JP2992162B2 - 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 mass flow meter based on the Coriolis principle, and more particularly to a vibrating tube which circulates a fluid and generates a Coriolis force and has a non-circular cross-sectional shape. And a straight tube type Coriolis flowmeter.

[0002]

2. Description of the Related Art One end or both ends of a flow tube through which a fluid to be measured flows is supported, and when the flow tube is vibrated around the supporting point in a direction perpendicular to the flow direction of the flow tube, the flow tube (oscillating tube) A mass flow meter (Coriolis flow meter) utilizing the fact that a phase difference proportional to the Coriolis force is generated between the vibrating portion and the supporting portions at both ends, and the Coriolis force is proportional to the mass flow rate is well known. The vibrating tube in these Coriolis flowmeters is an essential part and determines the characteristics of the flowmeter. The shape as a vibrating tube is roughly classified into a curved tube and a straight tube. The curved tube type is available in U-shaped, S-shaped, Ω-shaped, and J-shaped shapes.High-sensitivity mass flow detection is possible in that a shape for effectively extracting the Coriolis force can be selected. The disadvantage is that it becomes larger. In contrast, the straight pipe type is usually
Since the straight tube shaft is arranged in the flow direction, the shape is small, but the rigidity of the vibrating tube is high, the sensitivity is low, and the SN ratio is low.

As a known document related to the present invention, there is “Apparatus and Method for Continuously Measuring Flow” in JP-A-62-238419. This relates to a Coriolis flow meter using a straight pipe arranged in parallel as a vibrating pipe, and will be described below.

FIG. 5 is a view for explaining a conventional straight tube type Coriolis flowmeter. In FIG.
1, 56 are flanges, 52 is an inlet, 57 is an outlet, 5
3, 54, 58 and 59 are branch pipes, 60a and 60b are vibration pipes, 61 is an exciter, 62 and 63 are detectors, and 64 is a converter.

In FIG. 5, support members 50 and 55 are bilaterally symmetric and have branch pipes 53 and 54 and 58 and 59 communicating with an inlet 52 and an outlet 57, respectively.
And 58 and 54 and 59, vibrating tubes 60a and 60b formed of straight pipes having the same circular cross section are communicated in parallel with each other and fixedly supported. The vibrating tubes 60a and 60
b, an exciter 61 composed of a coil 61a and a core 61b is provided at the center thereof.
The core 61b is connected to the vibrating tube 60b,
1b is disposed so as to be inserted into the center of the coil 61a, and further includes a magnet 63a and a coil 63b between the support points of the exciter 61 and the support members 50 and 55 in the vibration tubes 60a and 60b. A detector 63 and a detector 62 including a magnet 62a and a coil 62b are provided.
These detectors 62 and 63 and the exciter 61 are
It is connected to the.

In the Coriolis flowmeter shown in FIG. 5, first, a coil 64 of an exciter 61 is driven by a converter 64, and a detection voltage output to a detection coil of either the detector 62 or 63 is supplied to the converter 64. A closed loop for positive feedback is formed so that the coil 61a is controlled to have a constant amplitude so as to attract and repel the core 61b, and the vibrating tubes 60a and 60b are vibrated in a reflection phase. The vibrating tubes 60a and 60b, through which the fluid flows due to the excitation, are driven in rotation directions opposite to each other with respect to the support point, so that the detectors 63 and 62 have the vibration detection signal by the excitation, the rotational angular velocity and the mass. Since the Coriolis force proportional to the vector product of the flow rates is superimposed and the Coriolis forces are in opposite phases, a phase difference signal proportional to the Coriolis force is detected between the detectors 62 and 63 and the converter 64 Is converted into a mass flow rate and output.

