Coriolis mass flowmeter

• US 20030131669A1
• Filed: 12/16/2002
• Published: 07/17/2003
• Est. Priority Date: 12/17/2001
• Status: Active Grant

• Current Assignee: Yokogawa Electric Corporation
• Original Assignee: Yokogawa Electric Corporation
• Inventors: Osawa, Norikazu
• Granted Patent: US 6,782,764 B2
• Time in Patent Office: Days
• 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 1/8472 having curved measuring conduits, i.e. whereby the measuring conduits' curved center line lies within a plane G01F1/8481 takes precedence
• CPC Class Codes: G01F 1/8477 with multiple measuring conduits

Abstract

A Coriolis mass flowmeter has a vibration tube through which a fluid to be measured flows so that the flow of the fluid in cooperation with angular vibration of the vibration tube generates Coriolis force which causes vibratory deformation of the vibration tube. The vibration tube has a curved configuration which is point-symmetry with respect to the median point between an upstream fixed end and a downstream fixed end of the vibration tube and which has three inflection points, and performs, while maintaining the curved configuration, simple harmonic oscillation such that each point on the vibration tube oscillates on an arc of a predetermined radius from a reference axis which is a straight line interconnecting the upstream fixed end and the downstream fixed end of the vibration tube.

Claims

1. A Coriolis mass flowmeter, comprising:

a vibration tube through which a fluid to be measured flows so that the flow of the fluid in cooperation with angular vibration of said vibration tube generates Coriolis force which causes vibratory deformation of said vibration tube;

wherein said vibration tube has a curved configuration which is point-symmetry with respect to the median point between an upstream fixed end and a downstream fixed end of said vibration tube and which has three inflection points, and performs, while maintaining the point-symmetrical curved configuration, simple harmonic oscillation such that each point on said vibration tube oscillates on an arc of a predetermined radius from a reference axis which is a straight line interconnecting said upstream fixed end and said downstream fixed end of said vibration tube.

2. A Coriolis mass flowmeter according to claim 1, further comprising:

an upstream ocillator and a downstream ocillator which are provided on said vibration tube;

an upstream compensation vibrator extending along said reference axis, said upstream compensation vibrator having one end fixed to said upstream ocillator so as to receive from said upstream ocillator a torsional force which acts around said reference axis in the phase inverse to that of the torsional force acting on said vibration tube, the other end of said upstream compensation vibrator being fixed to a portion of said vibration tube near said upstream fixed end so that the torsional force of the inverse phase and the torsional force on said vibration tube cancel each other at the fixed other end of said upstream compensation vibrator; and

a downstream compensation vibrator extending along said reference axis, said downstream compensation vibrator having one end fixed to said downstream ocillator so as to receive from said downstream ocillator a torsional force which acts around said reference axis in the phase inverse to that of the torsional force acting on said vibration tube, the other end of said downstream compensation vibrator being fixed to a portion of said vibration tube near said downstream fixed end so that the torsional force of the inverse phase and the torsional force on said vibration tube cancel each other at the fixed other end of said downstream compensation vibrator.

3. A Coriolis mass flowmeter, comprising:

a vibration tube through which a fluid to be measured flows;

ocillators for ocillating said vibration tube to vibrate said vibration tube; and

vibration sensors for sensing deformative vibration of said vibration tube caused by Coriolis force generated through cooperation between the flow of said fluid and angular vibration of said vibration tube;

wherein said vibration tube has a curved configuration which is point-symmetry with respect to the median point between an upstream fixed end and a downstream fixed end of said vibration tube and which has three inflection points, and performs, while maintaining the point-symmetrical curved configuration, simple harmonic oscillation such that each point on said vibration tube oscillates on an arc of a predetermined radius from a reference axis which is a straight line interconnecting said upstream fixed end and said downstream fixed end of said vibration tube; and

wherein said ocillators and said vibration sensors are arranged on said vibration tube such that the locations and masses of said ocillators and said vibration sensors are point symmetry with respect to said median point, and such that the center of gravity is located on said median point.

5. A Coriolis mass flowmeter according to claim 3 or 4, wherein said vibration tube is gently curved with small curvatures so as to be small in size and so as to reduce pressure loss of the fluid flowing therethrough.

6. A Coriolis mass flowmeter according to claim 3 or 5, wherein the distance W of a point on said vibration tube where the curvature is greatest from said reference axis substantially falls within the range of:

±

0.01≦

W/L≦

±

0.1

where L indicates the overall length of said vibration tube.

