JPS6158764B2 - - Google Patents

Description

Detailed Description of the Invention (a) Description of the technical field to which the invention pertains The present invention relates to a flowmeter or a current meter, and in particular to a Karman vortex flowmeter using a mechanical modulation device for light passing through an optical fiber element. or related to current meters.

More specifically, conventional light modulation methods include electro-optic light modulation, which utilizes the rotation of the optical surface by applying an electric field to a single crystal, and acousto-optic light modulation, which changes the refractive index of the medium by utilizing piezoelectric phenomena. Although this method has been put into practical use in the field of optical communications, the present invention relates to a current meter or flow meter that uses a purely mechanical modulation method that modulates the amount of light passing through an optical fiber using a mechanical input such as force or displacement. It is something.

(b) Description of the Background of the Invention Figures 1a, b, and c show a conventional method for mechanically modulating the amount of light passing through an optical fiber. In the figure, 1 is an input optical fiber, 2 is an output optical fiber, and 3 is a shutter.

FIG. 1a shows a system in which the deflection L of the shutter 3 is mechanically adjusted to modulate the amount of light passing through the output optical fiber 2.

FIG. 1b shows a misalignment type modulation method, in which light is modulated by adjusting the misalignment amount L.

FIG. 1c shows an angle shift type, in which the light is modulated by adjusting the angle θ.

Other methods include modulating the light by adjusting the distance between the end faces of optical fibers whose end faces face each other on the same axis, or using the increase in loss due to bending of the optical fiber, but these methods generally has poor sensitivity and is not widely used.

Typical dimensions of the input and output optical fibers 1 and 2 shown in FIG. 1 are that the core diameter is 100 μm, and the diameter of the cladding, which has a lower refractive index than the core, is often about 150 μm. For the core and cladding, there are inorganic types using quartz, organic types using acrylic resin, etc., or a combination of inorganic and organic types using quartz for the core and silicone resin for the cladding. has been done. There are also multimode step-index fibers in which the refractive index within the core is constant, and multimode gradient-index fibers in which the refractive index increases toward the center of the core. In addition to these, there are also single-mode fibers with extremely thin core diameters of several μm.

Although any of the above-mentioned types of fiber can be used in the mechanical light modulator used in the present invention, the last type of single-mode fiber has practical difficulties because it is difficult to align the optical connector.

The outer diameter of the optical fiber including the cladding is 150μm.
Therefore, it is difficult to align the optical fibers when configuring the modulation method as shown in FIG. Even if it fits well, it is equally difficult to maintain it. It is also vulnerable to dust adhering to the end face of the optical fiber. Trouble can also occur due to condensation on the end face.
Also, if you try to use it in water or other liquids,
The reality is that problems occur in a short period of time due to water scale formation, air bubbles adhering to the end surface, etc.

After all, conventional methods such as those shown in FIGS. 1a, b, and c can only be used for short periods of time in favorable environments such as laboratories.

As a result of intensive research and consideration in an attempt to eliminate the above-mentioned drawbacks inherent in the prior art, the present inventor inserted first and second optical fibers into the pores of an elastic body, and A mechanical light modulation device is invented, which is characterized in that a light modulation space in which no optical fiber exists is formed by separating both end faces of the light modulation space by a certain distance, and that the amount of light passing through the light modulation space is modulated by elastic bending of the light modulation space. Therefore, we have developed a new highly reliable mechanical light modulation device that does not require troublesome operations such as alignment, and does not deteriorate over time even under adverse environments. This light modulation device is an invention described in Japanese Patent Application No. 154814/1983, co-filed with the present application.

Next, the above-mentioned mechanical light modulation device, which is the basis of the present invention, will be explained in detail with reference to the drawings.

FIG. 2 is a diagram showing the basic configuration of the mechanical light modulation device. In the figure, reference numeral 11 indicates an input optical fiber, 12 indicates an output optical fiber, and 14 indicates a capillary tube through which the optical fibers 11 and 12 pass. No optical fiber exists between the end faces 15 and 16 of the input and output optical fibers 11 and 12. As will be described later, since light is modulated in the space between the end faces 15 and 16, this space will hereinafter be defined as a modulation space. The capillary tube 14 is made of metal or plastic material or the like. The input/output optical fibers 11 and 12 have a cladding on the core, but the cladding is omitted in FIG. 2.

