Patent Application
20220011187
This patent application claims priority to German Patent Application 10 2020 118 313.5, filed on Jul. 10, 2020.
No federal government funds were used in researching or developing this invention.
Not applicable.
Not applicable.
The invention relates to channel structures for optimizing the membrane function of oil-filled pressure sensors.
Various forms of pressure measuring cells are known from the prior art. Such pressure measuring cells are used in pressure gauges and convert a pressure into an electrical signal which can then be further processed. Pressure measuring cells are differentiated according to the underlying measuring principle, the materials involved in the process, and whether absolute or relative pressures can be measured.
According to the foregoing, there are, for example, capacitive pressure measuring cells that detect a change in pressure caused by the deformation of a membrane and a resulting change in capacity, resistive and piezoresistive pressure measuring cells in which deformation of a membrane is detected by means of strain gauges, for example, and the pressure is inferred from a change in resistance of the strain gauges, and piezoelectric pressure measuring cells that exploit the piezoelectric effect to determine pressure.
The differentiation according to the materials involved in the process, i.e. the materials that come into contact with the process environment and the process media, generally makes a distinction between metallic and ceramic pressure measuring cells, wherein one comprises a metallic membrane and the other a ceramic membrane. For manufacturing and metrological reasons, a base body of the pressure measuring cell is often made of the same material as the membrane. In terms of manufacturing technology, it is often easier to make a bond between the same or similar materials than between different materials. From a metrological point of view, it is advantageous to use materials with similar or ideally identical thermal expansion coefficients, which is also easier to achieve with the same or similar materials.
Whether absolute or relative pressures can be measured usually depends on whether a second pressure, e.g. an external pressure, is supplied to the backside of the membrane or whether the backside of the membrane is evacuated.
The present application assumes a metallic pressure measuring cell with a metallic base body, a metallic membrane arranged on the base body. A membrane chamber is formed between the membrane and the base body, which is connected to a sensor chamber in which a pressure sensor is arranged via a connecting channel. The chambers and the connecting channel are filled with a pressure transmitting medium.
The actual pressure sensor is usually made of a silicon chip. This chip consists of a membrane structured with piezoresistive resistors that bulges under pressure. The piezo chip is very sensitive to external influences and must therefore be hermetically encapsulated in most cases. It is therefore installed in a pressure-tight manner in a stainless steel housing, which is sealed at the front with a thin stainless steel membrane, thus forming the membrane chamber and the sensor chamber.
The chambers are filled with the pressure transmitting medium, typically a synthetic oil. In such a sensor, only the metallic membrane, in this case made of stainless steel, is in contact with the process, and the process pressure is transmitted to the chip membrane via the oil.
In order to keep temperature influences on the pressure measurement as low as possible, it is necessary to keep a volume located in the chambers and especially the volume of the membrane chamber as low as possible. It is also necessary that the metallic membrane is easily deflectable in the axial direction, but comparatively stiff in the radial direction.
In the prior art, this is achieved by the membrane comprising, in a cross-section view, a corrugated contour that favors deformation in the axial direction, i.e. in the direction in which the compressive force acts on the membrane, and is thus as stiff as possible in the radial direction. In order to keep the volume of the chamber as low as possible, a surface of the base body facing the membrane has a contour adapted thereto. From a manufacturing point of view, it is advantageous if the part of the base body facing the membrane is shaped accordingly and the membrane, only when it is attached to the base body, is molded from this shape of the base body. Specifically, the membrane is situated on the base body, e.g. welded to it, and then pressed onto and molded from the base body. This can be done, for example, by means of a stamp or by applying overpressure.
In this impression, not only the waveform of the surface of the base body facing the membrane is molded, but also the part where the connecting channel between the membrane chamber and the sensor chamber opens into the membrane chamber. This molding of the outlet of the connecting channel can result in the membrane being molded into the connecting channel such that the channel is closed by the membrane. The membrane virtually forms a plug, which closes the outlet of the connecting channel and thus makes it difficult or impossible to subsequently fill the chambers with the pressure transmitting medium.
In the prior art, the membrane is pulled back out of the outlet of the connecting channel by applying a vacuum or is given the desired contour before being connected to the base body.