4. A Coriolis mass flowmeter, comprising:

a vibration tube through which a fluid to be measured flows, said vibration tube having a curved configuration which is point-symmetry with respect to the median point between an upstream fixed end and a downstream fixed end of said vibration tube and which has three inflection points, said vibration tube performing, while maintaining the point-symmetrical curved configuration, simple harmonic oscillation such that each point on said vibration tube oscillates on an arc of a predetermined radius from a reference axis which is a straight line interconnecting said upstream fixed end and said downstream fixed end of said vibration tube;

ocillators for ocillating said vibration tube to vibrate said vibration tube, each of said ocillators having a magnet attached to said vibration tube and a coil disposed to oppose to said magnet;

vibration sensors for sensing deformative vibration of said vibration tube caused by Coriolis force generated through cooperation between the flow of said fluid and angular vibration of said vibration tube, each of said vibration sensors having a magnet attached to said vibration tube and a coil disposed to oppose said magnet; and

balancers attached to said vibration tube so as to cancel mass unbalance caused by vibration of said magnets;

wherein said magnets and said balancers are arranged on said vibration tube such that the locations and masses of said magnets and said balancers are point symmetry with respect to said median point, and such that the center of gravity is located on said median point.

7. A Coriolis mass flowmeter, comprising:

a vibration tube through which a fluid to be measured flows so that the flow of the fluid in cooperation with angular vibration of said vibration tube generates Coriolis force which causes vibratory deformation of said vibration tube

wherein said vibration tube includes;

a branching portion where the flow of said fluid branches into first and second channels;

a merging portion where said first and second channels merge in each other;

a first branch tube defining said first channel, said first branch tube having a curved configuration with three inflection points and point symmetry with respect to a first median point which is midst between a first upstream fixed end near said branching portion and leading to said first channel and a first downstream fixed end near said merging portion and leading from said first channel;

a second branch tube defining said second channel having one end connected to said branching portion and the other end connected to said merging portion, and having the same configuration as said first branch tube, said second branch tube extending in parallel with said first branch tube;

said Coriolis mass flowmeter further comprising;

ocillators fixed to said first and second branch tubes for ocillating said first and second branch tubes in such a manner that each point on said first branch tube performs simple harmonic oscillation on an arc of a predetermined radius from a first reference axis which is the straight line which interconnects said first upstream fixed end and said first downstream fixed end, while each point on said second branch tube performs simple harmonic oscillation on an arc of a predetermined radius from a second reference axis which is the straight line which interconnects a second upstream fixed end and a second downstream fixed end, and that said first and second branch tubes are in plane-symmetry with respect to a reference plane which is at an equal distance from a first plane containing said first branch tube and a second plane which is parallel to said first plane and contains said second branch tube; and

vibration sensors fixed to said first and second branch tubes, for sensing vibration of said first and second branch tubes.

8. A Coriolis mass flowmeter according to claim 7, wherein lead lines from said ocillators or from said vibration sensors are led externally of said mass flowmeter through the median points, through said upstream fixed ends, or through said downstream fixed ends.

9. A Coriolis mass flowmeter according to claim 8, further comprising:

a first balancer attached to said first branch tube and a second balancer attached to said second branch tube;

wherein said first balancer is provided such that the center of gravity of a system including said first branch tube, said ocillator or said vibration sensor attached to said first branch tube and said first balancer coincides with the median point of said first branch tube, and said second balancer is provided such that the center of gravity of a system including said second branch tube, said ocillator or said vibration sensor attached to said second branch tube and said second balancer coincides with the median point of said second branch tube.

10. A Coriolis mass flowmeter, comprising:

a vibration tube through which a fluid to be measured flows so that the flow of the fluid in cooperation with angular vibration of said vibration tube generates Coriolis force which causes vibratory deformation of said vibration tube;

wherein said vibration tube has a curved configuration which is point-symmetry with respect to the median point between an upstream fixed end and a downstream fixed end of said vibration tube and which has three inflection points, and performs, while maintaining the curved configuration, simple harmonic oscillation such that each point on said vibration tube oscillates on an arc of a predetermined radius from a reference axis which is a straight line interconnecting said upstream fixed end and said downstream fixed end of said vibration tube,

said Coriolis mass flowmeter further comprising an ocillator provided on said median point and arranged to apply to said vibration tube a torque about said reference axis or the central axis of said vibration tube.

11. A Coriolis mass flowmeter, comprising:

a vibration tube through which a fluid to be measured flows so that the flow of the fluid in cooperation with angular vibration of said vibration tube generates Coriolis force which causes vibratory deformation of said vibration tube;

ocillators provided on portions of said vibration tube near an upstream fixed end and near a downstream fixed end of said vibration tube, so as to apply to said vibration force a torque about the central axis of said vibration tube or about a reference axis which is a straight line interconnecting said upstream fixed end and said downstream fixed end of said vibration tube.

12. A Coriolis mass flowmeter according to claim 11, wherein said ocillators comprise at least one pair of ocillators, two ocillators of said pair being arranged along the outer peripheral surface of said vibration tube in symmetry with each other with respect to a plane containing the central axis of said vibration tube, said ocillators being secured to said vibration tube obliquely to said central axis so as to perform expansion and contraction obliquely to said central axis in opposite phases to each other, thereby applying torsional force to said vibration tube.

