JP3096181B2 - 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 a structure of a highly sensitive straight tube type Coriolis flow meter which is not affected by the environment such as the temperature and pressure of a measurement fluid.

[0002]

2. Description of the Related Art A phase difference is generated between a support portion and a central portion of a measuring tube by supporting the measuring tube at both ends and alternately driving a central portion of the supported measuring tube in a direction perpendicular to a support line. . This phase difference is based on the Coriolis force, and is a value proportional to the drive frequency and the mass flow rate. A straight pipe type Coriolis flow meter that detects the phase difference and measures the mass flow rate is well known.

In a straight pipe type Coriolis flowmeter, the shape is the simplest straight pipe, and it can be small in a direction perpendicular to the flow direction, but it can be small in a direction perpendicular to the axis of the measurement pipe. The rigidity is high, and it is necessary to lengthen it in the flow direction in order to detect it with high sensitivity. The shape is not always advantageous, and the resonance frequency is further reduced, so that it is easily affected by external vibration. As a conventional example of a straight tube type Coriolis flowmeter, a Coriolis flowmeter described in Japanese Patent Application Laid-Open No. 63-158419 has at least one measurement tube having both ends supported in a cylindrical support tube, and performs measurement. An annular diaphragm is provided in a support portion of the tube, and the measurement tube is suspended from the support tube via the annular diaphragm. According to this, when the measurement tube is fixed at both ends, a mechanical stress is generated depending on the temperature, which changes the natural frequency, and furthermore, the vibration energy of the measurement tube is transmitted to the support tube and the connection tube. I do. In order to improve this, the elastic deformation of the annular diaphragm is used, thereby eliminating the above-mentioned problems.

However, in the mass flow measuring device described above, the annular diaphragm vibrates in the direction perpendicular to the axis of the measuring tube at the center of the measuring tube with the annular diaphragm as a node, so that the stress is applied to the node supporting portion of the annular diaphragm. There is a problem that concentration is caused and the fatigue strength of this portion is weakened. Further, in the above-described conventional Coriolis flowmeter, the phase difference due to the Coriolis force is small, and the sensitivity is poor. In order to increase the sensitivity, it is necessary to select whether to increase the flow velocity by reducing the inner diameter of the measuring tube or to reduce the bending rigidity by using the measuring tube as a thin inner pipe.
When the flow velocity is increased, the pressure loss increases, and the vibration caused by the fluid flow also increases, and the SN ratio decreases. When a thin pipe is used, the diameter of the pipe changes due to the pressure of the measurement fluid, and not only the natural frequency changes, but also the bending rigidity changes, and there is a problem in that the accuracy is reduced.

[0005]

The present invention has been made in view of the above problems, and has as its object to provide a highly sensitive straight tube type Coriolis flowmeter without being affected by the environment such as temperature and pressure. It is.

[0006]

To achieve the above object, the present invention provides (1)
A support tube connected to a pipe through which a measurement fluid flows, a measurement tube through which a measurement fluid flows with an outer diameter smaller than the inner diameter of the support tube, and both ends of the measurement tube coaxially movable in the support tube only in the axial direction. And a plate spring having at least one end opening a through-hole communicating with the support tube and the inside of the measurement tube, and the plate spring as a node, and a central portion of the measurement tube in a direction perpendicular to an axis. A vibrating means to be driven, and a detector disposed between the vibrating means and the leaf spring, for detecting a phase difference of the measuring tube based on Coriolis force acting on the measuring tube, further comprising: (2) In the above (1), a flow dividing plate is provided in the measurement tube, the flow dividing plate dividing a cross section of the measurement tube into a plurality of sections parallel to a flow direction of a measurement fluid and perpendicular to a vibration direction. Hereinafter, description will be made based on embodiments of the present invention.

FIGS. 1 (a), 1 (b), 1 (c) and 1 (d) are views showing an example of a structure for explaining a Coriolis flowmeter according to the present invention. FIG. (B) The figure is (a)
FIG. 3C is a sectional view taken along line BB of FIG.
FIG. 3D is a sectional view taken along the line DD in FIG. 3A, wherein 1 is a support pipe, 2 and 3 are flanges, 4 is a measurement pipe, and 5 is a support ring. , 6, 16 are leaf springs, 7 is yoke, 8, 9 is tapered, 10 is a vibrator, 11, 12
Is a detector and 13 is a pressure equalizing chamber.

