JP2002031554A - Coriolis flow meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly sensitive Coriolis flow meter. SOLUTION: This Coriolis flow meter is constructed of a straight pipe having a sensor and allowing fluid as a flow rate measurement object to flow through it and two counter rods arranged on both sides of the straight pipe at an interval parallelly to each other. One end part of the straight pipe and one side end parts of the respective counter rods are fixed to one supporting body, while the other end part of the straight pipe and the other side end parts of the respective counter rods are fixed to the other supporting body, and a vibration generating device is provided in each of the straight pipe and the respective counter rods. Both of the supporting bodies are fixed to a rigid base board.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a Coriolis flowmeter,
The invention also relates to a density meter using a Coriolis flow meter.

[0002]

2. Description of the Related Art When vibration is applied to a pipe in which a fluid is flowing, a Coriolis force proportional to the mass flow rate acts on the fluid.
A Coriolis flow meter is a direct mass flow meter that measures a mass flow rate by vibrating a pipe (generally called a measurement tube) through which a fluid for measuring a flow rate flows and detecting a Coriolis force acting on the fluid. The Coriolis force is usually detected by measuring the elastic deformation and strain of the measuring tube. In addition to Coriolis flowmeters, besides mass flow rate,
It has the characteristic that the density, viscosity and temperature of the fluid can also be measured.

Since the Coriolis force is very small with respect to the force that vibrates the measuring tube, a measuring means for detecting the Coriolis force with high sensitivity is required. Therefore, a typical Coriolis flowmeter uses a U-shaped measurement tube having a large deformation with respect to Coriolis force. However, the U-shaped measurement tube has a problem that a pressure loss easily occurs in the fluid flowing inside. Therefore, it is difficult to improve the measurement accuracy of a Coriolis flowmeter using a U-shaped measurement tube. Further, when a U-shaped measurement tube is used for the Coriolis flowmeter, there is a problem that the flowmeter becomes large. For these reasons, a Coriolis flowmeter using a straight tube type measurement tube has been studied. Hereinafter, a Coriolis flowmeter using a straight tube type measurement tube will be referred to as a straight tube type Coriolis flowmeter.

[0004] The straight tube type Coriolis flowmeters are classified into Coriolis flowmeters using only one measurement tube (straight tube) and Coriolis flowmeters using an auxiliary straight tube in addition to the measurement tube. In each case, straight pipes such as measuring tubes
Each end is fixed to a support frame. A vibration generator is arranged at the center of the measurement tube. Means for detecting deformation or distortion of the measurement tube caused by Coriolis force is provided at a position between the vibration generator and the support frame arranged on the measurement tube.

A Coriolis flow meter using a plurality of straight pipes is described in Japanese Patent Application Laid-Open No. 3-41319. Figure 1
2 is a partial cross-sectional view showing the configuration of the Coriolis flowmeter described in the publication. The Coriolis flowmeter shown in FIG. 12 has a straight tube type measurement tube 3, a counter tube 4b,
And it is comprised of the auxiliary tube 4a which keeps a structural balance. The counter tube 4b and the auxiliary tube 4a are arranged in parallel on both sides of the measuring tube 3, respectively. A fluid for measuring the flow rate flows through the measurement tube 3.

[0006] The flow meter is connected to a system (plant or the like) for measuring the flow rate by flanges 1 provided at both ends of the measuring tube. The respective ends of the measurement tube 3, the counter tube 4b, and the auxiliary tube 4a are fixed to a vibration isolating frame (support frame). The measurement tube 3 and the counter tube 4b are designed to have substantially the same resonance frequency. At the center position of the measurement tube 3 and the counter tube 4b, a vibration generator 5 that gives primary bending vibration to those tubes is arranged. Sensors 6a and 6b are provided at symmetrical positions on both sides of the vibration generation device 5.
Is arranged. The sensors 6a and 6b detect deformation of the measurement tube 3 caused by Coriolis force.

