DE102009026991A1 - Potentiometric sensor for measuring potentiometric value of measuring medium, has ion-sensitive field effect transistor which consists of gate region, where the gate region is admittable with measuring medium - Google Patents

Abstract

The potentiometric sensor has an ion-sensitive field effect transistor which consists of a gate region. The gate region is admittable with the measuring medium. A housing is provided around the ion-sensitive field effect transistor with a housing opening. A sealing (6) is provided between the housing and the ion-sensitive field effect transistor. The sealing seals the housing around the gate-region together with the ion-sensitive field effect transistor. The sealing is eliminable from a plate material by a laser cutting method. An independent claim is also included for a laser cutting method for cutting a sealing of a potentiometric sensor.

Description

The present invention relates to a potentiometric sensor for measuring a potentiometric size of a measuring medium, having an ion-sensitive field-effect transistor which has a gate region, which gate region can be acted upon by the measuring medium.

Potentiometric sensors with an ion-sensitive field effect transistors, so-called ISFETs, are used to determine electrochemical potentials, in particular as pH sensors. Such sensors are, inter alia, in the review article "Thirty years of ISFETOLOGY [...]" by P. Bergveld in "Sensors and Actuators" B88 (2003) 1-20 discussed.

The U.S. Patent 5,833,824 discloses the construction of an ISFET sensor. An O-ring-shaped seal, here made of gold, between the housing, here made of aluminum, and the ISFET chip seals the ISFET sensor against the measuring medium. The ISFET chip in this case has a platinum layer around the exposed gate region of the chip, which is mounted over the ion-sensitive aluminum layer, and which is touched only by the O-ring-shaped seal. Gold as a sealing material is very expensive compared to other materials with comparable sealing effect.

As in the above U.S. Patent 5,833,824 discloses seals are also known from polymer materials. However, these seals are usually urgeformt from an elastomeric molding material, for. B. injected, or mechanically punched from a plate material. In the mentioned manufacturing process, a burr is formed on the seal, which is no longer removable in the very small dimensions of this component by selective Entgratungsverfahren, which are used in much larger components, since these methods are simply not applicable here. The prior art merely discloses methods for deburring such small components, wherein the sealing edges of the seal undergo a strong rounding. However, this so-called radius reduces the sealing effect and creates gaps between the surfaces to be sealed. Thus, such deburred seals are not suitable for hygienic applications.

On the other hand, if the gaskets are not deburred, there is a risk of influencing the measurement due to burr residue and fouling up to the destruction of the ion-sensitive surface of the ISFET chip. A diminished sealing effect passes through the burrs at the sealing edges. Gas bubbles collect on the ridges or in the gaps caused by the burrs, distorting the measurement. In addition to the described blistering there is still the risk of deposits on or between the burr fibers and thus also a non-given use of such seals or sensors equipped with such seals in hygiene applications.

The object of the invention is to provide a hygienic potentiometric sensor which is inexpensive to manufacture.

The object is achieved by a potentiometric sensor for measuring a potentiometric size of a measuring medium, with an ion-sensitive field effect transistor, which has a gate region, which gate region can be acted upon by the measuring medium, with a housing around the ion-sensitive field effect transistor at least one housing opening, through which housing opening the gate region can be acted upon by the measuring medium, and with a static seal between the housing and the ion-sensitive field-effect transistor, which seal together with the ion-sensitive field effect transistor seals the housing around the gate region, wherein the Seal is cut out of a plate material by means of a laser cutting process. Laser cutting is a thermal separation process, especially for plate-shaped material. However, the plate material itself may have been cut out of a bar-shaped material by the same laser cutting method in a previous process step.

A seal prevents unwanted material transfers from one room, here the gate region, into another room, here the interior of the housing. The seal of the invention performs no relative movement and is therefore static.

It is producible according to the invention in that it can be cut out by means of a laser from a plate, a relatively thin, flat and flat object. In particular, the sealing material or the material of the plate, from which the seal is ausschneidbar, an organic material, such as a polymer. Some elastomers have very good sealing properties among the polymers, as can be, for example, from fluoroelastomers and random copolymers with a saturated polymer backbone, such as. B. produce EPDM seals according to the invention.

