JPH05248910A - Coriolis flow meter - Google Patents

Abstract

PURPOSE:To eliminate such defects possessed by a straight pipe Coriolis flow meter as being easily subjected to outside vibration, having low sensitivity and causing noise due to the disturbance of fluid in a straight pipe by taking its advantage of a small size. CONSTITUTION:A drive unit 5 is provided at a center M-M between a straight pipe 4 and an outer cylinder 3 both of which are coaxially supported between supporting flanges 1, 2, so that the drive unit 5 can drive the straight pipe 4 in the direction perpendicular to a longitudinal direction at a preset amplitude so as to detect a phase difference signal arising from Coriolis force by means of detectors 6, 7. At this time, the straight pipe 4 is in an sectionally oblate shape which is short in diameter in a vibrating direction and long in a perpendicular direction thereto.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a mass flowmeter based on the Coriolis principle, and more specifically, a vibrating tube that circulates a fluid to generate a Coriolis force is a straight tube and has a non-circular cross-sectional shape. The present invention relates to a straight pipe 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 (vibrating tube) A mass flowmeter (Coriolis flowmeter) utilizing a fact that a phase difference proportional to the Coriolis force is generated between the oscillating portion and the both-end supporting portions 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 of the vibrating tube is roughly classified into a curved tube and a straight tube. The curved tube type has U-shape, S-shape, Ω-shape, J-shape, etc., and it is possible to detect the mass flow rate with high sensitivity because the shape for effectively extracting the Coriolis force can be selected. It has the disadvantage of becoming large. On the other hand, the straight pipe type is usually
Since the straight pipe axis is arranged in the flow direction, the shape is small, but the sensitivity is low due to the high rigidity of the vibrating pipe, and the SN ratio is lowered, so that there is a drawback that more attention must be paid to disturbance.

As a known document related to the present invention, there is "a device and method for continuously measuring a flow" in Japanese Patent Application Laid-Open No. 62-238419. This relates to a Coriolis flowmeter in which a straight pipe arranged in parallel is used as a vibrating pipe, and will be described below.

FIG. 5 is a view for explaining a conventional straight pipe type Coriolis flowmeter, in which 50 and 55 are support members and 5.
1, 56 is a flange, 52 is an inlet, 57 is an outlet, 5
3, 54, 58 and 59 are branch pipes, 60a and 60b are vibrating pipes, 61 is an exciter, 62 and 63 are detectors, and 64 is a converter.

In FIG. 5, the support members 50 and 55 are bilaterally symmetric and have branch pipes 53 and 54 and 58 and 59 which communicate with the inflow port 52 and the outflow port 57, respectively.
Between 58 and 54 and 59, vibrating tubes 60a and 60b, which are straight tubes having circular cross sections of the same size, are connected in parallel and fixedly supported in parallel with each other. The vibrating tubes 60a and 60
An exciter 61 including a coil 61a and a core 61b is provided at the center of the vibration tube 60a.
Side, the core 61b is on the side of the vibrating tube 60b, and the core 6 is
1b is arranged so as to be inserted in the center of the coil 61a, and is further composed of a magnet 63a and a coil 63b between the support points of the exciter 61 and the support members 50 and 55 in the vibrating tubes 60a and 60b. A detector 63 and a detector 62 including a magnet 62a and a coil 62b are provided.
The detectors 62 and 63 and the exciter 61 are the converter 64.
It is connected to the.

In the Coriolis flowmeter shown in FIG. 5, first, the converter 64 drives the coil 61 of the exciter 61, and the detector 64 outputs the detection voltage to the detector 62 or 63. The coil 61a is controlled to have a constant amplitude so as to attract and repel the core 61b by forming a closed loop for positive feedback, and the vibrating tubes 60a and 60b are vibrated in a reflection phase. Since the vibrating tubes 60a and 60b through which the fluid flows due to the vibration are driven in the opposite rotational directions with respect to the support points, the detectors 63 and 62 include a vibration detection signal due to the excitation, the rotational angular velocity, and the mass. Since the Coriolis force proportional to the vector product of the flow rate is superimposed and the Coriolis force has the opposite phase, 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 has a vibrating tube 60.
Reference characters a and 60b are straight pipes having a circular cross section, and each is supported in parallel by support members 50 and 55. Further, the support members 50 and 55 are connected to the flow tube by flanges 51 and 56. In this way, the vibrating tubes 60a and 60b are supported by the supporting members 50 and 55 on both sides.
The rigidity becomes higher in the direction perpendicular to the longitudinal direction of 60 and 60b. As a result, the amount of bending deformation of the vibrating tubes 60a and 60b due to the Coriolis force becomes small. That is, the phase difference signal due to the Coriolis force detected between the detectors 62 and 63 is small and is easily subject to disturbance, and the vibrating tubes 60a, 60
The SN ratio decreases due to the pipe vibration and external vibration exerted on b. In order to increase the detection signal, the vibrating tubes 60a, 6a
The wall thickness of 0b must be reduced to reduce the bending stiffness or the flow velocity of the measurement fluid must be increased. However, the vibrating tube 60
When the flexural rigidity of a and 60b is lowered, the measurement fluid is deformed by the pressure change, the resonance frequency is changed, the measurement error of the mass flow rate becomes large, and the pressure loss increases if the flow velocity in the vibrating tube is increased. Further, noise due to the turbulence of the measuring fluid in the straight pipe also causes a decrease in the SN ratio.

