JPH1048019A - Coriolis flow meter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a phase difference signal of a vibration tube in proportional to Coriolis force from electromagnetic noise at a driving portion and temperature influence of a measuring fluid. SOLUTION: Support bases 9a and 9b and support bases 10a and 10b of an optical cable are mounted at symmetrical positions from a driving portion 4 of vibration tubes 7 and 8 to be electromagnetic driven, and each optical cable for light projection or light reception are opposed thereto on one line in a vibration direction. A laser light from a laser light source 11 and a light reflected by a half mirror 12 are projected at optical fiber 19 and 20 on the light projection side. The laser light of the optical fibers 21 and 22 on the light reception side transmits the half mirror 14 and is collected, and an interference stripes whose number is in proportional to the Coriolis force is detected by a light detector 18. The laser light from the laser light source 11 transmitting the half mirrors 12 and 13 and the laser light on the light reception side reflected by the half mirror 13 are light interfered therewith, and the interference stripe of a period in proportional to a drive frequency is detected by the light detector 17.

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 method for converting a phase difference signal proportional to a Coriolis force acting on a vibrating tube through which a fluid flows into a number of interference fringes of a laser beam per unit time. And a Coriolis flow meter having a photodetector determined from the following.

[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 a support point in a direction perpendicular to the flow direction of the flow tube, the flow tube (vibration tube) A mass flow meter (Coriolis flow meter) utilizing the fact that the Coriolis force acting on the mass flow is proportional to the mass flow rate is 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 can detect mass flow rate with high sensitivity in that a shape for effectively extracting Coriolis force can be selected, but has a disadvantage that the shape becomes large. On the other hand, a straight tube type vibrating tube has a disadvantage in that the tube axis is arranged in the flow direction, so the shape is small, but 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. 5 is a view for explaining a conventional straight tube type Coriolis flowmeter. In FIG.
1, 46 are flanges, 42 is an inlet, 47 is an outlet, 4
3, 44, 48 and 49 are branch pipes, 50a and 50b are vibration pipes, 51 is an exciter, 52 and 53 are detectors, and 54 is a converter.

In FIG. 5, support members 40 and 45 are bilaterally symmetric and have branch pipes 43 and 44 and branch pipes 48 and 49 communicating with an inlet 42 and an outlet 47, respectively.
Vibration tubes 50a and 50b, which are straight tubes of the same size, are communicated in parallel with each other and are fixedly supported between 3 and 48 and branch tubes 44 and 49. An exciter 5 composed of a coil 51a and a core 51b is provided at the center of the vibrating tubes 50a and 50b.
1, the coil 51a is on the vibration tube 50a side, the core 51b is on the vibration tube 50b side, and the core 51b is a coil 5a.
1a, the exciter 51 and the supporting members 40 and 4 in the vibrating tubes 50a and 50b.
5, a detector 52 composed of a magnet 52a and a coil 52b and a detector 53 composed of a magnet 53a and a coil 53b are arranged. These detectors 52
And 53 and the exciter 51 are connected to a converter 54.

[0006] In the Coriolis flowmeter shown in FIG. 5, first, a coil 54 a of an exciter 51 is driven by a converter 54.
A closed circuit is formed to positively feedback the detection voltage output to either of the detection coils of the detectors 52 or 53 to the converter 54, and the coil 51a is controlled to have a constant amplitude so as to attract and repel the core 51b. And 50b
Is excited in the reflection phase. The vibrating tubes 50a and 50b, through which the fluid flows by the vibration, are driven in rotation directions opposite to each other with respect to the support point, so that the detectors 52 and 53 have a vibration detection signal by excitation and the rotational angular velocity and mass flow rate. Since the Coriolis force proportional to the vector product is superimposed and the Coriolis forces are in opposite phases, a phase difference signal proportional to the Coriolis force is detected between the detectors 52 and 53, and the converter 54 The phase difference signal is converted into a mass flow rate and output.