Of course, the materials of the sealing surfaces of the surrounding components which contact the seal play a decisive role in the tightness and therefore also in the choice of material for the seal. Accordingly, according to a further development of the sensor according to the invention at least one first sealing surface of the ion-sensitive field effect transistor, which contacts the seal in at least one point, in particular on at least one circumferential line, of tantalum (V) oxide. The housing also forms a sealing surface, here the second sealing surface, which is in direct contact with the seal in at least one point. In order to seal annular, the seal is touched on at least one circumferential line. The material of this second sealing surface of the housing is in particular PEEK.

Both the housing and the ion-sensitive field effect transistor may have a surface coating in the region of its sealing surface, d. H. the material of the first or second sealing surface may be different from the material of the ion-sensitive field effect transistor or of the housing. In this case, the respective surface of the housing and / or of the ion-sensitive field-effect transistor, which is in contact with the seal, forms the respective sealing surface. The first sealing surface thus forms a sealing surface pair with the second sealing surface and / or the second sealing surface forms a sealing surface pair with the third sealing surface.

The respective pairs of sealing surfaces close off the interior of the housing closely to the measuring medium. Gaskets are generally divided into touch seals and non-contact seals. Contact seals have at least one sealing surface, which sealing surface is in contact with a sealing surface. If the surfaces to be sealed against one another have spatial expanses, the seal and the sealing surfaces of the surrounding components touching the seal contact one another over many points of their respective sealing or sealing surfaces, for example over their entire respective sealing or sealing surface, and not only at one point.

According to a development of the sensor according to the invention, the seal has at least one first sealing surface which can be exposed to the measuring medium, which first sealing surface has an arithmetic average roughness value of at most 1 μm over its entire geometric surface. In particular, this value is less than 0.8 microns, or even less than 0.4 microns according to an embodiment of the invention.

According to a variant, the seal has a plurality of sealing surfaces, which contribute significantly to the sealing of the sensor. These sealing surfaces then have corresponding arithmetic mean roughness values. In an embodiment of the invention, each surface of the gasket has an arithmetic mean roughness value of at most 1 μm over its entire geometric surface.

According to further embodiments of the invention, the arithmetic mean roughness value of said sealing surfaces is less than 0.8 μm or even less than 0.4 μm. The definition of the arithmetic mean roughness, or sometimes called mean roughness, is found in "Dubbel - Paperback for Mechanical Engineering" 19th Edition F28 6.2.1 ,

The geometric surface is the ideal surface of a component, which is defined by the geometric description. The number of geometric surfaces is determined by the shape of the geometric body. For example, a cube has six geometric surfaces. A section through a body shows its geometric cross section; thus four geometric surfaces can be seen on a cube to stick to the example. The average roughness value is measured over a reference length. As a reference length here every distance within each of the geometric surface is considered.

Further developed, the seal has at least one first sealing surface which can be exposed to the measuring medium, which first sealing surface has a maximum profile height of at most 2 μm over its entire geometric surface. The arithmetic mean roughness value does not say anything about the distance of the maximum profile dome height to the maximum profile depth, ie about the possible radius or over the material protrusion at the interface of two surfaces. For this the maximum profile height is to be used. Likewise, according to the invention, the first and second sealing surfaces have a maximum profile height of at most 2 μm.

According to further embodiments of the invention, the maximum profile heights of said sealing surfaces and sealing surfaces are less than 1 micron, less than 0.8 microns or even less than 0.4 microns. The definitions of terms can be found again in "Dubbel - Paperback for Mechanical Engineering" 19th Edition F28 6.2.1 ,

In further embodiments, the said sealing surfaces and sealing surfaces have a maximum profile dome height and / or a maximum profile depth of at most 1.5 .mu.m, in particular of at most 1 .mu.m or they are less than 0.5 .mu.m.

