JP2786812B2 - Coriolis flow meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Coriolis flow meter, and more particularly, to the structure of a double straight tubular Coriolis flow meter.

[0002]

2. Description of the Related Art A measuring tube is supported at both ends, and a central portion of the supported measuring tube is alternately driven in a direction perpendicular to a support line, thereby providing a phase difference between the supporting portion and the central portion of the measuring tube. Occurs. This phase difference is based on the Coriolis force,
It is a value proportional to the drive frequency and the mass flow rate, and a Coriolis flow meter that detects the phase difference and measures the mass flow rate is well known. The shape of the measuring tube is roughly classified into a curved tube and a straight tube. In the bending tube method, when the bending tube is driven in a direction perpendicular to the plane, the Coriolis force is detected as a phase difference at a symmetric position of the bending tube generated around a symmetry axis of the bending tube.
When the drive frequency is constant, the phase difference is measured, for example, as a time difference when the two arms of the bending tube pass through the reference plane in the stationary state of the bending tube. This method has a feature that a higher detection sensitivity can be obtained by increasing the torsional moment of the curved tube at the portion where the phase difference is detected. Conversely, when the torsional moment is increased, the shape becomes larger.

On the other hand, a Coriolis flow meter of a straight pipe type is a straight pipe having the simplest shape, and can reduce the cross-sectional shape perpendicular to the flow. On the other hand, the so-called lateral stiffness in the direction perpendicular to the axis of the measuring tube in which the Coriolis force is generated is extremely large with respect to the torsional stiffness of the curved tube. Drops.

For this reason, in a straight tube type Coriolis flowmeter,
S is susceptible to external vibration and the temperature and pressure of the fluid to be measured.
The N ratio decreases. In order to increase the detection sensitivity, the measurement tubes made of the same material should be made thinner and longer, the lateral stiffness of the straight tube should be smaller, the flow of the fluid should be larger, and the vibration amplitude should be smaller. Need to be bigger.

As a result, the resonance frequency decreases and approaches the external vibration frequency, so that the external vibration is easily affected. When the vibration amplitude is increased, the vibration energy increases and the pressure increases.

[0006] In order to solve this drawback, the present applicant has
First, in a cylindrical outer casing having flanges at both ends, a double pipe formed coaxially and integrally with the outer casing can be moved in the axial direction so that the movement in the radial direction at both ends is restricted. The Coriolis flowmeter shown in FIG. 5 was proposed.

FIG. 5 is a sectional view in the flow direction of a conventional Coriolis flowmeter, which has a hollow cylindrical outer case 61 having connection flanges 62 at both ends. A coaxial double tube 63 is provided.

The double tube 63 is a component constituting a main part of the Coriolis flowmeter, and comprises a straight tubular inner tube 64 through which a fluid to be measured flows, and a hollow straight tubular outer tube 65. Both ends are coaxially fixed to the outer tube 65 by connecting blocks 66a and 66b.

At the center of the outer tube 65, a balance weight 67 is attached.
The weight of 7 is adjusted so that the (lateral) natural frequency of the inner tube 64 supported by the connection blocks 66a and 66b and through which the fluid to be measured flows is equal to the (lateral) natural frequency of the outer tube 65.

Furthermore, the inner tube 6 having the same natural frequency
4 and the center of the outer tube 65, the inner tube 64
A driving device 69 for driving the resonance of the inner tube 64 and the outer tube 65 in opposite phases is mounted, and a pair of sensors for detecting a phase difference of the inner tube 64 due to Coriolis force at a symmetric position of the double tube 63 with respect to the driving device 69. Sensor 70
a and 70b are provided.

The double pipe 63 constructed as described above is connected to the outer walls of the connecting blocks 66a and 66b and the connecting flange 6a.
The channels 62a, 62a opening into the channels 2, 62 are sealed by O-rings 68a, 68b, and the channels 62a, 62b
, The liquid to be measured is supported in a liquid-tight manner so as not to flow into the outer casing 61.

Further, the O-rings 68a and 68b are provided between the double tube 63 and the outer casing 61 when the temperature of the fluid to be measured flowing through the inner tube 64 is significantly different from the external temperature and a temperature difference occurs. It becomes an elastic member for removing the generation of internal strain of the double tube 63 caused by the difference in thermal expansion, and the outer casing 61
This has the effect of blocking the external vibration transmitted from the motor from reaching the double pipe 63.

