Vibratory transducer

• US 7,017,424 B2
• Filed: 05/08/2003
• Issued: 03/28/2006
• Est. Priority Date: 05/08/2002
• Status: Active Grant

• Current Assignee: Endress+Hauser Flowtec AG (Endress+Hauser AG)
• Original Assignee: Endress+Hauser Flowtec AG (Endress+Hauser AG)
• Inventors: Rieder, Alfred, Drahm, Wolfgang
• Primary Examiner(s): CYGAN, MICHAEL T
• Application Number:
  US10/431,573
• Publication Number:
  US 20030233868A1
• Time in Patent Office: 1,055 Days
• Field of Search: 738/613.51, 738/613.52, 738/613.54, 738/613.55, 738/613.57, 73/544.1
• US Class Current: 73/861.355
• CPC Class Codes: G01F 1/8409 constructional details
• CPC Class Codes: G01F 1/8413 means for influencing the flowmeter's motional or vibrational behaviour, e.g., conduit support or fixing means, or conduit attachments
• CPC Class Codes: G01F 1/8418 motion or vibration balancing means
• CPC Class Codes: G01F 1/8422 exciters
• CPC Class Codes: G01F 1/8427 detectors
• CPC Class Codes: G01F 1/849 having straight measuring conduits
• CPC Class Codes: G01N 11/167 Sample holder oscillates, e.g. rotating crucible
• CPC Class Codes: G01N 2203/0025 Shearing
• CPC Class Codes: G01N 2203/0094 Visco-elasticity
• CPC Class Codes: G01N 2203/0676 Force, weight, load, energy, speed or acceleration
• CPC Class Codes: G01N 9/002 using variation of the resonant frequency of an element vibrating in contact with the material submitted to analysis G01N9/34 takes precedence

Abstract

To conduct a fluid, the transducer has a flow tube which in operation is vibrated by an excitation assembly and whose inlet-side and outlet-side vibrations are sensed by means of a sensor arrangement. To produce shear forces in the fluid, the flow tube is at least intermittently excited into torsional vibrations about a longitudinal flow-tube axis. The transducer further comprises a torsional vibration absorber which is fixed to the flow tube and which in operation covibrates with the torsionally vibrating flow tube, thus producing reactive torques which at least partially balance torques developed in the vibrating flow tube. One of the advantages of the transducer disclosed is that it is dynamically balanced to a large extent even in the face of variations in fluid density or viscosity.

Claims

1. A vibratory transducer for a fluid flowing in a pipe, the transducer comprising:

a flow tube for conducting the fluid, said flow tube vibrates in operation and said flow tube communicating with the pipe via an inlet tube section, ending in an inlet end of the flow tube, and via an outlet tube section, ending in an outlet end of the flow tube;

an excitation assembly acting on the flow tube for vibrating the flow tube,

a sensor arrangement for sensing vibrations of the flow tube; and

a torsional vibration absorber which is fixed to the flow tube

wherein in operation the flow tube performs, at least intermittently, torsional vibrations about a longitudinal flow-tube axis at an instantaneous torsional frequency, f.sub.excT; and

wherein in operation the torsional vibration absorber vibrates, at least partially, out of phase with the torsionally vibrating flow tube.

2. A transducer as set forth in claim 1 wherein the vibrating torsional vibration absorber is driven exclusively by the vibrating flow tube.

3. A transducer as set forth in claim 1 wherein the torsional vibration absorber is fixed to the flow tube on the inlet and outlet sides.

4. A transducer as set forth in claim 1 wherein the torsional vibration absorber has a torsional natural frequency greater than 0.8 times the vibration frequency of the flow tube.

5. A transducer as set forth in claim 1 wherein the torsional vibration absorber has a torsional natural frequency less than 1.2 times the vibration frequency of the flow tube.

6. A transducer as set forth in claim 1 wherein the torsional vibration absorber is formed by an inlet-side absorber subunit and an outlet-side absorber subunit.

7. A transducer as set forth in claim 6, wherein respective torsional resonance frequencies, f61 , f62, of the absorber subunits are essentially equal to the torsional frequency at which the flow tube is excited in operation.

8. A transducer as set forth in claim 1, said transducer further comprising a transducer case coupled to the flow tube on the inlet and outlet sides.

