Multimodulus pressure sensor

• US 4,944,187 A
• Filed: 12/23/1988
• Issued: 07/31/1990
• Est. Priority Date: 12/23/1988
• Status: Expired due to Term

• Current Assignee: Rosemount Incorporated (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Frick, Roger L., Rud, Stanley E. Jr.
• Primary Examiner(s): Woodiel, Donald O.
• Application Number:
  US07/289,207
• Time in Patent Office: 585 Days
• Field of Search: 73/718, 73/720, 73/721, 73/724, 73/726, 73/727, 73/705, 73/706, 73/707, 73/708, 338/4, 361/283
• US Class Current: 73/718
• CPC Class Codes: G01L 9/0042 Constructional details associated with semiconductive diaphragm sensors, e.g. etching, or constructional details of non-semiconductive diaphragms details about the integration or bonding of piezoresistor in or on the diaphragm G01L9/0052 and G01L9/0057 respectively
• CPC Class Codes: G01L 9/0052 of piezoresistive elements circuits therefor G01L9/06
• CPC Class Codes: G01L 9/0072 using variations in capacitance
• CPC Class Codes: G01L 9/0073 using a semiconductive diaphragm
• CPC Class Codes: G01L 9/0079 with Fabry-Perot arrangements
• CPC Class Codes: G02B 26/001 based on interference in an adjustable optical cavity interference filters G02B5/28; devices or arrangements using multiple reflections in spectrometry or monochromators G01J3/26

Abstract

A pressure sensor utilizes the effect of different elastic moduli between layers or sections of different material that are bonded together to form a body, so that when the bonded material unit is subjected to a uniform hydrostatic external pressure, the differences in the elastic moduli of each of the materials will cause the materials to deflect in a predictable manner proportional to pressure. The amount of warpage or deflection of the body of material can be measured as a function of pressure. Specifically, two layers of materials, such as silicon and borosilicate glass, which have substantially different elastic moduli can be bonded across an interface surface to form an assembly, and when subjected to a substantially uniform pressure on the exterior surfaces the assembly will deflect for indicating applied pressure at relatively high pressure ranges. The bonded material assembly is placed in a fluid to provide a substantially uniform applied hydrostatic pressure on all exposed surfaces of the bonded material assembly.

Claims

1. A pressure sensor comprising:

a first quantity of solid material defining a volume having interface means thereon;

a second quantity of solid material having a different modulus of elasticity from the first quantity of material and having interface means thereon engaging the interface means of the first quantity of material for forming a unitary solid body;

means for simultaneously applying a substantially uniform hydrostatic pressure on surface portions of both the first and second quantities of material of the unitary body tending to compress the quantities of material at the interface means, whereby the unitary body will be stressed as a function of applied pressure; and

means associated with at least a portion of the unitary body for providing a signal indicating the applied hydrostatic pressure.

2. The pressure sensor as specified in claim 1 wherein said first and second quantities of material are selected to have substantially the same thermal coefficient of expansion.

3. The pressure sensor as specified in claim 1 wherein said interface means of the first and second materials comprise interface surfaces, said interface surfaces being bonded together whereby stresses are created when the unitary body formed of the first and second materials is subjected to external hydrostatic pressure.

4. The pressure sensor as specified in claim 3 wherein said two quantities of material comprise a uniform thickness layer when bonded together, the pressure sensor further comprising first means for mounting said layer with respect to a reference surface, and the means associated for indicating pressure comprising second means sensing deflection of said layer relative to the reference surface.

5. The pressure sensor as specified in claim 1 wherein said interface portions comprise surfaces that are bonded together.

6. The pressure sensor as specified in claim 1 wherein said first quantity comprises a beam, and the second quantity comprises a support, said beam and support being bonded together along interface portions of each of the beam and support, and other portions of said beam and support being spaced from each other whereby deflections between the two other portions occurs as a function of hydrostatic pressure in the interface portions of the beam and support.

