SENSOR FOR DETECTING AT LEAST ONE PROPERTY OF A FLUID MEDIUM IN AT LEAST ONE MEASUREMENT CHAMBER

Abstract

A sensor for detecting at least one property of a fluid medium in at least one measuring chamber. The sensor includes a sensor element having at least one heatable diaphragm and an electrical measuring bridge. The diaphragm is connected to the electrical measuring bridge. The sensor is furthermore designed to detect an electrical resistance of the measuring bridge. The sensor is designed to detect a pressure of the fluid medium based on the detected electrical resistance of the electrical measuring bridge.

Claims

1-10. (canceled)

11. A sensor configured to detect at least one property of a fluid medium in at least one measuring chamber, the sensor comprising: a sensor element having at least one heatable diaphragm and an electrical measuring bridge, wherein the diaphragm is connected to the electrical measuring bridge, wherein the sensor is configured to detect an electrical resistance of the measuring bridge, wherein the sensor is further configured to detect a pressure of the fluid medium based on the detected electrical resistance of the electrical measuring bridge.

12. The sensor as recited in claim 11, wherein the sensor is configured to vary an electrical heating voltage applied to the diaphragm, wherein the sensor is configured to detect the property of the fluid medium when a first heating voltage is applied to the diaphragm, and wherein the sensor is configured to detect the pressure of the fluid medium when a second heating voltage is applied to the diaphragm, wherein the second heating voltage is lower or higher than the first heating voltage.

13. The sensor as recited in claim 12, wherein the first heating voltage is selected such that a temperature of the diaphragm increases, wherein the second heating voltage is selected such that a temperature of the diaphragm remains substantially constant.

14. The sensor as recited in claim 11, wherein the electrical measuring bridge includes electrical resistors, wherein the resistors are arranged on the diaphragm in such a way that an electrical resistance of the resistors is proportional to the pressure of the fluid medium.

15. The sensor as recited in claim 11, wherein the sensor is configured to generate an adjustment value for the detected property of the fluid medium based on the detected pressure of the fluid medium.

16. The sensor as recited in claim 11, wherein the sensor further comprises: a temperature sensor element, wherein the temperature sensor element is configured to detect a temperature of the sensor element.

17. The sensor as recited in claim 16, wherein the sensor is configured to detect the property of the fluid medium based on the temperature of the diaphragm.

18. The sensor as recited in claim 11, wherein the sensor is configured to output an error signal when the detected pressure exceeds or reaches a predetermined threshold value.

19. The sensor as recited in claim 11, furthermore comprising an electrical heating element configured to heat the diaphragm.

20. The sensor as recited in claim 11, wherein the sensor is configured to detect an H.sub.2 content in a measuring gas.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Further optional details and features of the present invention can be found in the description below of preferred exemplary embodiments, which are illustrated schematically in the figures.

[0028] FIG. 1 shows a schematic illustration of a sensor for detecting at least one property of a fluid medium in at least one measuring chamber, according to an example embodiment of the present invention.

[0029] FIG. 2 shows a schematic illustration of an electrical circuit diagram of the sensor element of the sensor, according to an example embodiment of the present invention.

[0030] FIG. 3 shows a cross-sectional view of the sensor element, according to an example embodiment of the present invention.

[0031] FIG. 4 shows a further cross-sectional view of the sensor element, according to an example embodiment of the present invention.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

[0032] FIG. 1 shows a schematic illustration of a sensor 10 for detecting at least one property of a fluid medium 12 in at least one measuring chamber 14, in particular for detecting the H.sub.2 content in a measuring gas 16. The sensor 10 may be equipped, in particular, for use in a hydrogen fuel cell vehicle. However, other applications are also possible. The sensor 10 may comprise, in particular, one or more further functional elements (not illustrated in the figures), such as electrodes, electrode supply lines and contacts, multiple layers or other elements. Accordingly, the sensor 10 may be installed in the exhaust gas system of the hydrogen fuel cell vehicle (exhaust) or it may operate under atmospheric conditions (ambient). The measuring chamber may consequently be an exhaust gas system, anode section or interior space of the hydrogen fuel cell vehicle.

[0033] The sensor 10 comprises a sensor element 18. The sensor element 18 comprises at least one heatable diaphragm 20. A first electrical heating element 22 is arranged on the diaphragm 20. An upper side 24 of the diaphragm is exposed to a first reference chamber 26, which is closed off from the measuring chamber 14. The first reference chamber 26 is filled with a fluid medium of a known composition. An underside 30 of the diaphragm 20 can be exposed to the fluid medium 12.

[0034] The sensor element 18 furthermore comprises a reference diaphragm 32. A further electrical heating element 28 is arranged on the reference diaphragm 32. An upper side 36 of the reference diaphragm 32 is exposed to a second reference chamber 34, which is closed off from the measuring chamber 14. The second reference chamber 34 is filled with a fluid medium of a known composition. An underside 42 of the reference diaphragm 32 is exposed to a third reference chamber 38—this may be the same medium as that in the reference chamber 34—and separated from the fluid medium 12, for example by a media separation apparatus 44. It is explicitly pointed out that the first heating element 22 and the second heating element 28 may be formed in one piece. It is explicitly pointed out that the reference diaphragm 32 is optional. The overall structure may be realized, for example, in the form of a silicon wafer. The sensor 10 may furthermore have a housing 40, in which the sensor element 18 is arranged.