9. A transducer as set forth in claim 1 wherein additional masses are fixed to the flow tube.

10. A transducer as set forth in claim 1, comprising an antivibrator fixed to the flow tube at the inlet and outlet ends, particularly an antivibrator coaxial with the flow tube.

11. A transducer as set forth in claim 10 wherein grooves are formed in the antivibrator.

12. A transducer as set forth in claim 10 wherein a torsional resonance frequency of the antivibrator is chosen to be essentially equal to the torsional frequency at which the flow tube is excited in operation.

13. The vibratory transducer as claimed in claim 10 wherein the excitation assembly comprises at least one excitation coil and at least one armature, said excitation coil being fixed to an outside of the flow tube and said armature being fixed to a lever connected with said antivibrator.

14. The vibratory transducer as claimed in claim 13 wherein the excitation assembly acts differentially on the flow tube and the antivibrator via said excitation coil and said armature.

15. The vibratory transducer as claimed in claim 10 wherein the excitation assembly comprises at least one excitation coil and at least one armature, said excitation coil being fixed to a lever connected with said antivibrator and said armature being fixed to an outside of the flow tube.

16. The vibratory transducer as claimed in claim 15 wherein the excitation assembly acts differentially on the flow tube and the antivibrator via said excitation coil and said armature.

17. The vibratory transducer as claimed in claim 10 wherein the sensor arrangement senses also vibrations of said antivibrator.

18. The vibratory transducer as claimed in claim 17 wherein the sensor arrangement is operable to differentially sense vibrations of said flow tube and vibrations of said antivibrator.

19. The vibratory transducer as claimed in claim 1 wherein the sensor arrangement senses the motions of flow tube on an inlet side and an outlet side thereof.

20. The vibratory transducer as claimed in claim 19 wherein the sensor arrangement comprising a first sensor and a second sensor for converting motions of flow tube into corresponding first and second sensor signals, respectively.

21. The vibratory transducer as claimed in claim 20 wherein each of said first and second sensors is selected from a group consisting of electrodynamic velocity sensors, electrodynamic displacement sensors, acceleration sensors, resistive strain gages, piezoelectric strain gages and optoelectronic sensors.

22. The vibratory transducer as claimed in claim 10 wherein the antivibrator is in form of a tube.

23. The vibratory transducer as claimed in claim 10 wherein the torsional vibration absorber includes first and second rotators coupled to said flow tube via first and second torsion-spring bodies, respectively.

24. The vibratory transducer as claimed in claim 23 wherein the first rotator is fixed to an inlet end of said flow tube via said first torsion-spring body and wherein the second rotator is fixed to an outlet end of said flow tube via said second torsion-spring body.

25. The vibratory transducer as claimed in claim 1 wherein in operation the flow tube performs vibrations in a flexural mode about said longitudinal flow-tube axis.

26. The vibratory transducer as claimed in claim 25 wherein the sensor arrangement comprises a sensor coil being operable to sense both the torsional vibrations and the flexural vibrations.

27. A vibratory transducer as claimed in claim 25 wherein in operation the flow tube performs said torsional vibrations and said vibrations in the flexural mode simultaneously.

28. The vibratory transducer as claimed in claim 27 wherein the sensor arrangement comprises a sensor coil being operable to sense both the torsional vibrations and the flexural vibrations simultaneously.

29. The vibratory transducer as claimed in claim 10 wherein the inlet tube section and the outlet tube section are aligned with each other.

30. The vibratory transducer as claimed in claim 10 wherein the inlet tube section and the outlet tube section are aligned with each other and with said longitudinal flow-tube axis.

31. A meter for measuring a viscosity of a fluid flowing in a pipe, said meter comprising a vibratory transducer as set forth in claim 1.

32. A vibratory transducer for a fluid flowing in a pipe, the transducer comprising:

an essentially straight flow tube flow tube for conducting the fluid, said flow tube being operable to vibrate and said flow tube communicating with the pipe via an inlet tube section, which ends in an inlet end of the flow tube, and via an outlet tube section, which ends in an outlet end of the flow tube;

a torsional vibration absorber fixed to said flow tube, said torsional vibration absorber including first and second rotators coupled to said flow tube via first and second torsion-spring bodies, respectively, and an antivibrator extending essentially parallel to said flow tube;

an excitation assembly acting on said flow tube and said antivibrator for vibrating the flow tube; and

a sensor arrangement for sensing vibrations of the flow tube;

wherein in operation the flow tube performs, at least intermittently, torsional vibrations about an imaginary longitudinal flow-tube axis; and

wherein in operation the torsional vibration absorber vibrates, at least partially, out of phase with the torsionally vibrating flow tube.

