DEVICE FOR MEASURING PRESSURE

Abstract

Device for measuring pressure comprising a base body, and a diaphragm that is arranged on the base body such that the base body and the diaphragm at least partially enclose a cavity, wherein the diaphragm is embodied to be deformable in accordance with the external pressure incident on it, such that the magnitude of a spatial dimension of the cavity is correspondingly changed, wherein a position element is arranged to move in accordance with the diaphragm, wherein an inductive planar coil is arranged across the cavity and opposite to the position element, such that the position element and the inductive planar coil are separated, wherein the position element serves to influence the inductance of the coil in dependence on the magnitude of the separation.

Claims

1. A device for measuring pressure comprising: a base body; a diaphragm arranged on the base body such that the base body and the diaphragm at least partially enclose a cavity, and such that the diaphragm is configured to be exposed to an external pressure to be monitored, wherein the diaphragm is deformable in accordance with the external pressure incident on it, such that a distance in a spatial dimension of the cavity is correspondingly changed; a position element fixedly attached to the diaphragm and configured to move in accordance with the diaphragm; and an inductive planar coil arranged at least one of on or in the base body, across the cavity and opposite to the position element, such that the position element and the inductive planar coil are separated by the distance in the spatial dimension, wherein the position element influences an inductance of the coil dependent on the distance in the spatial dimension; wherein the device is configured to determine the external pressure based on the inductance of the inductive planar coil.

2. The device according to claim 1, further comprising a processing unit, wherein the processing unit comprises a signal generating unit electrically connected to the coil and configured to generated an electrical input signal that can be transmitted to the coil.

3. The device according to claim 2, wherein the processing unit comprises an evaluation unit comprising a signal receiving interface electrically connected to the coil and the signal generating unit, wherein the evaluation unit is configured to determine the external pressure based on an electrical output signal output from the coil to the signal receiving interface.

4. The device according to claim 3, wherein the processing unit comprises a sampling module configured to sample the output signal from the coil.

5. The device according to claim 1, wherein the position element comprises copper.

6. The device according to claim 1, wherein the position element comprises an electrically isolating and ferromagnetic material.

7. The device according to claim 1, wherein the diaphragm is formed from a ceramic material.

8. The device according to claim 1, wherein the diaphragm is formed from a metal.

9. The device according to claim 1, wherein the position element is substantially flat and has at least one of a rhombus or a hexagonal shape.

10. The device according to claim 1, wherein the coil comprises a printed conducting pathway on a substrate.

11. The device according to claim 1, wherein the coil comprises a first layer and a second layer, wherein the first and second layers are substantially aligned.

12. The device according to claim 1, wherein the coil comprises a single layer.

13. A method for measuring pressure with a device, the method comprising: exposing a diaphragm of the device to an external pressure to be monitored; and measuring the external pressure on a basis of a change in inductance of an inductive planar coil of the device; wherein the device comprises: a base body; the diaphragm arranged on the base body such that the base body and the diaphragm at least partially enclose a cavity, and wherein the diaphragm is configured to be deformable in accordance with the external pressure incident on it, such that a distance in a spatial dimension of the cavity is correspondingly deformed; a position element fixedly attached to the diaphragm and configured to move in accordance with the diaphragm; and the inductive planar coil arranged at least one of on or in the base body, across the cavity and opposite to the position element, such that the position element and the inductive planar coil are separated by the distance in the spatial dimension, wherein the position element influences the inductance of the coil dependent on the distance in the spatial dimension.

14. A differential pressure flow meter for measuring a flow of a liquid through a pipe comprising the device for measuring pressure according to claim 1.

15. A differential pressure level meter for measuring a level of a liquid in a container comprising the device for measuring pressure according to claim 1.

16. The device according to claim 4, wherein the sampling module comprises an analog to digital converter.

17. The device according to claim 6, wherein the electrically isolating and ferromagnetic material comprises at least one of Nickel-Zinc-Ferrite or Manganese-Zinc-Ferrite.

