JP2000249585A - Straight pipe single tube coriolis flowmeter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an accurate coriolis flowmeter that is composed so that no vibration energy can be leaked to the outside by essentially excluding temperature influence with a single tube configuration, at the same time maintaining vibration balance, and reducing drive energy. SOLUTION: A flow tube 4 is supported at an outer enclosure 1 by support springs 17 and 18 that can be moved in an axial direction at the inner position of openings at both the ends, thus composing a vibration support. Preferably, a counter balance system that is composed of a balance spring 14 and the like where a balance weight 12 is mounted is supported only by a pair of support springs 19 for the outer enclosure 1 at a central position in an axial direction of the flow tube 4. A drive device 7 drives the flow tube 4 in an inverse phase for the counter balance system. In this manner, no vibration is generated in the outer enclosure 1 due to the balance vibration system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a straight-tube single-tube Coriolis flowmeter, and more particularly, to a single-tube system, which maintains vibration balance, reduces driving energy, and prevents vibration energy from leaking to the outside. It relates to a straight pipe single tube Coriolis flowmeter.

[0002]

2. Description of the Related Art A Coriolis flowmeter utilizes the fact that the Coriolis force acting on a measuring tube when the measuring tube supported at both ends is vibrated is proportional to the mass flow rate of the medium to be measured. It measures the mass flow rate.

The shape of a measuring tube to be vibrated is roughly classified into a curved tube and a straight tube. A Coriolis flowmeter of a straight tube single tube is perpendicular to a single tube axis at the center of a single tube supported at both ends. When it vibrates in the direction, the displacement of the single tube due to the Coriolis force between the support portion and the central portion of the single tube, that is, the mass flow rate is detected as a phase difference signal. The single-tube Coriolis flowmeter is driven by a vibrator arranged at the center of the single tube in a primary vibration mode with the support points at both ends as nodes, and the central vibrator and the support points at both ends are provided. A phase detector is symmetrically disposed between each of them, and a phase difference acting on the single tube based on the Coriolis force is detected by the flow of the fluid to be measured.

[0004] Such single-tube Coriolis flow meters have attracted attention because of their features such as compactness and no liquid pool. However, in order to vibrate the single tube, the energy must not leak out. It is necessary to increase the weight of the flow meter itself or to firmly attach the flow meter, and there is a problem that it is actually difficult to obtain the desired accuracy. For this reason, it is known that a counterbalance tube coaxial or parallel to the measurement tube is vibrated in the opposite phase to maintain the vibration balance.

FIG. 9 is a conceptual diagram of a conventional parallel straight tube type Coriolis flow meter having a parallel counter tube, and FIG.
Numeral 0 indicates a conceptual diagram of a conventional double straight tube type Coriolis flow meter equipped with a coaxial counter tube.
The Coriolis flowmeter shown in FIG.
10 is provided in parallel with the flow tube 4, while FIG.
The Coriolis flowmeter has a coaxial counter tube 10 on the outer peripheral side of the flow tube 4.

In each of these types, a straight tubular flow tube 4 through which a fluid to be measured flows is coaxially fixed to a coaxial or parallel counter tube 10 by connecting blocks 6 on both sides thereof. Counter tube 10
Is adjusted so that the natural frequency of the flow tube 4 and the natural frequency of the counter tube 10 are equalized by the weight of the balance weight (not shown) attached to the counter tube 10. Further, a driving device 7 for driving the flow tube 4 in resonance with the counter tube 10 in a phase opposite to that of the counter tube 10 is attached to a central portion of the counter tube 10, and a pair of sensors 8 are provided at symmetrical positions on both sides of the driving device 7. 9 is provided to detect a phase difference of the flow tube 4 due to Coriolis force.

As described above, the parallel straight pipe type or double straight pipe type Coriolis mass flow meter has a simple and compact structure, maintains vibration balance, and stably detects a mass flow rate proportional to a phase difference. It is possible to do. However, such a Coriolis mass flowmeter is affected by temperature because the flow tube 4 is coaxially fixed to the counter tube 10 and the connecting block 6 on both sides thereof. When the temperature of the measurement fluid changes, the flow tube 4
Although the temperature changes immediately following the change, the temperature fluctuation of the counter tube 10 is delayed. For this reason, the flow tube 4 and the counter tube 10 have a difference in elongation, and a stress is generated in the connecting block 6 in the longitudinal direction, and the natural frequency of the tube changes due to a change in the spring constant caused by the difference. The Coriolis flowmeter using these counter tubes 10 requires additional means for countermeasures.