33. The vibratory transducer as claimed in claim 32 wherein the inlet tube section and the outlet tube section are aligned with each other.

34. The vibratory transducer as claimed in claim 32 wherein the inlet tube section and the outlet tube section are aligned with each other and with said longitudinal flow-tube axis.

35. The vibratory transducer as claimed in claim 32 wherein the excitation assembly comprises at least one excitation coil and at least one armature, said excitation coil being fixed to an outside of the flow tube and said armature being fixed to a lever connected with said antivibrator.

36. The vibratory transducer as claimed in claim 35 wherein the excitation assembly acts differentially on the flow tube and the antivibrator via said excitation coil and said armature.

37. The vibratory transducer as claimed in claim 32 wherein the excitation assembly comprises at least one excitation coil and at least one armature, said excitation coil being fixed to a lever connected with said antivibrator and said armature being fixed to an outside of the flow tube.

38. The vibratory transducer as claimed in claim 37 wherein the excitation assembly acts differentially on the flow tube and the antivibrator via said excitation coil and said armature.

39. The vibratory transducer as claimed in claim 32 wherein the sensor arrangement also senses vibrations of said torsional vibration absorber.

40. The vibratory transducer as claimed in claim 39 wherein the sensor arrangement is operable to differentially sense vibrations of said flow tube and vibrations of said antivibrator.

41. The vibratory transducer as claimed in claim 32 wherein the sensor arrangement senses the motions of flow tube on an inlet side and an outlet side thereof.

42. The vibratory transducer as claimed in claim 41 wherein the sensor arrangement comprising a first sensor and a second sensor for converting motions of flow tube into corresponding first and second sensor signals, respectively.

43. The vibratory transducer as claimed in claim 42 wherein each of said first and second sensors is selected from a group consisting of electrodynamic velocity sensors, electrodynamic displacement sensors, acceleration sensors, resistive strain gages, piezoelectric strain gages and optoelectronic sensors.

44. The vibratory transducer as claimed in claim 32 wherein the antivibrator is fixed to the flow tube on the inlet and outlet sides.

45. The vibratory transducer as claimed in claim 32 wherein the first rotator is fixed to an inlet end of said flow tube via said first torsion-spring body and wherein the second rotator is fixed to an outlet end of said flow tube via said second torsion-spring body.

46. The vibratory transducer as claimed in claim 32 wherein the antivibrator is in form of a tube.

47. The transducer as set forth in claim 46, comprising an antivibrator fixed to the flow tube at the inlet and outlet ends, particularly an antivibrator coaxial with the flow tube.

48. The vibratory transducer as claimed in claim 32 wherein in operation the flow tube performs vibrations in a flexural mode about said longitudinal flow-tube axis.

49. The vibratory transducer as claimed in claim 48 wherein the sensor arrangement is operable to sense both the torsional vibrations and the flexural vibrations.

50. The vibratory transducer as claimed in claim 48 wherein in operation the flow tube performs said torsional vibrations and said vibrations in the flexural mode simultaneously.

51. The vibratory transducer as claimed in claim 50 wherein the sensor arrangement is operable to sense both torsional vibrations and flexural vibrations simultaneously.

52. The vibratory transducer as claimed in claim 32 wherein in operation the flow tube vibrates at an instantaneous torsional frequency and wherein the torsional vibration absorber has a torsional natural frequency greater than 0.8 times the vibration frequency of the flow tube.

53. The vibratory transducer as claimed in claim 32 wherein in operation the flow tube vibrates at an instantaneous torsional frequency and wherein the torsional vibration absorber has a torsional natural frequency less than 1.2 times the vibration frequency of the flow tube.

54. The vibratory transducer as claimed in claim 32 wherein in operation the flow tube vibrates at an instantaneous torsional frequency and wherein a torsional resonance frequency of the antivibrator is chosen to be essentially equal to the torsional frequency at which the flow tube is excited in operation.

55. The vibratory transducer as claimed in claim 32, said transducer further comprising a transducer case coupled to the flow tube on the inlet and outlet sides.

56. A meter for measuring a viscosity of a fluid flowing in a pipe, said meter comprising a vibratory transducer as set forth in claim 32.