[0007] In the measurement tube of the Coriolis flowmeter having the structure shown in FIG. 12, primary vibrations are excited by the vibration generating device using the vibration-proof frames provided at both ends of the measurement tube as nodes. The Coriolis force acting on the fluid is expressed by the following equation. Fc = −2 m [ω] × [v] Here, [ω] is a vector of the vibration frequency ω,
[V] represents a vector of the flow velocity v of the fluid.

Another embodiment of a straight tube type Coriolis flowmeter using a plurality of rods is described in Japanese Patent Application Laid-Open No. H11-30543. FIG. 13 is a perspective view showing a configuration of a conventional Coriolis flowmeter described in the publication.
The Coriolis flowmeter shown in FIG. 13 includes a straight tube type measurement tube 3 and a pair of counter rods 4b. In the Coriolis flow meter shown in FIG. 13, a bar-shaped (not tubular) counter rod is used instead of the counter tube of the flow meter shown in FIG. The pair of counter rods are respectively arranged on both sides of the flow tube 3 in parallel. A fluid for measuring the flow rate flows through the measurement tube 3.

The flow meter is connected to a system for measuring the flow rate (plant or the like) by flanges 1 provided at both ends of the measuring tube. The measurement tube 3 and the counter rod 4b are designed to vibrate in opposite phases by the vibration generator 5. A pair of sensors 6a and 6b are arranged at symmetrical positions on both sides of the vibration generator 5. The sensors 6a and 6b detect deformation of the measurement tube 3 caused by Coriolis force.

FIG. 14 shows the result of analyzing the vibration leakage of the Coriolis flow meter modeled on the Coriolis flow meter shown in FIG. 13 by the finite element method. In the Coriolis flowmeter shown in FIG. 13, the length of the flange (support) along the longitudinal direction of the measurement tube was set to 1/10 of the length of the measurement tube. According to the analysis by the finite element method, the measurement tube in the primary bending vibration mode is placed on the support at a position from the end on the measurement tube side of each vibration isolating frame to 2/5 of the entire length of the support. It was found that a displacement close to 5% of the maximum displacement was generated. Such deformation of the support (flange) hinders detection of secondary bending vibration of the measurement tube caused by Coriolis force.

[0011]

A Coriolis flowmeter using a plurality of straight pipes (or counter rods) has a problem that the measurement sensitivity is lower than a flowmeter using a U-shaped measurement tube. An object of the present invention is to provide a straight tube type Coriolis flowmeter with high sensitivity. Another object of the present invention is to provide a density meter using a highly sensitive straight-tube Coriolis flowmeter.

[0012]

SUMMARY OF THE INVENTION In the Coriolis flowmeter using a plurality of tubes (or counter rods, etc.), the present inventor has proposed that a vibration of a measuring tube or a counter tube (or a counter rod) is generated by supporting a vibration isolating frame or the like. Vibration leakage was transmitted to the body, and this vibration leakage suppressed deformation and distortion of the measuring tube for measuring the flow rate, and found that sufficient sensitivity could not be obtained.

The present invention is a Coriolis flowmeter comprising a straight pipe provided with a sensor, through which a fluid to be subjected to flow measurement flows, and two counter rods arranged in parallel on both sides of the straight pipe with a space therebetween. Thus, one end of the straight pipe and one end of each counter rod are fixed to one support, and the other end of the straight pipe is separated from the other end of each counter rod. The straight pipe and each of the counter rods are provided with a vibration generator for vibrating the straight pipe and each of the counter rods so that their vibration phases are opposite to each other. A Coriolis flowmeter characterized in that the body is fixed on a rigid substrate. Preferred embodiments of the Coriolis flow meter of the present invention will be described below.

