JP2826011B2 - Coriolis flow meter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a Coriolis flowmeter, and more particularly, to a mass based on the principle of a straight tube type Coriolis in which a vibrating tube for generating a Coriolis force by flowing a fluid is slightly curved. It relates to a flow meter.

[0002]

2. Description of the Related Art Coriolis acting on a vibrating tube when one end or both ends of a flow tube (vibrating tube) through which a fluid to be flowed is supported and the vibrating tube is vibrated around a supporting point in a direction perpendicular to the flow direction. Coriolis flow meters that utilize the fact that the force of a force is proportional to the mass flow rate are well known. Therefore, the vibrating tube is an important part of the Coriolis flow meter, and determines the characteristics of the flow meter. The shape of the vibrating tube is roughly divided into a curved tube and a straight tube.The curved tube type vibrating tube can detect the mass flow rate with high sensitivity because the shape to select the Coriolis force effectively can be selected. Has the disadvantage of becoming larger. On the other hand, a straight tube type vibrating tube has a small shape because the tube axis is arranged in the flow direction, but has a disadvantage that the sensitivity is low and the S / N ratio is low, so that consideration must be given to disturbance. is there.

As a known document related to the present invention, there is “Apparatus and Method for Continuously Measuring Flow” in JP-A-62-238419. This relates to a Coriolis flowmeter using a straight tube supported at both ends in parallel as a vibrating tube, which will be described below.

FIG. 6 is a view for explaining a conventional straight tube type Coriolis flowmeter. In FIG.
1, 36 are flanges, 32 is an inlet, 37 is an outlet, 3
Reference numerals 3, 34, 38 and 39 denote branch pipes, reference numerals 40a and 40b denote vibration tubes, reference numeral 41 denotes an exciter, reference numerals 42 and 43 denote detectors, and reference numeral 44 denotes a converter.

In FIG. 6, support members 30 and 35 are bilaterally symmetric and have branch pipes 33 and 34 and 38 and 39 communicating with an inlet 32 and an outlet 37, respectively.
And 38 and 34 and 39, vibrating tubes 40a and 40b, which are straight tubes of the same size, are communicated in parallel with each other and fixedly supported. An exciter 41 composed of a coil 41a and a core 41b is provided at the center of the vibrating tubes 40a and 40b.
b is attached to the vibrating tube 40b so that the core 41b is inserted into the center of the coil 41a.
1 and a supporting point between the supporting members 30 and 35, a magnet 4
A detector 43 comprising a coil 3b and a coil 43b;
a and a detector 42 comprising a coil 42b. These detectors 42 and 43 and the exciter 41 are connected to a converter 44.

In the Coriolis flowmeter shown in FIG. 6, first, a coil 44a of an exciter 41 is driven by a converter 44,
A converter 44 forms a closed circuit for positively feeding back a detection voltage output to a detection coil of either the detector 42 or 43 in the converter 44, and the coil 41a is driven and controlled at a constant amplitude so as to attract and repel the core 41b. 40
a and 40b are excited in opposite phases. The vibrating tubes 40a and 40b, through which the fluid flows due to the excitation, are driven in opposite rotational directions with respect to the support points, so that the detectors 43 and 4
2 is superimposed with a drive detection signal due to the drive, and a Coriolis force proportional to the vector product of the angular velocity of the drive signal and the mass flow rate. Since the Coriolis force is generated as the opposite phase, a phase difference signal proportional to the Coriolis force is detected between the detectors 42 and 43, and the converter 44 converts and outputs the mass flow rate from the phase difference signal.

