pressure sensor, while an absolute or reference pressure acts on the second surface. In the case of differential pressure transducers, a first pressure and a second pressure of a process medium are applied to both surfaces. The measuring element bends depending on the existing relative pressure, which is calculated from the difference between the pressures applied to the two surfaces. This bending is converted by an electronic unit into an electrical signal dependent on the relative pressure, which is then available for further processing or evaluation. A distinction is made between capacitive and piezoresistive pressure sensors, among others.A large number of such pressure sensors are manufactured and distributed by companies in the Endress+Hauser Group.

[0005] A ceramic pressure sensor, for example, comprises a ceramic base body and a ceramic measuring diaphragm, which is pressure-tightly connected to the base body by means of an active brazing alloy, forming a measuring chamber. Furthermore, the pressure sensor typically comprises a transducer for converting a pressure-dependent deformation of the measuring diaphragm into an electrical primary signal, as well as a primary signal path extending through the base body. The transducer can be a capacitive or resistive transducer, for example. The primary signal path usually comprises at least one electrical feedthrough through the base body. Instead of ceramic pressure sensors, silicon chips are also known as pressure sensors, which are usually bonded to a silicon substrate. Ceramic pressure sensors, in particular, are often inserted into a housing of the pressure transducer by means of a sealing element, so that an interior of the housing is sealed off from the medium.Typically, elastomer sealing rings are used as sealing elements. Due to their elastic properties, these can compensate for the different linear expansions of the pressure sensor and the housing when temperatures change, thereby reducing mechanical stresses in the area of ​​the measuring diaphragm and maintaining high measurement accuracy even during temperature changes. A disadvantage of such elastomer sealing rings, however, is their poor sealing properties against certain gaseous media, such as hydrogen. These media can penetrate such a sealing ring into the interior of the housing and damage the internal components to such an extent that the pressure sensor fails over time.

[0006] The object of the present invention is therefore to provide a ceramic pressure sensor which has a long service life, particularly in hydrogen-containing media.

[0007] According to the invention, the object is achieved by a pressure measuring transducer for determining a first pressure of a medium, comprising a pressure sensor with a ceramic base body and a ceramic measuring diaphragm connected thereto by means of a joint, wherein the measuring diaphragm can be subjected to the first pressure, a housing bushing with an interior space and a support surface, wherein the pressure sensor is arranged in the interior space and is supported on the support surface in an edge region of the measuring diaphragm, and a first sealing element and a second sealing element, which are arranged between the support surface and the pressure sensor, wherein the second sealing element surrounds the first sealing element, so that an intermediate space is formed between the first sealing element and the second sealing element, and at least one ventilation opening, which is designed and arranged in the housing bushing,that a gas exchange takes place between the space and an environment of the pressure sensor.,

[0008] According to the invention, a gaseous medium or a gaseous component of the medium that enters the intermediate space through the first sealing element can escape from the intermediate space into the environment of the pressure sensor through the at least one ventilation opening. The gaseous medium or the gaseous component of the medium that penetrates the intermediate space through the first sealing element will generally only slowly pass into a rear space of the housing bushing due to the gas permeation coefficient of the second sealing element. The first sealing element and the second sealing element are in particular made of an elastomer or comprise an elastomer. The at least one ventilation opening ensures that the gas exchange between the intermediate space and the environment is so high that penetration and accumulation of the gaseous medium or the gaseous component in the rear space of the housing bushing is largely avoided.The rear chamber of the housing bushing refers to a section of the interior of the housing bushing that is located on a side of the second sealing element facing away from the intermediate space. This ensures a long service life of the pressure sensor, particularly in the case of media containing hydrogen gas. The first sealing element and / or the second sealing element are, in particular, annular in design.

[0009] In particular, the intermediate space is ring-shaped.

[0010] In a further development of the pressure transducer according to the invention, the first sealing element faces the medium, and the second sealing element is arranged facing away from the medium. In particular, the first sealing element is in contact with the medium, and the second sealing element is arranged on a side of the first sealing element facing away from the medium.

[0011] In one embodiment, the second sealing element has an inner diameter which is larger than an outer diameter of the first sealing element.