The driving device 7 and a pair of sensors 8 and 9
It is necessary to perform wiring to the counter tube 10 or the flow tube 4 that vibrates along the wiring. This is undesirable because it affects the vibration balance.

[0009]

SUMMARY OF THE INVENTION The present invention essentially eliminates the influence of temperature by adopting a single tube structure, while solving the problems of the single tube type Coriolis flow meter and maintaining the vibration balance. It is an object of the present invention to provide a novel high-precision straight tube single tube Coriolis flowmeter configured to reduce driving energy and prevent vibration energy from leaking to the outside.

Another object of the present invention is to provide a configuration in which wiring to a drive device and a sensor does not need to be performed on a vibrating portion, reliability is improved at low cost, and performance degradation is not hindered.

[0011]

A straight tube single tube Coriolis flowmeter according to the present invention comprises a straight flow tube 4 through which a fluid to be measured flows, a driving device 7 for vibrating the flow tube 4, and a flow device by the vibration. A pair of sensors 8 and 9 for measuring a mass flow rate by detecting a phase difference proportional to the Coriolis force acting on the flow tube 4 on both sides of the tube 4, and at least a flow tube 4;
An outer housing 1 that houses a driving device 7 and a pair of sensors 8 and 9 is provided. The flow tube 4 has a support spring 1 movable in the axial direction at a position inside the openings at both ends.
Respectively supported on the inner wall of the outer casing 1 by 7 and 18.
Construct a vibration fulcrum. Desirably balance weight 12
Is supported by the pair of support springs 19 at the axial center of the flow tube 4 with respect to the outer casing 1 alone. The driving device 7 drives the flow tube 4 in the opposite phase to the counterbalance system. As described above, due to the balance vibration method, vibration does not occur in the outer casing 1 and stable and accurate measurement can be performed.

Further, according to the present invention, both ends of the flow tube 4 are provided with means for absorbing relative displacement due to thermal expansion between the outer tube 1 and the outer case 1, for example, an enlarged opening or a flexible tube. Or flange 2 connected thereto
Is combined with Thereby, the axial stress can be further reduced.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a straight tube single tube Coriolis flow meter according to the present invention will be described in detail based on an embodiment with reference to the drawings. FIG. 1 is a longitudinal sectional view of an embodiment of the present invention, and FIG. 2 is a schematic perspective view with a part of the configuration removed. This Coriolis flow meter has a single straight tube through which a fluid to be measured flows, that is, a flow tube 4 made of, for example, stainless steel, Hastelloy, a titanium alloy, or the like. It has a hollow cylindrical case having connection flanges 2 at both ends, that is, an outer case 1, and this outer case 1 is balanced with at least the flow tube 4, the driving device 7 and the pair of sensors 8, 9, and the balance ring 13. The weight 12 and the like are accommodated, and are firmly fixedly connected to the flange 2 at both ends by welding (welded portion 3) or the like. The flange 2 is connected to an inlet pipe and an outlet pipe (not shown) by appropriate fixing means such as bolts.

The flow tube 4 is located inside the outer casing 1.
It is disposed coaxially with the outer casing 1 and its both side openings are liquid-tightly fixed to the inner wall of the outer casing 1 (or the flange 2 connected thereto). As a result, the fluid to be measured passes through the flow tube 4 from the inlet pipe (the illustrated configuration is symmetrical and any side can be used as the inlet side), and a liquid pool is formed in the outlet pipe. It is configured to be able to smoothly flow out without any occurrence.
The flow tube 4 is supported by axially movable leaf springs, that is, flow tube support springs 17 and 18 at positions inside the openings on both sides, respectively, and serves as a fulcrum of vibration. As described above, the flow tube supporting springs 17 and 18 fix the flow tube 4 in the left, right, up and down directions so as to be a fulcrum of the vibration of the flow tube 4, while supporting the flow tube 4 movably in the axial direction. Therefore, as shown in the figure, it is desirable to support the device in the horizontal direction perpendicular to the vibration direction, but it is also possible to support the device in the same vertical direction as the vibration direction, or to support the device in both the horizontal direction and the vertical direction. is there.

