Dual membrane sensor for temperature compensated pressure sensing

• US 7,334,480 B2
• Filed: 12/21/2006
• Issued: 02/26/2008
• Est. Priority Date: 10/18/2004
• Status: Expired due to Fees

• Current Assignee: Precision Mechatronics Pty Ltd
• Original Assignee: Silverbrook Research Pty Limited
• Inventors: Mallinson, Samuel George, Silverbrook, Kia
• Primary Examiner(s): Lefkowitz, Edward
• Assistant Examiner(s): Jenkins, Jermaine
• Application Number:
  US11/642,520
• Publication Number:
  US 20070144264A1
• Time in Patent Office: 432 Days
• Field of Search: 73700-756, 3612831-2834
• US Class Current: 73/700
• CPC Class Codes: B60C 23/0408 transmitting the signals by non-mechanical means from the wheel or tyre to a vehicle body mounted receiver
• CPC Class Codes: G01L 15/00 Devices or apparatus for measuring two or more fluid pressure values simultaneously
• CPC Class Codes: G01L 19/0636 using particle filters
• CPC Class Codes: G01L 9/0047 Diaphragm with non uniform thickness, e.g. with grooves, bosses or continuously varying thickness
• CPC Class Codes: G01L 9/0073 using a semiconductive diaphragm
• CPC Class Codes: G01L 9/125 with temperature compensating means non electric temperature compensating means G01L19/04

Abstract

A pressure sensor that has a sensor membrane for exposure to fluid at a pressure to be sensed, and a compensation membrane sealed from the fluid at the pressure to be sensed. Associated circuitry connected to the sensor membrane converts deflection into an output signal indicative of the fluid pressure. The circuitry also connects to the compensation membrane to convert deflection into an adjustment to the output signal that compensates for membrane deflection due to thermal expansion.

Claims

1. A pressure sensor comprising:

a sensor membrane formed from conductive material for exposure to fluid at a pressure to be sensed;

a compensation membrane formed from conductive material and sealed from the fluid at the pressure to be sensed; and

,

associated circuitry connected to the sensor membrane for converting deflection into an output signal indicative of the fluid pressure and connected to the compensation membrane for converting deflection into an adjustment to the output signal that compensates for membrane deflection due to thermal expansion;

wherein,

each membrane is less than 0.1 grams.

2. A pressure sensor according to claim 1 wherein the sensor membrane partially defines a first chamber containing fluid at a reference pressure, the compensation membrane is in a chamber sealed from the fluid at a pressure to be sensed.

3. A pressure sensor according to claim 2 further comprising:

a first recess defined in a substrate covered by the first membrane so as to define the first chamber, the first chamber containing a fluid at a reference pressure such that the first membrane deflects due to a pressure difference between the reference pressure and the fluid pressure; and

a second recess defined in the substrate covered by a capping member so as to define, and seal from the fluid pressure, the second chamber, the second membrane dividing the second chamber into sections fluidically sealed from each other such that the second membrane deflects at a predetermined pressure difference between the sections.

4. A pressure sensor according to claim 3 wherein the sensor is a capacitative sensor, with a conductive layer deposited in each of the first and second chambers and the first and second membranes are conductive, such that the conductive layer in the first chamber and the first membrane form capacitor electrodes and the deflection of the first membrane changes the capacitance which the associated circuitry converts to the output signal.

5. A pressure sensor according to claim 1 wherein the fluid pressure is air pressure within a pneumatic tire.

6. A pressure sensor according to claim 1 wherein the membranes are at least partially made from a metal-nitride compound.

7. A pressure sensor according to claim 1 wherein each membrane is approximately 0.5 μ

m thick.

8. A pressure sensor according to claim 1 wherein each membrane is circular with a diameter less than 500 microns.

9. A pressure sensor according to claim 1 wherein the membranes are laminates having at least two layers, at least one of the layers being at least partially formed from conductive material.

10. A pressure sensor according to claim 9 wherein the layers within the laminate are be formed from the deposition of different metal ceramics.

11. A pressure sensor according to claim 10 wherein the metal ceramics are metal nitrides or mixed metal nitrides.

12. A pressure sensor according to claim 9 wherein one or more of the layers of the laminate is metal.

13. A pressure sensor according to claim 1 wherein the membranes are non-planar.

14. A pressure sensor according to claim 13 wherein the membranes are corrugated.

15. A pressure sensor according to claim 14 wherein the flexible corrugated membranes each have a corrugation factor of 8.

16. A pressure sensor according to claim 15 wherein the sensor has a linear response up to about 1 MPa.

17. A pressure sensor according to claim 15 wherein the membrane corrugations have a period of between 5 microns and 15 microns.

18. A pressure sensor according to claim 17 wherein the membranes are substantially circular and the corrugations are annular.

19. A pressure sensor according to claim 14 wherein the corrugations have a substantially square-shaped cross-sectional profile.