In FIG. 1, a support tube 1 is attached to a pipe (not shown) through which a measurement fluid flows, and has a high rigidity in an axial direction.
The wall thickness is selected so that it is not deformed by the piping stress when it is mounted. A measuring pipe 4 made of a thin-walled pipe is provided in the supporting pipe 1, and is supported coaxially with the supporting pipe 1 by leaf springs 6 and 16.
The leaf springs 6 and 16 have the outer peripheral surface 6b fixed to the step portion 1a and the inner peripheral surface fixed to the support ring 5. The support ring 5 is a ring for reinforcing the measurement tube 4 welded to the outer peripheral surfaces of both ends of the measurement tube 4.

The plate springs 6 and 16 have the function of moving the measuring tube 4 in the axial direction and preventing the measuring tube 4 from moving in the radial direction perpendicular to the axis. I do. At least one of the leaf springs 6 and 16 has a through hole 6a communicating with a cylindrical pressure equalizing chamber 13 formed by the support tube 1 and the measurement tube 4. FIG.
Then, as shown in FIG.
6 also shows an example in which an opening is provided. (B) In the leaf spring 6 shown in the figure, a plurality of through holes 6a are opened in the circumferential direction, and a small diameter through hole 16a is opened in the leaf spring 16 on the other end side.

In FIG. 1, a leaf spring 6 has a plurality of through holes 6.
a has a small-diameter through-hole 16a opened in the leaf spring 16, but in the present invention, it is not necessary to dispose a through-hole in both the leaf springs 6 and 16, and one of them, for example, The measurement fluid may be closed by opening the through hole 16a only on the flow side leaf spring 16 side and eliminating the through hole 6a of the front end leaf spring 6. The point is that the pressure in the pressure equalizing chamber 13 between the support pipe 1 and the measurement pipe 4 and the pressure in the measurement pipe 4 are equal, the pressure difference in the measurement pipe 4 is eliminated, and the measurement pipe 4 can be moved in the axial direction. . When the dynamic pressure of the measurement fluid flowing from the pipe to the measurement pipe 4 acts on the leaf springs 6 and 16, the fluid moves in the pressure direction in which the measurement pipe 4 acts, so that the fluid pressure acts on the leaf springs 6 and 16. So that the taperings 8 and 9 are separated by a minute gap,
They are attached before and after the leaf springs 6,16, respectively.

A yoke 7 having a high magnetic permeability is fixed by welding or the like to a part or the periphery of the outer peripheral surface of the central part of the measuring tube 4. An exciter 10 is provided. The vibrator 10 is connected to an external power supply (not shown), and includes a coil or the like that drives the yoke 7 at a constant frequency and amplitude. The external power supply frequency is preferably the natural vibration of the support tube 1. In FIG. 1, only a part of the yoke 10 facing the vibrator 10 is shown. However, in order to prevent the measuring tube 4 from being deformed by driving, the measuring tube 4 may be wound in the circumferential direction at this part. Instead of electromagnetic driving, piezoelectric strain or the like may be used.

Further, a detector 11 is mounted between the exciter 10 and the leaf spring 6 and a detector 12 is mounted between the vibrator 10 and the leaf spring 16 on the support tube 1, respectively. Exciter 10
The vibration of the measuring tube 4 on which the Coriolis force acting on the measuring fluid flowing in the measuring tube 4 by the driving of the measuring tube 4 is detected. The detectors 11 and 12 have the same detection characteristics, and may be of an optical type or an electromagnetic type.

Next, the operation of the Coriolis flowmeter configured as described above will be described. First, the measurement fluid flows in the direction of arrow Q, and is narrowed by the taper ring 8 so as to be measured.
Flows into the pressure equalizing chamber 13 through the inside of the measurement pipe 4 and the through hole 6a of the leaf spring 6 without applying dynamic pressure to the supported leaf spring 6. At this time, the measurement fluid is in the smaller area of the through hole of the leaf spring, here, the through hole 1 of the leaf spring 16.
6a according to the ratio between the area of 6a and the sectional area of the measuring tube 4.
Therefore, the pressure inside and outside the measuring tube 4 becomes equal, and no stress due to fluid pressure acts on the measuring tube 4, so that the wall pressure of the measuring tube 4 may be thin.

In the measuring tube 4, a vibrator 10 is connected via a yoke 7.
When the sample fluid is vibrated from above, Coriolis forces opposite to each other act on the measurement fluid in the upstream measurement and the downstream measurement with respect to the vibrator 10. That is, the detectors 11 and 12 output signals in which the Coriolis force is superimposed on the vibration of the in-phase component, the in-phase vibration component is removed from the signals, and the inverse proportional to the mass flow rate is removed. Only the phase difference signal due to the phase Coriolis force is extracted, and the mass flow rate proportional to the Coriolis force is measured.