[0007]

In the above-described conventional Coriolis flowmeter, the vibrating tubes 50a and 50b are straight tubes, and are supported in parallel by supporting members 40 and 45, respectively.
Further, the support members 40 and 45 are connected to the flow tube by flanges 41 and 46. Therefore, the vibration tubes 50a and 50
A tension or compression force acts on b in the axial direction by vibration. On the other hand, the measurement fluid is diverted into the vibration tubes 50a and 50b at an equal flow rate, and is excited by the exciter 51 at the center in order to detect the mass flow rate. As a result, a tensile stress having a frequency twice as high as the excitation frequency acts on the support members 40 and 45. However, since the temperature and pressure conditions of the measurement fluid are different depending on the purpose, stress acts on the vibrating tubes 50a and 50b in the axial direction and the tube wall direction.
a, 50b. The change in the natural frequency of the vibrating tube is sought based on the principle of generation of Coriolis force. Causes errors in mass flow.
Further, since the straight pipe supported at both ends has a large bending rigidity, the deformation of the straight pipe due to the Coriolis force is small and the sensitivity is low, so that the detection signals of the detectors 52 and 53 are required to have an excellent SN ratio. . However, the detectors 52 and 53 are near the electromagnetically driven exciter 51, and the detectors 52 and 53 having the detection coils receive electromagnetic noise from the exciter 51 and the like. Further, the detectors 52 and 53 are affected by the temperature of the fluid flowing through the vibrating tube, causing a change in the impedance of the coil and a change in the magnetic flux. There was a problem in outputting a high-sensitivity signal with an excellent ratio.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has a photodetector that is highly sensitive and free from electromagnetic noise without being affected by the measurement accuracy due to the conditions of the measurement fluid. It is intended to provide a flow meter.

[0009]

The invention according to claim 1 comprises two vibrating tubes supported at two spaced apart points, and driving means for alternately driving the vibrating tubes around a supporting position. A pair of optical cable support bases installed so as to oppose the two vibrating tubes to the vibrating tube up to the position supported by the means and the two points, and the respective paired supports On the line connecting the bases, for the light emitting and receiving optical cables disposed facing each other, a laser light source for emitting the light emitting optical cable, and a laser light from the laser light source and one of the light receiving optical cables. Vibration detection means for detecting the driving frequency and amplitude of the vibrating tube from interference fringes with the laser light, and mass flow detection means for detecting Coriolis force from the number of interference fringes of laser light from both light receiving optical cables It is characterized by consisting of , It has been, is obtained by such a light detector free from the temperature influence of the electromagnetic noise and the measurement fluid from the outside with high sensitivity.

According to a second aspect of the present invention, in the Coriolis flowmeter according to the first aspect, a convex mirror is provided on a support of the optical cable for light emission, and a concave mirror is provided on a support of the optical cable for light reception. The reflected laser light is reflected by the convex mirror and the concave mirror, and the reflected laser light is transmitted to the optical cable for receiving light, thereby simplifying the position adjustment of the optical fiber for transmitting and receiving light and improving efficiency. This is to enable light detection.

According to a third aspect of the present invention, in the Coriolis flowmeter according to the first aspect, an optical axis between the light emitting optical cable and the light receiving optical cable is provided near a support for the light emitting optical cable. And a concave lens is provided, so that light detection is possible even if the sending / receiving optical fiber has a slightly reduced mounting accuracy.

According to a fourth aspect of the present invention, in the Coriolis flowmeter according to the first aspect, a light reflector is provided on a support of each of the light receiving optical cables, and the laser light reflected by each of the light reflectors is used as the laser light. It is characterized in that light is received via an optical cable for light emission, so that the optical cable for light reception of each pair of optical cables is eliminated, and light can be received efficiently at low cost.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION

(Invention of Claim 1) FIG. 1 is a view for explaining an embodiment of the invention of claim 1, and FIG. 1 (a) is a sectional view taken along line AA of FIG. 1 (b). 1 (b) is an arrow B in FIG. 1 (a).
FIG. 1C is a sectional view taken along line CC of FIG. 1A.
FIG. 2 is a sectional view taken along a line, in which 1 is a cylindrical body, 2 is a support member,
Is an exciter, 7, 8 are vibrating tubes, 9 (9a, 9b), 10
(10a, 10b) is an optical cable support, 11 is a laser light source, 12, 13, and 14 are translucent mirrors (hereinafter, referred to as half mirrors), 15 is a shielding plate (hereinafter, referred to as a shielding plate), and 16 is a lens. , 17, 18 are photodetectors, 19, 2
Reference numerals 0, 21, 22 denote optical cables, and reference numeral 23 denotes an optical connector. In the Coriolis flowmeter shown in FIG. 1A, both ends of vibrating tubes 7 and 8 having the same dimensions and curved with the same radius of curvature are supported by supporting members 2 and 2 in a cylindrical body 1, and the curved surfaces are parallel to each other. The center of curvature is arranged so as to be in the same direction with respect to the axis of the cylindrical body 1, and the measurement fluid flows evenly in the arrow Q direction.
The exciter 4 includes an electromagnetic coil and a core.
The coil and the core are fixed to the vibrating tubes 7 and 8 and driven so as to approach and repel each other in the direction of arrow F. The optical cable support 9 is a pair of the optical cable supports 9a and 9b. The optical cable support 9a is on the vibrating tube 7, and the optical cable support 9b is on the vibrating tube 8 at a plane perpendicular to the axis of the vibrating tubes 7,8. Is fixed on the straight line indicated by the vibration arrow F. Similarly, the optical cable support 10 is the optical cable support 1.
Oa and 10b are paired, and the support 10a for the optical cable is fixed to the vibration tube 7 and the support 10b for the optical cable is fixed to the vibration tube 8 on a straight line in the vibration direction indicated by the arrow F. A light projecting optical cable 19 is fixed to the optical cable support 9a and a light receiving optical cable 21 is fixed to the optical cable support 9b so as to have a common linear optical path. Similarly, a light projecting optical cable 20 is fixed to the optical cable support 10a and a light receiving optical cable 22 is opposed to the optical cable support 10b so as to project light. Optical cable 19 ~
Reference numeral 22 denotes, for example, a single mode optical fiber, which is connected to an optical connector 23 provided outside the cylindrical body 1 through a through hole 1a opened in the cylindrical wall of the cylindrical body 1. FIG.
In the above description, the vibrating tubes 7 and 8 are curved tubes, but may be two parallel tubes of the same diameter or coaxial straight tubes of different diameters. Further, as the material of the vibrating tubes, it is desirable to use materials having the same material and substantially equal linear expansion coefficients.