[0007]

In the above-mentioned conventional Coriolis flowmeter, the vibrating tubes 40a and 40b are straight tubes, each of which is supported in parallel by supporting members 30 and 35. Further, the support members 30 and 35 are connected to the flow tube by flanges 31 and 36. Therefore, the vibration tubes 40a and 40b
Is subjected to a tension or a compression force in the axial direction by vibration. On the other hand, the measurement fluid is diverted into the vibrating tubes 40a and 40b at an equal flow rate, and is excited by the exciter 41 at the center in order to detect the mass flow rate. As a result, the support member 30,
In the vicinity of the support position 35, a tensile stress having a frequency twice as high as the excitation frequency acts. However, since the temperature and pressure conditions of the measurement fluid differ depending on the purpose, stress acts on the vibrating tubes 40a and 40b in the axial direction and the tube wall direction, and these stresses are caused by the natural vibration of the vibrating tubes 40a and 40b. It is a factor that changes the number. Since the mass flow is an amount proportional to the drive frequency, a change in the natural frequency of the vibrating tube becomes an error factor. In addition, since the straight pipe supported at both ends has a large bending rigidity, there is a problem that the deformation of the straight pipe due to the Coriolis force is small, and the sensitivity is low.

The present invention has been made in view of the above situation, and provides a Coriolis flowmeter capable of measuring a mass flow rate with high sensitivity without being affected by measurement accuracy depending on the conditions of a measurement fluid. It was made for the purpose.

[0009]

According to a first aspect of the present invention, there is provided a tubular body having both end faces, and a straight pipe which is supported by the both end faces in the tubular body and is curved within an elastic limit for flowing a measurement fluid. A vibrating tube, driving means for vibrating in a direction perpendicular to a plane including a curved axis of the vibrating tube at a center portion of the vibrating tube, and a Coriolis of the vibrating tube provided between the driving means and the both end surfaces. And a sensor that detects the phase difference due to the force of
As a result, the deformation of the vibrating tube due to temperature change or pressure change occurs in a specified direction, so that the effect of deformation is small, compensation is easy, and the effective span of the vibrating tube is longer. This is to increase the phase difference detection sensitivity.

According to a second aspect of the present invention, there is provided a tubular body having both end faces, and a straight pipe which is supported by the both end faces in the tubular body and is curved within an elastic limit for flowing a measurement fluid, and has the same length. Two vibrating tubes having a radius of curvature, driving means for driving each of the vibrating tubes so as to approach and separate from each other at a central portion of the vibrating tubes, and a driving means for each of the vibrating tubes and the both end faces. Characterized in that it is provided with a sensor that detects a phase difference due to the Coriolis force of the vibrating tube, thereby increasing the bending radius by increasing the radius of curvature of the two vibrating tubes, An advantage similar to that of the first aspect is obtained.

According to a third aspect of the present invention, there is provided the Coriolis flowmeter according to the second aspect, wherein the two vibrating tubes are positioned in parallel, so that the shape of the main body is reduced by being positioned in parallel. Therefore, the same effect as that of the second aspect can be obtained.

According to a fourth aspect of the present invention, in the Coriolis flowmeter according to the second aspect, the two vibrating tubes are located symmetrically with respect to the center axis in the longitudinal direction of the cylindrical body. Thus, stable vibration can be achieved by eliminating the influence of vibration on both end faces at the cylindrical end face support position, and the same effect as the invention of claim 2 can be obtained.

[0013]

FIG. 1 is a diagram for explaining a basic structure of an embodiment of the present invention, and FIG.
FIG. 1B is a sectional view taken along the line AA of FIG. 1B, and FIG.
1 is a cross-sectional view taken along the line BB of FIG. 1, wherein 1 is a cylindrical body, 2 is a support member, 3 is a vibrating tube, 4 is an exciter, and 5 and 6 are detectors.

In FIG. 1, a cylindrical body 1 is, for example, a cylindrical body, and support members 2 and 2 are fixed to both ends of the cylindrical body 1. Both ends of the vibrating tube 3 which is curved within the elastic limit are penetrated and fixed to the supporting members 2 and 2. For this reason, the support members 2
2 is provided with a through hole 2a penetrating at an angle equal to the inclination of both ends of the vibration tube 3. The vibrating tube 3 is formed by inserting both ends of a straight tube into the through hole 2a of the support member 2 and bending the straight tube between the support members 2 and 2 in a direction perpendicular to the axis with a stress within the elastic limit of the straight tube. It is fixed to the body 1 at both ends. An exciter 4 is attached to the center of the vibrating tube 3 in the longitudinal direction, and detectors 5 and 6 are provided between the exciter 4 and the support members 2 at both ends.