[0013]

Only the O-rings 68a and 68b elastically support the double tube 63. The O-rings 68a and 68b are made of an organic material such as synthetic rubber, and the elastic modulus is affected by temperature. Change. Further, since the ring 68 comes into contact with the fluid to be measured flowing in the flow path 62a of the connection flange 62, the O-ring 68a is affected by the pressure change of the fluid to be measured, and the tightening force changes due to the pressure change, thereby affecting the resonance frequency. give.

As described above, the double tube 63 expands and contracts in accordance with the temperature of the fluid flowing through the inner tube 64, and reduces thermal strain between the double tube 63 and the outer casing 61 by the O-rings 68a and 68b.
Can be removed by elastic deformation, but at the same time the support position changes, affecting the vibration of the double pipe 63,
The support structure of the double tube 63 by the O-rings 68a and 68b is desired to have improved stability against temperature changes.

According to the present invention, a double tube in which the natural frequency of the outer tube is made equal to the natural vibration of the inner tube by attaching a balance weight to the outer tube, the supporting point of which is affected by the temperature and pressure of the fluid to be measured. It is an object of the present invention to provide a Coriolis flowmeter that has a supporting means for stably supporting the mass flow and a density that can be measured stably.

[0016]

In order to achieve the above object, the present invention provides: (1) a hollow cylindrical outer casing having connection flanges at both ends, and radial movement within the outer casing is restricted. A straight tubular coaxial double pipe arranged so as to be movable in the axial direction, an inner tube through which the fluid to be measured flows through the connection flange, and an outer tube having both ends fixed to the inner tube. A weight attached to the outer tube, a balance weight for making the lateral natural frequency of the outer tube equal to the lateral natural frequency of the inner tube, and a drive for resonantly driving the inner tube and the outer tube. And a sensor for detecting a phase difference proportional to the Coriolis force acting on the inner tube by the resonance drive. (2) In the above (1), the outer casing and the double pipe are connected to each other. The double (3) The supporting surface is supported by a short fence-shaped leaf spring extending in a radial direction perpendicular to the vibration in a direction parallel to the vibration direction at the vibrating node portion. The casing and the double pipe are connected by a flexible tube having a large elastic force in a direction perpendicular to the axis, which is axially expandable and contractible at an end of the inner tube and a flow path opened to the connection flange. (4) In the above (1), the outer casing and the double pipe are liquid-tightly connected to each other by a flexible tube that can expand and contract in the axial direction at a flow path opening to the connection flange and at an end of the inner tube. Connected, and at the vibrating node of the double pipe, the supporting surface is supported by a short fence-shaped leaf spring extending in a radial direction perpendicular to the vibration and parallel to the vibration direction. ) In (1) above, The inner tube extends from the fixed portion of the tube and the outer tube to the connection flange side, and an end of the extended inner tube extends to the connection flange side as a nozzle tube. The outer casing and the double pipe are connected by fixing a flow path opened to the connection flange.

[0017]

The measuring tube through which the fluid to be measured flows is a single inner tube, and a double tube is formed by attaching a balance weight to the outer tube having the same lateral natural frequency as the inner tube. The main part of the Coriolis flowmeter, which can measure the mass flow rate and the density by resonantly driving the heavy pipe, is placed in an outer casing having connection flanges at both ends.
The metal support means, which is movable in the axial direction and is restricted from moving in the radial direction, provides stable support for a long period without being affected by temperature and pressure.

[0018]

【Example】

Embodiment 1 (corresponding to claims 1 and 2) FIG. 1 is a view for explaining Embodiment 1 of a Coriolis flowmeter according to the present invention, and FIG. 1 (a) is an arrow A in FIG. 1 (b).
FIG. 1B is a cross-sectional view taken along line BB of FIG. 1A, and FIG. 1C is a cross-sectional view taken along line CC of FIG. 1A. Inside, 1 is an outer casing, 2 is a connection flange, 3 is a double tube, 4 is an inner tube, 5 is an outer tube, 6a, 6b
Is a connecting block, 7 is a balance weight, 8a, 8b,
8c and 8d are leaf springs, 9 is a driving device, 10a and 10b are sensors, and 11a and 11b are O-rings.