[0008]

[Purpose] The present invention has been made in view of the above-mentioned circumstances, and by taking advantage of the small size of a straight pipe type Coriolis flowmeter, it is difficult to be affected by external vibration, has high sensitivity, and further has a measuring fluid. The purpose of the present invention is to provide a Coriolis flowmeter in which noise due to the turbulence of the flow is reduced.

[0009]

In order to achieve the above object, the present invention provides (1)
A straight pipe through which the measurement fluid flows, a support means for supporting both ends of the straight pipe, a driving means for vibrating the straight pipe in a direction perpendicular to the longitudinal direction at the central portion of the straight pipe, and the driving means. In a Coriolis flowmeter comprising a detector for detecting a phase difference due to the Coriolis force acting on the straight pipe, the cross-sectional shape of the straight pipe being perpendicular to the axis of the vibration direction and the vibration. The tube wall spacing in each axial direction is long in the direction perpendicular to the vibration direction symmetrically with respect to the axis in the different directions, or (2) a plurality of parallelly arranged measuring fluids are arranged. A straight pipe, branch pipes joined to both ends of the straight pipe to distribute the measurement fluid to each straight pipe in a uniform flow, support means for supporting the branch pipe, and the straight pipe at the central portion of the straight pipe. A drive means for vibrating in the opposite phase and the drive means are provided between the support portion. In a Coriolis flowmeter comprising a detector for detecting a phase difference due to the Coriolis force acting on the straight pipe, a cross-sectional shape of the straight pipe is symmetrical with respect to an axis in a vibration direction and an axis in a direction perpendicular to the vibration. , The axial wall surface interval of each tube is made longer in the direction perpendicular to the vibration than the vibration direction interval, and further, (3) above (1) or (2)
In the above, the straight pipe is deleted in a predetermined section of the central portion, and the deleted portion is connected by a flexible tube, and further, (4)
In any one of the above 1 to 3, the cross-sectional shape of the straight pipe is an ellipse having a short axis in the vibration direction, and further (5)
In any one of 1 to 3 above, the cross-sectional shape of the straight pipe is a rectangular shape having a short side in a vibration direction, and
(6) In any one of 1 to 3 above, the cross-sectional shape of the straight pipe is a rhombus having a short diameter in the vibration direction,
(7) In any one of the above items 1 to 6, a guide fin having a predetermined length extending from both straight pipe walls toward the axial center in the inner diameter direction of the straight pipe cross section is provided. Hereinafter, description will be given based on examples of the present invention.

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

In FIG. 1 (a), the straight pipe 4 is shown in FIG. 1 (b).
As shown in, the cross-sectional shape is axisymmetric with respect to the X-X axis and the Y-Y axis, and the interval between the tube wall surfaces in the XX axis direction is longer than the interval between the tube wall surfaces in the YY axis direction. 1 (b) shows an elliptic tube. The straight pipe 4 is fixedly inserted through both ends 4a and 4b into the central portions of the support flanges 1 and 2, and an outer cylinder 3 having both ends fixed to the support flanges 1 and 2 is provided on the outer periphery of the straight pipe 4. Thus, the support flanges 1, 2 and the outer cylinder 3 and the straight pipe 4 are integrally formed. Further, a drive device 5 is attached to 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 with each other, and its 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 5b, and the core 5c is fixed to the straight pipe 4 by the shaft fixing metal fitting 5d. Further, detectors 6 and 7 having a coil axis in the Y-Y axis direction are provided at positions symmetrical with respect to the central portion M between the support flanges 1 and 2 and the drive device 5. The detectors 6 and 7 are the same and are composed of coils 6a and 7a and magnets 6c and 7c, and the coils are attached to the inner wall of the outer cylinder 3 via the support bases 6b and 7b.
7c is provided on the wall of the straight pipe 4 by means of shaft fixing fittings 6d and 7d.