The exciter 4 includes, for example, a coil 4a and a core 4b, and the core 4b is inserted into the coil 4a.
The coil 4a is connected to an oscillator (not shown) and driven by a constant amplitude sine wave signal. The sine wave signal can be efficiently excited by selecting a frequency equal to the natural frequency when the fluid flows into the vibrating tube 3 fixed at both ends. The detectors 5 and 6 have the same principle structure. For example, a coil 5a and a magnet 5b are disposed to face each other, and a sine wave generated in the coil 5a with the vibration of the magnet 5b fixed to the vibrating tube 3. Detect signal.

In the Coriolis flow meter, the vibrating tube 3 is driven by a sine wave by the exciter 4 so that the position of the vibrating tube 3 at the detectors 5 and 6 is opposite to the vector product of the mass flow rate of the measuring fluid and the exciting frequency. Coriolis forces in the same direction are generated. The Coriolis force is detected as a phase difference signal between the detectors 5 and 6. At this time, since the vibrating tube 3 is previously bent within the elastic limit, even if the vibrating tube 3 receives an internal stress in the axial direction due to a change in temperature and pressure, it only deforms in the bending direction. The effect of temperature and pressure can be reduced.

FIG. 2 is a view for explaining an embodiment of the second and third aspects of the present invention. FIG. 2 (a) is a sectional view taken along line AA of FIG. 2 (b), and FIG. b) is a view taken along the line BB in FIG.
FIG. 2C is a sectional view taken along the line CC of FIG. 2A, wherein 7 and 8 are vibrating tubes, 9 and 10 are optical cable supports, 11 is a laser light source, 12 , 13 and 14 are translucent mirrors (hereinafter referred to as half mirrors), 15 is a shield plate (hereinafter referred to as a shield plate), 16 is a lens, 17 and 18 are photodetectors, and 19, 20, 21 and 22 are optical cables. , 23
Numeral denotes an optical connector, and portions having the same functions as those in FIG. 1 are denoted by the same reference numerals as those in FIG.

In the Coriolis flowmeter shown in FIG. 2A, two vibrating tubes 78 having the same dimensions and the same radius of curvature, which are curved within the elastic limit, are provided in the cylindrical body 1 by the support members 2, 2. Both ends are supported and arranged so that the curved surfaces are parallel to each other, and the measurement fluid flows evenly in the arrow Q direction. The coil and the core of the exciter 4 are fixed to the vibrating tubes 7 and 8 and FIG.
Are driven so as to approach and repel each other in the direction of arrow F. Optical cable supports 9 and 10 are attached to the sensor mounting positions of the vibrating tubes 7 and 8, respectively. The optical cable supports 9 are paired with the optical cable supports 9a and 9b.
Similarly, the optical cable support 10 is fixed to face the vibrating tubes 7 and 8, respectively. Further, each of the optical cable supports 9a, 9b, 9c, 9d has an optical cable 1
Reference numerals 9, 21, 20, and 22 are fixed to face each other so that light can be transmitted and received. The optical cables 19 to 22 are connected to the optical connector 23 outside the cylindrical body 1 through the through holes 1a in the cylindrical body 1 cylindrical wall.

The laser light source 11 emits coherent light of a single frequency such as a He-Ne (helium / neon) laser, and the coherent light reflected by the half mirror 12 is simultaneously separated by the optical cables 19 and 20 and transmitted. Is done. The laser light on the optical cable 19 side propagates in space between the optical cable supports 9a and 9b and is transmitted to the optical cable 21 and transmitted through the half mirror 14 to the lens 1
6 is incident. At this time, the laser light reflected by the half mirror 14 is shielded by the shield plate 15.

The laser light on the side of the optical fiber 20 propagates in space between the optical cable supports 10a and 10b, is transmitted to the optical fiber 22, and the laser light transmitted through the half mirror 14 enters the lens 16. The light and darkness of the number of interference fringes per unit time in proportion to the phase displacement difference at the detection position by light interference with the laser light from the optical cable 21 are electrically converted by the photodetector 18 and the Coriolis between the vibrating tubes 7 and 8 is detected. An electric signal corresponding to the force is obtained. The reflected laser light from which the laser light from the optical cable 22 is reflected by the half mirror 14 is reflected again by the half mirror 13, and the reflected laser light interferes with the laser light transmitted through the half mirrors 12 and 13 to cause interference fringes. The amplitude and the natural frequency of the vibrating tubes 7 and 8 are detected by the photodetector 17. From the above, a mass flow meter can be obtained.