The outer casing 1 is a hollow cylindrical body having connection flanges 2 and 2 at both ends, and the connection flanges 2 and 2 are connected to a flow pipe (not shown) through which a fluid to be measured flows.
Are provided with flow passages 2a and 2b.

The double tube 3 is a main part of a Coriolis flow meter in which both ends are coaxially fixed by connecting blocks 6a and 6b to a straight inner tube 4 and a straight outer tube 5. A balance weight 7 is fixed to the wall in the vibration direction at the center of the balance weight. The weight of the balance weight 7 is selected so that the natural frequency of the inner tube 4 through which the fluid to be measured flows and the natural frequency of the outer tube 5 are equal.

At the center between the inner tube 4 and the outer tube 5, a driving device 9 for resonatingly driving the vibrations of the inner tube 4 and the outer tube 5 in opposite phases is attached.
Further, the displacement of the inner tube 4 with respect to the outer tube 5 is detected at a symmetrical position with respect to the driving device 9, and the inner tube 4 is detected.
Sensors 10a and 10b for obtaining a phase difference proportional to the Coriolis force acting on the sensor are attached.

The double pipe 3 is provided inside the outer casing 1 on the outer periphery of the connecting blocks 6a and 6b, coaxially with the outer casing 1, and O-rings 11a,
The inner tube 4 and the outer tube 5 are sealed and elastically supported by 11b, and further elastically supported by diametrically extending leaf springs 8a and 8b and 8c and 8d at a position where the inner tube 4 and the outer tube 5 are connected. The leaf springs 8a, 8b and 8c, 8d
The axis connecting a and 8b and the axis connecting the leaf springs 8c and 8d are arranged parallel to each other. Each leaf spring 8a, 8
b, 8c and 8d are short fence-shaped flat plates extending in a plane parallel to the vibration direction of a line connecting the driving device 9 and the balance weight 7 and in a radial direction perpendicular to the vibration direction.

The double tube 3 of the Coriolis flowmeter according to the first embodiment shown in FIG. 1 is driven by the driving device 9 in a vertical direction indicated by arrows (± F). Since the center of gravity of the balance weight 7 is in the vibration direction indicated by the vertical direction of the arrow, the inner tube 4 and the outer tube 5 are driven to resonate in the opposite phases.

The Coriolis force proportional to the mass flow rate can be obtained from the phase difference signal between the signals output from the sensors 10a and 10b, and the density of the fluid to be measured can be obtained from the resonance frequency.

When the inner tube 4 and the outer tube 5 constituting the double tube 3 are driven by resonance, the connecting blocks 6a,
6b slightly vibrates in the axial direction according to the drive amplitude. if,
When the supporting direction of the double tube 3 with respect to the outer casing 1 by the leaf spring is set to the direction of resonance drive, the leaf spring vibrates minutely in the axial direction, and at the same time, bends and vibrates around the axis perpendicular to the axis with slight rotation. . For this reason, the center of gravity of the double pipe 3 moves in the minute rotation direction.

On the other hand, the leaf springs 8a, 8 shown in FIG.
When supported in the direction perpendicular to the resonance drive direction as in b and 8c, 8d, the plate spring 8
The a, 8b and 8c, 8d undergo only slight torsional vibration accompanying the vibration of the double pipe 3, and there is no displacement in the vibration direction, and the double pipe 3 is stably supported.

According to the Coriolis flowmeter of the first embodiment shown in FIG. 1, the double tube 3 having the balance weight 7 is driven in resonance, thereby eliminating the sensitivity defect of the straight tube type and enabling high sensitivity detection. At the same time, the double pipe 3 is elastically supported by short fence-shaped leaf springs 8a, 8b and 8c, 8d extending in a direction perpendicular to the driving direction in a plane in the driving direction, and the O-rings 11a, 11b Since only the action of sealing the path 2a and the inside of the outer casing 1 is provided, a Coriolis flowmeter which is stable for a long time and which is not affected by temperature or pressure without changing the elastic coefficients of the O-rings 11a and 11b or changing with time is used. Can be provided.

