Differential pressure sensor with line pressure measurement

• US 8,234,927 B2
• Filed: 06/08/2010
• Issued: 08/07/2012
• Est. Priority Date: 06/08/2010
• Status: Active Grant

• Current Assignee: Rosemount Incorporated (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Schulte, John P., Tyson, David G., Klosinski, Andrew J.
• Primary Examiner(s): ALLEN, ANDRE J
• Application Number:
  US12/796,023
• Publication Number:
  US 20110296926A1
• Time in Patent Office: 791 Days
• Field of Search: 7700-756
• US Class Current: 73/718
• CPC Class Codes: G01L 13/025 using diaphragms
• CPC Class Codes: G01L 15/00 Devices or apparatus for measuring two or more fluid pressure values simultaneously
• CPC Class Codes: G01L 9/0072 using variations in capacitance

Abstract

A pressure sensor assembly for sensing a pressure of a process fluid includes a sensor body having a cavity formed therein and first and second openings to the cavity configured to apply first and second pressures. A diaphragm in the cavity separates the first opening from the second opening and is configured to deflect in response to a differential pressure between the first pressure and the second pressure. A capacitance based deformation sensor is provided and configured to sense deformation of the sensor body in response to a line pressure applied to the sensor body.

Claims

1. A pressure sensor assembly for sensing a pressure of a process fluid, comprising:

a sensor body having a cavity formed therein and first and second openings to the cavity configured to apply first and second pressures;

a diaphragm in the cavity separating the first opening from the second opening responsive to a differential pressure;

a first electrode mounted outside of the sensor body arranged to form a first capacitance with the sensor body, wherein the first capacitance varies in response to line pressure of the process fluid due to deformation of the sensor body; and

measurement circuitry coupled to the electrode arranged to measure the line pressure based upon the first capacitance.

2. The apparatus of claim 1 including a second electrode mounted outside the sensor body and wherein a second capacitance is formed between the second electrode mounted and the sensor body.

3. The apparatus of claim 1 including a second electrode mounted outside of the sensor body and wherein the measurement circuitry has an output related to line pressure based upon a first capacitance measured using the first electrode and a second capacitance using the second electrode.

4. The apparatus of claim 1 including an insulating plate configured to carry the electrode.

5. The apparatus of claim 4 wherein the insulating plate is mounted to the sensor body.

6. The apparatus of claim 5 wherein the insulating plate is mounted to a support which mounts to the sensor body.

7. The apparatus of claim 4 wherein the insulating plate is mounted to a capillary tube coupled to the sensor body.

8. The apparatus of claim 1 including a differential pressure sensor associated with the diaphragm having an output related to differential pressure based upon movement of the diaphragm within the cavity.

9. The apparatus of claim 8 wherein the output is based upon a variable capacitance which is formed by the diaphragm.

10. The apparatus of claim 1 wherein the line pressure measurement is compensated based upon temperature.

11. A process transmitter for measuring pressure of the process fluid including the pressure sensor of claim 1.

12. A method for measuring differential pressure and line pressure of a process fluid comprising:

mounting a deflectable diaphragm in a cavity in a sensor body;

applying a first pressure of the process fluid to one side of the deflectable diaphragm in the cavity;

applying a second pressure of the process fluid to another side of the deflectable diaphragm in the cavity;

determining differential pressure based upon deflection of the deflectable diaphragm;

forming a first capacitance with a first electrode positioned outside of the sensor body, the first capacitance formed between the electrode and the sensor body and having a capacitance which changes based upon deformation of the sensor body due to a line pressure of the process fluid; and

determining a line pressure of the process fluid based upon changes in the capacitance.

13. The method of claim 12 including providing a second electrode mounted outside of the sensor body and wherein the line pressure is determined based upon a first capacitance measured using the first electrode and a second capacitance using the second electrode.

14. The method of claim 12 including determining differential pressure by measuring upon movement of the diaphragm within the cavity based upon a diaphragm capacitance.

15. The method of claim 12 including compensating the line pressure measurement based upon temperature.