Now, if the input optical fiber 11 is fixed and the output optical fiber 12 is bent by an angle θ as shown by the broken line in FIG. 2, the modulation space will be bent as shown by the broken line and the amount of light passing through the output fiber 12 will be Decrease.

FIG. 3a shows a case where the deflection angle θ of the output optical fiber 12 is vibrated at an angular frequency ω and θ=θmsinωt. The amount of transmitted light in this case is shown in FIG. 3b.

In FIG. 3b, curve A shows the case where the inner wall of the capillary tube 14 is roughened or blackened by applying black paint. Light passes only when the input and output fibers 11 and 12 are in a straight line as shown in FIG. If there is a slight deflection angle, the light will be absorbed by the inner wall of the capillary tube, and the amount of output light will become zero, resulting in a sharp pulse-like output as shown by curve A. Curve B in FIG. 3b shows the case where the degree of blackening of the inner wall of the capillary tube 14 is reduced. In this case, some of the light reflected by the inner wall is transferred to the output optical fiber 1.
2, the output light amount is increasing. curve C
1 shows a case where the inner wall of the capillary tube 14 has a substantially mirror surface. In this case, the amount of light passing through increases further;
Since there is almost no absorption of light on the inner wall of the capillary, the light passes through without loss, and the alternating current component in curve C becomes small. As will be described later, the present invention utilizes this alternating current component, so curve C is not preferable. Therefore, an appropriate degree of blackening is required to increase the alternating current component in the output waveform.

As is clear from FIG. 3b, the mechanical angular frequency is ω, but the angular frequency of the fundamental wave of the AC component in the output light amount is 2ω. The two points that are practically important in such a deflection angle modulator are that the amount of alternating current in the amount of passing light is large, and that the amount of light changes suddenly at a small deflection angle.

Generally, when a multimode step-index fiber is used as a white light source, the light emitted from the end face 15 in FIG. 2 spreads out in a cone shape in the modulation space with an apex angle of about 20 degrees. Therefore, even if the output fiber is in line with the input fiber,
Only a small amount of light enters the end face 16 of the output fiber, and most of it is absorbed by the inner wall of the capillary tube 14. In order to reduce the spread of cone-shaped light, it is effective to place a minute condensing lens adjacent to the end face 15 of the input fiber. It is also advantageous to place a lens just in front of the end face 16 of the output fiber. It is also effective to arrange a rod lens that functions equivalently to the lens. It is also effective to fill the space between both end faces of the input/output optical fiber with a transparent solid or liquid whose refractive index matches that of the core. Such a medium is called a matching agent. Prevents light spreading and reduces Fresnel reflection loss at the end face.

As shown by the broken line 17 in Fig. 2, when the capillary tube in the modulation space is crushed by a plane perpendicular to the plane of the paper to narrow the optical path, the amount of light changes suddenly with a slight change in the deflection angle, and the output waveform becomes pulse-like. , subsequent waveform shaping becomes advantageous. Crushing as shown in reference numeral 17 reduces the stress generated on the surface of the capillary tube due to the bending angle θ, and is also advantageous in terms of fatigue failure of the capillary tube due to vibration. Instead of squishing, the same effect can be obtained by stretching the modulation space and reducing the circular cross-sectional area of the modulation space.

If a reflecting mirror is placed on the end face 16 of the output optical fiber in FIG. 2, the light from the input optical fiber 11 returns to the input optical fiber 11 again. This returning light is also modulated by the deflection angle θ. Since the returned light can be easily separated from the incident light, this reflection method eliminates the need for the output optical fiber 12, the input optical fiber also serves as the output optical fiber, and only one fiber is required.

As is clear from the above explanation, by passing the optical fiber through the capillary tube, the cores of the input and output optical fibers are automatically aligned by the capillary tube, so there is no need for the troublesome alignment operation as in the past. . Once inserted into the capillary tube, the core and end face of the optical fiber are protected by the capillary tube 14.
It will not deteriorate over time. That is, since the modulation space is protected by the capillary tube 14, it will not deteriorate due to dust or condensation, and high reliability can be maintained even under adverse environments. Further, by selecting the material of the capillary tube 14, it can operate with sufficient reliability even in corrosive gases and liquids, which has great practical effects. Furthermore, by collapsing the capillary tubes in the modulation space and narrowing the optical path, light modulation can be achieved with a slight change in the deflection angle, which is extremely advantageous in practice.