[0012] In a further embodiment, the first sealing element and the second sealing element are made of different materials. The first sealing element can, for example, be designed to have a low permeation coefficient for liquid and / or solid components of the medium.

[0013] A further embodiment provides that the second sealing element has a lower gas permeation coefficient than the first sealing element. This ensures that a gaseous medium or a gaseous component of the medium penetrates the rear space or the intermediate space more slowly through the second sealing element than through the first sealing element, so that the gaseous medium or the gaseous component can escape from the intermediate space through the at least one ventilation opening more quickly than they can enter the rear space through the second sealing element.

[0014] Advantageously, the at least one ventilation opening is sealed with a gas-permeable and moisture-impermeable membrane. The membrane allows gas exchange between the space and the environment while simultaneously preventing liquids and solids from penetrating the space. Such semi-permeable membranes are made, for example, of a polymer, particularly Gore-Tex®.

[0015] In particular, the membrane is mounted within the at least one ventilation opening or in an end region of the at least one ventilation opening. The membrane can be arranged such that it closes the at least one ventilation opening from a side of the housing socket facing the pressure sensor or from a side of the housing socket facing away from the pressure sensor. The membrane can be mounted, for example, on an outer wall or an inner wall of the housing socket. It is also possible to mount the membrane in the at least one ventilation opening. The membrane can be mounted using adhesive bonding, soldering, or other joining techniques.

[0016] The pressure transducer preferably comprises a plurality of ventilation openings. A plurality of ventilation openings, as defined in the application, means that two or more ventilation openings are provided. By providing a plurality of ventilation openings, the gas exchange rate between the intermediate space and the environment is increased, thereby further reducing the accumulation of the gaseous medium or gaseous component in the rear space. Advantageously, two ventilation openings are arranged opposite one another. This increases the gas exchange for gaseous media or gaseous components that are lighter or heavier than air, regardless of the installation direction of the pressure transducer.

[0017] In particular, the numerous ventilation openings are arranged in a circle. This is particularly advantageous in the case of a circular gap.

[0018] In one embodiment, the pressure sensor has a support ring designed to set a defined distance between the first sealing element and the second sealing element. The support ring is arranged in the intermediate space. Aging effects can lead to changes in the inner and outer diameters of the first sealing element and the second sealing element. The support ring thus prevents a reduction or enlargement of the intermediate space and simultaneously ensures that the intermediate space corresponds to the at least one ventilation opening. The support ring is, in particular, circular in shape. For example, the support ring comprises a metal or is made of a metal.

[0019] In a further embodiment, the support ring has at least one axially arranged through-bore. By inserting the support ring into the intermediate space, the intermediate space is divided into a side facing the at least one ventilation opening and a side facing away from the at least one ventilation opening. By means of the at least one axially arranged through-bore, gas exchange is enabled within the intermediate space, i.e., between the side of the intermediate space facing the at least one ventilation opening and the side facing away from the at least one ventilation opening. Preferably, several through-bores are arranged in the support ring.

[0020] In a further development, the support ring has at least one circumferential recess. The at least one recess is, in particular, a radially circumferential recess. The at least one circumferential recess can be configured as a circumferential groove. The at least one recess is, in particular, designed for gas exchange along the intermediate space.

[0021] In particular, the at least one circumferential recess is arranged on a side of the support ring facing the at least one ventilation opening and / or a side facing away from the at least one ventilation opening. In particular, the at least one circumferential recess is arranged such that a gas exchange takes place between the at least one recess and the at least one ventilation opening. If the at least one circumferential recess is arranged on the side of the support ring facing the at least one ventilation opening, the at least one circumferential recess can be arranged and configured such that it overlaps with the at least one ventilation opening.In the event that the at least one circumferential recess is arranged on the side of the support ring facing away from the at least one ventilation opening, at least one axial through-bore can additionally be arranged in the support ring in order to enable gas exchange between the side of the support ring facing away from the at least one ventilation opening and the environment.

[0022] The present invention will be explained in more detail below with reference to the following figures 1-8. They show:

[0023] Fig. 1 : a schematic representation of a pressure sensor according to the invention.