Embodiment 2 (corresponding to claims 1 and 3) FIG. 2 is a view for explaining a Coriolis flowmeter according to Embodiment 2, in which 21 is an outer casing, 22 is a connection flange,
23 is a double tube, 24 is an inner tube, 25 is an outer tube, 26a and 26b are connection blocks, 27 is a balance weight, 28a and 28b are flexible tubes, 29 is a driving device, and 30a and 30b are sensors.

The Coriolis flow meter according to the second embodiment is, like the first embodiment, provided in a cylindrical outer housing 21 having an empty space 21a having connection flanges 22 and 22 at both ends. A pipe 23 is provided. The double tube 23 has an inner tube 24 and an outer tube 25 similarly to the double tube 3.
Are connected coaxially by connecting blocks 26a, 26b, a balance weight 27 is fixed to the center of the outer tube 25, the natural vibration of the inner tube 24 is adjusted to be equal, and the drive device 29 drives the device in resonance, and the sensor is driven. 30
A and 30b have a function of detecting a phase difference signal proportional to the Coriolis force.

The inner tube 24 is longer than the outer tube 25 and protrudes from the connection blocks 26a and 26b toward the connection flange 22. One ends of the flexible tubes 28a and 28b are coaxially fixed to the protruding ends of the inner tube 24. The other ends of the flexible tubes 28a, 28b are fixed to the ends of the connection flanges 22, 22, respectively. Inner tube 24 and flexible tubes 28a, 2 projecting from connecting blocks 26a, 26b of double tube 23
8b is fixed to the end face of the connection flange 22 at the end face and coaxially mounted in the outer casing 21.
A hole 22b communicating with the vacant room 21c from the second and second holes 22 is formed.

The flexible tubes 28a and 28b are
For example, it is embodied by a thick metal bellows and expands and contracts in the axial direction, but unlike ordinary bellows, has a large bending rigidity and is hard to bend. Such flexible tubes 28a and 28b are obtained by bellows made of a thick metal.

According to the Coriolis flow meter according to the second embodiment,
As in the first embodiment, a Coriolis flowmeter capable of measuring the mass flow rate or the density without being affected by the temperature or pressure of the fluid to be measured can be provided.

Third Embodiment (corresponding to Claims 1 and 4) FIG. 3 is a view for explaining a Coriolis flowmeter according to a third embodiment, and FIG. 3 (a) is viewed from an arrow in FIG. 3 (b). FIG. 3B is a cross-sectional view taken along the line BB of FIG. 3A, where 31 is an outer casing, 32 is a connection flange, 33
Is a double tube, 34 is an inner tube, 35 is an outer tube,
36a and 36b are connection blocks, 37 is a balance weight, 38a, 38b, 38c and 38d are leaf springs, 39 is a drive device, 40a and 40b are sensors, and 41 is a flexible tube.

The Coriolis flow meter according to the third embodiment shown in FIG. 3 has the same connection flanges 3 at both ends as in the first and second embodiments.
In a cylindrical outer casing 31 having two and 32, a double pipe 33 coaxial with the outer casing 31 is supported, which is movable in the axial direction and is restrained from moving in the radial direction. It has a support structure.

The double pipe 33 is provided with a balance weight 37, a driving device 39, and sensors 40a and 40b, which have the same functions as those of the second and third embodiments, and therefore will not be described here. .

The double pipe 33 coaxially fixed by the connecting blocks 36a and 36b is a short fence-shaped leaf spring 38a, which extends in a radial direction perpendicular to the vibration on a plane parallel to the vibration direction driven by resonance. 38b and 38c, 38d make the outer casing 3
Further, one ends of flexible tubes 41a and 41b such as bellows are fixed to ends of the inner tube 34 which is longer than the outer tube 35 and is longer than the outer tube 35 and protrudes from the connection blocks 36a and 36b toward the connection flange 32. The other ends of the flexible tubes 41a and 41b are fixed to ends of holes 32a formed in the connection flange 32.

The leaf springs 38a, 38b and 38c, 38
d is the leaf springs 8a, 8b and 8c shown in the first embodiment,
A short fence-shaped flat plate similar to 8d is disposed so as to extend in a radial direction perpendicular to the vibration direction on a plane parallel to the vibration direction, and both ends are fixed to the connection blocks 36a and 36b and the outer casing 1. ing.