The laser light source 11 is a light source that emits coherent light of a single frequency, such as a He—Ne (helium / neon) laser. The laser light emitted from the laser light source 11 is reflected by the half mirror 12 and at the same time, an optical cable 19. , 20 and projected. The laser beam on the side of the light emitting optical cable 19 is transmitted to the support bases 9a and 9a of the optical cable.
and the light propagates through the light receiving optical cable 21 to reach the half mirror 14. The laser light transmitted through the half mirror 14 enters the lens 16. At this time, the laser light reflected by the half mirror 14 is shielded by the shield plate 15.

The laser light on the other side of the light emitting optical fiber 20 propagates in space between the support bases 10a and 10b of the optical cable, is transmitted to the light receiving optical fiber 22, and is transmitted through the half mirror 14 to the lens 16. Incident on. The light detector 18 detects light and darkness of the number of interference fringes per unit time, which is proportional to the phase displacement difference at the detection position, by light interference with the laser light from the optical cable 21, and performs electrical conversion to convert the light into vibration tubes 7 and 8. An electric signal corresponding to the Coriolis force of the above is obtained. The laser light from the light receiving optical cable 22 is reflected by the half mirror 14 and again reflected by the half mirror 13, and the reflected laser light is reflected by the half mirror 1.
The interference between the laser light from the laser light source 11 and the laser light from the laser light source 11 forms interference fringes, and the amplitude and the natural frequency of the vibration tubes 7 and 8 are detected by the photodetector 17.

A method of detecting the amplitude and the natural frequency of the vibration tubes 7 and 8 will be described with reference to the drawings. FIG. 2 is a diagram for explaining the principle of detecting the amplitude and the natural frequency of the vibrating tube.
FIG. 2B is a diagram showing the propagation of laser light between the optical fiber supports 10, and FIG. 2B is a diagram showing the relationship between interference fringes and vibration amplitude and frequency. As shown in FIG. 2A, the vibrating tube 7 at the positions of the optical fiber supports 10a and 10b.
And (8) are represented by oblique lines (A) and (B) and dotted lines (A '),
As shown by (B '), suction and repulsion are repeated with amplitudes a and b, respectively. According to this vibration, the spatial propagation distance of the laser light between the optical cable supports 10a and 10b changes. The rate of change of the spatial distance depends on the excitation.
It changes in a sine wave shape as indicated by S in (b). Since this change speed is a displacement amount per unit time, interference fringes having a density proportional to the speed are made incident on the photodetector 17 by interfering with the laser light from the laser light source 11. That is, at the intermediate point P, the density of the interference fringes becomes maximum at the maximum speed, and A,
At the turning point of B, the density of the interference fringes becomes minimum at the lowest speed. The turning points A and B are detected from the pulse width conversion signal of the pulse C obtained by electrically converting the signal, and the time per amplitude, that is, the vibration frequency is detected.

The magnitude of the vibration amplitude of the vibrating tubes 7 and 8 is calculated by dividing the number of interference fringes (the number of pulses C) generated per second by the cycle calculated based on the pulse C. You. This amplitude signal is used as an amplitude control signal.

