JPH0642992A - Coriolis flowmeter - Google Patents

Abstract

PURPOSE:To enable measuring large flowrate with low pressure loss, high sensitivity and stably by eliminating the cross force acting on the support plate in the axis direction of a vibration pipe in the case the vibration pipe of straight pipe fixed at the both ends to the support plate is driven at the center. CONSTITUTION:In between support plates 2 and 6 of support pipes 1 and 5, even pairs of vibration pipes consisting each pair of two parallel vibration pipes 9 and 10, and 11 and 12 are arranged in parallel. Vibrators 13 and 14 are driven by an oscillator 19 and a phase shifter 20 with sine wave phase shift for 90 degree so that each pair is opposite to each other. The phase shift of the signals from detectors 15 and 16 is detected by a phase shift detector 21 and the phase shift of the signal from detectors 17 and 18 is detected by a phase shift detector 22, they are arranged in-phase with a phase shifter 23 and added by an adder 24, and from the added value, the mass flowrate is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Coriolis flowmeter, and more particularly to a straight pipe type Coriolis flowmeter composed of a plurality of pairs of straight pipes in which vibration pipes through which a fluid to be measured flows are parallel.

[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 flow meter (Coriolis flow meter) that utilizes the fact that the Coriolis force acting on is proportional to the mass flow rate is well known. The vibrating tube in this Coriolis flowmeter 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 can detect the mass flow rate with high sensitivity in that the shape for effectively extracting the Coriolis force can be selected, but the shape becomes large. On the other hand, in the straight tube type, since the vibrating tube is arranged in the flow direction, the shape is small, but the sensitivity is low, and the SN ratio is lowered, so that there is a drawback that more consideration must be given to disturbance. is there.

A known document relating to the present invention is "apparatus and method for continuously measuring flow" in Japanese Patent 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 tube type Coriolis flowmeter, in which 50 and 55 are support members and 5.
1, 56 are flanges, 52, 57 are inflow / outflow ports, 53, 5
4, 58 and 59 are branch pipes, 60a and 60b are vibrating pipes, 6
1 is an exciter, 62 and 63 are detectors, and 64 is a converter.

In the figure, the support members 50 and 55 are bilaterally symmetrical and have branch pipes 53 and 54 and 58 and 59 which communicate with the inflow and outflow ports 52 and 57, respectively.
Between 8 and 54 and 59, vibration tubes 60a and 60b, which are straight tubes of the same size, are connected in parallel and fixedly supported in parallel with each other. A coil 6 is provided at the center of the vibrating tubes 60a and 60b.
An exciter 61 composed of 1a and a core 61b is provided,
The coil 61a is disposed on the vibrating tube 60a side, the core 61b is disposed on the vibrating tube 60b side, and the core 61b is inserted in the center of the coil 61a.
A detector 63 including a magnet 63a and a coil 63b and a detector 62 including a magnet 62a and a coil 62b are provided between the support points of the exciter 61 and the support members 50 and 55 at 0b. There is. The detectors 62 and 63 and the exciter 61 are connected to a converter 64.

In the Coriolis flowmeter shown in FIG. 5, the coil 64 of the exciter 61 is first driven by the converter 64, and the converter 64 outputs the detection voltage output to the detection coil of either the detector 62 or 63. The coil 61a is controlled to have a constant amplitude so as to form a closed loop for positive feedback so as to attract and repel the core 61b, 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 rotational directions opposite to each other with respect to the support points, the vibration detection signals by the excitation, the rotational angular velocity and the mass flow rate are applied to the detectors 63 and 62. The Coriolis force proportional to the vector product is superimposed, a phase difference signal proportional to the Coriolis force is detected between the detectors 62 and 63, and the converter 64 converts and outputs the mass flow rate.