7. The pressure sensor as specified in claim 1 wherein the means associated for indicating the applied hydrostatic pressure comprises optical sensing means to sense deflection of the unitary body with respect to a reference position.

8. The pressure sensor as specified in claim 7 wherein the optical sensing means comprise an interferometer for sensing the deflection.

9. The pressure sensor of claim 1 in combination with a housing having a dividing wall separating the housing into first and second separate chambers, a first unitary body mounted in a first chamber and a second unitary body mounted in the second chamber, the means associated for indicating the applied pressure comprising means for separately indicating the deflections of the respective first and second bodies relative to the housing, the first and second chambers being subjected to different hydrostatic pressures so the means for separately indicating deflections provides an indication of the differential in hydrostatic pressure between the first and second chambers.

10. The pressure sensor of claim 1 wherein said means associated for indicating pressure comprises strain gauge means sensing strain in the unitary body.

11. The pressure sensor of claim 1 wherein the means associated for indicating pressure comprise a capacitor sensing the deflection.

12. The pressure sensor of claim 1 wherein strain gauge means are integrally formed on the first quantity of solid material thereby forming the second quantity of material to indicate stress in the unitary body caused by hydrostatic pressure on the unitary body.

13. A pressure sensor apparatus comprising:

a unitary body flexure member of two solid materials, the unitary body being made of a first quantity of material defining a first volume of solid material;

a second quantity of material having a different elastic moduli from the first quantity of material defining a second volume of solid material, the first and second volumes of material being integrally formed along an interface portion; and

means for applying a substantially uniform hydrostatic pressure on exposed portions of both of the first and second quantities of material of the unitary body flexure member and tending to change the volume of both the first and second quantities to affect the interface portions sufficient to cause measurable deflection of at least portions of the unitary body flexure member from a reference position as a function of applied pressure.

14. The apparatus as specified in claim 13 wherein said first and second volumes of material are selected to have substantially the same thermal coefficient of expansion.

15. The apparatus as specified in claim 14 wherein said two volumes of solid material comprise a substantially uniform thickness layer when bonded together, first means to mount said layer with respect to a reference surface, and second means sensing deflection of said layer relative to the reference surface.

16. The pressure sensor of claim 15 wherein said second means comprises capacitive deflection sensing means on the reference surface and on the layer which permit determining the pressure related deflection of said layer.

17. The pressure sensor of claim 15 wherein said second means comprises an optical means for sensing deflections of the layer.

18. The pressure sensor of claim 17 wherein the optical means further comprise an interferometer.

19. The pressure sensor of claim 13 and a layer of a third material bonded to the first mentioned layer, said third material having a different thermal expansion coefficient from the other materials selected to reduce temperature induced deflection errors of the pressure sensor.

20. An apparatus for sensing a fluid pressure, comprising:

a first body disposed in the fluid having a first surface, the pressure tending to compress the first body at a first rate;

a second body disposed in the fluid having a second surface joined to the first surface, the pressure tending to compress the second body at a second rate different from the first rate;

the pressure compressing the joined bodies at different rates to cause the joined bodies to distort; and

means attached to the joined bodies for sensing the distortion and converting to an output indicating the pressure.

21. The apparatus of claim 20 wherein the joining constrains a length on the first surface to be substantially equal to a length on the second surface, thereby distorting the joined bodies.

22. The apparatus of claim 20 wherein the pressure causes the joined first and second surfaces to curl, and the sensing means sense the curling.

23. An apparatus for sensing a fluid pressure, comprising:

a body disposed in the fluid having a first region which the pressure tends to compress at a first rate integral with a second region which the pressure tends to compress at a second rate, different from the first rate, the pressure distorting the body due to the difference in the rates of compression; and

means attached to the body for sensing the distortion of the body and providing an output signal indicative of the pressure.

24. The apparatus of claim 23 wherein the pressure causes the body to bow, and the sensing means sense the bowing of the body.

25. The apparatus of claim 24 wherein the body is a strip bowing along its length responsive to the pressure.