Next, the operation of the Coriolis flowmeter of the present invention constructed as 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 to attract and repel the core 5c. Since the Y-Y axis direction is the minor axis 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 to the case where a straight pipe having a circular cross section with the same cross-sectional area is driven. And small energy is enough. On the other hand, in the direction perpendicular to the driving direction, on the contrary, the rigidity is higher than that of the straight pipe having the circular cross section. This means that the resonance frequency in the X-X axis direction becomes high, and the frequency ratio with the low-frequency pipe vibration becomes large, and the influence of external vibration becomes small.

When the flow Q of the measuring fluid is in the direction of the arrow,
The Coriolis force acts on the straight pipe 4 by driving the driving device 5. The Coriolis force is proportional to the vector product of the mass flow rate of the measured fluid and the rotational angular velocities of the supporting portions 4a and 4b of the straight pipe 4, so that the Coriolis force between the detector 6 and the detector 7 is the axis of the straight pipe 4. On the other hand, the forces become opposite to each other, and a phase difference proportional to the Coriolis force occurs between them. This phase difference is a value proportional to the mass flow rate of the measurement fluid.

2A and 2B are views for explaining another embodiment of the Coriolis flowmeter according to the present invention. FIG. 1A is a longitudinal sectional view and FIG. 1B is an arrow view of FIG. 1A. It is a YY figure, and in the figure, 11 and 12 are support flanges, 13 is an outer cylinder, and 14 and 1.
5 is a branch pipe, 16 and 17 are straight pipes, 18 is a drive device, 1
9 and 20 are detectors.

In the Coriolis flowmeter shown in FIG. 2 (a), both ends of the straight pipes 16 and 17 are provided in a space surrounded by the support flanges 11 and 12 and the outer cylinder 13, and branch ports 14b of the branch pipes 14 and 15 are provided. And 15b and between the branch ports 14c and 15c are fixed in parallel, and the branch pipes 14 and 15 are
The measurement fluid flowing in from the inflow port 14a is divided into the branch ports 14
b and 14c are divided into equal flow rates, and the fluids from the branch ports 15b and 15c are merged at the flow outlets 15a at equal flow rates and flow out. 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 long diameters of the straight pipes 16 and 17 (the X-X axis direction) are parallel. Further, the driving device 18 and the detectors 19 and 20 are arranged in the same manner as in the case of FIG. 1, but the coil and the core or the magnet are provided in the straight pipes 16 and 17 in the direction in which the axes coincide with the Y-Y axis. Be done.

The Coriolis flowmeter shown in FIG. 2A has a straight tube 1
Since the straight pipes 16 and 17 vibrate in the direction of the minor axis, the straight pipes 16 and 17 are vibrated in a direction in which the rigidity is low, and the rigidity is high in the XX axis direction and the resonance frequency is also high, so that the influence of the external vibration part is affected. Detectors 19 and 2 that are difficult to receive and that are driven by Coriolis force
Since the phase difference signal between 0 is doubled, the sensitivity becomes higher than that in the case of FIG.

3 (a) and 3 (b) are views for explaining still another embodiment of the Coriolis flowmeter according to the present invention. FIG. 3 (a) is a longitudinal sectional view and FIG. 3 (b). 3 is a line YY in FIG. 3 (a), and in the figure, reference numerals 21 and 22 are flexible tubes, and parts having the same functions as those in FIG. 2 are denoted by the same reference numerals as those in FIG. ..

FIG. 3 (a) shows the straight pipes 16, 17 of the Coriolis flowmeter of FIG. 2 (a) with the central portions of the straight pipes 16 and 17 evenly deleted, and the flexible pipes 21 and 22 connected to the deleted portions. The coil support base 18b is provided with the removed ends 17a and 17 of the straight pipe 17.
The shaft fixing metal fitting 18d is fixed over the vicinity of b and the straight pipe 16
The ends 16a and 16b are fixed to each other. When the bending rigidity of the flexible tubes 21 and 22 is ignored, the straight tube 16 is divided into the branch tube 15 and the branch tube 14, and the branch ports 15b and 14 respectively.
b is a cantilever with each of them as a fulcrum, and the straight pipe 17 is a branch pipe 1
It is a cantilever with the branch ports 14b and 15b of 4, 15 serving as fulcrums, respectively. Therefore, as compared with the straight tubes 16 and 17 of FIG. Moreover, since the diameter is short in the driving direction (Y-Y axis), the rigidity in the XX axis direction is high, and a Coriolis flowmeter that is less affected by external vibration can be obtained.