The straight tube single tube Coriolis flow meter of the present invention further includes a counter balance system. In the illustrated example, the counter balance system includes a balance ring 14 supported on the inner wall of the outer casing 1 by a balancer support spring 19 at the axial center of the flow tube 4 (the center on the inlet side and the outlet side). . The mass of the balance ring 14 and the spring constant of the balancer support spring 19 are selected so as to be substantially equal to the primary natural frequency of the flow tube 4 filled with the fluid, and the natural frequency of the flow tube 4 is substantially the same. This is the result of canceling the inertial force.
The balance ring 14 is formed concentrically outside the flow tube 4 and is supported by a pair of balancer support springs 19 from both sides in a lateral direction perpendicular to the vibration direction. Thus, the balance ring 14
Except for being supported by the outer casing 1 by the balancer support spring 19, it is not directly supported by the flow tube 4 or the outer casing 1, so if the temperature of the fluid to be measured changes and the flow tube 4 Even if there is a difference in elongation between the and the counterbalance system, this does not cause a stress.

At the axial center of the flow tube 4 in the axial direction, a driving device 7 for driving the flow tube 4 in an opposite phase to the balance ring 14 is provided. The drive device 7 itself can be of a conventional configuration with a coil on one side and a magnet on the other side driven in opposite phase. In the illustrated example, a hole is made in the center of the balance ring, and a drive coil is arranged on the outer peripheral side of the balance ring so as to surround the hole.On the other hand, a cylindrical rod-shaped magnet passes through the hole made in the balance ring and further passes through the center of the coil. It is attached to the outer peripheral side of the flow tube 4 so as to pass through the space (see FIGS. 3 and 4). With this configuration, the influence of the wiring to the drive coil on the vibrating portion can be minimized, and the wiring can be wired to the inner wall of the outer casing 1 that does not vibrate. Although the balancer support spring 19 is configured by a pair of leaf springs and supports the counterbalance system in a horizontal direction perpendicular to the vibration direction, the balancer support spring 19 is not limited to this. The counterbalance system is fixed in the transverse direction perpendicular to the vibration, and has a spring constant that can be driven in substantially the same phase as the natural frequency of the flow tube 4 in the vibration direction and relatively opposite in phase. If so, it is possible to use any configuration of spring or to support it with a greater number of springs.

The driving device 7 vibrates the flow tube 4 in a primary mode of its natural vibration. 3 and 4 are views showing the relative positional relationship between the flow tube driven in the opposite phase and the balance ring. FIG. 3 shows when the flow tube 4 is at the bottom dead center with respect to the balance ring 14, and FIG. 4 shows when the flow tube 4 is at the top dead center. Thus, by causing the flow tube 4 to vibrate in the opposite phase with respect to the balance ring 14, it is possible to suppress the vibration to the outer casing 1.

When a fluid flows through the flow tube 4, the Coriolis force is opposite in the inflow side and the outflow side from the center where the vibration speed is maximum, and the flow tube is
It will undulate. Although this is called a second-order mode component, the flow tube is displaced in such a manner that the first-order mode vibration based on the excitation by the driving device and the second-order mode oscillation based on the Coriolis force are superimposed. The pair of sensors 8 and 9 are installed at positions where the second-order mode component is maximized on both sides of the driving device 7 to detect a phase difference of the flow tube 4 due to Coriolis force. The sensors 8 and 9 are
It can be normal in itself, and in the example shown,
A cylindrical rod-shaped magnet is provided on the outer peripheral side of the flow tube 4, while a coil is mounted on the inner wall of the outer casing 1 via a sensor coil mounting fixture fixed thereto. As described above, the sensor of the present invention has a configuration in which the wiring to the coil can be attached without affecting the vibration of the vibrating part at all.