Figure 2 shows the simplest example of the mechanical light modulation device used in the present invention, but if the deflection angle θ is set large and the function of an optical switch is provided, multiple modulation spaces can be connected in series or parallel. By connecting
Since OR circuits, AND circuits, and other logic circuits can be configured, complex logic circuits that respond to multiple mechanical inputs can be realized. In such optical switches, the modulation space is bent in advance to block the light, and then the input and output optical fibers are aligned in a straight line using mechanical input to allow the light to pass (normally closed contact). There is a method (normally open contact) that bends the modulation space using mechanical input, which is the opposite of this.

In the configuration example described above, a capillary tube is used for convenience of explanation, but the capillary tube is not essential. For example, a modulation space is constructed by arranging input and output optical fibers to face each other in an elastic body with pores perforated.
It is clear that when an elastic body is bent, light is modulated in the same way as a capillary tube.

In FIG. 2, if the end face 16 of the output optical fiber 12 is cut obliquely with respect to the central axis of the output optical fiber 12, the deflection angle θ=θmsinωt
The fundamental angular frequency of the alternating current component of the output light when vibrated at 2ω can also be set to ω instead of 2ω.

Now, as conventional devices of this type that utilize Karman vortices, there are those that detect Karman vortices thermally, those that detect them as differential pressure, those that detect them using ultrasonic waves, and those that magnetically detect tail vibration caused by vortices. There are methods that measure the alternating force that acts on the vortex generator as a reaction to the Karman vortex generation using a piezoelectric element or a strain gauge. Each of these methods has its advantages and disadvantages, but the following (1) to (4) are common disadvantages.

(1) Generally complex and expensive.

(2) Because it uses an electrical method, there is a problem with explosion safety.

(3) For the same reason as (2) above, it is vulnerable to electromagnetic induction.

(4) It is difficult to measure the flow rate of small diameters, and the inner diameter is approximately 50mm.
The degree is minimal.

(c) Description of the purpose of the invention The present invention has been made in order to solve the above-mentioned drawbacks inherent in this type of technology by paying attention to the above-mentioned circumstances of the prior art. The object of the present invention is to provide a new flow meter or current meter which can be integrally molded, can be constructed at an extremely low cost, is essentially safe against explosions, and is free from electromagnetic induction.

(d) Structure of the Invention In order to achieve the above object, the Karman vortex flowmeter according to the present invention comprises a Karman vortex generator disposed perpendicularly to the flow of fluid, and a Karman vortex generator installed downstream of the Karman vortex generator. a vibrating tail fin, and inserting first and second optical fibers into the pores of the elastic body at the connection portion between the vortex generator and the oscillating tail fin or into the tail fin; The optical modulator is configured by providing a light modulation device that forms a light modulation space in which no optical fiber exists by separating both end faces of the fiber by a certain distance, and elastically deforms the modulation space by vibration of the tail wing to modulate the optical fiber. It is characterized by modulating the amount of light passing between the two.

(e) Description of Embodiments of the Invention Next, a preferred embodiment of the present invention will be specifically described with reference to the drawings.

FIG. 4 is a sectional view showing an embodiment of the present invention in which the mechanical light modulation device shown in FIG. 2 is applied to a Karman vortex flow meter. Figure 5 is a side view when the right pipe in Figure 4 is removed, Figure 6 is a sectional view taken along line 6-6 in Figure 4 and seen in the direction of the arrow, and Figure 7 is light modulation. It is an enlarged sectional view of a part.

4 to 7, reference numeral 30 indicates a pipe through which fluid flows in the direction of arrow 31. In FIGS. A ring-shaped gasket 33 is sandwiched between a flange 32 formed at the end of the pipe 30 and fixed with bolts 34. The inner diameter of the ring-shaped gasket 33 is equal to the inner diameter of the pipe 30. A Karman vortex generator 35 is inserted perpendicularly to the fluid flow and diametrically. Both ends of the vortex generator 35 are fixed to the ring-shaped gasket 33 by connecting bodies 36. As shown in FIG. 6, the Karman vortex generator 35 has a trapezoidal cross section and generates a regular Karman vortex street 37 within a certain Reynolds number range.