However, when the through-hole 16a is open, the flow rate of the fluid flowing through the through-hole 16a becomes an error of the flow rate measured by the measuring pipe 4. In order to remove this error,
If the area of 6a is made small so that the pressure difference between the inside and outside of the measuring tube 4 can be eliminated, this error can be ignored. Further, the through hole 6a is closed, and the through hole 16a is closed.
By eliminating the error, the measurement tube 4
Pressure effect on the pressure can be eliminated. This configuration is particularly effective when the measurement fluid is a gas.

FIGS. 2A and 2B are views showing an example of a measuring tube of another embodiment of the Coriolis flowmeter according to the present invention.
1A is a side sectional view, and FIG. 2B is a sectional view taken along the line BB in FIG. 1A. In FIG. The same reference numerals as in FIG. 1 are used.

The plurality of flow dividing plates 14 divide the measuring tube 4 in a plane parallel to the flow direction, that is, the axial direction, and at right angles to the axis, and are particularly applied to a Coriolis flow meter for gas or a solid-gas two-phase flow. I do. As is well known, the Coriolis force is represented by an amount proportional to the vector product of the mass flow rate of the measurement fluid flowing in the measurement tube 4 and the excitation angular velocity. Does not transmit, accurate Coriolis force,
That is, a mass flow rate cannot be obtained. However, by dividing the flow by the flow dividing plate 14, the vibration is evenly transmitted to the diverted gas, so that the conventional disadvantage is solved. In addition, since the flow dividing plate 14 is perpendicular to the vibration direction, The rigidity in the direction does not increase, and the mass flow rate of the gas can be measured efficiently.

[0018]

As apparent from the above description, the present invention has the following effects. (1) Since both ends of the measuring tube are coaxially supported by the supporting tube by the leaf spring, the thermal distortion of thermal expansion due to a temperature change of the measuring fluid or the like acting on the measuring tube is removed, and at least one of the leaf springs is used. Since the through-hole is opened and the pressure in the cylindrical chamber formed by the support tube and the measurement tube is made equal to the pressure in the measurement tube, no pressure distortion occurs in the measurement tube. That is, since the measurement tube is not affected by the temperature and the pressure, the thickness of the measurement tube can be reduced, and a Coriolis flowmeter having high sensitivity and a small influence on the external environment can be obtained even in a straight tube type. (2) Since the inside of the measurement tube is partitioned in parallel with the flow, uniform vibration can be given even to a compressible fluid such as gas. Therefore, a high-precision gas mass flow rate can be obtained,
A gas Coriolis flowmeter that is less expensive than an indirect gas mass flowmeter that uses a conventional thermometer, pressure gauge, and a computing device can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a structure for explaining a Coriolis flowmeter according to the present invention.

FIG. 2 is a diagram showing an example of a measurement tube of another embodiment of the Coriolis flow meter according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Support pipe, 2, 3 ... Flange, 4 ... Measuring pipe, 5 ... Support ring, 6, 16 ... Leaf spring, 7 ... Yoke, 8 ... Taper ring, 10 ... Exciter, 11, 12 ... Detector , 13: Equalizing chamber, 14: Dividing plate.

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-63-158420 (JP, A) JP-A-1-189520 (JP, A) JP-A-4-223224 (JP, A) JP-A-4- 270922 (JP, A) JP-A-62-170819 (JP, A) JP-B 64-10770 (JP, B2) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01F 1/84

Claims (2)

(57) [Claims] 1. A support pipe connected to a pipe through which a measurement fluid flows, a measurement pipe through which a measurement fluid flows with an outer diameter smaller than the inner diameter of the support pipe, and the measurement pipe capable of moving only in the axial direction in the support pipe. A plate spring that coaxially supports both ends of the tube, a through-hole communicating with the support tube and the inside of the measurement tube at least on one end side, a plate spring serving as a node, and a central portion of the measurement tube. A vibrating means driven in a direction perpendicular to the axis, a detector arranged between the vibrating means and the leaf spring, for detecting a phase difference of the measuring pipe based on Coriolis force acting on the measuring pipe; A Coriolis flowmeter comprising: 2. A flow dividing plate, wherein a flow dividing plate is provided in the measuring pipe so as to divide the cross section of the measuring pipe into a plurality of sections which are parallel to a flow direction of a measurement fluid and are perpendicular to an exciting direction. Coriolis flowmeter as described.