Both the arithmetic mean roughness values, the maximum profile heights, the maximum tread depths and the maximum tread heights are given in μm. They are measured in the unassembled state of the seal. By installing the seal, a force acts on the seal, so that it seals certain surfaces to each other. As a result, the seal is at least partially compressed. However, the seal is designed so that its edges in the region of the gate Region, ie z. B. the edges, which are formed by the first and second sealing surface and the first and third sealing surface, do not undergo too large rounding, ie in particular that the first sealing surface in the mounted state of the seal is substantially flat.

In addition to the materials or material pairings of the sealing and sealing surfaces of course, the surface qualities of the sealing surfaces of the housing and / or the ion-sensitive field effect transistor have an influence on the seal quality. According to a further development of the invention, therefore, the arithmetic mean roughness of the first sealing surface of the ion-sensitive field effect transistor over its entire geometric surface is less than 1 micron. Likewise, for the second sealing surface of the housing, a maximum arithmetic average roughness value of 1 μm applies.

According to further exemplary embodiments of the invention, the arithmetic mean roughness value of said sealing surfaces is less than 0.8 μm or even less than 0.4 μm.

A further development of the invention provides that the seal is a flat gasket, in particular that the seal is an annular flat gasket, which has a rectangular ideal cord cross-section. The dimensions of an annular flat gasket are defined by the inner diameter and the cord thickness and the cord width. If the line has a square cross section, the line height and line width are the same. As an ideal cross section, analogous to the ideal surface, the cross section of a body is designated, which is defined by the geometric description. The ideal cross section is thus z. B. reflected in drawings. The shape deviations of the real body, such. As roughness, can then be described starting from the ideal body. Ideal bodies are virtually impossible to produce. The same applies to ideal surfaces.

So lay the cross sections of the string, such. B. a rectangular cross section, the geometric surfaces and thus the sealing surfaces of the seal firmly.

According to one embodiment of the invention, the annular flat gasket has a rectangular ideal cord cross-section. Another embodiment, however, shows a triangular ideal cord cross-section. But also lenticular or round cross-section are conceivable. A circular ideal cord cross-section makes the so-called O-ring from the annular flat gasket, in which case string width or cord height pass into the cord diameter. According to a further embodiment example, the shape and dimension of the housing opening substantially corresponds to the shape and dimension of the seal, d. H. that in particular the ideal diameter of the housing opening is equal to the ideal inner diameter of the annular seal.

According to training, the inner diameter of the annular seal is at most 3 mm. In particular, the inner diameter of the annular seal is less than 2 mm, or even less than 1.5 mm. In this case, the cord height, sometimes also referred to as cord thickness, and / or the cord width is a maximum of 1 mm, in particular, it is less than 0.5 mm, or less than 0.35 mm. In a variant according to the invention, the inner diameter of the annular seal is 1.5 mm and the cord is at least 0.35 mm high or wide.

A variant of the sensor according to the invention can be seen in that the seal has at least one exposing the measuring medium first sealing surface and a second sealing surface and a third sealing surface, which first sealing surface in the mounted state of the potentiometric sensor the measuring medium can be exposed, which second sealing surface with a first Sealing surface of the ion-sensitive field effect transistor tightly seals, and which third sealing surface with a second sealing surface of the housing seals, wherein the measuring medium exposable first sealing surface and the second sealing surface form a first edge and wherein the measuring medium exposable first sealing surface and the third sealing surface a form second edge, with no crater rests over the edges and wherein the edges have radii which are smaller than 2.7 microns or even only 2 microns. The seal is thus an annular flat gasket and has a rectangular geometric cross-section of the cord. It laterally delimits an area around the gate region of the ion-sensitive field-effect transistor, which can be exposed to the measuring medium. It lies between the ion-sensitive field effect transistor and the housing and is pressed in between these two components. The housing has a housing opening over the gate region of the ion-sensitive field effect transistor, through which the measurement medium can penetrate in the area around the gate region. Furthermore, the housing has deformations which correspond at least partially in the shape and size of the cord cross-section of the seal, by means of which deformations the seal is received and supported in the housing. Intersect z. B. two surfaces, each with an arithmetic average roughness of 0.8 microns and a maximum profile height of 0.8 microns, so created at the intersection of the two surfaces, ie at the edge, a maximum radius of 2.7 microns or a chamfer with a distance from the edge of 0.8 μm times the root of 2, which is about 1.1 μm results. The same applies to the other profile heights according to the invention. In this variant of the invention, at least the first, second and third sealing surfaces have an arithmetic average roughness value of at most 0.8 μm and a maximum profile height of 0.8 μm.