The above-mentioned conventional Coriolis flowmeter is a vibration tube 60.
a and 60b are straight pipes having a circular cross section, each of which is supported in parallel by supporting members 50 and 55. Further, the support members 50 and 55 are connected to the flow tube by the flanges 51 and 56. Since the vibration tubes 60a and 60b are supported by the supporting members 50 and 55 in this manner, the vibration tubes 60a and 60b are supported.
And 60b have higher rigidity in the direction perpendicular to the longitudinal direction. As a result, the amount of bending deformation of the vibrating tubes 60a and 60b due to the Coriolis force is reduced. That is, the phase difference signal due to the Coriolis force detected between the detectors 62 and 63 is small and easily subject to disturbance, and the vibration tubes 60a and 60
The S / N ratio decreases due to piping vibration or external vibration exerting on b. In order to increase the detection signal, the vibration tubes 60a, 60
It is necessary to reduce the thickness of Ob to reduce the bending rigidity or increase the flow rate of the measurement fluid. However, the vibration tube 60
If the bending stiffnesses a and 60b are reduced, the fluid is deformed due to a change in the pressure of the measurement fluid, and the resonance frequency is changed. As a result, the measurement error of the mass flow rate is increased. In addition, noise due to turbulence of the measurement fluid in the straight pipe causes a reduction in the SN ratio.

[0008]

The present invention has been made in view of the above-mentioned circumstances, and has the advantage that a straight tube type Coriolis flowmeter is small in size. It is an object of the present invention to provide a Coriolis flowmeter which has reduced noise caused by turbulence in the flow of air.

[0009]

To achieve the above object, the present invention provides (1)
A straight pipe through which the measurement fluid flows, supporting means for supporting both ends of the straight pipe, driving means for vibrating the straight pipe at a central portion of the straight pipe in a direction perpendicular to the longitudinal direction, and the driving means And a detector provided between the support means and the detector for detecting a phase difference due to Coriolis force acting on the straight pipe, wherein a cross-sectional shape of the straight pipe is changed in a vibration direction .
A short diameter ellipse or (2) flow of the measurement fluid
A straight pipe which causes, support means for supporting both ends of the straight tube,
A direction perpendicular to the longitudinal direction at the center of the straight pipe
In a Coriolis flowmeter, comprising: a driving means for vibrating the straight pipe, and a detector provided between the driving means and the supporting means and detecting a phase difference caused by Coriolis force acting on the straight pipe; The cross-sectional shape is a diamond with a short diameter in the vibration direction.
And (3) parallel flow of the measurement fluid
A plurality of straight pipes arranged, and joined to both ends of the straight pipes,
A branch pipe for uniformly distributing the measurement fluid to the straight pipe of
Support means for supporting the straight pipe, and extending the straight pipe at the center of the straight pipe.
Vibrates in opposite directions to each other in a direction perpendicular to the hand direction
A driving unit, and a driving unit provided between the driving unit and the supporting unit.
Phase difference due to Coriolis force acting on the straight pipe
A Coriolis flowmeter comprising a detector to know
The cross-sectional shape of the straight pipe is an ellipse with a short diameter in the direction of vibration , and (4) a plurality of parallel pipes through which the measurement fluid flows.
Number of straight pipes, and measured at each straight pipe joined at both ends of the straight pipe
A branch pipe for distributing a fluid in a uniform flow, and a support for supporting the branch pipe;
Holding means, and the straight pipe at a central portion of the straight pipe with respect to the longitudinal direction.
Driving means for vibrating in opposite directions in a direction perpendicular to each other;
The straight pipe provided between the driving means and the supporting means;
Detector that detects the phase difference due to Coriolis force acting on the surface
In a Coriolis flowmeter consisting of:
The shape is a rhombus with a short diameter in the vibration direction, and (5)
In the above (1) to (4) , the internal length of the cross section of the straight pipe
A predetermined length of gas extending radially from both straight pipe walls to the axis
Providing the id fins, and (6) the above (1) to
In (5) , the straight pipe is deleted at a predetermined section in the center.
The removed portion is connected by a flexible tube . Hereinafter, a description will be given based on examples of the present invention.