In the above description, the cross-sectional shape of the vibrated straight pipe is described as an ellipse having a constant thickness, but it is not limited to an ellipse, and the rigidity in the direction perpendicular to the vibration is higher than the rigidity in the vibrating direction of the straight pipe. Any cross-sectional shape of Figure 4 (a)
(D) is a figure which shows the cross-sectional shape of the straight pipe of the Coriolis flowmeter in this invention.

FIG. 4 (a) has a circular outer shape 30 and an elliptic inner diameter, and has a sectional shape in which the bending rigidity in the axis XX direction is higher than the bending rigidity in the axis YY direction. There is. Figure 4
In (b), the cross-sectional shape is a rectangle 32, and the YY axis direction is the short side and the XX axis direction is the long side. In FIG. 4C, the cross-sectional shape is a rhombus 33, and the YY axis direction is the short side XX.
The axial direction is chosen as the long side. FIG. 4D shows an elliptical tube 34.
Guide fins 35 and 36 are projected from the tube walls 34a and 34b toward the axis O in the long axis direction of the inside of the tube with the same length. Not only the bending rigidity in the direction is further increased, but also the guide fins 35,
36 enhances the rectification effect. As a result, the noise component due to the turbulence of the flow is reduced in the detection signal, and a detection signal with a good SN ratio can be obtained. The guide fins 35, 36 may be provided in the XX axis direction of each cross-sectional shape of FIGS. 4 (a) to 4 (c).

[0021]

As is apparent from the above description, according to the present invention, the bending rigidity of the cross-sectional shape of the straight pipe to be the vibrating tube is reduced in the vibration direction, and the bending rigidity in the direction perpendicular to the vibration is increased. The effect is obtained. 1. The driving energy for obtaining the phase difference signal between the detectors based on the constant Coriolis force can be reduced. 2. External vibrations, mainly pipe vibrations, are often vertical vibrations, but if the direction of high bending rigidity of a straight pipe is changed to the vertical direction, the resonance frequency will also increase and the external vibration effect will be reduced, resulting in a Coriolis signal with an excellent SN ratio. Be done. 3. Since the straight pipe is flat, it has a rectifying effect on 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 drawings]

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

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

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

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

FIG. 5 is a diagram for explaining a conventional straight tube type Coriolis flowmeter.

[Explanation of symbols]

1, 2 ... Support flange, 3 ... Outer cylinder, 4 ... Straight pipe, 5 ... Driving device, 6, 7 ... Detector.

Claims (7)

[Claims] 1. A straight pipe through which a fluid to be measured flows, supporting means for supporting both ends of the straight pipe, and driving means for vibrating the straight pipe in a direction perpendicular to the longitudinal direction at the central portion of the straight pipe. When,
In a Coriolis flowmeter comprising a detector provided between the drive means and the support means for detecting a phase difference due to Coriolis force acting on the straight pipe, a cross-sectional shape of the straight pipe is defined as an axis in a vibration direction. A Coriolis flowmeter, which is symmetrical with respect to an axis in a direction perpendicular to the vibration and has a tube wall spacing in each axial direction which is long in a direction perpendicular to the vibration. 2. A plurality of straight pipes arranged in parallel through which a measurement fluid flows, branch pipes joined to both ends of the straight pipe to distribute the measurement fluid to each straight pipe in a uniform flow, and the branch pipes. And a drive means for vibrating the straight pipe in opposite phases at the central portion of the straight pipe, and a Coriolis force acting on the straight pipe, the drive means being provided between the drive means and the support portion. In a Coriolis flowmeter consisting of a detector that detects the phase difference due to
The cross-sectional shape of the straight pipe is symmetrical with respect to the axis in the vibration direction and the axis in the direction perpendicular to the vibration, and the interval between the pipe wall surfaces in each axial direction is longer in the direction perpendicular to the vibration than the interval in the vibration direction. Coriolis flowmeter characterized by. 3. The straight pipe is deleted in a predetermined section in the central portion,
The Coriolis flowmeter according to claim 1 or 2, wherein the deleted portion is connected by a flexible tube. 4. The Coriolis flowmeter according to claim 1, wherein a cross-sectional shape of the straight pipe is an ellipse having a short diameter in a vibration direction. 5. The Coriolis flowmeter according to claim 1, wherein the cross section of the straight pipe has a rectangular shape with a short side in a vibration direction. 6. The Coriolis flowmeter according to claim 1, wherein a cross-sectional shape of the straight pipe is a rhombus having a short diameter in a vibration direction. 7. Coriolis according to claim 1, further comprising guide fins of a predetermined length extending from both straight pipe walls toward the axial center in the inner diameter direction of the straight pipe cross section. Flowmeter.