Capacitive pressure transducer for measuring the pressure of a medium adjacent to the measuring cell

Abstract

The invention relates to a capacitive pressure transducer for measuring the pressure of a medium adjacent to the pressure transducer, which has a resilient measuring diaphragm, of which the first side is at least partially in contact with the medium and of which the second side, which faces away from the medium, comprises a measuring electrode and, for measuring a temperature, a resistance element made of a material having a temperature dependent resistance. Furthermore, the pressure transducer has a base body, which is arranged to oppose the second side of the measuring diaphragm, with a counter electrode, which forms a measuring capacitance with the measuring electrode. According to the invention, the resistance element is formed as a resistive layer disposed between the second side of the measuring diaphragm and the measuring electrode.

Claims

1. A capacitive pressure transducer for measuring a pressure of a medium adjacent to the pressure transducer, comprising a resilient measuring diaphragm, of which the first side is at least partially in contact with the medium and of which the second side, which faces away from the medium, comprises a measuring electrode, and, for measuring a temperature, a resistance element made of a material having a temperature dependent resistance; and a base body, which is arranged to oppose the second side of the measuring diaphragm, with a counter electrode, which forms a measuring capacitance with the measuring electrode, wherein the resistance element is formed as a resistive layer disposed between the second side of the measuring diaphragm and the measuring electrode, wherein the resistive layer and the measuring electrode are separated from each other by means of an insulating layer.

2. The pressure transducer, as claimed in claim 1, wherein the resistive layer and the measuring electrode are designed to be essentially congruent with each other.

3. The pressure transducer, as claimed in claim 1, wherein the resistive layer is structured.

4. The pressure transducer, as claimed in claim 3, wherein the resistive layer is structured so as to have a meandering shape.

5. The pressure transducer, as claimed in claim 1, wherein the measuring diaphragm and/or the base body is/are made of a ceramic material.

6. The pressure transducer, as claimed in claim 1, wherein the resistive layer is formed with a surface area that is larger than the area of the measuring electrode.

7. A pressure transmitter, comprising a pressure transducer, as claimed in claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a line drawing evidencing, in schematic form, a sectional view of a pressure transducer as an exemplary embodiment according to the invention.

(2) FIG. 2 is a line drawing evidencing an enlarged detail from FIG. 1.

(3) FIG. 3 is a line drawing evidencing a first exemplary embodiment of a structured resistive layer.

(4) FIG. 4 is a line drawing evidencing a second exemplary embodiment of a structured resistive layer.

DETAILED DESCRIPTION OF THE INVENTION

(5) The invention is a capacitive pressure transducer for measuring the pressure of a medium, adjacent to the pressure transducer, comprising a resilient measuring diaphragm, of which the first side is at least partially in contact with the medium and of which the second side, which faces away from the medium, comprises a measuring electrode and, for measuring the temperature, a resistance element made of a material having a temperature dependent resistance; and comprising a base body, which is arranged opposite the second side of the measuring diaphragm, with a counter electrode, which forms a measuring capacitance with the measuring electrode, is characterized, according to the invention, in that the resistance element is formed as a resistive layer between the second side of the measuring diaphragm and the measuring electrode.

(6) The advantage of such a pressure transducer according to the invention lies in the fact that virtually the entire available surface of the measuring diaphragm can be used for the resistive layer; and, as a result, the temperature conditions over the entire measuring diaphragm is considered in the temperature measurement, so that only small temperature errors occur.

(7) Furthermore, it has been found with this pressure transducer of the invention that a rapid or more specifically an abrupt change in the temperature of the medium can be detected just as fast and directly.

(8) It is possible to produce such a resistive layer with the same process as in the production of the measuring electrode, where in this case the two layers are separated from each other by means of an insulating layer. In order to produce the measuring electrode and the resistive layer, the same material, for example, gold, may be used; or different materials, such as, for example, gold for the measuring electrode and platinum/platinum compounds for the resistive layer, may be used.

(9) It is particularly advantageous according to one embodiment of the invention, if the resistive layer and the measuring electrode are designed to be more or less congruent to each other. As a result, both the measuring electrode and the resistive layer can be produced with the same mask.

(10) Furthermore, the resistive layer is structured, according to one embodiment of the invention, preferably so as to have a meandering structure. Then the insulating layer is used simultaneously as a planarization layer of the structured resistive layer, so that the measuring electrode can be applied to the planar insulating layer.

(11) Finally, it is advantageous if the measuring diaphragm and/or the base body is/are made of a ceramic material.

(12) The pressure transducer according to the invention can be used advantageously to build pressure transmitters.

DETAILED DESCRIPTION OF THE FIGURES

(13) This capacitive measuring cell 1 comprises a measurement chamber 6, which is formed by a ceramic base body 3 and a measuring diaphragm 2, which is also made of ceramic. In order to produce the pressure tight measurement chamber 6, the measuring diaphragm 2 and the base body 3 are separated at the edge by way of a spacer 3a, which is made, for example, of glass, glass solder or a glass alloy, and are connected to each other.

(14) With its external first side 2a the measuring diaphragm 2 is in contact with a medium, the pressure of which is to be measured with the measuring cell 1. The internal second side 2b of the measuring diaphragm 2 is coated with a resistive layer 4 made of a material exhibiting a temperature dependent resistance. This resistive layer 4 is designed either (i) to be formed over the entire surface and in a circular shape, or (ii) to have a meandering structure. Connecting leads 4a, 4b are run at the edge over the spacer 3a and the base body 3 to an electronic unit (not shown). The resistive layer 4 warms up in accordance with the measuring diaphragm 2, so that consequently the resistance value changes as a function of the temperature of the measuring diaphragm 2 and is evaluated as a measurement value for determining the temperature of the measuring diaphragm.