(1) The shape and mass of the counter rod are
Equal to each other. (2) The shape and mass of the counter rod are equal to that of a straight pipe. (3) The length of each of the two supports is 3/10 or more of the length of the straight pipe. (4) The length of each of the two supports is in the range of 3/10 to 10/10 of the length of the straight pipe. (5) The thickness of each of the two supports is larger than the diameter of the straight pipe. (6) The lengths of the two supports are equal to each other. (7) Each of the two supports is fixed to the rigid substrate via an elastic body. In addition, the length of the support means the length of the support along the longitudinal direction of the straight pipe, and the thickness of the support is along the direction perpendicular to the plane formed by the straight pipe and the counter rod. Means the length of the support.

The present invention is also a density meter comprising a straight pipe provided with a sensor through which a fluid to be subjected to density measurement flows, and two counter rods arranged in parallel on both sides of the straight pipe at intervals. Thus, one end of the straight pipe and one end of each counter rod are fixed to one support, and the other end of the straight pipe is separated from the other end of each counter rod. The straight pipe and each of the counter rods are provided with a vibration generator for vibrating the straight pipe and each of the counter rods so that their vibration phases are opposite to each other. There is also a densitometer characterized in that the body is fixed on a rigid substrate. Preferred embodiments of the density meter of the present invention are the same as those of the Coriolis flow meter of the present invention.

[0016]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a perspective view showing a configuration of an example of a Coriolis flow meter according to the present invention, and FIG. 2 is a plan view thereof. The vibration generator and the sensor are described only in FIG. The Coriolis flowmeter of the present invention includes a measurement tube (straight pipe) 3 through which a fluid for measuring a flow rate flows, and two counter tubes (counter rods) 4a and 4b. In the Coriolis flowmeter illustrated in FIGS. 1 and 2, a straight tube type tube (counter tube) is used as a counter rod. Counter tube 4a
And 4b are arranged in parallel on both sides of the measuring tube 3, respectively. One end of the measurement tube 3 and one end of each counter tube are fixed to the support 2a. The other end of the measurement tube 3 and the other end of each counter tube are fixed to the support 2b.
The supports 2a and 2b are fixed on the rigid substrate 11.

The measuring tube 3 is a system for measuring the flow rate by means of flanges 1 provided at both ends thereof (plant or the like).
Connected to. Between the measurement tube 3 and the respective counter tubes 4a and 4b, vibration generators 5a and 5b each composed of a magnet and a coil are arranged. When the vibration generator 5a attracts the flow tube 3 and the counter rod 4a, the vibration generator 5b moves the flow tube 3 and the counter rod 4b away from each other. In order to detect the Coriolis force generated by the vibration, a sensor 6a is disposed at a position between the vibration generator 5a and the support 2a. Similarly, a sensor 6b is arranged at a position between the vibration generator 5a and the support 2b. The sensors 6a and 6b are symmetrically arranged on both sides of the vibration generator 5a. Each of the sensors 6a and 6b is composed of a piezoelectric element or a combination of a magnet and a coil.

The supports 2a and 2b, the measuring tube 3, and the counter tubes 4a and 4b are usually made of a metal material such as stainless steel, Hastelloy, and titanium alloy.
Examples of the material forming the rigid substrate 11 include metal and ceramic. No fluid needs to flow through the counter tube. The cross-sectional shape of the counter tube (counter rod) is not limited to a circle, but may be a polygon or an ellipse. It is preferable that the shape and mass of the counter tube and the measuring tube 3 are equal. The mass of the measurement tube means the mass of the straight pipe when the fluid to be measured is filled inside. When a vibration generating device or a sensor is arranged on the measuring tube (straight tube) or the counter rod, it is preferable that the straight tube and the two counter rods have the same shape and mass in a state where they are arranged. When a straight pipe similar to the measurement tube is used as the counter rod, the fluid to be measured can be sealed in the straight pipe. FIG.
In L1, L1 means the length of the measurement tube 3. L
2 means the length of the support blocks 2a and 2b along the longitudinal direction of the measuring tube.