[0024] Fig. 2: a schematic representation of a pressure sensor according to the invention connected to a container.

[0025] Fig. 3: a schematic representation of a front view of the pressure sensor according to the invention. Fig. 4: an embodiment of the pressure sensor according to the invention with a membrane.

[0026] Fig. 5: a further embodiment of a pressure sensor according to the invention with a membrane.

[0027] Fig. 6: a further embodiment of a pressure sensor according to the invention with a membrane.

[0028] Fig. 7: an embodiment of a pressure sensor according to the invention with a support ring.

[0029] Fig. 8a-b: a schematic representation of the support ring.

[0030] The pressure sensor 1 according to the invention can be configured as a relative, absolute, or differential pressure sensor. The pressure sensor 1 shown in Fig. 1 comprises a pressure sensor with a ceramic base body 4 and a ceramic measuring diaphragm 6. The base body 4 and the measuring diaphragm 6 are connected to one another by means of a joint 5, in particular in a pressure-tight manner, with a pressure chamber 22 enclosed between the base body 4 and the measuring diaphragm 6.

[0031] The pressure sensor 3 has, in particular, an electromechanical transducer (not shown) for detecting a pressure-dependent deformation of the measuring diaphragm 6. The transducer can be designed as a capacitive transducer with at least one capacitor, wherein the capacitor has a capacitance that can be varied depending on the pressure-induced deflection of the measuring diaphragm 6. The at least one capacitor is formed by a measuring electrode applied to the side of the measuring diaphragm 6 facing the base body 4 and a counter electrode applied to an end face of the base body 4 facing the measuring diaphragm. The pressure-dependent capacitance of the capacitor is detected via measuring electronics (not shown) connected to the measuring electrode and the counter electrode. The measuring electronics can be designed to convert the capacitance into a pressure-dependent measuring signal and to provide it for further evaluation and / or processing.

[0032] The pressure sensor 1 further comprises a housing bushing 7, which comprises an interior space 8 and a support surface 9. The housing bushing 7 has, in particular, a cylindrical shape. The support surface 9 is designed, in particular, as a projection or shoulder. The pressure sensor 3 is arranged in the interior space 8 and supported in an edge region 6a of the measuring diaphragm 6 on the support surface 9 by means of the first sealing element 10 and the second sealing element 11. The first sealing element 10 and the second sealing element 11 are arranged between the support surface 9 and the pressure sensor 3. In particular, the first sealing element 10 faces the medium 2 or is in contact with the medium. The second sealing element 11 surrounds the first sealing element 10, such that an intermediate space 12 is formed between the two sealing elements 10, 11. The intermediate space is, for example, annular.The second sealing element 11 can have an inner diameter that is larger than the outer diameter of the first sealing element 10. In particular, the first sealing element 10 and the second sealing element 11 are arranged in the same plane. The first sealing element 10 and the second sealing element 11 can be made of an elastomer or comprise an elastomer. The two sealing elements 10, 11 can be made of different materials. For example, a material of the second sealing element 11 can be selected such that it has a lower gas permeation coefficient than the first sealing element 10.

[0033] As shown in Fig. 2, the pressure sensor 1 according to the invention can be attached to a container 21 by means of a process connection 20. The container 21 comprises a medium 2, which is, for example, gaseous or has at least one gaseous component, in particular hydrogen gas. The gaseous medium 2 or a gaseous component of the medium 2 can, to a certain extent, enter the intermediate space 12 through the first sealing element 10. The second sealing element 11 initially ensures that the gaseous medium 2 or the gaseous component does not immediately enter a rear space 19 of the housing bushing. To prevent the gaseous medium 2 or the gaseous component from accumulating in the intermediate space 12 and penetrating the rear space 19 over time, the pressure sensor 1 has at least one ventilation opening 13.The at least one ventilation opening 13 is configured and arranged in the housing socket 7 such that a gas exchange takes place between the intermediate space 12 and an environment 14 of the pressure sensor 1. In particular, the at least one ventilation opening 13 is arranged such that the at least one ventilation opening 13 overlaps the intermediate space 12.