By applying a vacuum, however, the membrane is deformed again in the opposite direction, so that minimizing the volume of the membrane chamber is not optimal. If the membrane is formed before it is joined to the base body, deviations can occur in both the shaping and the alignment of the membrane in relation to the base body, so that minimizing the volume of the membrane chamber is not optimal with this approach either.
The task of the present invention is to disclose a metallic pressure measuring cell as well as a method for manufacturing such a pressure measuring cell, wherein the drawbacks of the prior art are avoided.
This task is solved by a metallic pressure measuring cell with the features described herein as well as a described method for manufacturing a metallic pressure measuring cell. Advantageous further developments are also disclosed herein.
In a preferred embodiment, a metallic pressure measuring cell (1) having a base body (3), a metallic membrane (5) situated on the base body (3), wherein a membrane chamber (51) is formed between the membrane (5) and the base body (3), a pressure sensor (7) situated in a sensor chamber (71) of the base body (3), wherein a connecting channel (9) is formed between the membrane chamber (51) and the sensor chamber (71) and the chambers are filled with a pressure transmitting medium (13) for transmitting a pressure acting on the membrane (5), characterized in that the membrane (5) comprises a surface structure (53), which, in a plan view, at least overlaps an outer contour of an inlet area (91) of the connecting channel (9) into the membrane chamber (51).
In another preferred embodiment, the metallic pressure measuring cell (1) as described herein, characterized in that the membrane (5) comprises at least one channel which, in a plan view, overlaps at least once the outer contour of the inlet area (91) of the connecting channel (9) into the membrane chamber (51).
In another preferred embodiment, the metallic pressure measuring cell (1) according to one of the preceding claims, characterized in that the membrane (5) comprises, in a cross-sectional view, a surface contour (55) corresponding to a wall of the base body (3) directly opposite to the membrane (5).
In another preferred embodiment, the metallic pressure measuring cell (1) according to claim 3, characterized in that the surface contour (55) comprises a cosine-shaped profile.
In another preferred embodiment, the metallic pressure measuring cell (1) according to one of claims 2 to 4, characterized in that the at least one channel is designed to run at least in sections in the radial direction (R).
In another preferred embodiment, the metallic pressure measuring cell (1) according to one of claims 2 to 5, characterized in that the at least one channel, in plan view of the membrane (5), is spiral-shaped at least in sections.
In another preferred embodiment, the metallic pressure measuring cell (1) according to one of claims 2 to 6, characterized in that the at least one channel is formed starting from a center point of the membrane (5) in plan view up to at least ¼, in particular at least ⅓ of a radius (r) of the membrane (5).
In another preferred embodiment, the metallic pressure measuring cell (1) according to any one of claims 2 to 7, characterized in that
the membrane (5) comprises at least 2, preferably at least 3, 4, 6 or 8 channels.
In another preferred embodiment, the metallic pressure measuring cell (1) according to one of the preceding claims, characterized in that the surface of the membrane (5) is roughened at least in sections.
In another preferred embodiment, the metallic pressure measuring cell (1) according to one of the preceding claims, characterized in that the pressure sensor (7) is designed as a piezo sensor.
In another preferred embodiment, the metallic pressure measuring cell (1) according to one of the preceding claims, characterized in that the connecting channel (9) opens centrally into the membrane chamber (51).
In another preferred embodiment, a method for manufacturing a metallic pressure measuring cell (1) as described herein, comprising the following steps:
providing a base body (3) comprising a membrane chamber (51) with a predetermined surface contour (55), a sensor chamber (71) and a connecting channel (9) between the membrane chamber (51) and the sensor chamber (71),
providing a metallic membrane (5) comprising at least one surface structure (53) which, in a plan view, at least overlaps an outer contour of an inlet area (91) of the connecting channel (9) into the membrane chamber (51),
attaching the metallic membrane (5) to the base body (3),
molding of the surface contour (55) of the base body (3) onto the membrane (5) and
filling of at least membrane chamber (51), sensor chamber (71) and connecting channel (9) with a pressure transmitting medium (13).
In another preferred embodiment, the method as described herein, characterized in that the surface structure (53) comprises at least one channel, which is introduced into the membrane (5).
