METHOD AND APPARATUS FOR PRESSURE MEASUREMENT USING QUARTZ CRYSTAL

• US 20100132471A1
• Filed: 12/03/2008
• Published: 06/03/2010
• 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.
• Granted Patent: US 7,870,791 B2
• Time in Patent Office: Days
• US Class Current: 73/702
• CPC Class Codes: G01F 1/363 with electrical or electro-mechanical indication G01F1/37 and G01F1/38 take precedence
• CPC Class Codes: G01F 1/383 with electrical or electro-mechanical indication
• CPC Class Codes: G01L 13/02 using elastically-deformable members or pistons as sensing elements
• CPC Class Codes: G01L 9/0022 of a piezoelectric element

Abstract

A pressure sensor includes a sensor which is arranged to couple to a process pressure. A quartz crystal is coupled to the sensor and is configured to measure pressure of fluid in the sensor body. An output from the quartz crystal is related to pressure applied to the sensor body by the process pressure.

Claims

1. A pressure sensor, comprising:

a sensor body configured to receive a pressure of a process fluid; and

a quartz crystal mounted to the sensor body wherein the quartz crystal has a resonate frequency which is related to the pressure received by the sensor body; and

circuitry configured to measure the resonate frequency of the quartz crystal and responsively provide an output indicative of the pressure of the process fluid as a function of the resonate frequency of the quartz crystal.

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

3. The apparatus of claim 1 wherein the sensor body has a length and the quartz crystal is configured to sense stress in an axial direction.

4. The apparatus of claim 1 wherein the quartz crystal is configured to sense stress along a beam axis.

5. The apparatus of claim 4 wherein the beam axis is at an angle with respect to a longitudinal axis of the sensor body.

6. The apparatus of claim 1 wherein the quartz crystal comprises an AT cut crystal.

7. The apparatus of claim 1 wherein the quartz crystal comprises an elongate crystal having ends mounted to the sensor body.

8. The apparatus of claim 1 wherein the quartz crystal includes a vibrating beam section.

9. The apparatus of claim 1 wherein the sensor body comprises an elongate tube having a slight curvature.

10. The apparatus of claim 1 wherein the quartz crystal comprises a quartz tuning fork configuration.

11. The apparatus of claim 10 wherein the quartz crystal has a base which is mounted to the sensor body.

12. The apparatus of claim 10 wherein a resonant frequency of the quartz crystal is related to density of fluid within the sensor body.

13. The apparatus of claim 10 wherein a resonant frequency of the quartz crystal is related to an energy leak of acoustic energy applied to the sensor body from the quartz crystal.

14. The apparatus of claim 1 wherein the sensor body couples to a differential pressure sensor.

15. The apparatus of claim 13 wherein the sensor body comprises a tube coupled across a restrictive element in a pipe, the apparatus further including a second quartz crystal mounted to the sensor body, wherein the differential pressure across the restriction is related to a differential pressure.

16. The apparatus of claim 15 wherein the differential pressure is related to flow through the process piping.

17. The apparatus of claim 1 wherein the sensor body couples to a second pressure sensor.

18. The apparatus of claim 17 including a second sensor body coupled to the second pressure sensor and wherein the second pressure sensor is configured to measure a differential pressure related to a pressure of a fluid within the sensor body and the second sensor body.

19. A method of measuring a pressure of a process fluid comprising,

receiving the pressure of the process fluid in a sensor body;

causing a quartz crystal mounted to the sensor body to resonate at a frequency; and

measuring a resonant frequency change of the quartz crystal and providing an output related to the pressure of the process fluid based upon the resonant frequency change.

20. The method of claim 19 including providing an isolation diaphragm to isolate a fill fluid carried in the sensor body from the process fluid.

21. The method of claim 19 wherein the sensor body has a length and is configured to experience stress in an axial direction in response to pressure.

22. The method of claim 19 wherein the quartz crystal is configured to sense stress along abeam axis of the sensor body.

23. The method of claim 22 wherein the beam axis is at an angle with respect to a longitudinal axis of the sensor body.

24. The method of claim 19 wherein the quartz crystal comprises an AT cut crystal.

25. The method of claim 19 wherein the quartz crystal comprises an elongate crystal having ends mounted to the sensor body.

26. The method of claim 19 wherein the quartz crystal includes a vibrating beam section.

27. The method of claim 19 wherein the quartz crystal comprises a quartz tuning fork configuration.

28. The method of claim 27 wherein the quartz crystal has a base which is mounted to the sensor body.

29. The method of claim 27 wherein a resonant frequency of the quartz crystal is related to density of fluid within the sensor body.

30. The method of claim 27 wherein a resonant frequency of the quartz crystal is related to an energy leak of acoustic energy applied to the sensor body from the quartz crystal.

31. The method of claim 19 wherein the sensor body comprises a tube coupled across a restrictive element in a pipe and the method includes providing a second quartz crystal mounted to the sensor body, wherein a differential pressure across the restriction is related to a differential pressure.