On the other hand, the laser light transmitted through the half mirror 14 from the light receiving optical cables 21 and 22 is transmitted to the vibrating tubes 7 and 8.
Are formed as interference fringes due to a difference in spatial propagation distance between the optical cable supports 9 and 10 and enter the photodetector 18 via the lens 16 and are detected as electric signal pulses proportional to the number of interference fringes. Since this pulse signal is a phase difference signal based on the Coriolis force acting on the fluid flowing through the vibrating tubes 7 and 8, the mass flow rate can be obtained, for example, as the number of pulses per cycle.

(Invention of claim 2) The invention according to claim 2 is directed to a pair of optical cables 19 and 21 and an optical cable 20 for projecting and receiving light on the support bases 9 and 10 of each optical cable.
And 22 are not arranged on the same line, but are transmitted and received via light reflectors of, for example, convex and concave mirrors whose reflection angles are adjustable.

FIG. 3A is a partial sectional view for explaining an embodiment of the second aspect of the present invention, in which 9c and 9d are shown.
Is a support plate, 30a is a convex mirror, and 30b is a concave mirror. Parts that perform the same operations as in FIG. 1 are denoted by the same reference numerals as in FIG.

In FIG. 3A, a convex mirror 30a is provided on the optical cable support 9a, and a concave mirror 30b is provided on the optical cable support 9b so as to face each other at an angle of 45 °. Further, support plates 9c and 9d are integrally fixed to the support bases 9a and 9b of the optical cable, respectively, and the optical cables 19 and 21 are supported in parallel with the convex mirror 30a and the concave mirror 30b, respectively. The light is reflected by the convex mirror 30a and propagates to the concave mirror 30b, so that the reflected light enters the optical cable 21. According to this optical path, the laser light scattered by the scattering angle of the convex mirror 30a is collected by the concave mirror 30b,
By selecting the light collection angle, light collection within the assembly accuracy range becomes possible.

According to a third aspect of the present invention, a concave lens is provided between the support for the light emitting optical cable and the support for the light receiving optical cable in the vicinity of the support for the light emitting optical cable. The laser beam emitted is scattered so that light can be received by the optical cable for light reception even if there is some light loss.

FIG. 3B is a partial view for explaining the third embodiment of the present invention. In FIG. 3B, reference numeral 30c denotes a concave lens, and the same working portions as those in FIG. Reference numbers are attached. In FIG. 3 (b), the optical cables 19 and 21 face each other and the optical cable supports 9a and 9 are opposed to each other.
b, the support 9a of the optical cable 19 for light emission and the support 9b of the optical cable 21 for light reception
By providing the concave lens 30c on the optical path near b, the emitted laser light is scattered and the scattered light is enlarged and incident on the light receiving optical cable 21 with a predetermined area, so that the mounting position accuracy is slightly reduced. Can receive light correctly. Also, in FIGS. 3A and 3B, the optical cables 19 and 21 are used.
Are fixed to the supports 9a and 9b, respectively, so that
However, when the optical cable is fixed to the cylindrical body 1, the optical cable is not vibrated and is convenient for holding.

(Invention of Claim 4) According to the invention of Claim 4, a light reflector is provided on a support base of a light receiving optical cable, and a laser beam projected from the light projecting optical cable toward the light reflector is generated by the light reflector. The light is reflected by the reflector and received by the light projecting optical cable.

FIG. 4 is a partial view for explaining an embodiment of the invention according to claim 4, in which 24, 25 and 26 are half mirrors, 27 is a reflecting mirror, 28 and 29 are optical cables, Reference numerals 30 and 31 denote reflectors, and the same reference numerals as in FIG.

The light detection system shown in FIG. 4 is a system in which a single optical cable for transmitting and receiving light is used. Laser light source 1
The laser light emitted from 1 is transmitted to the half mirrors 24 and 2
5, the light is branched into optical cables 28 and 29, respectively, is spatially propagated from the positions of the support bases 9a and 10a of the optical cables, and is reflected by reflectors 30 and 31 such as mirrors and prisms. The transmitted light reaches the half mirror 25. The laser light of the outgoing side optical cable 28 reflected by the half mirror 25 is cut off by the shield plate 15, but the laser reflected light from the inflow side optical cable 29 passes through the mirror 27 and the half mirror 26 and becomes a laser light source. Form interference fringes with laser light from 11,
The interference fringes are detected by the light detector 17 and converted into electric signals, and the frequencies and amplitudes of the vibrating tubes 7 and 8 are obtained from the electric signals. The laser light from the optical cables 28 and 29 transmitted through the half mirrors 25 and 24 forms bright and dark light of interference fringes according to the mass flow rate through the lens 16, and the bright and dark light is detected by the photodetector 18 to generate electric light. The mass flow rate is determined from the electric signal according to the phase difference between the vibrating tubes 7 and 8.