FIGS. 6A and 6B are diagrams showing vibration waveforms of a conventional Coriolis flowmeter, and FIG. 6A shows a vibration tube 60a.
6B is a diagram showing the vibration of the vibrating tube 60b. In the figure, Aa and Ab and Ba and Bb are the vibrating tube 60b.
The vibrations of a and 60b and changes in the axial force acting on the support members 50 and 55 are shown. As shown in the figure, in the straight tube type Coriolis flowmeter, when the vibrating tubes are driven in opposite phases, tensile stress in the axial direction having a double frequency acts on the support member. Tensile stress is applied to the support members 50 and 55
Since it is added in and becomes a high-order alternating load of 2 times,
Exciting the outside through the supporting members 50 and 55, or making the zero point unstable will have various adverse effects. In particular, when a plurality of pairs of vibrating tubes are arranged in parallel and driven in the same phase in order to measure a large flow rate with a low pressure loss, there is a problem that the influence is doubled.

[0008]

[PROBLEMS] The present invention has been made in view of the above circumstances, and in a straight pipe type Coriolis flowmeter, the advantage that the straight pipe type Coriolis flowmeter is small is utilized, and a vibrating tube that is a straight pipe is used. Coriolis that can be measured with high sensitivity by canceling the alternating load of double frequency that acts on the supporting member of the vibrating tube in the axial direction of the vibrating tube when it is driven, eliminating the adverse effect caused by the alternating load and reducing the pressure loss. The purpose is to provide a flow meter.

[0009]

In order to achieve the above object, the present invention provides (1)
An even number of pairs of vibrating pipes in which two parallel straight pipes through which the fluid to be measured circulates are paired, supporting means for supporting the vibrating pipes at both ends, and two vibrating pipes in each pair are centered in the longitudinal direction. Oscillate in an opposite phase in the direction perpendicular to the flow, and oscillate half pairs of the even-numbered vibrating tubes so as to have a phase difference of 90 ° with respect to the other half pairs; A detector for detecting the phase difference between the upstream portion and the downstream portion, and an adding means for adding the absolute value of the phase difference generated between the even-numbered pairs of detectors. Further, (2) in the above (1), in the outer cylinder capable of interposing a structure in which the vibrating tube, the supporting means, the driving means and the detector are integrally formed in the flow tube, By fixing and storing at least one of the supporting means,
(3) In any one of the above (1) or (2), a pressurizing means for applying a constant compressive force is arranged between the supporting means for supporting both ends of the vibration tube, and further, (4) In any one of the above (1) to (3), the parallel surface of the vibrating tube formed by a pair of parallel straight tubes is set to each straight tube with respect to the line of intersection with the parallel surface of the other vibrating tube. It is characterized by arranging so as to be symmetrical positions.

1 (a) and 1 (b) are views for explaining a Coriolis flowmeter of the present invention, in which 1,5 are support tubes,
2, 6 are support plates, 3, 7 are support holes, 4, 8 are mounting flanges, 9, 10, 11, 12 are vibrating tubes, 13, 14 are exciters, 15, 16, 17, 18 are detectors, 19 is an oscillator,
20 is a 90 ° phase shifter, 21 and 22 are phase difference detectors, 23
Is a phase shifter, and 24 is an adder.

In the figure, the support pipes 1 and 5 have the same shape and have flanges 4 and 8, respectively, and are interposed in a flow pipe (not shown) to connect the inflow port 4a and the outflow port 8a. Support plates 2 and 6 are arranged so as to face the inlet 4a and the outlet 8a, and 4 or an even number of support holes 3, 7 of 4 or more are opened through the support plates 2 and 6. . Both ends of the vibration pipes 9, 10, 11, 12 having the same natural frequency are fixed to the support holes 3, 7 as straight pipes. In addition, in FIG. 1A, four lines are arranged in a plane for ease of description.
As shown in (b), the vibrating tubes 9 and 10 make a pair, and the vibrating tubes 11 and 12 make another pair, and an even number of pairs are formed with the smallest unit being an even number. Vibration tube pair 9
The surface including the and 10 and the surface including the vibrating tubes 11 and 12 intersect as shown.