18. The device according to claim 10, wherein the coil comprises a printed conducting pathway on a printed circuit board.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The invention will next be described with reference to the following figures. They show:

[0040] FIG. 1 a schematic diagram of an embodiment of the inventive pressure sensor;

[0041] FIG. 2a, b respectively, a perspective view of a double layered planar coil and a perspective view of a planar coil and a position element;

[0042] FIG. 3a, b a top view of a planar coil and the border of a hexagonal shaped position element, and a top view of a planar coil and the border of a rhombus shaped position element;

[0043] FIG. 4 a graphical representation of the progression of the induction of a planar coil in dependence on a spatial variation of the positioning element in a direction parallel to the plane of the coil at three distinct distances from the coil in a direction perpendicular to the plane of the coil;

[0044] FIG. 5 a graphical representation of the dependence of the induction of the planar coil with respect the distance between the position element and the planar coil in the direction perpendicular to the plane defined by the coil;

[0045] FIG. 6 a schematic representation of an embodiment of the inventive device for pressure measurement;

[0046] FIG. 7 a schematic diagram of a system comprising a pipeline for carrying a fluid such as a liquid and an embodiment of the device;

[0047] FIG. 8 a schematic diagram of a further application of an embodiment of the inventive device for measuring pressure, wherein the device is used to measure the fill level of a tank; and

[0048] FIG. 9 a schematic diagram of a further fill level measurement application of an embodiment of the inventive device.

DETAILED DESCRIPTION

[0049] FIG. 1 shows a schematic diagram of an embodiment of the inventive pressure sensor having a base body 3 and a diaphragm 5, which is exposed to an external pressure Pex. The base body 3 and the diaphragm 5 enclose a cavity 7. Situated within the cavity 7 is a printed circuit board PCB. A planar coil 11 is arranged on the printed circuit board PCB. The planar coil 11 is electrically connected to a processing unit 13. The processing unit 13 can be arranged directly on the base body 3, and a housing enclosing the processing unit 13 can be integrally formed with the base body 3. Alternatively, the base body 3 and the processing unit 13 can be spatially separated from each other, such that the processing unit is located remotely from the external pressure Pex or process pressure to be monitored and/or measured. This variability is depicted by the dotted lines tt showing the electrical lines running between the planar coil 11 and the processing unit 13 as well as between the housing enclosing the processing unit 13 and the base body 3.

[0050] The processing unit comprises a signal generating unit 17 for transmitting an electric signal to the planar coil 11. A receiving interface 19 is provided to receive and sample the electrical signal from the planar coil 11. The relative difference between the input and output signals of the coil 11 is influenced by the inductance H of the coil 11.

[0051] The processing unit 13 further comprises a communications interface 21 for exchanging information with external devices. The interface 21 is depicted as a communications line having two conductive pathways. The communications interface 21 can however also be a single conducting pathway, or even a wireless communications interface 21.

[0052] A position element 9 is fixed to the diaphragm 5. The position element 9 is situated across the cavity 7 from the planar coil 11 and is separated from the planar coil 11 by a distance d. When a pressure is incident on the diaphragm 5, the diaphragm 5 can deform such that the distance d changes. The change in the distance d influences the inductance H of the planar coil 11 due to properties of the position element 9. The position element 9 can for example be conductive, such that eddy currents form due to the changing magnetic field produced by the coil 11 when a signal is input from the processing device. These eddy currents in turn contribute to the magnetic field and can contribute to a change in the electric potential within the metal conductive pathway of the coil 11, thereby influencing the input signal. This influence, or the result thereof, can be monitored in the processing unit 13 by examining the output signal of the coil 11 received via the receiving interface 19. On the basis of this examination, which is essentially a determination of the inductance H of the coil 11, a conclusion regarding the distance of separation of the coil 11 and the position element 9 can be reached. On the basis of this conclusion, the incident pressure can be determined.