When the double pipe 33 is driven by resonance by the driving device 39, the leaf springs 38a, 38b and 38c, 38
d generates a small torsional vibration and a small vibration in the axial direction accompanying the vibration of the double pipe 33, and the fine vibration is absorbed by the flexible tubes 41a and 41b, and the leaf springs 38a and 3b.
Since the rigidity of the planes 8b, 38c and 38d in the plane direction is large, the vibration of the double pipe 33 accompanying the movement of the center of gravity does not occur.

Further, the double tube 33 and the outer casing 31 due to thermal expansion are provided.
Can be absorbed without adversely affecting the vibration mode.

Embodiment 4 (corresponding to claims 1 and 5) FIG. 4 is a view for explaining a Coriolis flowmeter according to embodiment 4, in which 51 is an outer casing, 52 is a connection flange,
53 is a double tube, 54 is an inner tube, 55 is an outer tube, 56a and 56b are connection blocks, 57 is a balance weight, 58a and 58b are nozzle tube parts, 59 is a driving device, and 60a and 60b are sensors.

The structure of a cylindrical outer casing 51 having connection flanges 52 at both ends and a balance weight 57, a double pipe 53 having a driving device 59 and sensors 60a and 60b are as follows.
The outer casing 1 and the double pipe 3 shown in FIG.
The description of the double tube 53 will be omitted.

Both ends of the inner tube 54 are connected to the connecting block 5.
Nozzle tube portions 58a and 58b are connected to both ends protruding toward the connection flange 52 side from 6a and 56b and having one end having the same diameter as the inner tube 54 and expanded toward the other end. The connection flanges 52 are fixed to the edge portion 52a by the different diameter circular holes provided in the holes 52b penetrating the 52. The nozzle tube portions 58a and 58b may be formed integrally with the inner tube 54 and have an enlarged end portion in a tapered shape.

Since the nozzle tubes 58a and 58b have high rigidity in the radial direction, are easily elastically deformed in the axial direction, and are flexible, the double tube 53 is provided at both ends of the inner tube 54 with the nozzle tubes 58a and 58b. With a simple structure in which the 58b is provided, a Coriolis flowmeter that can move in the axial direction and is hardly displaced in the radial direction can be provided.

[0044]

As is apparent from the above description, the double straight pipe type Coriolis flow meter according to the present invention has the following effects. Advantageous Effect According to Claim 1: Resonance is achieved by fixing a balance weight to the outer tube of a double tube comprising an inner tube having a single straight measuring tube and an outer tube having both ends fixed to the inner tube. It is drivable, and it is constructed so that it can move in the axial direction inside the outer casing and is constrained from moving in the radial direction, so the support point is stable, and stable mass flow rate and unaffected by the temperature and pressure of the fluid to be measured Density can be measured. In addition, since the measurement tube is a single inner tube, there is no stagnation of the fluid to be measured in the measurement tube, maintenance is easy, and cavitation does not occur because the fluid to be measured flows in a linear direction, and resonance driving is performed. Therefore, high sensitivity can be obtained even with a small driving energy. Advantageous Effect Corresponding to Claim 2: Since both ends of the double pipe extend in the radial direction perpendicular to the vibration and are supported by a short fence-shaped leaf spring having a surface parallel to the vibration, the same effect as in Claim 1 can be obtained. can get. According to the third aspect of the present invention, since both ends of the inner tube of the double pipe are projected outward and the flexible tube is attached to the protruding end, the supporting point of the vibrating double pipe is stabilized, and the fluid to be measured is A Coriolis flowmeter that is not affected by temperature or pressure can be provided. Advantageous Effect Corresponding to Claim 4: Since the double tube is supported in the outer casing by the leaf spring described in Claim 1 and the flexible tube described in Claim 3, the same effects as in Claims 2 and 3 are obtained. . Advantageous effect according to claim 5: With a simple structure in which the inner tube of the double tube is protruded to the outside of the connection block and the protruding end is formed as a nozzle tube which expands outward, and the expanded portion is fixed in the connection flange. The same effect as the first aspect is obtained.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a Coriolis flow meter according to a first embodiment of the present invention.