Balance ring 14 and balancer support spring 1
9, the spring constant of the support spring 19 and the balance ring 1 are adjusted so that the natural frequency of the counterbalance system is equal to the natural frequency of the flow tube 4.
The mass of 4 is selected. In the illustrated example driven in the vertical direction from the upper side of the flow tube 4, the balance weight 12 is desirably attached (below the balance ring), and can be adjusted so that the natural frequencies substantially match.

FIG. 5 is a diagram showing another example of the counter balance system. In the illustrated example, the counter balance system includes a counter balancer 13 having a U-shaped cross section supported on the outer casing 1 by a pair of balancer support springs 19. Further, the balance weight 12 having an appropriate shape such as a square rod or a plate as shown in the figure can be mounted symmetrically in the lateral direction perpendicular to the vibration direction and in the axial direction of the flow tube. With such a configuration, the driving device 7 drives the flow tube 4 in a phase opposite to that of the counter balancer 13 in the same manner as described with reference to FIGS. Can be planned.

FIG. 6 is a diagram showing still another example of the counter balance system. In the illustrated example, the counter balance system can be configured by a block-shaped counter balancer 13 supported on the outer casing 1 by a pair of balancer support springs 19. Also, this counter balancer 13
Has a balance weight 1 for adjusting the natural frequency.
2 can be attached. The driving device 7 drives the flow tube 4 in a phase opposite to that of the counter balancer 13 as in the above-described example.

The counter balancer 13 is formed in a ring configuration concentric with the flow tube 4 as in the above-described example or in a U-shaped configuration so as to surround the counter tube. However, such a structure is not always necessary for the operation thereof, and as shown in FIG. In addition, any material having a natural frequency substantially matching that of the flow tube 4 may be used. Therefore, as long as the counter balance 13 has a symmetrical shape in the supporting direction and the axial direction of the flow tube 4, the counter balance 13 has an arbitrary shape such as a rectangle or a circle, and can be hollow or solid. be able to.

Thus, the Coriolis flowmeter of the present invention is:
A counter balance system or counter balancer 13 is connected to the outer casing 1 by a balancer support spring 19, not directly connected to the flow tube 4, and the flow tube 4 is an axially movable flow tube support spring 1.
Since it is supported by 7 and 18, no excessive stress is generated in the flow tube. However, the stress can be further reduced by employing a stress absorbing means in the connection between the flow tube 4 and the outer casing 1.

FIG. 7 shows an example in which an enlarged opening is used as a stress absorbing means. Except for the connection to the flow tube 4 and the inner wall of the outer casing 1, the flow tube 4 is the same as the Coriolis flow meter described with reference to FIG. The flow tube 4 has enlarged openings 21 on both sides of the inlet side and the outlet side, the openings of which are integrally extended outward. And the end of this enlarged opening 21 is
It is fixed to the inner wall of the outer casing 1 or the inner wall of the flange 2 welded (welded portion 3) thereto. With such a configuration,
Since the end fixing portion of the flow tube 4 has high rigidity in the radial direction, is easily elastically deformed in the axial direction, and is flexible, the relative displacement due to the thermal expansion between the flow tube 4 and the outer casing 1 also vibrates. It is possible to absorb without affecting the mode.

FIG. 8 shows an example in which a flexible tube is used as the stress absorbing means. Except for the connection of the flow tube 4 and the flange 2 to the inner wall, it is the same as the Coriolis flow meter described with reference to FIG. The opening end of the flow tube 4 is coaxially fixed to one end of the flexible tube 22 on both sides of the inlet side and the outlet side. The other end of each flexible tube 22 is connected to a flange 2.
Is fixed to the end. With such a configuration, relative displacement due to thermal expansion between the flow tube 4 and the outer casing 1 can be absorbed without affecting the vibration mode.

[0026]

According to the present invention, a counterbalance in which the flow tube is supported on the outer case by a plate spring movable on both sides in the axial direction to form a vibration fulcrum, while the flow tube is supported only by the support spring on the outer case. System, and the drive unit drives the flow tube in the opposite phase to this counterbalance system.Therefore, there is no vibration in the outer casing, and a stable high-precision straight tube single tube Coriolis flowmeter is possible. Becomes

Further, there is no axial stress on the flow tube due to the temperature change, and the temperature range is expanded, and the change in stability due to the temperature change is reduced.

