Method and apparatus for pressure measurement using fill tube

• US 7,954,383 B2
• Filed: 12/03/2008
• Issued: 06/07/2011
• Est. Priority Date: 12/03/2008
• Status: Active Grant

• Current Assignee: Rosemount Incorporated (Emerson Electric Company)
• Original Assignee: Rosemount Incorporated (Emerson Electric Company)
• Inventors: Lu, Liangju, Hedtke, Robert C., Willcox, Charles R.
• Primary Examiner(s): Caputo; Lisa M
• Assistant Examiner(s): JENKINS, JERMAINE L
• Application Number:
  US12/327,050
• Publication Number:
  US 20100132472A1
• Time in Patent Office: 916 Days
• Field of Search: None
• US Class Current: 73/718
• CPC Class Codes: G01L 13/021 using deformable tubes
• 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 23/12 by changing capacitance or inductance
• CPC Class Codes: G01L 23/125 by changing capacitance
• CPC Class Codes: G01L 23/145 by magnetostrictive elements
• CPC Class Codes: G01L 9/0029 using variations in inductance
• CPC Class Codes: G01L 9/003 using variations in capacitance
• 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 fill tube which is arranged to couple to a process pressure. A sensor is coupled to the fill tube and is configured to measure pressure of fluid in the fill tube as a function of a change of a physical property of the fill tube. Circuitry is provided to measure pressure using the pressure sensor, and to measure pressure based upon the change of the physical property of the fill tube.

Claims

1. A pressure sensor, comprising:

a differential pressure sensor having a first port, a second port and an output related to a differential pressure between the first and second ports;

a first fill tube arranged to couple the first port to a first process pressure;

a second fill tube arranged to couple the second port to a second process pressure; and

a fill tube physical property sensor coupled to the first tube configured to measure a pressure of fill fluid in the first tube as a function of a change of a physical property of the first fill tube.

2. The apparatus of claim 1 wherein the physical property comprises deformation of the first fill tube.

3. The apparatus of claim 1 wherein the physical property comprises stiffness of the first fill tube.

4. The apparatus of claim 1 wherein the fill tube physical property sensor measures a magnetic property of the first fill tube.

5. The apparatus of claim 4 wherein the fill tube physical property sensor is arranged to measure oscillations in the first fill tube.

6. The apparatus of claim 5 wherein the frequency of oscillations is related to the line pressure.

7. The apparatus of claim 4 including circuitry configured to resonate as a function of the magnetic property.

8. The apparatus of claim 7 including a node stop arranged to reflect vibrations in the sensor body.

9. The apparatus of claim 4 including a drive coil which is driven at a desired frequency and arranged to induce a magnetic flux in the sensor body, and a sense coil.

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

11. The apparatus of claim 4 including a bias magnet adjacent the fill tube configured to apply a bias magnetic field.

12. The apparatus of claim 4 wherein the circuitry is further configured to measure a temperature of the fill tube as a function of the magnetic property.

13. The apparatus of claim 4 wherein the magnetic property comprises magnetic permeability.

14. The apparatus of claim 13 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.

15. The apparatus of claim 4 wherein the circuitry is configured to sense a B field resultant from an applied AC magnetic field.

16. The apparatus of claim 15 wherein the circuitry is further configured to oscillate at a frequency based on the magnetic permeability property.

17. The apparatus of claim 1 including a pressure sensor coupled to the second fill tube.

18. The apparatus of claim 17 including measurement circuitry arranged to measure a differential pressure based upon an output from the fill tube physical property sensor and the second pressure sensor.

19. The apparatus of claim 1 wherein the first fill tube is configured as a Bourdon tube.

20. The apparatus of claim 1 wherein the fill tube physical property sensor comprises a strain gauge coupled to the first fill tube.

21. The apparatus of claim 1 wherein the fill tube physical property sensor comprising a capacitor arranged to have a capacitance with the first fill tube which changes as a function of line pressure.

22. The apparatus of claim 1 wherein the fill tube physical property sensor is further configured to measure temperature as a function of a change of the physical property of the first fill tube.

23. The apparatus of claim 1 wherein the fill tube physical property sensor comprises a quartz element.

24. A method for measuring pressures in an industrial process, comprising:

coupling a first fill tube to the process to measure a first process pressure;

coupling a second fill tube to the process to measure a second process pressure;

measuring a differential pressure using a differential pressure sensor coupled to the first and second fill tubes; and

measuring a line pressure of the process fluid based upon a change in a physical property of the first fill tube.

25. The method of claim 24 wherein the physical property comprises deformation of the first fill tube.

26. The method of claim 24 wherein the physical property comprises stiffness of the first fill tube.

27. The method of claim 24 wherein measuring line pressure comprising measuring a magnetic property of the first fill tube.

28. The method of claim 27 including providing a drive coil which is driven at a desired frequency and arranged to induce a magnetic flux in the fill tube body.

29. The method of claim 27 wherein the fill tube is configured to resonate mechanically due to the magnetostrictive effect and as a function of the applied process pressure.

30. The method of claim 29 wherein measuring line pressure comprises measuring oscillations in the first fill tube.

31. The method of claim 30 including providing a node stop arranged to reflect vibrations in the sensor body.