Exciters 13 and 14 are arranged at the central portion in the longitudinal direction of each pair of vibrating tubes.
On the other hand, detectors 15 and 16 are arranged between the support plates 3 and 6, respectively. The exciters 13 and 14 are electromagnetic drive means having the same specifications, for example, the coil 13a and the coil 13a.
And a core 13b inserted in the hollow part of the core. Further, the detectors 15 to 18 are also electromagnetic detectors having the same specifications, and are composed of, for example, a coil 15a and a magnet 15b, and are arranged so as to face each other in a non-contact manner with the vibrating tubes 9 to 12.

The oscillator 19 causes the exciters 13 and 14 to have a natural frequency of the vibrating tubes 9 to 12 and a 90 ° phase shifter 20 so that the vibrating tubes 11 and 12 are 90 ° out of phase with the vibrating tubes 9 and 10. The natural frequency is obtained by positively feeding back and amplifying the output of the detection coil 17a to the oscillator, driving the coil 14b, and controlling the amplitude to be constant. The phase difference between the detectors 15 and 16 is detected by the phase difference detector 21, and the phase difference between the detectors 17 and 18 is detected by the phase difference detector 22. A phase shifter 23 is connected to the phase difference detector 21, and the output signal of the phase difference detector 22 is made into the same phase and added by an adder 24 and output from an output terminal 25. The method of addition between the phase difference detectors 21 and 23 is not limited to the method shown in the figure, and digital addition or other method in which absolute values are added may be used.

Next, the Coriolis flowmeter according to the present invention will be described with reference to FIGS. 2 (a) and 2 (b) are diagrams for explaining a driving waveform for driving the vibration tube, and FIG. 3 is a diagram for explaining a cross load acting on the support plate.
FIG. 2A is a diagram showing a phase difference between the exciters 13 and 14, in which the vertical axis represents the amplitude and the horizontal axis represents the time, and the vibrating tubes 9 and 10 have a sinusoidal wave sin ωt with an amplitude 2α and a frequency ω. 2 and the vibrating tubes 11 and 12 are driven in the opposite phase of a sinusoidal wave of cos ωt that is advanced by 90 ° with the same amplitude 2α. ) 1
80 ° out of phase. The vibrating tube 11 and the vibrating tube 12 are further driven by αcosωt and −αcosωt, which are opposite in phase by 90 ° between αsinωt and −αsinωt.

3 (a) and 3 (b) are views showing an alternating load acting on the supporting plate, FIG. 3 (a) is an alternating load acting on the supporting plate 2, and FIG. 3 (b) is a supporting plate 6. Shows the alternating load acting on. With each alternating load, when the vibrating tubes 9 to 12 are linear, the tensile force acting on the support plates 2 and 6 is zero, but when the amplitude of the vibrating tubes 9 to 12 is the peak value, the tensile force peaks. It becomes a value. That is, the frequency of the pulling force is twice the driving frequency of the vibrating tubes 9 to 12. Moreover, since the alternating frequency for driving the vibrating tubes 9 and 10 and the alternating frequency for driving the vibrating tubes 11 and 12 are 90 ° out of phase with each other, the tensile forces acting on the support plates 2 and 6 are in opposite phases to cancel each other. Therefore, the combined force of tensile force becomes a constant value. As shown,
The vibrating tubes 9 to 12 are provided between the support plates 2 and 6 by providing a pressurizing means for applying a compressive stress of 1/2 the amplitude β.
Since the pulling and compressing forces due to the drive are not applied and there is no external vibration influence, it is possible to stably measure a large flow with a low pressure loss.

FIG. 4 is a side sectional view for explaining another embodiment of the Coriolis flowmeter of the present invention. In the figure, 30 is an outer cylinder and 31 is a hollow chamber, which has the same function as in FIG. Are given the same reference numerals.

In the figure, the outer cylinder 30 has its outer circumferences joined at the outer circumferences of the support tubes 1 and 5, surrounds the vibrating tubes 9 to 12, and is connected so as to integrally form a Coriolis flowmeter. Composed of materials with the same coefficient. The Coriolis flowmeter is driven in the same manner as the Coriolis flowmeter without the outer cylinder 30 shown in FIG. 1 by driving paired vibrating tubes 9 and 10 and 11 and 12 with sine waves having 90 ° different phases. Vibration does not occur at all parts of the central portion B of the position 13, the position A of the support plate 2 and the position A'of the support plate 5.