Further, the number of manufacturing steps such as brazing is not so large as in the case of the double straight pipe type in which the inner and outer double tubes are connected using a connecting body on both sides, so that the tube can be easily manufactured at low cost. .

Further, since it is not necessary to wire the driving device and the sensor on the vibrating portion, the reliability can be improved at low cost, and the effect of not deteriorating the performance is produced.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a straight tube single tube Coriolis flow meter showing an embodiment of the present invention.

FIG. 2 is a perspective view schematically showing a straight pipe single tube Coriolis flowmeter shown in FIG.

FIG. 3 is a diagram illustrating a case where a flow tube driven in an opposite phase is at a bottom dead center with respect to an outer casing;

FIG. 4 is a diagram illustrating a case where a flow tube driven in an opposite phase is at a top dead center with respect to an outer casing;

FIG. 5 is a diagram showing another example of the counter balance system.

FIG. 6 is a diagram showing still another example of a counter balance system.

FIG. 7 is a diagram showing an example in which an enlarged opening is used as a stress absorbing unit.

FIG. 8 is a diagram showing an example in which a flexible tube is used as a stress absorbing means.

FIG. 9 is a conceptual diagram showing a conventional parallel straight tube type Coriolis flow meter provided with a parallel counter tube.

FIG. 10 is a conceptual diagram showing a prior art double straight tube type Coriolis flow meter provided with a coaxial counter tube.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Outer housing 2 Connection flange 3 Weld part 4 Flow tube 6 Connecting block 7 Drive device 8 Sensor 9 Sensor 10 Counter tube 12 Balance weight 13 Counter balancer 14 Balance ring 17 Flow tube support spring 18 Flow tube support spring 19 Balancer support spring 21 Enlarged Opening 22 Flexible tube

Claims (6)

[Claims] 1. A flow tube having a straight tube through which a fluid to be measured flows, a driving device for vibrating the flow tube, and a phase difference proportional to Coriolis force acting on the flow tube on both sides of the flow tube due to the vibration. A straight tube single tube Coriolis flowmeter comprising a pair of sensors for measuring mass flow rate by detecting, and at least the flow tube, the driving device and an outer housing for accommodating the pair of sensors; At positions inside the opening, each is supported on the inner wall of the outer casing by a plate spring movable in the axial direction to form a vibration fulcrum, and the outer casing is positioned at the axial center of the flow tube with respect to the outer casing. A counterbalance system supported only by a support spring, wherein the driving device includes the flow tube Driven in opposite phase to the counter balance system, straight pipe single tube Coriolis flowmeter, characterized in that. 2. The straight tube single tube Coriolis flowmeter according to claim 1, wherein the counter balance system comprises a balance ring having a ring configuration arranged concentrically outside the flow tube. 3. The mass of the balance ring and the spring constant of a support spring supporting the balance ring are selected so as to be substantially equal to the primary natural frequency of the flow tube filled with fluid, and are substantially the same as the flow tube. 3. The straight tube single tube Coriolis flowmeter according to claim 2, wherein the oscillating inertial force is canceled as a natural frequency. 4. The counter balance system according to claim 1, further comprising a balance weight capable of finely adjusting the mass.
A straight tube single tube Coriolis flowmeter according to any one of claims 1 to 3. 5. The flow tube according to claim 1, wherein both ends of the flow tube are connected to the outer housing or a structure connected thereto through means for absorbing a relative displacement caused by thermal expansion between the outer housing and the flow tube. The straight tube single tube Coriolis flowmeter according to any one of claims 1 to 4. 6. The means for absorbing relative displacement includes an enlarged opening extending outward on both sides of an inlet side and an outlet side of the flow tube, and an end of the enlarged opening is formed on the outside of the flow tube. The straight tube single tube Coriolis flowmeter according to claim 5, wherein the straight tube single tube Coriolis flowmeter is coupled to a housing or a configuration coupled thereto.