DE20004245U1 - Pressure measuring device - Google Patents

Description

Pressure measuring device

The present invention relates to a pressure measuring device and/or a pressure sensor with a measuring capacitor which has at least two capacitor electrodes whose distance from one another can be changed at least in a partial area by applying pressure.

A pressure measuring device is an arrangement with at least one pressure sensor and a device for processing signals generated by the pressure sensor.

State of the art

Pressure sensors are known in which a capacitor can be subjected to pressure. The application of pressure causes the electrodes of the capacitor to move closer together. This is accompanied by a change in the capacitor's capacitance. This change can be recorded by an evaluation device and converted into a pressure measurement value.

The disadvantage is that with known capacitive pressure sensors the measurement results are often inaccurate due to climatic influences and aging. This is particularly undesirable for safety-relevant measurements.

Subject of the invention

According to the invention, the pressure measuring device and/or the pressure sensor has a reference capacitor. A pressure measuring device is understood to be an arrangement with at least one pressure sensor and a device for processing signals generated by the pressure sensor. This makes it possible to compensate for influencing factors that are difficult to determine, such as aging and moisture.

It may be appropriate that the extent of the change in capacitance of the reference capacitor when the pressure measuring device and/or the pressure sensor is subjected to a pressure to be measured depends on the extent of the

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The difference in the capacitance change provides additional information for evaluating the measured signals.

It may be useful that when the device and/or the pressure sensor is subjected to a pressure to be measured, the strength of the pressure acting on the measuring capacitor is different from the strength of the pressure acting on the reference capacitor. This means that even when using capacitors of the same construction, different signal curves can be achieved with the measuring capacitor and the reference capacitor.

It may be useful for the reference capacitor to have a shielding device which prevents at least part of the pressure acting in the vicinity of the reference capacitor from affecting the reference capacitor. The difference in the signals from the measuring capacitor and the reference capacitor is thus maintained even if the reference capacitor is installed in areas subject to high pressure. Shielding can be achieved inexpensively, for example, by attaching grids, metal sheets or stiffening the electrodes.

It may be useful for the measuring capacitor and the reference capacitor to be arranged at a distance from each other. This allows the reference capacitor to be kept free from pressure without additional components.

It may be useful for the measuring capacitor and the reference capacitor to be located close to each other. Both capacitors are therefore exposed to similar climatic conditions.

It may be expedient for the electrodes of the measuring capacitor and the electrodes of the reference capacitor to be arranged at least partially with their surfaces facing each other.

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If the capacitors are arranged one above the other, the pressure acting on both capacitors is the same for both capacitors. In addition, the two capacitors can be combined to form a sensor module that is easier to handle.

It may be useful for the electrodes of the measuring capacitor and the electrodes of the reference capacitor to be arranged at least partially with their side edges facing each other. By arranging the capacitors next to each other, a very flat sensor can be created.

It may be useful for the measuring capacitor and/or the reference capacitor, which are used to detect the pressure acting on a measuring object, to be integrated into the measuring object. This means that the pressure sensor is better protected and causes less interference.

It may be expedient for the measuring capacitor and/or the reference capacitor to be arranged in the seat base and/or in the seat back of a motor vehicle seat. This makes it possible to detect the use of a seat and/or its back by a user.

It may be expedient for the measuring capacitor and/or the reference capacitor to have at least one electrically non-conductive dielectric, particularly in the form of a spacer layer, which spaced the capacitor electrodes of the respective capacitor from each other and/or from the other capacitor. This enables a compact design of the pressure sensor.

It may be expedient that a first dielectric is arranged between the electrodes of the measuring capacitor, that a second dielectric is arranged between the electrodes of the reference capacitor, and that the first and the second dielectric have different

have compressibility. This means that a different change in capacitance can be achieved even when the two capacitors are subjected to the same pressure.

It may be useful for the two dielectrics to have different densities. In the case of foams in particular, the compressibility can be easily adjusted via the density of the materials.

It may be useful for a capacitor electrode to be part of both the measuring capacitor and the reference capacitor. This saves electrodes. In the simplest case, the number of electrodes can be reduced from four to three. The amount of wiring required is also reduced.

It may be expedient for the pressure sensor to have three capacitor electrodes and two dielectrics, which are arranged one behind the other, alternately overlapping each other, whereby two capacitor electrodes with a dielectric in between form a capacitor. One of the capacitors forms the measuring capacitor. The second forms the reference capacitor. This embodiment can be produced inexpensively as a film composite.

It may be useful for the electrical capacitance of the measuring capacitor and the reference capacitor to be the same or similar. This makes the signals from the capacitors easier to compare.

It may be useful for at least two measuring capacitors to be assigned to at least one reference capacitor. This allows a measuring arrangement consisting of several measuring capacitors to be monitored with just one reference capacitor. This is cost-effective and still enables the desired safety improvement.

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It may be useful for at least two reference capacitors to be assigned to at least one measuring capacitor. This allows the safety of the arrangement to be increased by redundancy in the reference capacitor.