In another preferred embodiment, the method as described herein, characterized in that the at least one channel is introduced into the membrane (5) by a machining method, in particular by milling, turning or engraving.
In another preferred embodiment, the method as described herein, characterized in that the at least one channel is introduced into the membrane (5) by a remodeling process, in particular by stamping.
In another preferred embodiment, the method as described herein, characterized in that the membrane (5) is welded to the base body (3).
In another preferred embodiment, the method as described herein, characterized in that the surface structure (53) is produced at least partially by roughening, in particular sandblasting and/or laser machining.
An inventive metallic pressure measuring cell having a base body, a metallic membrane situated on the base body, wherein a membrane chamber is formed between the membrane and the base body, a pressure sensor situated in a sensor chamber of the base body, wherein a connecting channel is formed between the membrane chamber and the sensor chamber and the chambers are filled with a pressure transmitting medium for transmitting a pressure acting on the membrane, is characterized in that the membrane comprises a surface structure, which, in a plan view, at least overlaps an outer contour of an inlet area of the connecting channel into the membrane chamber.
A surface structure within the meaning of the present application is a roughness exceeding the natural surface roughness of the material of the membrane or an additional structure introduced into the membrane by recesses or elevations. More specifically, these are surface structures that are introduced into the membrane before it is connected to the base body.
In this way, a surface of the membrane is created that prevents sealing of an inlet opening of the connecting channel into the membrane chamber. The surface structure ensures that at least an initial quantity of pressure transmitting medium always enters the membrane chamber and that the membrane is lifted and filled by the pressure of the pressure transmitting medium during filling.
Information on direction is defined in the present application as follows:
The membrane defines a membrane plane spanned by a circumferential connection of the membrane to the base body. Starting from this membrane plane, an axial direction is defined by a surface standard on the membrane plane. The radial direction extends from a center point of the membrane, in a plan view of the membrane plane. In plan view means looking at the membrane of the measuring cell in axial direction. A cross section is to be understood as a section with a plane spanned by the axial direction and the radial direction.
The membrane preferably has a circular outer contour in plan view.
In a preferred embodiment, the membrane can comprise at least one channel, that, in a plan view, intersects at least once the outer contour of the inlet area of the connecting channel into the membrane chamber. Such a channel, by its design as a recess opposite the membrane surface, ensures that pressure transmitting medium enters and fills the membrane chamber even when the membrane is deformed into the connecting channel. Channels can be introduced into the membrane particularly easily and thus represent a cost-effective variant for a surface structure according to the invention.
In order to minimize the volume of the membrane chamber, it is useful if the membrane comprises a surface contour corresponding to a wall of the base body directly opposite to the membrane in a section perpendicular to a membrane plane. Such a corresponding surface structure can be achieved by directly molding a surface shape of the base body.
Said molding can be performed, for example, by applying an overpressure to the membrane, e.g. by a gas or liquid, and thus pressing it against the surface of the base body that faces it. Due to the thinness of the membrane, it thus undergoes a plastic deformation and adopts the surface contour of the base body.
As an added benefit, the surface contour is undulating for this purpose. A undulating contour allows flexibility of the membrane in axial direction and rigidity of the membrane in radial direction. It is advantageous if the surface contour comprises a cosine-shaped profile in a cross-sectional view starting from a center point of the membrane. This means that the contour comprises a wave crest at the center point, which counteracts the sealing of the connecting channel, which usually opens centrally into the membrane chamber.
In plan view of the membrane, the at least one channel is preferably designed to run in the radial direction at least in sections. In one embodiment, the at least one channel extends completely in the radial direction.
In one variant, the at least one channel can be spiral-shaped at least in sections in plan view of the membrane. Such a spiral design has the advantage of overlapping a undulating contour of the membrane, making it less conspicuous than channels running in the radial direction.
To ensure that the membrane chamber is filled safely, it is advantageous if the at least one channel, measured from a center point of the membrane in plan view, is formed to at least ¼, or more specifically at least ⅓ of a radius of the membrane. It should be noted that only the measurement of the extension of the channel is made starting from the center of the membrane. The channel itself does not necessarily have to start at the center of the membrane. In particular, if multiple channels are provided, it is even advantageous if these are not formed starting at the center of the membrane, since the membrane could otherwise be weakened at this point due to the repeated processing.