13. A Coriolis mass flowmeter, comprising:

a vibration tube through which a fluid to be measured flows so that the flow of the fluid in cooperation with angular vibration of said vibration tube generates Coriolis force which causes vibratory deformation of said vibration tube;

wherein said vibration tube has a curved configuration which is point-symmetry with respect to the median point between an upstream fixed end and a downstream fixed end of said vibration tube and which has three inflection points, and performs, while maintaining the curved configuration, simple harmonic oscillation such that each point on said vibration tube oscillates on an arc of a predetermined radius from a reference axis which is a straight line interconnecting said upstream fixed end and said downstream fixed end of said vibration tube;

said Coriolis mass flowmeter further comprising;

vibration sensors arranged to oppose each other across said vibration tube at a plane which is equally spaced from said upstream fixed end and said downstream fixed end of said vibration tube.

14. A Coriolis mass flowmeter according to claim 13, wherein said vibration sensors includes:

a first vibration sensor disposed on a straight line which contains said median point and which is perpendicular to a vibration tube plane containing the curve of said vibration tube, said first vibration sensor being sensitive only to the vibration component that is perpendicular to said vibration tube plane; and

a second vibration sensor disposed on a straight line which contains said median point and which is sensitive only to the vibration component that is parallel to said vibration tube plane and perpendicular to said reference axis.

15. A Coriolis mass flowmeter according to claim 13, wherein said vibration sensors are arranged on a straight line which contains said median point and which is perpendicular to a vibration tube plane containing the curve of said vibration tube, such that said vibration sensors are highly sensitive to the vibration component in the direction perpendicular to said vibration tube plane and has small sensitivity to the vibration component in the direction parallel to said vibration tube plane and perpendicular to said reference axis, thereby increasing the ratio of the amplitude of Coriolis vibration to the amplitude of the ocillated vibration.

16. A Coriolis mass flowmeter according to claim 13, wherein said vibration sensors are arranged in point-symmetry with respect to said median point and have sensitivity only to vibration components in the direction perpendicular to the vibration tube plane which contains the curve of said vibration tube, thereby increasing the ratio of the amplitude of Coriolis vibration to the amplitude of the ocillated vibration.

17. A Coriolis mass flowmeter, comprising:

a vibration tube through which a fluid to be measured flows so that the flow of the fluid in cooperation with angular vibration of said vibration tube generates Coriolis force which causes vibratory deformation of said vibration tube

wherein said vibration tube includes;

a branching portion where the flow of said fluid branches into first and second channels;

a merging portion where said first and second channels merge in each other;

a first branch tube defining said first channel, said first branch tube having a curved configuration with three inflection points and point symmetry with respect to a first median point which is midst between a first upstream fixed end near said branching portion and leading to said first channel and a first downstream fixed end near said merging portion and leading from said first channel;

a second branch tube defining said second channel having one end connected to said branching portion and the other end connected to said merging portion, and having the same configuration as said first branch tube and contained in the same plane as said first branch tube, the position of said second branch tube being determined by translationally moving the position of said first branch tube;

said Coriolis mass flowmeter further comprising;

ocillators for ocillating said first and second branch tubes; and

vibration sensors for sensing the vibration of said first and second branch tubes.

18. A Coriolis mass flowmeter according to claim 17, wherein said ocillators are arranged for ocillating said first and second branch tubes while maintaining the point-symmetry configurations of said first and second branch tubes, in such a manner that each point on said first branch tube performs simple harmonic oscillation on an arc of a predetermined radius from a first reference axis which is the straight line which interconnects said first upstream fixed end and said first downstream fixed end, while each point on said second branch tube performs simple harmonic oscillation on an arc of a predetermined radius from a second reference axis which is the straight line which interconnects a second upstream fixed end and a second downstream fixed end, and that said first and second branch tubes vibrate in the same vibration mode and at the same frequency in opposite phases to each other.

19. A Coriolis mass flowmeter according to claim 17 or 18, wherein lead lines from said ocillators or from said vibration sensors are led externally of said mass flowmeter through the median points, through said upstream fixed ends, or through said downstream fixed ends.

20. A Coriolis mass flowmeter according to one of claims 17 to 19, further comprising:

a first balancer attached to said first branch tube and a second branch tube attached to said second branch tube;

wherein said first balancer is provided such that the center of gravity of a system including said first branch tube, said ocillator or said vibration sensor attached to said first branch tube and said first balancer coincides with the median point of said first branch tube, and said second balancer is provided such that the center of gravity of a system including said second branch tube, said ocillator or said vibration sensor attached to said second branch tube and said second balancer coincides with the median point of said second branch tube.