[0053] FIGS. 2a and 2b respectively show a perspective view of a double layered planar coil 11 and a perspective view of a planar coil 11 and a position element 9. The double layered planar coil 11 can be fabricated on a substrate such as a printed circuited board. For example, the upper layer can be arranged on a first side of a printed circuit board PCB, and the lower side can be arranged on a second side of the board. A connecting portion of the coil 11 is shown, which serves to connect the two layers. In FIG. 2b, a position element 9 is displayed. The position element 9 is rhombus, i.e. diamond, shaped. The position element 9 is flat, having height to width and height to breadth ratios which are each well below 1 to 5. The position element 9 is copper.

[0054] FIGS. 3a and 3b respectively show a top view of a planar coil 11 along with the border of a hexagonal shaped position element 9, and a top view of a planar coil 11 along with the border of a rhombus shaped position element 9. The position element 9 as defined through the border as shown is in each case centered i.e. aligned with respect to the coil 11. It is known, that geometries such as those shown are especially effective for influencing the inductance H of the planar coil 11.

[0055] FIG. 4 shows a graphical representation of the progression of the induction of a planar coil 11 in dependence on a spatial variation of the position element 9 in a direction parallel to the plane of the coil 11 at three distinct distances from the coil 11 a direction perpendicular to the plane of the coil 11. In particular, when the position element 9 is centered over the coil 11 as depicted in FIGS. 3a and 3b, the influence of the position element 9 on the inductance H of the coil 11 is maximized. The position element 9 used here is conducting. Therefore the inductance H of the coil 11 is reduced with a decreasing separation distance between the position element 9 and the coil 11.

[0056] The first line L1 shows the progression of the inductance H when the coil 11 is positioned around 450 micrometers from the position element 9 in the direction perpendicular to the plane of the coil 11. The second line L2 i.e. progression shows the inductance H of the coil 11 when the position element 9 is separated from the coil 11 by 300 micrometers in the direction perpendicular to the plane of the coil 11. The third progression i.e. line L3 shows the inductance H of the coil 11 when the position element 9 is separated from the coil 11 by 150 micrometers in the direction perpendicular to the plane of the coil 11. Measurements of the coil 11 inductance H can be performed at this scale with an accuracy of +/5%.

[0057] FIG. 5 shows a graphical representation of the dependence of the induction H of the planar coil 11 with respect to the distance between the position element 9 and the planar coil 11 in the direction perpendicular to the plane defined by the coil 11, in particular when the planar coil 11 and the position element 9 are aligned with respect to each other. The positions and inductances H as shown in FIG. 5 reflect the positions and resulting inductances H of the progression shown in FIG. 4. As can be seen, the dependence of the inductance H of the coil 11 is strongly dependent on the position of the position element 9, which is in this case also conductive. The use of a non-conducting ferrite position element 9 can cause an inverse of the dependence, such that with increasing distance between the planar coil 11 and the position element 9, the inductance H decreases. This is due to the magnetic conducting properties of the ferrite material.

[0058] FIG. 6 shows a schematic representation of a device 1 for pressure measurement that is suitable for use in applications wherein a differential pressure measurement is required. Here, the diaphragm 5 is exposed to pressure on both on a side external Pex to the cavity 7 as well as on the side Pcav within the cavity 7. The differential pressure (P=PexPcav) can thereby be determined. The unequal pressure across the diaphragm 5 surface causes the diaphragm 5 together with the position element 9 (a copper or ferrite activator) to move towards the inductive planar coil 11. The gap d between the position element 9 and the planar coil 11 is thereby reduced. When a copper position element 9 i.e. activator is used, this movement of the diaphragm 5 and position element 9 towards the planar coil 11 will induce stronger eddy currents on the position element 9, thereby forcing the inductance H value of the planar coil 11 to be reduced with respect to its nominal value.