FIGS. 1A and 1B are views for explaining a Coriolis flowmeter according to the present invention. FIG. 1A is a side sectional view, and FIG. 1B is an arrow of FIG. 1A. FIG. 2 is a sectional view taken along the line Y-Y, in which 1, 2 are support flanges, 3 is an outer cylinder, 4 is a straight pipe, 5 is a driving device, and 6, 7 are detectors.

In FIG. 1A, a straight pipe 4 is shown in FIG.
As shown in the figure, the cross-sectional shape is axially symmetric with respect to the XX axis and the YY axis, and the interval between the tube walls in the XX axis direction is longer than the interval between the tube walls in the YY axis direction. 1 (b) shows an elliptical tube. The straight pipe 4 is inserted and fixed to the center of the support flanges 1 and 2 at both ends 4a and 4b, and an outer cylinder 3 having both ends fixed to the support flanges 1 and 2 is provided on the outer circumference of the straight pipe 4. The support flanges 1, 2 and the outer cylinder 3 and the straight pipe 4 are integrally formed. Further, a driving device 5 is mounted on the central portion M of the straight pipe 4 and the outer cylinder 3. The driving device 5 has a coil 5a and a core 5c arranged coaxially, and this axis is in the minor axis YY direction of the straight pipe 4. The coil 5a is fixed to the inner wall of the outer cylinder 3 by the support base 5b, and the core 5c is fixed to the straight pipe 4 by the shaft fixing bracket 5d. Further, detectors 6 and 7 having a coil axis in the YY axis direction are provided at positions symmetrical with respect to a central portion M between the support flanges 1 and 2 and the driving device 5. The detectors 6 and 7 are the same and include coils 6a and 7a and magnets 6c and 7c. The coils are mounted on the inner wall of the outer cylinder 3 via the support bases 6b and 7b.
Reference numeral 7c is provided on the pipe wall of the straight pipe 4 by shaft fixing brackets 6d and 7d.

Next, the operation of the Coriolis flowmeter of the present invention configured as described above will be described. The straight pipe 4 is driven by an AC driving current applied to the coil 5a of the driving device 5, and attracts and repels the core 5c. Since the Y-Y axis direction is the minor diameter direction in the cross section of the straight pipe 4, the bending rigidity of the straight pipe 4 is the smallest, and when driven at a predetermined amplitude, compared with the case where a straight pipe having a circular cross section of the same cross-sectional area is driven. Energy is small. On the other hand, in a direction perpendicular to the driving direction, conversely, the rigidity is higher than that of a straight pipe having a circular cross section. This means that the resonance frequency in the X-X axis direction increases, and the frequency ratio with respect to the low-frequency pipe vibration increases, thereby reducing the influence of external vibration.

When the flow Q of the measurement fluid is in the direction of the arrow,
The Coriolis force acts on the straight pipe 4 by the driving of the driving device 5. The Coriolis force is proportional to the vector product of the mass flow rate of the measurement fluid and the rotational angular velocities at the support portions 4a and 4b of the straight pipe 4. Therefore, the Coriolis force between the detector 6 and the detector 7 is the axis of the straight pipe 4. And a phase difference proportional to the Coriolis force is generated between them. This phase difference is a value proportional to the mass flow rate of the measurement fluid.

FIG. 2 is a view for explaining another embodiment of the Coriolis flowmeter according to the present invention. FIG. 1 (a) is a longitudinal sectional view, and FIG. FIG. 11 is a YY diagram, in which 11, 12 are support flanges, 13 is an outer cylinder, 14, 1
5 is a branch pipe, 16 and 17 are straight pipes, 18 is a drive unit, 1
Reference numerals 9 and 20 denote detectors.