In another embodiment of the invention, each surface of the seal over its entire geometric surface an arithmetic mean roughness of at most 1 .mu.m, in particular at most 0.8 .mu.m. In short, the seal is then essentially burr-free and sharp-edged.

Here, as in a further embodiment of the invention, the seal is elastically clamped between the housing and ion-sensitive field effect transistor. The seal experiences a force on at least one sealing surface. If the gasket has a rectangular string cross-section, the second and third sealing surfaces experience a surface pressure in the size that seals the gasket tightly. By chemical processes, eg. As evoked by aggressive measuring media, high temperatures or sterilization conditions, many seal materials change over time, a relaxation begins, for example. Due to the elastic clamping of the seal with the specified surface pressure, the sensor is sealed for a longer period of time.

Furthermore, the object underlying the invention is achieved by a laser cutting method for cutting a seal of a potentiometric sensor according to the invention, wherein the laser cutting method is designed so that the seal is essentially burr-free and sharp edged.

The invention will be explained in more detail with reference to the following figures.

1 shows schematically a seal made of an elastomeric material which has been mechanically punched out of a plate material,

2 shows a potentiometric sensor of the prior art in partial section,

3 shows a potentiometric sensor according to the invention in partial section.

In 1 is an annular flat gasket 6 represented, which was mechanically punched out of a plate material, which corresponds to the prior art. You can see strong protruding ridges 12 which also in the ring inside 17 demonstrate. There is in the installed state of the seal 6 the gate region of the ion-sensitive field effect transistor 2 localized. fraying 16 from the one or more rests shown 12 On the one hand, they themselves influence the measurement or even lead to destruction of the ion-sensitive field-effect transistor, on the other hand they are responsible for a reduced sealing effect.

2 on the other hand, discloses a potentiometric sensor 1 with a mechanically punched and then deburred seal 6 in cross section. A similar picture would result with a seal, which was cut out of a plate material by means of a jet of water. Since selective deburring of this magnitude is no longer possible, all burrs are removed, the edges of the gasket 6 are however strongly rounded. The resulting radii lead in the installed state of the seal 6 between housing 4 and ion-sensitive field effect transistor 2 to columns 13 which is an insert of the sensor 1 in hygiene critical processes seem impossible, because through the column 13 the efficiency of a cleaning is greatly reduced.

3 now shows a potentiometric sensor according to the invention 1 in cross section. At the seal 6 In this example, this is an annular flat gasket 6 with rectangular ideal cross section. By clamping the seal 6 between the case 4 and the ion-sensitive field effect transistor 2 gets the seal 6 a slightly different shape, here trapezoidal. Inscribed are the string width 18 and the string height 19 the seal. The inner diameter 20 the seal substantially corresponds to the diameter of the circular housing opening 5 through which the gate region 3 of the ion-sensitive field effect transistor 2 can be acted upon by the measuring medium.

The seal 6 seals together with the sealing surfaces 10 . 11 of the housing 4 and the ion-sensitive field effect transistor 2 the housing 4 against the measuring medium. This is the seal 6 around the gate region 3 of the ion-sensitive field effect transistor 2 appropriate. This is exposed to the measuring medium.