It may be expedient for the pressure measuring device to have an evaluation device for evaluating the signal from the pressure sensor and for the evaluation device to be arranged at a spatial distance from the measuring capacitor and/or the reference capacitor. The size of the sensor attached to the measuring object can thus be further reduced.

It may be expedient for a device for detecting whether a vehicle seat is occupied to have a pressure measuring device and/or a pressure sensor according to one of the preceding claims. Such a detector device also works correctly under the strong climatic fluctuations prevailing in a vehicle.

characters

The following description deals with possible embodiments of the invention. These statements are to be understood as examples only and are made with reference to:

Fig. 1 Cross section through a first embodiment of a pressure sensor.
Fig. 2 Cross section through a second embodiment of a pressure sensor.

Description of the invention

Fig. 1 shows a pressure sensor 1. This has a measuring capacitor 3 and a reference capacitor 13.

The measuring capacitor 3 has a flat capacitor electrode 5. A dielectric 21 with a height 9 is applied flatly to this. The dielectric 21 is in turn covered by a second, flat capacitor electrode 7.

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The reference capacitor 13 also has a first flat capacitor electrode 15. A dielectric 23 is arranged on this, which has a height of 10. The height 9 and the height 10 of the dielectrics 21 and 23 are the same when the pressure sensor is not under load. The dielectric 23 is covered by a capacitor electrode 17, which is also flat.

The measuring capacitor 3 and the reference capacitor 13 are arranged next to each other. The capacitor electrodes 5 and 15 face each other with their side edges and are arranged in alignment with each other. The dielectrics 21, 23 each face each other with one of their side edges. The electrodes 7, 17 of the two capacitors each run parallel to the electrodes 5, 15 and are electrically connected to each other in the present embodiment.

The pressure sensor 1 is connected to an evaluation device (not shown) via electrical lines 31, 32, 33. The capacitor electrode 5 is connected via line 31, the electrode 7, 17 via line 33 and the electrode 15 via a line 32.

In the present embodiment, the capacitor electrodes are each made of copper foil. The electrodes 7, 17 are formed in the embodiment from a single, flatly arranged foil.

The dielectrics 21, 23 consist of a plastic foam with different densities. They therefore have different compressibility.

If the pressure sensor 1 is subjected to a pressure ρ, the capacitor electrodes 5 and 15 approach the electrodes 7, 17. Due to different compressibility of the dielectrics 21, 23, the degree of

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approximation in the measuring capacitor 3 will be different from the degree of approximation in the reference capacitor 13. As a result, the change in capacitance of the two capacitors will also be different from each other.

Fig. 2 shows a pressure sensor 1 with a measuring capacitor 3 and a reference capacitor 13. The measuring capacitor 3 has a first capacitor electrode 5 and a second capacitor electrode 7. These are formed by flat copper foils arranged parallel to one another. A flat dielectric 21 is provided between the capacitor electrodes 5, 7. It is formed by an electrically non-conductive, elastically deformable plastic.

A reference capacitor 13 is arranged on the measuring capacitor 3. In the exemplary embodiment, the electrode 7 of the measuring capacitor 3 simultaneously forms an electrode 17 of the reference capacitor 13. A dielectric 23 is provided flat on the capacitor electrode 17. A further capacitor electrode 15 is applied to the dielectric 23.

The electrode 15 is connected to an evaluation device (not shown) via a connecting line 32, the electrode 7, 17 via a connecting line 33 and the capacitor electrode 5 via an electrical connecting line 31.

To measure the pressure, at least one of the two outer electrodes 5, 15 is subjected to a pressure ρ. The pressure ρ acts in particular on the surface of the relevant electrode 5, 15 facing away from the respective capacitor 3, 13.

This leads to a compression of at least the flexible dielectric 21, 23 adjacent to the affected electrode 5, 15, at least in a partial area 11. Depending on the sensor installation and sensor materials, the pressure ρ can, however, also lead to a simultaneous deformation of both dielectrics 21, 23.

As a result, the electrodes 15 and 17 or the electrodes 5 and 7 move closer to each other. This leads to a change in the capacitance of the measuring capacitor 3 and/or the reference capacitor 13. Due to the different compressibility of the dielectrics 21, 23, the change in distance between the electrodes in the two capacitors 3, 13 and thus the change in capacitance of the two capacitors are different from each other.

The two examples show pressure sensors that combine a measuring and reference capacitor. However, it is also possible to arrange the two capacitors separately as separate sensors. The reference capacitor could also be provided outside the measuring object, while the measuring capacitor is integrated into it.

It is of course also possible to provide the advantageous design features mentioned above in addition or as an alternative.