In the Coriolis flowmeter shown in FIG. 2A, both ends of straight pipes 16 and 17 are connected to branch ports 14b of branch pipes 14 and 15 in a space surrounded by support flanges 11 and 12 and outer cylinder 13. And 15b and between the branch ports 14c and 15c are fixed in parallel.
The measuring fluid flowing from the inflow port 14a is
b and 14c, the fluid flows from the branch ports 15b and 15c at the same flow rate at the outlet 15a. As shown in FIG. 2B, the straight pipes 16 and 17 have, for example, an elliptical cross-sectional shape having a minor axis on the axis YY and a diameter on the axis XX. In this posture, the major diameters (XX axis direction) of the straight pipes 16 and 17 are parallel. The driving device 18 and the detectors 19 and 20 have the same arrangement as in FIG. 1, but the coils and the cores or the magnets are provided on the straight pipes 16 and 17 so that the axes coincide with the YY axis. Can be

The Coriolis flow meter shown in FIG.
Vibration occurs in the short diameter direction of the pipes 6 and 17, so that the straight pipes 16 and 17 are vibrated in a direction in which the rigidity is small. In the XX axis direction, the rigidity is high and the resonance frequency is high. Detectors 19 and 2 that are hard to receive and that use Coriolis force
Since the phase difference signal between 0 is doubled, the sensitivity is further increased as compared with the case of FIG.

FIGS. 3A and 3B are views for explaining still another embodiment of the Coriolis flowmeter according to the present invention. FIG. 3A is a longitudinal sectional view, and FIG. Is a YY line taken in the direction of the arrow in FIG. 3 (a). In the drawing, reference numerals 21 and 22 denote flexible tubes, and the same reference numerals as in FIG. .

FIG. 3 (a) shows the Coriolis flowmeter of FIG. 2 (a) in which the central portions of the straight tubes 16 and 17 are equally removed, and the removed portions are connected to flexible tubes 21 and 22. The coil support 18b is connected to the cut ends 17a and 17
b, and is fixed to the vicinity of the straight pipe 16d.
Is fixed over the vicinity of the end portions 16a and 16b of the end portion. If the bending stiffness of the flexible pipes 21 and 22 is neglected, the straight pipe 16 becomes the branch pipe 15 and the branch pipe 14, and the branch ports 15b and 14 respectively.
b becomes a cantilever with each supporting point, and the straight pipe 17 is a branch pipe 1
It becomes a cantilever with the branch ports 14b and 15b of 4 and 15 as fulcrums. Therefore, the rigidity is further reduced as compared with the case where the straight pipes 16 and 17 in FIG. In addition, since the diameter is short in the driving direction (Y-Y axis), the rigidity in the XX axis direction is increased, and a Coriolis flowmeter with less influence of external vibration can be obtained.

In the above description, the cross-sectional shape of the vibrating straight pipe is described as an ellipse having a constant thickness. However, the shape is not limited to an ellipse. Any cross-sectional shape may be used. FIG. 4 (a)
(D) is a figure which shows the cross-sectional shape of the straight pipe | tube of the Coriolis flowmeter in this invention.

FIG. 4A shows an outer shape of a circle 30, an inner diameter of an ellipse, and a cross-sectional shape in which the bending rigidity in the axis XX is higher than the bending rigidity in the axis YY. I have. FIG.
In (b), the cross-sectional shape is a rectangle 32, and the short side is in the YY axis direction and the long side is in the XX axis direction. In FIG. 4C, the cross-sectional shape is a rhombus 33, and the Y-Y axis direction is XX with the short side.
The axial direction is selected as the long side. FIG. 4D shows an elliptical tube 34.
The guide fins 35, 36 project from the tube walls 34a, 34b toward the axis O at equal lengths in the longitudinal direction of the inside of the tube. Not only is the bending rigidity in the direction further increased, but also the guide fins 35,
36 increases the rectification effect. As a result, a noise component based on the disturbance of the flow is reduced in the detection signal, and a detection signal with a good SN ratio is obtained. The guide fins 35 and 36 may be provided in the XX axis direction of each cross-sectional shape of FIGS.

