Method and apparatus for pressure measurement using magnetic property

• US 8,327,713 B2
• Filed: 12/03/2008
• Issued: 12/11/2012
• Est. Priority Date: 12/03/2008
• Status: Active Grant

• Current Assignee: Rosemount Incorporated (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Willcox, Charles R.
• Primary Examiner(s): Caputo, Lisa
• Assistant Examiner(s): JENKINS, JERMAINE L
• Application Number:
  US12/327,057
• Publication Number:
  US 20100132473A1
• Time in Patent Office: 1,469 Days
• Field of Search: None
• US Class Current: 73/722
• CPC Class Codes: G01L 13/06 using electric or magnetic pressure-sensitive elements
• CPC Class Codes: G01L 15/00 Devices or apparatus for measuring two or more fluid pressure values simultaneously
• CPC Class Codes: G01L 9/0029 using variations in inductance
• CPC Class Codes: G01L 9/10 by making use of variations in inductance , i.e. electric circuits therefor
• CPC Class Codes: G01L 9/16 by making use of variations in the magnetic properties of material resulting from the application of stress

Abstract

A pressure sensor includes a sensor body which is arranged to couple to a process pressure. The sensor body has a magnetic property which changes as a function of pressure applied by a process fluid. A sensor is coupled to the sensor body and is configured to measure pressure of fluid in the sensor body as a function of a change of magnetic property of the sensor body.

Claims

1. A pressure sensor, comprising:

a sensor body having a magnetic property comprising magnetostriction or permeability of the sensor body which changes as a function of an applied pressure of a process fluid;

a pressure coupling adapted to couple the sensor body to a process fluid; and

circuitry configured to measure the magnetic property of the sensor body and provide an output indicative of the pressure as a function of the magnetic property.

2. The apparatus of claim 1 wherein the circuitry is configured to resonate as a function of the magnetic property.

3. The apparatus of claim 1 wherein the circuitry includes a drive coil which is driven at a desired frequency and arranged to induce a magnetic flux in the sensor body, the circuitry further including a sense coil.

4. The apparatus of claim 1 wherein the sensor body is configured to resonate mechanically due to a magnetostrictive effect and at a frequency related to the applied process pressure.

5. The apparatus of claim 4 including a node stop arranged to reflect vibrations in the sensor body.

6. The apparatus of claim 1 including a bias magnet adjacent the sensor body configured to apply a bias magnetic field.

7. The apparatus of claim 1 wherein the circuitry is further configured to measure a temperature of the sensor body as a function of the magnetic property.

8. The apparatus of claim 1 wherein the magnetic property comprises magnetic permeability.

9. The apparatus of claim 8 wherein the changes in the magnetic permeability of the sensor body is a function of strain placed on the sensor body due to the applied process pressure.

10. The apparatus of claim 1 wherein the circuitry is configured to sense a B field resultant from an applied AC magnetic field.

11. The apparatus of claim 10 wherein the circuitry is further configured to oscillate at a frequency based on the magnetic permeability property.

12. The apparatus of claim 1 including a second sensor body having a magnetic property which changes as a function of an applied pressure and wherein the circuitry is configured to measure a differential pressure based upon changes in the magnetic properties of the sensor body and the second sensor body.

13. The apparatus of claim 1 wherein the sensor body comprises a fill tube.

14. The apparatus of claim 1 including an isolation diaphragm configured to isolate a fluid in the sensor body from the process fluid.

15. The apparatus of claim 1 including a differential pressure sensor coupled to the sensor body configured to measure a differential pressure.

16. A method of measuring a pressure of the process fluid, comprising:

receiving the pressure of the process fluid in a sensor body, the sensor body having a magnetic property comprising magnetostriction or permeability of the sensor body which changes as a function of the applied pressure;

sensing a change in the magnetic property of the sensor body; and

providing an output indicative of the pressure based upon a sensed change of the magnetic property.

17. The method of claim 16 including a resonating circuit which is a function of the magnetic property.

18. The method of claim 17 including providing a drive coil which is driven at a desired frequency and arranged to induce a magnetic flux in the fill tube body.

19. The method of claim 17 wherein the circuitry is further configured to oscillate at frequency based on the magnetic permeability.

20. The method of claim 16 wherein the sensor body is configured to resonate mechanically due to the magnetostrictive effect and as a function of the applied process pressure.

21. The method of claim 20 including providing a node stop arranged to reflect vibrations in the sensor body.

22. The method of claim 16 including providing a bias magnet adjacent the sensor body configured to apply a bias magnetic field.

23. The method of claim 16 including measuring a temperature of the sensor body as a function of the magnetic property.

24. The method of claim 16 wherein the magnetic property comprises magnetic permeability.

25. The method of claim 24 wherein the changes in the magnetic permeability of the sensor body is a function of strain placed on the sensor body due to the applied process pressure.

26. The method of claim 16 including sensing a B field resultant from an applied AC magnetic field.

27. The method of claim 16 including providing a second sensor body having a magnetic property which changes as a function of an applied pressure measuring a differential pressure based upon changes in the magnetic properties of the sensor body and the second sensor body.

28. The method of claim 16 wherein the sensor body comprises a fill tube.

29. The method of claim 16 including providing an isolation diaphragm configured to isolate a fluid in the sensor body from the process fluid.