The seal 6 itself receives its contours by means of a laser cutting process. This has the first, the second and the third sealing surface 7 . 8th . 9 a very small roughness on, which causes the seal 6 is essentially burr-free and sharp-edged. If all the sealing surfaces have very little roughness over their respective entire geometric surface, then the overall shape deviation from the geometric body is very small. Now also the sealing surfaces 10 . 11 of the housing 4 and the ion-sensitive field effect transistor 2 have a low roughness, the sealing effect of this sealing system is good. At least the case 4 has an annular housing shoulder in this example 14 on, a recess showing the seal 6 at least partially absorbs and supports. The force here on the ion-sensitive field effect transistor 2 in the direction of the housing 4 acts and thus the sealing surfaces 10 . 11 of the housing 4 and the ion-sensitive field effect transistor 2 on the second and third sealing surfaces 8th . 9 the seal 6 For example, pressing is done with a spring 15 applied or initiated.

LIST OF REFERENCE NUMBERS

1

Potentiometric sensor

2

Ion-sensitive field effect transistor

3

Gate region

4

casing

5

housing opening

6

poetry

7

First sealing surface

8th

Second sealing surface

9

Third sealing surface

10

First sealing surface of the ion-sensitive field effect transistor

11

Second sealing surface of the housing

12

ridge

13

gap

14

housing shoulder

15

feather

16

fraying

17

ring Affairs

18

string width

19

string height

20

Inner diameter of the annular seal

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

• US 5833824 [0003, 0004]

Cited non-patent literature

• "Thirty years of ISFETOLOGY [...]" by P. Bergveld in "Sensors and Actuators" B88 (2003) 1-20 [0002]
• "Dubbel - Paperback for Mechanical Engineering" 19th Edition F28 6.2.1 [0015]
• "Dubbel - Paperback for Mechanical Engineering" 19th Edition F28 6.2.1 [0018]

Claims (9)

Potentiometric sensor ( 1 ) for measuring a potentiometric size of a measuring medium, with an ion-sensitive field effect transistor ( 2 ), which has a gate region ( 3 ), which gate region ( 3 ) can be acted upon by the measuring medium, with a housing ( 4 ) around the ion-sensitive field effect transistor ( 2 ) with at least one housing opening ( 5 ), through which housing opening ( 5 ) the gate region ( 3 ) can be acted upon by the measuring medium, and with a seal ( 6 ) between housing ( 4 ) and ion-sensitive field effect transistor ( 2 ), which seal ( 6 ) together with the ion-sensitive field effect transistor ( 2 ) the housing ( 4 ) around the gate region ( 3 ), characterized in that the seal ( 6 ) is cut out of a plate material by means of a laser cutting process. Potentiometric sensor ( 1 ) according to claim 1, characterized in that seal ( 6 ) at least one of the measuring medium exposable first sealing surface ( 7 ), which first sealing surface ( 7 ) has over its entire geometric surface an arithmetic mean roughness of at most 1 .mu.m, in particular at most 0.8 microns. Potentiometric sensor ( 1 ) according to claim 1 or 2, characterized in that seal ( 6 ) at least one of the measuring medium exposable first sealing surface ( 7 ), which first sealing surface ( 7 ) has over its entire geometric surface a maximum profile height of at most 2 microns. Potentiometric sensor ( 1 ) according to one of claims 1 to 3, characterized in that the seal ( 6 ) is a flat gasket. Potentiometric sensor ( 1 ) according to one of claims 1 to 4, characterized in that the seal ( 6 ) has a maximum height of 0.5 mm. Potentiometric sensor ( 1 ) according to one of claims 1 to 5, characterized in that the material of the seal ( 6 ) is an organic material. Potentiometric sensor ( 1 ) according to one of claims 1 to 6, characterized in that the seal ( 6 ) elastic between housing ( 4 ) and ion-sensitive field effect transistor ( 2 ) is clamped. Potentiometric sensor ( 1 ) according to one of claims 1 to 7, characterized in that at least one first sealing surface ( 7 ) of the ion-sensitive field effect transistor ( 2 ) the seal ( 6 ) touched on at least one circumferential line, and that the first sealing surface ( 7 ) consists of tantalum (V) oxide. Laser cutting process for cutting a seal ( 6 ) of a potentiometric sensor ( 1 ) according to one of claims 1 to 8, characterized in that the laser cutting process is designed so that the seal ( 6 ) is essentially burr-free and sharp-edged.

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