The counter rod (or counter tube) of the flow meter of the present invention is symmetrically arranged on both sides of the measuring tube so as to obtain the vibration mode of the tripod tuning fork vibrator. Such an arrangement is different from the arrangement of the conventional counter rod which equalizes the resonance frequency of the flow tube and the counter tube. FIG. 3 shows a perspective view of a tripod tuning fork vibrator. In the present invention, a desired vibration mode can be excited only by balancing the flow tube and the counter rod (or the counter tube).

In the Coriolis flowmeter of the present invention, the vibration mode used for detecting the generated Coriolis force corresponds to the secondary bending vibration mode of the arm of the tripod tuning fork vibrator shown in FIG. It is known that a tripod tuning fork type vibrator can obtain very stable vibration, and is widely used for a resonator or the like. FIG. 4A shows the primary bending vibration mode of the tripod tuning fork vibrator, and FIG. 4B shows the secondary bending vibration mode. In FIG. 4, the dotted lines indicate the deformation of the vibrator.
In the present invention, the primary bending vibration mode of the tripod tuning fork vibrator is used to generate vibrations of the measurement tube and the counter tube, and the secondary bending vibration mode of the tripod tuning fork vibrator is used to detect deformation occurring in the measurement tube. Used for

FIG. 5 is a perspective view showing the structure of another example of the flow meter of the present invention. In the Coriolis flowmeter shown in FIG. 5, each of the supports is fixed to a rigid substrate 11 via an elastic body 10 (for example, made of silicon rubber or the like). With such a configuration, the flow meter can be protected from external vibration.

FIGS. 6 and 7 show the structure of still another example of the flow meter of the present invention. In the flow meter having the configuration shown in FIGS. 6 and 7, each of the supports 2 a and 2 b is fixed to the rigid substrate 11 via the elastic body 10. In the configuration of FIG. 6, the thickness of each of the supports 2 a and 2 b is preferably larger than the diameter of the measurement tube 3. Further, the thickness of each of the supports 2a and 2b is preferably larger than the diameter of each of the counter tubes 4a and 4b.

Measurement tube 3 and counter tube 4a
And 4b, two vibration generators each including a magnet 8a and a coil 9a and a magnet 8b and a coil 9b are arranged. A magnet 8c and a sensor 7c are disposed on both sides of each counter tube as balance weights. In FIG. 7, sensors 7c provided on the measurement tube and the counter tube are provided for the purpose of balancing the flow meter in the lateral direction. The sensor 7c disposed on the measurement tube can also detect deformation of the measurement tube due to Coriolis force.

FIGS. 8 to 11 show the results of analyzing the deformation of the tube and the support of the flow meter shown in FIG. 1 by the finite element method. Each drawing shows the results of analysis for both the primary bending vibration mode and the secondary bending vibration mode.

FIG. 8 shows that the length (L2) of the support along the longitudinal direction of the measuring tube is two times the length L1 of the measuring tube.
In the case of / 10 (L2 / L1), the results of analyzing the displacement generated in the tube and the support by the finite element method are shown. FIG. 8A shows the displacement in the primary bending vibration mode.
FIG. 8B shows the displacement in the second-order bending vibration mode. As shown in FIG. 8A, the displacement of the support from the end on the measurement tube side to 2/5 of the entire length of the support is the maximum of the measurement tube in the primary bending vibration mode. It is 1% or less with respect to the displacement. FIG. 8B
As shown in, the displacement of the support from the end on the measurement tube side to 2/5 of the entire length of the support is
Approximately 5% of the maximum displacement of the measuring tube in the second-order bending vibration mode. In the second order bending vibration mode, approximately 5% displacement of the support is acceptable.

FIG. 9 shows that the length (L2) of the support along the longitudinal direction of the measuring tube is three times the length L1 of the measuring tube.
In the case of / 10 (L2 / L1), the results of analyzing the displacement generated in the tube and the support by the finite element method are shown. FIG. 9A shows the displacement in the primary bending vibration mode.
FIG. 9B shows the displacement in the second-order bending vibration mode. As shown in FIG. 9A, the displacement of the support from the end on the measurement tube side to 2/5 of the entire length of the support is the maximum of the measurement tube in the primary bending vibration mode. It is 1% or less with respect to the displacement. FIG. 9B
As shown in, the displacement of the support from the end on the measurement tube side to 2/5 of the entire length of the support is
It is 2% or less with respect to the maximum displacement of the measurement tube in the secondary bending vibration mode. In the second order bending vibration mode, displacements of less than about 2% of the support are acceptable.
In the secondary bending vibration mode, since the deformation of the support is as small as 2% or less, it does not affect the deformation of the measurement tube in the secondary bending vibration for detecting the Coriolis force.