[0035] FIG. 2 shows a schematic illustration of an electrical circuit diagram of the sensor element 18 of the sensor 10. This shows the sensor element 18 with the diaphragm 20 and the reference diaphragm 32. An electrical heating voltage U.sub.H can be applied to the first heating element 22 to heat the diaphragm 20 (likewise to the heating element 28 to heat the reference diaphragm 32). The heating voltage U.sub.H is provided by a voltage source 46. The diaphragm 20 and the reference diaphragm 32 are connected to an electrical measuring bridge 48. The measuring bridge 48 is, for example, a Wheatstone bridge. For this purpose, the measuring bridge 49 is formed, for example, by four resistors 50, of which two resistors 50 are arranged on the diaphragm 20 and two resistors 50 are arranged on the reference diaphragm 32. An electrical bridge voltage U.sub.B of the measuring bridge 48 can be tapped at two points between the resistors 50 of the diaphragm 20 and the reference diaphragm 32.

[0036] FIG. 3 shows a cross-sectional view of the sensor element 18. The sensor 10 furthermore comprises a temperature sensor element 52. The temperature sensor element 52 is designed to detect a temperature of the sensor element 18 or its silicon chip. To this end, the temperature sensor element 52 is arranged at the edge of the diaphragm 20 or adjacent to the diaphragm 20. The sensor 10 is designed to detect the property of the fluid medium 12 based on the temperature of the diaphragm 20. FIG. 4 shows a further cross-sectional view of the sensor element 18. In particular, FIG. 4 shows the sensor element 18 with a deformed diaphragm 20. The sensor 10 is furthermore designed to detect an electrical resistance of the measuring bridge 48. The sensor 10 is therefore furthermore designed to detect a pressure of the fluid medium 12 based on the detected electrical resistance of the electrical measuring bridge 48. As explained above, the electrical measuring bridge 48 comprises the electrical resistors 50. The resistors 50 are arranged on the diaphragm 20 in such a way that an electrical resistance value of the resistors 50 is proportional to the pressure of the fluid medium 12, as explained in more detail below.

[0037] The sensor 10 is designed for varying an electrical heating voltage U.sub.H applied to the diaphragm 20. In particular, the sensor 10 is designed to detect the property of the fluid medium 12 when a first heating voltage U.sub.H is applied to the diaphragm 20. The sensor 10 is designed to detect the pressure of the fluid medium 12 when a second heating voltage U.sub.H is applied to the diaphragm 20, the second heating voltage U.sub.H being lower or higher than the first heating voltage U.sub.H. The first heating voltage U.sub.H is selected such that a temperature of the diaphragm 20 increases. The second heating voltage U.sub.H is selected such that a temperature of the diaphragm 20 remains substantially constant or does not increase. The sensor 10 is furthermore designed to generate an adjustment value for the detected property of the fluid medium 12 based on the detected pressure of the fluid medium 12. The sensor 10 is furthermore designed to output an error signal if the detected pressure exceeds or reaches a predetermined threshold value.

[0038] A mode of operation or function of the sensor 10 according to the present invention is described below. A first electrical heating voltage U.sub.H is applied to the first heating element 22 to heat the diaphragm 20. In this case, the measuring bridge 48 is supplied with a voltage which is high enough to heat the diaphragm 20. In addition, the reference diaphragm 32 may therefore also be heated by the second heating element 28. With this, different temperatures are established in the region of the diaphragm 20 and the reference diaphragm 32 owing to the different thermal conductivity of the gases which contact the diaphragm 20 and the reference diaphragm 32. The temperature of the sensor element 18 or its silicon chip is detected by the temperature sensor element 52. This temperature corresponds, in a first approximation, to the ambient temperature if the sensor element 18 is not additionally heated. The bridge signal which represents the difference between the temperatures of the measuring diaphragm 20 and the reference diaphragm 32 is tapped as shown in FIG. 2. The measurement of the thermal conductivity is based on the fact that the diaphragm 20 is cooled by the fluid medium 12 to be measured. The higher the thermal conductivity of the fluid medium 12 to be measured, the stronger the cooling of diaphragm 20. By measuring the temperature of the diaphragm 20, it is therefore possible to infer the thermal conductivity of the medium and, indirectly, its H.sub.2 level.

[0039] To detect the pressure of the fluid medium 12, the sensor 10 alters the heating voltage U.sub.H. A second electrical heating voltage U.sub.H is applied to the first heating element 22. In this case, the measuring bridge 48 is supplied with a very low voltage so that the diaphragm 20 does not become heated. If the fluid medium 12 results in a higher pressure on the underside 30 of the diaphragm 20 than on the upper side 24 of the diaphragm 20, the diaphragm 20 bends, as illustrated in FIG. 4. The resistors 50 on the diaphragm 20 become longer and the resistance value therefore increases. The increase in the resistance may be measured when the second heating voltage U.sub.H is applied. The resistance value of the resistors 50 increases with the increase in the pressure difference between the underside 30 and the upper side 24 of the diaphragm 20. For the H.sub.2 measurement, the pressure component may be taken into account as an adjustment factor to increase the sensor accuracy.

[0040] The present invention may be verified by analyzing the signal of a sensor which is based on a thermal conductivity principle. If such a sensor emits a signal when a pressure is applied, corresponding pressure detection must be available (if a separate pressure sensor is not installed).