[0034] By means of the at least one ventilation opening 13, the intermediate space 12 can be ventilated in such a way that an accumulation of the gaseous medium 2 or the gaseous component is largely avoided. The at least one ventilation opening 13 can be arranged in the region of the support surface 9.

[0035] In addition to the embodiments shown, each of which has two sealing elements 10, 11, it is also possible to use more than two sealing elements and more than one intermediate space to prevent the accumulation of the gaseous medium 2 or the gaseous component in the rear space 9. For example, the second sealing element 11 can in turn be surrounded by a third sealing element (not shown), so that a further intermediate space is formed between the second sealing element and the third sealing element and which is in gas exchange with the environment of the pressure sensor by means of further ventilation openings.

[0036] Instead of a single ventilation opening 13, as shown in Figures 1 and 2, the pressure sensor 1 can also have a plurality of ventilation openings 13. Such an arrangement of ventilation openings 13 is shown in Figure 3, which represents a front view of the pressure sensor 1 and a top view of the measuring diaphragm 6. For clarity, the outlines of the pressure sensor 3, the first sealing element 10, and the second sealing element 11 are shown in dashed lines. In the example shown, the ventilation openings 13 are arranged along the intermediate space 12, i.e., between the first sealing element 10 and the second sealing element 11.

[0037] To prevent moisture from entering the intermediate space 12, a gas-permeable and moisture-impermeable membrane 15 can be provided, which is arranged such that it closes the at least one ventilation opening 13. For example, the membrane 15 is arranged in an end region 13a of the at least one ventilation opening 13, as shown in Fig. 4. If a plurality of ventilation openings 13 are present, a single membrane 15 can close the plurality of ventilation openings 13, or a plurality of membranes 15 can be arranged to each close one or more of the ventilation openings 13. Fig. 5 shows a further arrangement of the membrane 15, which is arranged in the end region 13a of the ventilation opening 13 opposite to Fig. 4. The membrane 15 can be attached to an outer wall or inner wall of the housing bushing 7. Fig.6 shows an arrangement of the membrane 15 within the at least one ventilation opening 13.

[0038] Optionally, the pressure sensor 1 can have a support ring 16, in particular an annular one, which is shown in Figures 7-8. The support ring 16 is designed to set a defined distance between the first sealing element 10 and the second sealing element 11. The support ring 16 can be designed to prevent a change in the spatial extent of the intermediate space 12. The support ring 16 is arranged in particular in the intermediate space 12. For example, the support ring 16 is designed as a separate component which is introduced into the intermediate space 12. The support ring 16 can also be designed as a section of the housing bushing 7. In particular, the support ring is made of a material that is less easily deformed than elastomers, for example a metal, in particular stainless steel, or ceramic. The support ring 16 can have at least one axially arranged through-bore 17.The through-bore 17 is particularly designed such that gas exchange takes place within two sections of the intermediate space 12 formed by the support ring 16. As can be seen in Fig. 7, the intermediate space 12 is divided into two sections by the support ring 16: an upper section, which, via the ventilation opening 13, is in gas exchange with the environment 14, and a lower section, which, without the axial through-bore 17, would not be in gas exchange with the environment 14.

[0039] In addition, the support ring 16 can have at least one circumferential recess 18. The at least one circumferential recess 18 is designed in particular to improve gas exchange within the intermediate space 12. By introducing the at least one recess 18, the gas volume in the intermediate space 12 is increased. For example, the at least one recess 18 can be arranged on a side of the support ring 16 facing the at least one ventilation opening 13 and / or a side facing away from the at least one ventilation opening 13. The support ring 16 can, for example, be designed such that, after assembly, it fills the entire height between the measuring membrane 6 and the housing bushing 7. In such cases in particular, the at least one circumferential recess 18 improves gas exchange within the intermediate space 12. The at least one circumferential recess 18 is in particular annular.

