Fluid pressure sensing system and differential pressure unit therefor

• US 3,901,082 A
• Filed: 10/01/1973
• Issued: 08/26/1975
• Est. Priority Date: 10/01/1973
• Status: Expired due to Term

• Current Assignee: ITT Corporation (ITT, Inc.)
• Original Assignee: La Verne Dean Lyon
• Inventors: Lyon, La Verne Dean
• Primary Examiner(s): Queisser, Richard C.
• Assistant Examiner(s): Rasco, Marcus S.
• Application Number:
  US05/402,035
• Time in Patent Office: 694 Days
• Field of Search: 73/47R,398AR,408,393 92/97,104,130,131,133
• US Class Current: 73/708
• CPC Class Codes: G01F 1/38 the pressure or differential pressure being measured by means of a movable element, e.g. diaphragm, piston, Bourdon tube or flexible capsule
• CPC Class Codes: G01L 13/025 using diaphragms

Abstract

A differential pressure unit including an annular body with a hole therethrough, and two metal diaphragms sealed over respective openings into the hole at opposite ends of the body. A post rigidly connects central portions of the diaphragms to keep them spaced apart a constant predetermined distance different from the unstressed (post not connected) diaphragm spacing. The result is a ten to one reduction of the rate of change of output with respect to temperature.

Claims

1. A differential pressure unit comprising:

a rigid body having first and sEcond annular surfaces, said body having a centrally disposed hole therethrough located about said axis;

first and second circular and generally planar stiff diaphragms but more flexible than said body, said first and second diaphragms having annular portions fixed relative to said body first and second annular surfaces, respectively, said first and second diaphragms having central portions of first and second diameters, respectively, said diaphragm central portions being spaced apart a first predetermined distance when said diaphragms are unstressed;

a post rigid relative to said diaphragms and movable axially in said hole and having first and second opposite ends rigidly fixed relative to the central portions of said first and second diaphragms, respectively, to keep said diaphragm central portions spaced apart a constant second predetermined distance independent of any deflection of either one of said diaphragms, said first and second predetermined distances being different from each other;

input means to supply first and second fluids under pressure outside said body to one side of said first and second diaphragms, respectively, the other sides of said diaphragms facing each other; and

output means connected between said post and said body for producing an output in accordance with the difference between the pressures of said first and second fluids, respectively.

2. The invention as defined in claim 1, wherein utilization means are connected from the output of said output means.

3. The invention as defined in claim 2, wherein said utilization means includes a milliammeter calibrated in gallons per minute.

4. The invention as defined in claim 2, wherein said second predetermined distance exceeds said first predetermined distance by between about 0.015 inch to 0.060 inch.

5. The invention as defined in claim 3, wherein said post has a length such that the difference between said predetermined distances is sufficient to cause the rate of change of the output of said output means with respect to temperature to be less than it would be if said predetermined distances were the same.

6. The invention as defined in claim 5, wherein said second predetermined distance is greater than said first predetermined distance.

7. The invention as defined in claim 1, wherein said post has a length such that the difference between said predetermined distances is sufficient to cause the rate of change of the output of said output means with respect to temperature to be less than it would be if said predetermined distances were the same.

8. The invention as defined in claim 1, wherein said first predetermined distance is larger than said second predetermined distance.

9. The invention as defined in claim 1, wherein said second predetermined distance is larger than said first predetermined distance.

10. The invention as defined in claim 1, wherein said body first annular surface has a predetermined inside diameter, said first predetermined distance being larger than said second predetermined distance by an amount between about 1.0 to 4.0 percent of said predetermined inside diameter when the difference between the pressures of any fluids on said diaphragms is equal to zero.

11. The invention as defined in claim 1, wherein said second predetermined distance exceeds said first predetermined distance by between about 0.015 to 0.060 inch.