[0018]

As is apparent from the above description, the present invention has the following effects. (1) Effect corresponding to claim 1: Two vibration tubes are used as a pair, and an even number of pairs have a vibration phase of 90 °.
Since different sine waves are driven, there is no fluctuation in the tensile force generated between the supporting means due to the driving, and since it has a constant value, the vibrating tube is vibrated stably, and no zero point occurs even in long-term measurement. Since even pairs of two parallel vibration tubes are connected in parallel, the pressure loss is small and a large flow rate can be measured.
Since the Coriolis force detected by each pair of vibration tubes is added, it can be detected with high sensitivity. When an abnormality occurs from any one of the pair of vibrating tubes, the abnormality can be notified by referring to the flow rate measurement values of other normal pairs, and the normal value can be calculated without stopping the measurement. (2) Effect corresponding to claim 2: Since the vibrating tube is configured to be integrally housed in the outer cylinder, pressure is introduced into the hollow chamber without transmitting vibration to the outside, and the measuring liquid is introduced. It is possible to provide a stable and small flow meter capable of measurement without being affected by the pressure by making the pressure equal to the pressure. (3) Effect corresponding to claim 3: By applying a constant compressive force between the support plates of the vibrating tube, external force to the support plates is eliminated, and stable driving can be provided. (4) Effect corresponding to claim 4: Since the surface of the pair of parallel vibrating tubes intersects with the surface of another pair of parallel vibrating tubes, a measurement error occurs due to disturbance. Also, the average value of the above two pairs of vibrating tubes is taken, and this is doubled to calculate the total flow rate to obtain the flow rate signal, thereby making it possible to reduce the instantaneous error and improve the total flow rate measurement accuracy.

[Brief description of drawings]

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

FIG. 2 is a diagram for explaining drive waveforms for driving a vibration tube.

FIG. 3 is a diagram showing an alternating load acting on a support plate.

FIG. 4 is a side sectional view for explaining another embodiment of the Coriolis flowmeter of the present invention.

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

FIG. 6 is a diagram showing a vibration waveform of a conventional Coriolis flowmeter.

[Explanation of symbols]

1, 5 ... Support tube, 2, 6 ... Support plate, 3, 7 ... Support hole, 4, 8
… Mounting flange, 9,10,11,12… Vibration tube, 1
3, 14 ... Exciter, 15, 16, 17, 18 ... Detector,
19 ... Oscillator, 20 ... 90 ° phase shifter 21, 22 ... Phase difference detector, 23 ... Phase shifter, 24 ... Adder, 30 ... Outer cylinder,
31 ... Hollow chamber.

Claims (4)

[Claims] 1. An even number of pairs of vibrating pipes having two parallel straight pipes through which a fluid to be measured flows, support means for supporting the vibrating pipes at both ends, and two vibrations in each pair. The tube is vibrated in the opposite direction in the direction perpendicular to the flow with the center in the longitudinal direction.
A drive unit that vibrates so as to have a phase difference of 0 °, a detector that is provided in a section between the drive unit and the support unit, and that detects a phase difference between an upstream portion and a downstream portion; A Coriolis flowmeter, comprising: an addition means for adding the absolute value of the phase difference generated between the detectors. 2. A structure in which the vibrating tube, the supporting means, the driving means and the detector are integrally formed is housed by fixing at least one of the supporting means in an outer cylinder which can be inserted in the flow tube. The Coriolis flowmeter according to claim 1, wherein 3. The Coriolis flowmeter according to claim 1 or 2, wherein a pressurizing means for exerting a constant compressive force is arranged between supporting means for supporting both ends of the vibrating tube. 4. A parallel plane of a vibrating tube formed by a pair of parallel straight tubes is arranged such that each pair of straight tubes is symmetrical with respect to a line of intersection with the parallel planes of other pairs of vibrating tubes. The Coriolis flowmeter according to claim 1, wherein the Coriolis flowmeter is provided.