Claims (20)

1. Pressure measuring device and/or pressure sensor ( 1 ) with a measuring capacitor ( 3 ) which has at least two capacitor electrodes ( 5 , 7 ), the distance ( 9 ) between which can be changed at least in a partial area ( 11 ) by applying pressure, characterized in that the pressure measuring device and/or the pressure sensor ( 1 ) has a reference capacitor ( 13 ). 2. Pressure measuring device and/or pressure sensor according to claim 1, characterized in that the extent of the change in capacitance of the reference capacitor ( 13 ) when the pressure measuring device and/or the pressure sensor ( 1 ) is subjected to a pressure to be measured is different from the extent of the change in capacitance of the measuring capacitor ( 3 ). 3. Pressure measuring device and/or pressure sensor according to claim 1 or 2, characterized in that when the device and/or the pressure sensor ( 1 ) is subjected to a pressure to be measured, the strength of the pressure acting on the measuring capacitor ( 3 ) is different from the strength of the pressure acting on the reference capacitor ( 13 ). 4. Pressure measuring device and/or pressure sensor according to one of the preceding claims, characterized in that the reference capacitor ( 13 ) has a shielding device which prevents at least part of the pressure acting in the vicinity of the reference capacitor ( 13 ) from acting on the reference capacitor ( 13 ). 5. Pressure measuring device and/or pressure sensor according to one of the preceding claims, characterized in that the measuring capacitor ( 3 ) and the reference capacitor ( 13 ) are arranged spatially spaced from one another. 6. Pressure measuring device and/or pressure sensor according to one of the preceding claims, characterized in that the measuring capacitor ( 3 ) and the reference capacitor ( 13 ) are arranged spatially close to one another. 7. Pressure measuring device and/or pressure sensor according to one of the preceding claims, characterized in that the electrodes ( 5 , 7 ) of the measuring capacitor ( 3 ) and the electrodes ( 15 , 17 ) of the reference capacitor ( 13 ) are arranged at least partially with their surfaces facing each other. 8. Pressure measuring device and/or pressure sensor according to one of the preceding claims, characterized in that the electrodes ( 5 , 7 ) of the measuring capacitor ( 3 ) and the electrodes ( 15 , 17 ) of the reference capacitor ( 13 ) are arranged at least partially with their side edges facing each other. 9. Pressure measuring device and/or pressure sensor according to one of the preceding claims, characterized in that the measuring capacitor ( 3 ) and/or the reference capacitor ( 113 ), which serve to detect a pressure acting on a measuring object, are integrated into the measuring object. 10. Pressure measuring device and/or pressure sensor according to one of the preceding claims, characterized in that the measuring capacitor ( 3 ) and/or the reference capacitor ( 13 ) are arranged in the seat base and/or in the seat back of a motor vehicle seat. 11. Pressure measuring device and/or pressure sensor according to one of the preceding claims, characterized in that the measuring capacitor ( 3 ) and/or the reference capacitor ( 13 ) has at least one electrically non-conductive dielectric ( 21 , 23 ), in particular in the form of a spacer layer, which spaced the capacitor electrodes ( 5 , 15 , 7 , 17 ) of the respective capacitor ( 3 , 13 ) from one another and/or from the respective other capacitor ( 3 , 13 ). 12. Pressure measuring device and/or pressure sensor according to one of the preceding claims, characterized in that a first dielectric ( 21 ) is arranged between the electrodes ( 5 , 7 ) of the measuring capacitor ( 3 ), that a second dielectric ( 23 ) is arranged between the electrodes ( 15 , 17 ) of the reference capacitor ( 13 ), and that the first and the second dielectric ( 21 , 23 ) have different compressibility. 13. Pressure measuring device and/or pressure sensor according to one of the preceding claims, characterized in that the two dielectrics ( 21 , 23 ) have different densities. 14. Pressure measuring device and/or pressure sensor according to one of the preceding claims, characterized in that a capacitor electrode ( 7 , 17 ) is a component of both the measuring capacitor ( 3 ) and the reference capacitor ( 13 ). 15. Pressure measuring device and/or pressure sensor according to one of the preceding claims, characterized in that the pressure sensor ( 1 ) has three capacitor electrodes ( 5 , 15 , 7 , 17 ) and two dielectrics ( 21 , 23 ), which are arranged one behind the other in an alternating manner, whereby two capacitor electrodes ( 5 , 15 , 7 , 17 ) with a dielectric ( 21 , 23 ) lying between them form a capacitor ( 3 , 5 ). 16. Pressure measuring device and/or pressure sensor according to one of the preceding claims, characterized in that the electrical capacitance of the measuring capacitor ( 3 ) and the reference capacitor ( 13 ) are the same or of a similar size. 17. Pressure measuring device and/or pressure sensor according to one of the preceding claims, characterized in that at least two measuring capacitors are assigned to at least one reference capacitor. 18. Pressure measuring device and/or pressure sensor according to one of the preceding claims, characterized in that at least two reference capacitors are assigned to at least one measuring capacitor. 19. Pressure measuring device according to one of the preceding claims, characterized in that the pressure measuring device has an evaluation device for evaluating the signal of the pressure sensor ( 1 ) and that the evaluation device is arranged spatially spaced from the measuring capacitor ( 3 ) and/or the reference capacitor ( 13 ). 20. Device for detecting whether a vehicle seat is occupied, characterized in that the detector device comprises a pressure measuring device and/or a pressure sensor according to one of the preceding claims.