[0059] If a ferrite material is used for the position element 9, a different effect will occur. Because the ferrite material is electrically nonconductive, i.e. an insulator, no eddy current is produced in the ferrite. Rather, due to the relative permeability, which can be greater than one hundred, the position element 9 behaves as the magnetic field concentrator, or magnetic conductor for the field produced by the planar coil 11. This in turn increases the inductance H value of the planar coil 11 with respect to its nominal value.

[0060] FIG. 7 shows a schematic diagram of a system comprising a pipeline 23 for carrying a fluid that is a liquid and an embodiment of the device. The liquid flows past a barrier provided within the pipeline 23. On a first side of the barrier, the pressure of the fluid has a first value. The pressure of the liquid within the pipeline 23 is diverted to the side of the diaphragm 5 external to the cavity 7 of an inventive measuring device, such as the one shown in FIG. 6. On a second side of the barrier, which is generally on the downstream side with respect to the liquid flow within the pipeline 23, the pressure of the liquid has a second value that differs from the first value depending on the speed of the flow. The pressure at this point is diverted to the cavity 7 of the inventive device 1 for measuring pressure, and the inside of the cavity 7 is therefore exposed. Since the pressure difference varies depending on the flow properties, such as velocity, of the liquid in the pipeline 23, the flow can be measured by determining the difference in pressure.

[0061] In a flow measurement application such as the one depicted in FIG. 7, the planar coil 11 can be coated with an insulating, i.e. non-conducting, coating such as paint or Teflon i.e. PTFE. This has a negligible effect on the inductance H of the coil 11, but provides a valuable protection for the coil 11 during exposure to the materials flowing in the pipeline 23. An inductance H based pressure measurement device 1 therefore provides a very reliable & robust measurement technique as by dielectric changes, dust and moisture have little influence on the inductance H. The solution is also a very cost effective solution to the flow measurement problem.

[0062] FIG. 8 shows a schematic diagram of a further application of an embodiment of the inventive device 1 for measuring pressure, wherein the device 1 is used to measure the fill level of a tank 25. Here, the tank 25 is filled to a level h with a liquid. The tank 25 i.e. container is exposed to atmospheric pressure. The pressure at the bottom of the tank 25 is therefore directly coupled to the fill level of the tank 25. The device 1 is exposed to the pressure at the bottom of the tank 25, and the cavity 7 of the device 1 is exposed to atmospheric pressure. This gauge pressure device 1 can therefore measure the differential pressure due to the liquid filling the container.

[0063] FIG. 9 shows a schematic diagram of a further fill level measurement application of an embodiment of the inventive device. A tank 25 i.e. container is shown as in FIG. 8. However, the tank 25 is closed and pressurized to a certain pressure. The pressure at any point in the tank 25 is a summation of the pressure of the liquid filling the tank 25 above said point, and the ambient pressure provided by the gas near the top of the closed tank 25. To measure the differential pressure, the pressure of the gaseous area of the tank 25 is diverted to the cavity 7 of the inventive device. The pressure at a certain point, which can be near the bottom of the tank 25, is diverted to the external surface of the diaphragm 5 of the device 1. Therefore, the pressure build up in the tank 25 is neutralized, and the pressure due to the liquid in the tank 25 is proportional to the deformation of the diaphragm 5.

[0064] The systems of device 1 for measuring pressure and container as depicted in FIGS. 8 and 9 can be provided with at least one valve to permit a simplified installation of the device 1.

REFERENCE CHARACTERS

[0065] 1 Device [0066] 3 base body [0067] 5 diaphragm [0068] 7 cavity [0069] 9 a position element [0070] 11 inductive planar coil [0071] 13 processing unit [0072] 15 housing [0073] 17 signal generating unit [0074] 19 receiving interface [0075] 21 communications interface [0076] 23 pipeline [0077] 25 tank/container [0078] PCB printed circuit board [0079] Pcav pressure cavity [0080] Pex external pressure [0081] Vd spatial dimension [0082] d magnitude of the spatial dimension [0083] H inductance H changing inductance [0084] h liquid level in tank [0085] L1 first line [0086] L2 second line [0087] L3 third line