12. A differential pressure unit comprising:

a rigid body having first and second annular surfaces in parallel planes spaced apart a first predetermined distance, said annular surfaces being concentric about the same axis, said body having a centrally disposed hole therethrough located about said axis;

first and second circular and generally planar stiff diaphragms but more flexible than said body, said first and second diaphragms having annular portions fixed relative to said body first and second annular surfaces, respectively, concentrically about said axis, said first and second diaphragms having cEntral portions of first and second diameters, respectively;

a post rigid relative to said diaphragms and movable axially in said hole and having first and second opposite ends rigidly fixed relative to the central portions of said first and second diaphragms, respectively, to keep said diaphragm central portions spaced apart a constant second predetermined distance independent of any deflection of either one of said diaphragms, said first and second predetermined distances being different from each other;

input means to supply first and second fluids under pressure outside said body to one side of said first and second diaphragms, respectively, the other sides of said diaphragms facing each other; and

output means connected between said post and said body for producing an output in accordance with the difference between the pressures of said first and second fluids, respectively, utilization means being connected from the output of said output means, said utilization means including a milliammeter calibrated in gallons per minute, said post having a length such that the difference between said predetermined distances is sufficient to cause the rate of change of the output of said output means with respect to temperature to be less than it would be if said predetermined distances were the same, said body first annular surface having a predetermined inside diameter, said first predetermined distance being larger than said second predetermined distance by an amount between about 1.0 to 4.0 percent of said predetermined inside diameter when the difference between the pressures of any fluids on said diaphragms is equal to zero.

13. The invention as defined in claim 12, wherein the interior of said body is filled with a thermally expansible liquid.

14. The invention as defined in claim 13, wherein said body annular surfaces have the same respective inner and outer diameters, said diaphragms having the same size and shape, and being made out of the same material processed in the same way.

15. A differential pressure unit comprising:

an annular central body having a hole therethrough and having opposite annular surfaces;

first and second diaphragms fixed around said body surfaces, respectively, each of said diaphragms having a central portion, said diaphragm central portions being spaced apart a first predetermined distance when said diaphragms are unstressed; and

a post having its opposite ends connected to respective central portions of said diaphragms to hold said diaphragm central portions a constant second predetermined distance apart, said post extending through said body hole, one of said predetermined distances being larger than the other.

16. A differential pressure unit comprising:

a rigid body having first and second annular surfaces in parallel planes spaced apart a first predetermined distance, said annular surfaces being concentric about the same axis, said body having a centrally disposed hole therethrough located about said axis;

first and second circular and generally planar stiff diaphragms but more flexible than said body, said first and second diaphragms having annular portions fixed relative to said body first and second annular surfaces, respectively, concentrically about said axis, said first and second diaphragms having central portions of first and second diameters, respectively;

a post rigid relative to said diaphragms and movable axially in said hole and having first and second opposite ends regidly fixed relative to the central portions of said first and second diaphragms, respectively, to keep said diaphragm central portions spaced apart a constant second predetermined distance independent of any deflection of either one of said diaphragms, said first and second predetermined distances being different from each other;

input means to supply first and second fluids under pressure outside said body to one side of said first and second diaphragms, respectively, the other sides of said diaphragms facing each other; and

output means connecteD between said post and said body for producing an output in accordance with the difference between the pressures of said first and second fluids, respectively, utilization means being connected from the output of said output means, said utilization means including a milliammeter calibrated in gallons per minute, said post having a length such that the difference between said predetermined distances is sufficient to cause the rate of change of the output of said output means with respect to temperature to be less than it would if said predetermined distances were the same, said second predetermined distance exceeding said first predetermined distance by between about 0.015 inch to 0.060 inch.

17. A differential pressure unit comprising:

a rigid body having first and second annular surfaces, said body having a centrally disposed hole therethrough located about said axis;

first and second circular and generally planar stiff diaphragms but more flexible than said body, said first and second diaphragms having annular portions fixed relative to said body first and second annular surfaces, respectively, said first and second diaphragms having central portions of first and second diameters, respectively, said diaphragm central portions being spaced apart a first predetermined distance when said diaphragms are unstressed;

a post rigid relative to said diaphragms and movable axially in said hole and having first and second opposite ends rigidly fixed relative to the central portions of said first and second diaphragms, respectively, to keep said diaphragm central portions spaced apart a constant second predetermined distance independent of any deflection of either one of said diaphragms, said first and second predetermined distances being different from each other;

input means to supply first and second fluids under pressure outside said body to one side of said first and second diaphragms, respectively, the other sides of said diaphragms facing each other; and

output means connected between said post and said body for producing an output in accordance with the difference between the pressures of said first and second fluids, respectively, utilization means being connected from the output of said output means, said utilization means including a milliammeter calibrated in gallons per minute, said post having a length such that the difference between said predetermined distances is sufficient to cause the rate of change of the output of said output means with respect to temperature to be less than it would be if said predetermined distances were the same, said second predetermined distance being greater than said first predetermined distance, said first diaphragm having a modulus of elasticity different from that of said second diaphragm.