[0027]

According to the first aspect of the present invention, there are provided two vibrating tubes supported at two spaced apart points, and driving means for alternately driving the vibrating tubes around a supporting position. 2
A pair of optical cable supporting bases installed so as to oppose the two vibrating tubes to the vibrating tube up to a position supported by a point, and a line connecting the paired supporting stands. , An optical cable for light emission and light reception arranged opposite to
A laser light source for projecting light onto the light emitting optical cable, and vibration detecting means for detecting a driving frequency and amplitude of the vibrating tube from interference fringes between the laser light from the laser light source and the laser light from one of the light receiving optical cables. And the mass flow rate detecting means for detecting the Coriolis force from the number of interference fringes of the laser light from both light receiving optical cables, so that it does not receive electromagnetic noise from an electromagnetically driven exciter, etc. A phase difference signal proportional to the drive frequency and the Coriolis force can be detected with high sensitivity and high accuracy.

According to a second aspect of the present invention, in the Coriolis flowmeter according to the first aspect, a convex mirror is provided on a support of the light emitting optical cable, and a concave mirror is provided on a support of the light receiving optical cable. Since the laser light from the optical cable is reflected by the convex mirror and the concave mirror and the reflected laser light is transmitted to the light receiving optical cable, the adjustment of the alignment of the optical fibers for projecting and receiving light can be omitted.

According to a third aspect of the present invention, in the Coriolis flowmeter according to the first aspect, an optical axis between the light emitting optical cable and the light receiving optical cable near the support of the light emitting optical cable. Since the concave lens is provided on the upper part, it is possible to correctly receive light even if the mounting position accuracy is slightly reduced.

According to a fourth aspect of the present invention, in the Coriolis flow meter according to the first aspect, a light reflector is provided on a support of each of the light receiving optical cables, and the laser light reflected by the light reflector is provided. Since the light is received via the optical cable for light emission, an optical cable for light reception becomes unnecessary,
Further, by adjusting the posture of the mounting position of the reflector, it is possible to transmit and receive light efficiently.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining an embodiment of the invention of claim 1;

FIG. 2 is a diagram illustrating the principle of detecting the amplitude and the natural frequency of a vibrating tube.

FIG. 3A is a partial view for explaining an embodiment of the second aspect of the present invention, and FIG. 3B is a partial cross-sectional view for explaining an embodiment of the third aspect of the present invention.

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

FIG. 5 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, 4 ... Exciter, 7 and 8 ... Vibration tube, 9 (9a, 9b), 10 (10a and 10b) ... Optical cable support base, 11 ... Laser light source, 12 and 13 , 1
4 translucent mirror (half mirror), 15 shielding plate (shield plate), 16 lens, 17, 18 photodetector, 19,
20, 21, 22 ... optical cable, 23 ... optical connector, 2
4, 25, 26: half mirror, 27: reflecting mirror,
28, 29: Optical cable, 30, 31, Reflector, 30c
…concave lens.

Claims (4)

[Claims] 1. A vibration device comprising: two vibrating tubes supported at two spaced apart points; and driving means for alternately driving the vibrating tubes around a supporting position, to a position supported by the driving means and the two points. And a pair of optical cable supporting bases installed so as to oppose the two vibrating pipes, and a pair of optical cable supporting bases facing each other on a line connecting the paired supporting bases. The optical cable for light emission and light reception, the laser light source for projecting light onto the optical cable for light emission, and the interference fringe between the laser light from the laser light source and the laser light from one of the light reception optical cables, A Coriolis flow rate characterized by comprising vibration detecting means for detecting the driving frequency and amplitude of the tube, and mass flow rate detecting means for detecting the Coriolis force from the number of interference fringes of the laser light from both light receiving optical cables. Total. 2. A convex mirror is provided on a support of the light projecting optical cable, a concave mirror is provided on a support of the light receiving optical cable, and the laser light from the light projecting optical cable is reflected by the convex mirror and the concave mirror. 2. The reflected laser light is transmitted to the light receiving optical cable.
The Coriolis flowmeter described in 1. 3. A concave lens is provided on an optical axis between the light emitting optical cable and the light receiving optical cable in the vicinity of a support for the light emitting optical cable.
The Coriolis flowmeter described in 1. 4. A light reflecting body is provided on a support of each of said light receiving optical cables, and said laser light reflected by said light reflecting bodies is received via said light projecting optical cable. 2. The Coriolis flowmeter according to 1.