It may be advantageous if the membrane comprises at least 2, preferably at least 3, 4, 6 or 8 channels. A plurality of channels can serve to ensure that the membrane chamber is not sealed as a result of the molding of the surface contour of the base body in the inlet area of the connecting channel.
Overall, in the scenario of a plurality of channels, it is advantageous if the channels do not cross to prevent the membrane from weakening.
Additionally or alternatively, it is advantageous if the surface of the membrane facing the base body is roughened at least in sections. In particular, it is advantageous if the surface of the membrane facing the base body is roughened in an area overlapping the outer contour of the inlet area of the connecting channel into the membrane chamber.
The pressure sensor can be configured as a piezo sensor, in particular a piezoelectric or piezoresistive pressure sensor.
The connecting channel preferably opens centrally into the membrane chamber. A centric outlet of the connecting channel into the membrane chamber results in a symmetrical structure, which is particularly advantageous with regard to thermally or otherwise induced tensions.
A method according to the invention for manufacturing a metallic pressure measuring cell according to one of the preceding claims comprises the following steps:
In that the metallic membrane comprises at least one surface structure which, in a plan view, at least overlaps an outer contour of an inlet area of the connecting channel into the membrane chamber, it is achieved that an outlet of the connecting channel is not sealed when the surface contour of the base body is molded. This ensures that the membrane chamber can be filled with pressure transmitting medium.
Since the surface structure of the membrane is introduced into a surface of the membrane facing the base body, the surface structure is introduced into the membrane before it is bonded to the main body.
In this regard, the surface structure preferably comprises at least one channel that is introduced into the membrane. In particular, such a channel can be introduced into the membrane by a machining process, especially by milling, turning or engraving. For example, the at least one channel can already be introduced into the membrane during its manufacture.
As an alternative to a machining process, the at least one channel can be introduced into the membrane by a remodeling process, in particular by stamping. This can in particular be advantageous if the membrane is obtained as a purchased part, or if for other reasons it is not possible to intervene in the manufacturing process of the membrane. This is particularly advantageous if subsequent machining of the membrane, which typically has a thickness of between 0.01 mm and 0.2 mm, is not possible due to manufacturing reasons.
In one embodiment form, the membrane is welded to the base body. The membrane can be welded to the base body by laser welding or resistance welding, for example.
Additionally or alternatively, the surface structure can be produced by roughening, in particular sandblasting and/or laser machining. A roughened surface prevents a sealing effect caused by the membrane when molding the surface contour of the base body. This can be used to ensure filling of the membrane chamber in addition to channels or as an alternative.
Preferred embodiments, features and characteristics of the proposed field device correspond to those of the proposed method and vice versa.
Advantageous configurations and variants of the invention emerge from the subclaims and the following description. The features listed individually can be combined with one another in any technically sensible manner, as well as with the features explained in more detail in the following description, and can constitute other advantageous variants of the invention.
The pressure measuring cell 1 essentially comprises a metallic base body 3, a metallic membrane 5 arranged at the front of the base body 3 in the axial direction A, and a pressure sensor 7 arranged in a sensor chamber 71 formed in the base body 3.
The sensor chamber 71 is fluidly connected via a connecting channel 9 to a membrane chamber 51 formed between the base body 3 and the membrane 5.
The sensor chamber 71 is closed in the rear direction by a sealing element 80, wherein the sealing element 80 comprises a plurality of cable bushings. The pressure sensor 7 is arranged in the sensor chamber 71. The pressure sensor 7 has a sensor chip 73 as a pressure-sensitive element, which is arranged on the sealing element 80 via a sensor carrier 75. On the front side, the sensor chip 73 is contacted by a front contact 77 and on the rear side by a rear contact 79, each of which passes through one of the passages through the sealing element 80. A rear part of a membrane of the sensor chip 73 can be subjected to either an ambient pressure or a reference pressure via a pressure equalization line 72, which is also led through the sealing element 80 to the rear side of the sensor chip 73, or the cavity located behind the sensor chip 73 can be evacuated so that an absolute pressure (reference pressure is the vacuum) can be measured.