FIG. 2 is a diagram for explaining a Coriolis flow meter according to a second embodiment.

FIG. 3 is a diagram for explaining a Coriolis flowmeter according to a third embodiment.

FIG. 4 is a diagram for explaining a Coriolis flowmeter according to a fourth embodiment.

FIG. 5 is a sectional view of a conventional Coriolis flow meter in a flow direction.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Outer housing, 2 ... Connection flange, 3 ... Double tube, 4 ... Inner tube, 5 ... Outer tube, 6a, 6b ... Connection block, 7 ... Balance weight, 8a, 8b, 8c, 8d ...
Leaf spring, 9 ... Drive device, 10a, 10b ... Sensor, 11
a, 11b O-ring, 21 outer casing, 22 connecting flange, 23 double pipe, 24 inner tube, 25 outer tube, 26a, 26b connecting block, 27 balance weight, 28a, 28b possible Flexible tube, 29 ... Drive device, 30a, 30b ... Sensor, 31 ... Outer casing, 32 ...
Connection flange, 33: double tube, 34: inner tube, 3
5 ... outer tube, 36a, 36b ... connecting block, 3
7. Balance weight, 38a, 38b, 38c, 38
d: leaf spring, 39: drive device, 40a, 40b: sensor, 41: flexible tube, 51: outer casing, 52:
Connection flange, 53: double tube, 54: inner tube, 5
5 ... outer tube, 56a, 56b ... connecting block, 5
7 ... balance weight, 58a, 58b ... nozzle tube,
59: drive device, 60a, 60b: sensor.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kenichi Matsuoka 3-10-8 Kamiochiai, Shinjuku-ku, Tokyo Inside the oval company (72) Inventor Kimihiro Ichinose 3-108 Kamiochiai, Shinjuku-ku, Tokyo (56) References JP-A-5-248913 (JP, A) JP-A-6-94501 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01F 1/84

Claims (5)

(57) [Claims] 1. A hollow cylindrical outer casing having connection flanges at both ends, and a straight tubular coaxial two-piece, which is constrained in the outer casing to be movable in the radial direction and is movable in the axial direction. With heavy pipes,
An inner tube through which the fluid to be measured flows through the connection flange, an outer tube having both ends fixed to the inner tube, and a weight fixed to the outer tube, the lateral natural frequency of the outer tube being set to the inner side. A balance weight for equalizing the lateral natural frequency of the tube, a drive device for driving the inner tube and the outer tube in resonance, and detecting a phase difference proportional to Coriolis force acting on the inner tube by the resonance drive. A Coriolis flowmeter characterized by comprising a sensor that performs measurement. 2. A short fence-shaped leaf spring in which the outer casing and the double pipe are supported at a vibrating node of the double pipe, with a support surface parallel to a vibration direction and extending in a radial direction perpendicular to the vibration. The Coriolis flowmeter according to claim 1, wherein the Coriolis flowmeter is supported by: 3. The method according to claim 1, wherein the outer casing and the double pipe are connected to each other at a flow path opening to the connection flange and an end of the inner tube.
The Coriolis flowmeter according to claim 1, wherein the Coriolis flowmeter is connected by a flexible tube that can expand and contract in the axial direction and has a large elastic force in a direction perpendicular to the axis. 4. The method according to claim 1, wherein the outer casing and the double pipe are provided at a flow path opening to the connection flange and at an end of the inner tube.
It is connected in a fluid-tight manner with a flexible tube that can expand and contract in the axial direction, and at the vibrating node portion of the double pipe, a support surface is parallel to the vibration direction and has a short fence shape extending in a radial direction perpendicular to the vibration. The Coriolis flowmeter according to claim 1, wherein the Coriolis flowmeter is supported by a leaf spring. 5. The inner tube extends from the fixing portion of the inner tube and the outer tube of the double tube to the connection flange side, and the extended end of the inner tube extends toward the connection flange side. The Coriolis flowmeter according to claim 1, wherein the outer casing and the double pipe are connected by fixing the outer circumference of the nozzle pipe and a flow path opened to the connection flange, as a nozzle pipe.