In the above description, the case where the vibrating tubes 7 and 8 have the same radius of curvature and are parallel has been described. However, there are other combinations of arrangements, which will be described below.

FIGS. 3A and 3B are views for explaining an embodiment of the invention according to claim 4, wherein FIG. 3A is an embodiment of the invention according to claim 4, and FIG. FIG. 7B is a diagram showing the operation of the vibrating tube in the BB section of FIG. 1 and FIG. 2 are denoted by the same reference numerals as those in FIG. 1 and FIG.

The Coriolis flowmeter shown in FIG. 3 has two vibrating tubes 7 and 8 having the same radius of curvature curved within the elastic limit.
The planes including the bending axes of the vibrating tubes 7 and 8 are parallel and the vibrating tubes 7 and 8
Are overlapped on a line perpendicular to the plane including the bending axis, and the centers of curvature of the vibrating tubes 7 and 8 are located symmetrically with respect to the central axis in the longitudinal direction of the cylindrical body. The vibrating tubes 7 and 8 are shown in FIG.
As shown in (b), the vibrating tubes 7 and 8 are driven by the exciter 4 in a direction indicated by an arrow on a straight line connecting the centers of the vibrating tubes 7 and 8.

FIG. 4 is a view for explaining another embodiment of the present invention of claim 4. FIG. 4 (a) is another embodiment of the present invention of claim 4, and FIG. FIG. 4B is a diagram showing the direction of vibration of the vibrating tube on the line BB in FIG. 4A, and portions performing the same operations as those in FIGS. 1 and 2 are denoted by the same reference numerals as in FIGS. 1 and 2. is there.

In the Coriolis flowmeter shown in FIG. 4, two vibrating tubes 7 and 8 having the same radius of curvature curved within the elastic limit are
The vibration tubes 7 and 8 are arranged symmetrically with respect to the central axis in the longitudinal direction of the cylindrical body 1 so as to be arranged on the same plane including the central axis of the cylindrical body 1 and spaced apart from each other in the cylindrical body 1. The center positions of the vibrating tubes 7 and 8 are closest, and both ends are farthest apart. As shown in FIG. 4B, the vibrating tubes 7 and 8 have arrows (+ Y _1, −Y ₁ ) and (−Y ₂ , + Y ₂ ) (| Y ₁ | =
| Y ₂ |) is driven by the exciter 4 so as to approach / separate from each other.

FIG. 5 is a diagram for explaining still another embodiment of the invention of claim 4, and FIG. 5 (a) is a diagram showing still another embodiment of the invention of claim 4, FIG. (B), FIG.
(C) is a diagram showing the vibration direction of the vibrating tube on the line BB in FIG. 5 (a), and the same operation as in FIG. 1 and FIG. Numbered.

In the Coriolis flowmeter shown in FIG. 5, two vibrating tubes 7 and 8 having the same radius of curvature curved within the elastic limit are
The vibration tubes 7 and 8 are arranged symmetrically with respect to the central axis in the longitudinal direction of the cylindrical body 1 so as to be arranged on the same plane including the central axis of the cylindrical body 1 and spaced apart from each other in the cylindrical body 1. The center positions of the vibrating tubes 7 and 8 are farthest apart, and both ends are closest. As shown in FIG. 5B, the vibrating tubes 7 and 8
Arrows (+ Y ₁ , −Y ₁ ), (−Y ₂ ,
+ Y ₂ ) direction, or (+ X ₁ ,
−X ₁ ) and (−X ₂ , + X ₂ ) are driven by the exciter 4 in a direction obliquely crossing the paper surface.

As described above, in the Coriolis flowmeter shown in FIGS. 3 to 5, the centers of curvature of the vibrating tubes 7 and 8 are symmetrically located with respect to the central axis in the longitudinal direction of the cylindrical body 1. The stress on the support position of the cylindrical body 1 due to the vibrations of (8) and (8) is balanced, and stable vibration is obtained.