[0040] It is particularly advantageous if the support ring 16 has at least one axial through-bore 17 in addition to the at least one circumferential recess 18. Fig. 8 shows such an arrangement with two circumferential recesses 18, which are arranged on a side of the support ring 16 facing the at least one ventilation opening 13 and / or on a side facing away from the at least one ventilation opening 13. Fig. 8a shows a support ring 16 in plan view with five axial through-bores 17. The line between the two points A and B indicates the cross-section of the support ring 16, which is shown in Fig. 8b. At point B, two circumferential recesses 18 are shown, while at point A, in addition to the two circumferential recesses 18, the axial through-bore 17 can also be seen in cross-section. List of reference symbols

[0041] 1 pressure sensor

[0042] 2 Medium

[0043] 3 Pressure sensor

[0044] 4 basic bodies

[0045] 5 joint

[0046] 6 measuring membrane

[0047] 6a Edge area of ​​the measuring membrane

[0048] 7 Housing socket

[0049] 8 Interior

[0050] 9 Support surface

[0051] 10 first sealing element

[0052] 11 second sealing element

[0053] 12 space

[0054] 13 Ventilation opening

[0055] 14 Surroundings

[0056] 15 Membran

[0057] 16 Support ring

[0058] 17 Through hole

[0059] 18 Deepening

[0060] 19 backcourt

[0061] 20 process adapters

[0062] 21 container

[0063] 22 pressure chamber

Claims

Patent claims 1 . Pressure measuring transducer (1) for determining a first pressure (p1) of a medium (2), comprising a pressure sensor (3) with a ceramic base body (4) and a ceramic measuring diaphragm (6) connected thereto by means of a joint (5), wherein the measuring diaphragm (6) can be subjected to the first pressure (p1), a housing bushing (7) with an interior space (8) and a support surface (9), wherein the pressure sensor (3) is arranged in the interior space (8) and is supported on the support surface (9) in an edge region (6a) of the measuring diaphragm (6), and a first sealing element (10) and a second sealing element (11), which are arranged between the support surface (9) and the pressure sensor (3), wherein the second sealing element (11) surrounds the first sealing element (10), so that an intermediate space (12) is formed between the first sealing element (10) and the second sealing element (11), and at least one ventilation opening (13), which designed in such a way and arranged in the housing socket (7),that a gas exchange takes place between the intermediate space (12) and an environment (14) of the pressure sensor (1).

2. Pressure sensor (1) according to one of the preceding claims, wherein the intermediate space (12) is annular.

3. Pressure sensor (1) according to one of the preceding claims, wherein the first sealing element (10) is arranged facing the medium (2) and the second sealing element (11) is arranged facing away from the medium (2).

4. Pressure measuring sensor (1) according to one of the preceding claims, wherein the second sealing element (11) has an inner diameter which is larger than an outer diameter of the first sealing element (10).

5. Pressure sensor (1) according to one of the preceding claims, wherein the first sealing element (10) and the second sealing element (11) are made of different materials.

6. Pressure sensor (1) according to one of the preceding claims, wherein the second sealing element (11) has a lower gas permeation coefficient than the first sealing element (10).

7. Pressure sensor (1) according to one of the preceding claims, wherein the at least one ventilation opening (13) is closed with a gas-permeable and moisture-impermeable membrane (15).

8. Pressure sensor (1) according to one of the preceding claims, wherein the membrane (15) is mounted within the at least one ventilation opening (13) or in an end region (13a) of the at least one ventilation opening (13).

9. Pressure sensor (1) according to one of the preceding claims, wherein the pressure sensor (1) comprises a plurality of ventilation openings (13).

10. Pressure sensor (1) according to one of the preceding claims, wherein the plurality of ventilation openings (13) are arranged in a circle.

11. Pressure sensor (1) according to one of the preceding claims, wherein the pressure sensor (1) has a support ring (16) which is designed to set a defined distance between the first sealing element (10) and the second sealing element (11).

12. Pressure sensor (1) according to claim 11, wherein the support ring (16) has at least one axially arranged through-bore (17).

13. Pressure sensor (1) according to one of claims 11-12, wherein the support ring (16) has at least one circumferential recess (18).

14. Pressure measuring sensor (1) according to one of claims 11-13, wherein the at least one circumferential recess (18) is arranged on a side of the support ring (16) facing the at least one ventilation opening (13) and / or a side facing away from the at least one ventilation opening (13).

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