[0021]

As is apparent from the above description, according to the present invention, the cross-sectional shape of the straight pipe serving as the vibrating pipe has a small bending rigidity in the vibration direction and a high bending rigidity in the direction perpendicular to the vibration. The effect is obtained. 1. Driving energy for obtaining a phase difference signal between detectors based on a constant Coriolis force can be reduced. 2. External vibrations, mainly pipe vibrations, often have vertical vibrations.However, when the direction of high bending stiffness of a straight pipe is set to the vertical direction, the resonance frequency also increases, reducing the influence of external vibrations and obtaining a Coriolis signal with an excellent SN ratio. Can be 3. Since the straight pipe is flat, there is an effect of rectifying the measurement fluid. Further, by providing the guide fin inside the straight pipe, the rectification effect is improved, and a Coriolis signal having an excellent SN ratio can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a diagram for explaining another embodiment of the Coriolis flow meter according to the present invention.

FIG. 3 is a view for explaining still another embodiment of the Coriolis flow meter according to the present invention.

FIG. 4 is a view showing a cross-sectional shape of a straight pipe of the Coriolis flowmeter according to the present invention.

FIG. 5 is a view for explaining a conventional straight tube type Coriolis flow meter.

[Explanation of symbols]

1, 2, support flange, 3 outer cylinder, 4 straight pipe, 5 drive, 6, 7 detector.

Claims (6)

(57) [Claims] 1. A straight pipe through which a measurement fluid flows, supporting means for supporting both ends of the straight pipe, and driving means for vibrating the straight pipe at a central portion of the straight pipe in a direction perpendicular to the longitudinal direction. And a detector provided between the driving means and the support means and configured to detect a phase difference due to Coriolis force acting on the straight pipe, wherein a cross-sectional shape of the straight pipe is changed in a vibration direction . A Coriolis flowmeter characterized by a short diameter ellipse . 2. A straight pipe through which a measurement fluid flows, and a straight pipe of the straight pipe.
A supporting means for supporting both ends, a driving means for vibrating the straight pipe in a direction perpendicular to a longitudinal direction at a central portion of the straight pipe, and a driving means provided between the driving means and the supporting means; A Coriolis flowmeter comprising a detector for detecting a phase difference caused by a Coriolis force acting on a pipe, wherein a cross-sectional shape of the straight pipe is a rhombus having a short diameter in a vibration direction. 3. A parallel arrangement for flowing a measurement fluid.
A plurality of straight pipes, and each straight pipe is joined to both ends of the straight pipe and measured.
A branch pipe for distributing a constant fluid in a uniform flow, and supporting the branch pipe
A supporting means, and a pair of the straight pipes in a longitudinal direction at a central portion of the straight pipe.
Drive means for vibrating in opposite directions in the direction perpendicular to each other
Provided between the driving means and the support means,
Detects phase differences due to Coriolis forces acting on straight pipes
In the Coriolis flowmeter consisting of
A Coriolis flowmeter characterized in that the surface shape is a short ellipse in the vibration direction . 4. A parallel arrangement for flowing a measurement fluid.
A plurality of straight pipes, and each straight pipe is joined to both ends of the straight pipe and measured.
A branch pipe for distributing a constant fluid in a uniform flow, and supporting the branch pipe
A supporting means, and a pair of the straight pipes in a longitudinal direction at a central portion of the straight pipe.
Drive means for vibrating in opposite directions in the direction perpendicular to each other
Provided between the driving means and the support means,
Detects phase differences due to Coriolis forces acting on straight pipes
In the Coriolis flowmeter consisting of
A Coriolis flowmeter characterized in that the surface shape is a rhombus with a short diameter in the vibration direction . 5. A straight pipe in a direction of an inner major axis of a cross section of said straight pipe.
Provide guide fins of a predetermined length that extend from the wall toward the axis.
Coriolis flowmeter to any one of claims 1 to 4 serial <br/> mounting, characterized in that digit. 6. The straight pipe is deleted at a predetermined section in a central portion,
The Coriolis flowmeter according to any one of claims 1 to 5 , wherein the deleted portion is connected by a flexible tube .