[0029]

According to the first aspect of the present invention, there is provided a tubular body having both end faces, and a straight vibrating pipe which is supported by the both end faces in the tubular body and is curved within an elastic limit for flowing a measurement fluid. A driving means for vibrating in a direction perpendicular to a plane including a bending axis of the vibrating tube at a central portion of the vibrating tube; and a driving means provided between the driving means and the both end faces, and provided by Coriolis force of the vibrating tube. Since it is composed of a sensor that detects the phase difference, the direction of deformation due to temperature change and pressure change of the vibrating tube can be determined, and the effect of deformation of the vibrating tube can be reduced. Become. Furthermore, since the effective span is lengthened by bending the vibrating tube within the elastic limit, the phase difference detection sensitivity is higher than that of the straight vibrating tube.

According to the second aspect of the present invention, the tubular body having both end faces and the straight pipe supported by the both end faces in the tubular body and curved within the elastic limit for flowing the measurement fluid have the same length. Two vibrating tubes having the same radius of curvature, driving means for driving each of the vibrating tubes so as to approach and separate from each other at the center of the vibrating tubes, and the driving means and the both end faces of each of the vibrating tubes. And a sensor for detecting a phase difference due to the Coriolis force of the vibrating tube.
The bending accuracy of the two vibrating tubes can be improved.

According to the third aspect, in the Coriolis flowmeter according to the second aspect, since the two vibrating tubes are positioned in parallel, the size of the main body can be reduced in addition to the effect of the second aspect. Can be.

According to a fourth aspect of the present invention, in the Coriolis flowmeter according to the second aspect, the two vibrating tubes are positioned so that their respective centers of curvature are symmetrical with respect to the central axis in the longitudinal direction of the cylindrical body. Therefore, in addition to the effect of the second aspect, in addition to the effect of the vibration tubes 7 and 8, the stress generated near the supporting position of the cylindrical body generated by vibration is balanced, and the vibration of the vibration tubes 7 and 8 is stabilized.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a basic structure according to an embodiment of the present invention;

FIG. 2 is a diagram for explaining an embodiment of the invention according to claims 2 and 3;

FIG. 3 is a view for explaining an embodiment of the invention according to claim 4;

FIG. 4 is a diagram for explaining another embodiment of the invention of claim 4;

FIG. 5 is a view for explaining still another embodiment of the invention of claim 4;

FIG. 6 is a view for explaining a conventional straight tube type Coriolis flow meter.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Cylindrical body, 2 ... Support member, 3, 7, 8 ... Vibration tube, 4 ...
Exciter, 5, 6 detector, 9, 10 optical cable support, 11 laser light source, 12, 13, 14 translucent mirror (half mirror), 15 shielding plate (shield plate), 16
... Lens, 17, 18 ... Photodetector, 19, 20, 21,
22 ... optical cable, 23 ... optical connector.

Claims (4)

(57) [Claims] 1. A tubular body having both end surfaces, and
Curved within the elastic limit supported by the both end faces and flowing the measurement fluid
The vibrating tube at the center of the vibrating tube
Driving means for vibrating in a direction perpendicular to a plane including the bending axis;
The vibration tube is provided between the driving means and the both end faces.
And a sensor that detects the phase difference due to Coriolis force.
Coriolis flowmeter, characterized in that the. 2. A tubular body having both end faces, and
Curved within the elastic limit supported by the both end faces and flowing the measurement fluid
Two straight tubes of equal length and the same radius of curvature
A vibrating tube and each of the vibrating tubes are separated from each other at a central portion of the vibrating tube.
Driving means for driving the vibrating tubes,
The vibrating tube is provided between the driving means and the both end faces.
It consists of a sensor that detects the phase difference due to the Rioli force
Coriolis flowmeter, characterized in that. 3. The Coriolis flowmeter according to claim 2, wherein the two vibrating tubes are positioned in parallel . 4. The method according to claim 1, wherein the two vibrating tubes have respective centers of curvature.
3. The Coriolis flowmeter according to claim 2, wherein the Coriolis flowmeter is located symmetrically with respect to a center axis in a longitudinal direction of the tubular body .