In the embodiment shown in
In the present embodiment, the membrane 5 is connected to the base body 3 by a circumferential joint 57, in this case a weld. In the present cross-sectional view, the membrane 5 comprises an undulating surface contour corresponding to a surface contour of a wall of the base body 3 facing the membrane 5. This undulating surface contour 55 ensures that the membrane 5 is flexible in the axial direction A, whereas the greatest possible rigidity is achieved in the radial direction R.
The surface contour 55 of the membrane 5 is transferred from the base body 3 to the membrane 5 during the manufacture of the pressure measuring cell 1. For this purpose, the membrane 5 is pressurized from the front after it has been attached to the base body 3, such that it is molded into the membrane bed formed by the base body 3.
The membrane 5 is shown in
For illustration purposes, an inlet area 91 with which the connecting channel 9 enters the membrane chamber 51 through the base body 3 is shown in the center of the membrane 5.
This inlet area 91 also deforms onto the membrane 5 when pressure is applied to the membrane 5 to mold the surface contour of the base body 3, so that this entry requirement 91 or its outer contour can be clearly seen on the membrane 5. For the sake of clarity, the undulating surface contour 55 of the membrane 5, as transferred to the membrane 5 by the deformation of the surface contour of the base body 3, is not shown in
To ensure that the membrane chamber 51 is filled with pressure transmitting medium 13, the membrane 5 in the embodiment shown in
The channels 53 are dimensioned to extend outwardly in the radial direction R about one-third of a radius r of the membrane 5.
The channels 53 are introduced into a surface of the membrane 5 before it is connected to the base body 3 of the pressure measuring cell 1. During the deformation of the membrane bed, the channels 53 previously formed in the membrane surface remain intact, so that subsequently, when the pressure measuring cell 1 is filled with the pressure transmitting medium 13, the latter can flow through the channels 53 into the membrane chamber 51 and safely fill it.
The membrane 5 shown in
As with the membranes shown in
It is worth noting at this point that roughening the surface of the membrane 5 can also be carried out in addition to introducing channels, as described in connection with
In a first step of a method for manufacturing a metallic pressure measuring cell 1 according to the present application, a metallic base body with a membrane, with a predetermined surface contour, a sensor chamber 71 and a connecting channel 9 between the membrane chamber 51 and the sensor chamber 71 is provided. Furthermore, a metallic membrane 5 is provided which comprises at least one surface structure 53 which, in a plan view, at least overlaps an outer contour of the inlet area 91 of the connecting channel 9 into the membrane chamber 51. In the next step, the metallic membrane 5 is attached to the base body 3 and, in a further step, a surface contour of the base body 3 is molded onto the membrane. In a further step, the pressure sensor 7 is arranged in the sensor chamber 71 and this is closed at the rear side by means of a sealing element 80. In a final step, the membrane chamber, the sensor chamber and the connecting channel are filled with the pressure transmitting medium 13. This step is illustrated in
As shown in
1 Pressure measuring cell
3 Base body
5 Membrane
7 Pressure sensor
9 Connecting channel
11 Inlet
13 Pressure transmitting medium
51 Membrane chamber
53 Surface structure/channel
55 Surface contour
57 Connection
71 Sensor chamber
72 Pressure equalization
73 Sensor chip
75 Sensor carrier
77 Front contact
79 Rear contact
80 Sealing element
91 Inlet area
A Axial direction
R Radial direction
r radius
Unless indicated otherwise, identical reference numbers in the figures identify identical components with the same function. The terms drive unit and drive are used interchangeably herein.
The references recited herein are incorporated herein in their entirety, particularly as they relate to teaching the level of ordinary skill in this art and for any disclosure necessary for the commoner understanding of the subject matter of the claimed invention. It will be clear to a person of ordinary skill in the art that the above embodiments may be altered or that insubstantial changes may be made without departing from the scope of the invention. Accordingly, the scope of the invention is determined by the scope of the following claims and their equitable equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2020 118 313.5 | Jul 2020 | DE | national |