(15) A measuring electrode 7 is arranged in a centered manner on the resistive layer 4 with the interposition of an insulating layer. According to FIG. 1, this measuring electrode 7 is designed with a diameter that is smaller than the diameter of the resistive layer 4, where in this case both the measuring electrode 7 and the resistive layer 4 protrude into the region of the spacer 3a; and their respective connecting leads 4a, 4b and 7a respectively run in the glass solder layer. In the present exemplary embodiment the resistive layer 4 is formed with a surface area that is larger than the area of the measuring electrode 7. That is, the resistive layer 4 extends beyond the measuring electrode 7 in the radial direction. This feature has the advantage that direct contact with each layer can be made without having to run additional leads.

(16) However, the layer of the measuring electrode 7 and the resistive layer 4 may also be produced so as to be congruent with each other.

(17) If the resistive layer 4 is structured so as to have a meandering shape, then the insulating layer is also used simultaneously as a planarization layer of the resistive layer 4, so that the measuring electrode 7 can be applied onto this planarized resistive layer 4. Then the connecting leads 4a, 4b of the resistive layer 4 can be arranged, for example, on radially opposite sides and can run through the glass seam 3a.

(18) In an additional embodiment, which is not shown in greater detail here, the resistive layer 4 can also be formed with a surface area that is selected to be smaller than the area of the measuring electrode 7 and is arranged so as to be spaced apart from the circumferential glass seam 3a. In this case a temperature averaging over a central region of the measuring diaphragm 2 is achieved, so that any impact of a mounting arrangement, which is thermally a carrier due to its larger mass relative to the measuring diaphragm 2, is suppressed.

(19) This measuring electrode 7 forms, together with a circular counter electrode 8, which is arranged so as to be on the opposite surface of the base body 3, a measuring capacitor, the measured capacitance of which is a function of the deflection of the measuring diaphragm 2, where in this case the deflection is caused by the pressure of the medium. The counter electrode 8 is enclosed by a circular ring shaped reference electrode 9, which, together with the measuring electrode 7, forms a reference capacitor, the reference capacitance of which is virtually constant due to its position at the outer edge of the measurement chamber 6, in which the measuring diaphragm shows essentially no deflection. The measuring electrode 7, the counter electrode 8 and the reference electrode 9 are connected to an electronic unit (not shown) of the measuring cell 1 by means of the connecting leads 7a, 8a and 9a respectively.

(20) FIG. 2 shows an enlarged detail from FIG. 1 in the region of the connecting leads of the resistive layer 4.

(21) FIG. 2 shows very clearly a layered structure consisting of a measuring electrode 7, an insulating layer 10, a resistive layer 4 and a measuring diaphragm 2. As can be seen in FIG. 2, both the measuring electrode 7 and the resistive layer 4 are formed as far as into the radially arranged glass seam 3a, which is also used as a spacer 3a. This arrangement makes it possible for the connecting leads 7a, 4a, 4b, which run perpendicular to the measuring electrode and the resistive layer through the glass seam 3a, to make contact with both the measuring electrode 7 and the resistive layer 4.

(22) It is also easy to see from FIG. 2 that the insulating layer 10 extends beyond the measuring electrode 7 in the radial direction, so that the net result is a reliable insulation of the measuring electrode 7 with respect to the resistive layer 4.

(23) In addition, FIG. 2 also shows as an additional option that the second connecting lead 4b can be connected internally to the measuring electrode 7 in order to measure the temperature, so that the temperature measurement can take place between the electrodes 7a and 4a. As a result, there is no need to lead out the connecting lead 4b.

(24) FIG. 3 shows, as seen in a plan view, a first exemplary embodiment of a resistive layer 4 with respect to how it can be used in the sensor from the FIGS. 1 and 2.

(25) In the exemplary embodiment from FIG. 3, the metallization for the resistive layer 4 is carried out over the entire surface and has a U shaped recess, in order to produce a sufficiently long current path and, thus, a sufficiently large resistance. Inside this recess there is the second connecting lead 4b, which extends into this recess in the manner of a tongue.

(26) FIG. 4 shows an additional exemplary embodiment of a resistive layer 4 in a plan view, where in this embodiment the resistive layer 4 is designed so as to have a meandering shape on a circular surface area. By providing a plurality of meanders or more specifically a plurality of loops it is possible to produce, as compared with the exemplary embodiment from FIG. 3, a very long current path and, thus, also to produce a much larger resistance to the temperature measurement. In the exemplary embodiment from FIG. 4 the connecting leads 4a, 4b of the resistive layer are arranged on the radially opposite sides of the resistive layer 4, but can also be run immediately adjacent to each other through the spacer 7a by means, for example, of a conductor track, which runs in the circumferential direction, as shown in the FIGS. 1 and 2.

(27) In this measuring cell 1, the pressure measuring signals, which are affected by the measurement errors and which are generated by the measuring capacitor, are corrected or more specifically are compensated for, according to a specified algorithm, by means of temperature values, which are determined from the temperature dependent resistance measuring values of the resistive layer 4.

LIST OF REFERENCE NUMBERS

(28) 1 pressure transducer 2 measuring diaphragm 2a first side of the measuring diaphragm 2 2b second side of the measuring diaphragm 2 3 base body 3a spacer 4 resistive layer 4a first connecting lead of the resistive layer 4 4b second connecting lead of the resistive layer 4 6 measurement chamber of the pressure transducer 1 7 measuring electrode 7a connecting lead of the measuring electrode 7 8 counter electrode 8a connecting lead of the counter electrode 9 reference electrode 9a connecting lead of the reference electrode

(29) 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.