FIG. 10 shows a case where the length of the support (L2) along the longitudinal direction of the measuring tube is 6/10 (L2 / L1) of the length L1 of the measuring tube, and the tube and the supporting member The result of having analyzed the displacement which occurred by the finite element method is shown. FIG. 10 shows the displacement in the first-order bending vibration mode.
FIG. 10A shows the displacement in the secondary bending vibration mode in FIG.
(B). As shown in FIG. 10 (a), 2/1/2 of the entire length of the support from the end on the measurement tube side of the support.
The displacement at positions up to 5 is 1% or less of the maximum displacement of the measuring tube in the first-order bending vibration mode. As shown in FIG. 10B, the displacement of the support from the end on the measurement tube side to 2/5 of the entire length of the support is the maximum of the measurement tube in the secondary bending vibration mode. It is 1% or less with respect to the displacement. In the secondary bending vibration mode, since the deformation of the support is as small as 1% or less, it does not affect the deformation of the measurement tube in the secondary bending vibration for detecting the Coriolis force.

The results in FIGS. 9 and 10 show that the length of the support relative to the length of the measuring tube should be 3/10 or more in order to detect with high sensitivity the Coriolis force generated in the measuring tube in the secondary bending vibration. It should be noted that Therefore, in order to make the Coriolis flowmeter highly sensitive, the longer the length of the support along the longitudinal direction of the measuring tube, the better. However, if the length of the support is extremely long, there is a disadvantage that the flow meter becomes large. Accordingly, the upper limit of the length of the support is preferably practically such that L2 / L1 is up to about 10/10.

The modes of bending vibration, such as first-order bending vibration and second-order bending vibration, are not limited to the direction perpendicular to the plane formed by the measuring tube and the two counter tubes. FIG. 11A shows a first-order bending vibration mode in a plane formed by the measurement tube and the two counter tubes. And FIG. 11 (b)
Shows a second-order bending vibration mode on the same plane. Also in these cases, the deformation of the measurement tube in the secondary bending vibration mode is used for detecting the Coriolis force acting on the measurement tube.

[0030]

According to the straight tube type Coriolis flow meter of the present invention, the length of the support for fixing the measuring tube and the like is set to 3/10 or more of the length of the flow tube. By designing the length of the Coriolis flowmeter support in this way, the measurement tube and counter tube can almost contain the energy of vibration, and the flowmeter has high sensitivity to prevent leakage of vibration energy to the outside. can do. And the energy required to vibrate the measuring tube is
Since there is no vibration leakage, the size may be small, and the driving device can be downsized. Further, by fixing the support to the rigid substrate (preferably via an elastic body), it is possible to provide a Coriolis flowmeter which is less affected by vibration in the usage environment of the flowmeter and has higher sensitivity. In addition, by using such a Coriolis flow meter, a highly sensitive density meter can be provided.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a configuration of an example of a Coriolis flow meter according to the present invention.

FIG. 2 is a plan view of the Coriolis flow meter of the present invention shown in FIG.

FIG. 3 is a perspective view of a tripod tuning fork vibrator.

4A and 4B are diagrams illustrating a vibration mode of a tripod tuning fork vibrator, wherein FIG. 4A illustrates a primary bending vibration mode, and FIG. 4B illustrates a secondary bending vibration mode.

FIG. 5 is a perspective view showing the configuration of another example of the Coriolis flowmeter of the present invention.

FIG. 6 is a perspective view showing a configuration of still another example of the Coriolis flow meter of the present invention.

FIG. 7 is a plan view of the Coriolis flow meter of the present invention shown in FIG.

8A and 8B are diagrams showing displacement of the tube and the support when the length of the support is 2/10 of the length of the measurement tube in the Coriolis flowmeter shown in FIG. (B) shows the displacement in the next bending vibration, and (b) shows the displacement in the second bending vibration.

FIG. 9 is a view showing displacement of a tube and a support when the length of the support is 3/10 of the length of a measurement tube in the Coriolis flowmeter shown in FIG. 1; (B) shows the displacement in the next bending vibration, and (b) shows the displacement in the second bending vibration.

10 is a diagram showing displacement of a tube and a support when the length of the support is 6/10 of the length of a measurement tube in the Coriolis flowmeter shown in FIG. 1; FIG. (B) shows the displacement in the next bending vibration, and (b) shows the displacement in the second bending vibration.

11A shows a first-order bending vibration mode in a plane formed by a flow tube and two counter tubes, and FIG. 11B shows a second-order bending vibration in the same plane.

FIG. 12 is a partial cross-sectional view showing a configuration of an example of a conventional Coriolis flow meter.

FIG. 13 is a perspective view showing the configuration of another example of a conventional Coriolis flowmeter.

FIG. 14 is a diagram showing an analysis result of displacement of a tube and a support in primary bending vibration in a Coriolis flow meter of a form modeled on the Coriolis flow meter of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Flange 2a, 2b Support 3 Measurement tube 4a, 4b Counter rod 5a, 5b Vibration generator 6a, 6b Sensor 7a, 7b, 7c Sensor 8a, 8b, 8c Magnet 9 Anti-vibration frame 9a, 9b Coil 10 Elastic body 11 Rigidity Substrate L1 Length of measuring tube L2 Length of support

Claims (9)

[Claims] 1. A Coriolis flowmeter comprising a straight pipe provided with a sensor, through which a fluid to be subjected to flow rate measurement flows, and two counter rods arranged in parallel on both sides of the straight pipe with an interval therebetween. One end of the straight pipe and one end of each counter rod are fixed to one support, and the other end of the straight pipe and the other end of each counter rod are separately supported. Each of the straight pipe and each of the counter rods is fixed to the body, and a vibration generator is provided for each of the straight pipe and each of the counter rods to vibrate the straight pipe and each of the counter rods so that the vibration phases thereof are opposite to each other.
The Coriolis flowmeter is characterized in that the two supports are fixed on a rigid substrate. 2. The Coriolis flowmeter according to claim 1, wherein the shape and the mass of the two counter rods are equal to each other. 3. The Coriolis flowmeter according to claim 2, wherein the shape and mass of the counter rod are equal to those of the straight pipe. 4. The apparatus according to claim 1, wherein the length of each of the two supports is at least 3/10 of the length of the straight pipe.
The Coriolis flowmeter described in 1. 5. The length of each of the two supports is in the range of 3/10 to 10/10 of the length of the straight pipe.
The Coriolis flowmeter described in 1. 6. The Coriolis flowmeter according to claim 1, wherein the thickness of each of the two supports is larger than the diameter of the straight pipe. 7. The Coriolis flowmeter according to claim 1, wherein the lengths of the two supports are equal to each other. 8. The Coriolis flowmeter according to claim 1, wherein each of the two supports is fixed to a rigid substrate via an elastic body. 9. A density meter comprising a straight pipe provided with a sensor, through which a fluid to be subjected to density measurement flows, and two counter rods arranged in parallel on both sides of the straight pipe with a space therebetween. One end of the straight pipe and one end of each counter rod are fixed to one support, and the other end of the straight pipe and the other end of each counter rod are connected to another support. The straight pipe and each of the counter rods are provided with a vibration generator for vibrating the straight pipe and each of the counter rods so that the vibration phases thereof are opposite to each other, and both of the support members are rigid. A densitometer fixed on a substrate.