Here, the generation frequency of the vortex row 37 is determined from the pipe 3
When the average flow velocity of the fluid in 0 is v and the width of the vortex generator 35 is D, the frequency is expressed as follows: =St·v/D (1). However, St is a dimensionless quantity called the Strouhal number, and is a constant having a value of approximately 0.18. Since the frequency and the average flow velocity v are in a directly proportional relationship, by measuring the frequency, the average flow velocity v, that is, the flow rate of the fluid can be determined.

Conversely, since the frequency, that is, the modulation frequency, changes by changing the flow rate or velocity of the fluid, it is clear that the Karman flowmeter of the present invention can be used as it is as an optical modulation device. .

On the downstream side of the Karman vortex generator 35, a tail 38 is provided.
is installed. A constriction 39 is formed at the connection between the tail 38 and the vortex generator 35. The tail 38 vibrates as indicated by an arrow 40 at a frequency corresponding to the frequency at which the Karman vortex is generated. The presence of the window 41 further facilitates the vibration of the tail fin 38.

The input optical fiber 11 is an optical connector (not shown)
It passes through the inside of the vortex generator 35 as shown by the broken line. The input light inputted from the input optical fiber 11 is modulated at the constricted portion 39 and is extracted from the output optical fiber 12 to the outside.

FIG. 7 is an enlarged sectional view of the constricted portion 39. A capillary tube 14 is passed through a constriction 39 between the vortex generator 35 and the tail 38 . The input optical fiber 11 and the output optical fiber 12 are passed through the capillary tube 14 and define a modulation space 42 between their end faces. Due to the bending (elastic deformation) of the modulation space 42 due to the vibration of the tail 38, the amount of passing light is modulated.

The materials of the vortex generator 35, tail fin 38, etc. will be determined by the fluid to be measured, but plastic is more preferable than metal. As is clear from FIGS. 4 to 6, the vortex generator 35 and the tail fin 38 are axially symmetrical with respect to the central axis of the pipe 30, so that it is easy to integrally mold them from a plastic material. As a plastic material, polyacetal resin, polypropylene resin, fluororesin, etc. have an appropriate elastic modulus,
It is advantageous in terms of corrosion resistance. Elastomers such as rubber are also suitable. However, it is undesirable for the vortex generator to vibrate, so in that case it is necessary to insert vibration-preventing ribs.

Although the capillary tube 14 shown in FIG. 7 is not essential, it is easier to mold the metal capillary tube by passing an optical fiber through it in advance.

Figures 4 to 6 show examples of measuring the flow velocity in a pipe, but as a modification, the wind velocity in the atmosphere can also be measured by forming a long vortex generator into a rod shape and attaching a tail to its tip. . Furthermore, by attaching a plurality of tail blades to a long vortex generating body, it is possible to measure the flow velocity distribution, which is convenient for measuring the flow velocity distribution in waterways and the like.

In this embodiment, the cross-sectional shape of the Karman vortex generator 35 is formed into a trapezoidal shape as shown in FIG. In short, any material that stably generates Karman vortices over a wide range of Reynolds numbers is sufficient.

In addition, the constriction 39 and the window 41 in FIGS. 4 to 7
are not essential and may not be provided. When trying to widen the measurement range, the tail fin 38 and constriction 39 inevitably become weaker. To prevent damage during the production process or during excessive input, the tail 38
It is practically useful to install a stopper to limit the vibration amplitude as necessary. This stopper has been omitted in the above description.

In the present embodiment described above, the light is modulated by the constricted portion 39, but it is clear that the light modulating portion may be formed within the tail fin instead by forming the entire tail fin to be soft and bendable.

Further, although the cross-sectional shape of the optical fiber and capillary tube is circular, it is not necessarily circular, and oval, square, etc. can be used without much difference in function and effect. The only difference is that the shape is easier to obtain.

(f) Description of Effects of the Invention The Karman vortex flowmeter according to the present invention is constructed as described above and solves all of the above-described drawbacks of the conventional flowmeter. That is, since it can be integrally formed by molding, it can be constructed at an extremely low cost. Furthermore, because it uses optical methods, it is inherently safe against explosions and has no electromagnetic induction. In addition, it can be fully put into practical use for pipes with inner diameters up to about 10 mm, and has the advantage that there are few factors that limit the lower limit of pipe inner diameters, so it has great practical effects.

Although the present invention has been described above with reference to its preferred embodiments, it goes without saying that these are merely illustrative and do not have a limiting meaning. Therefore, without departing from the spirit of the present invention, the present invention may be implemented with various modifications other than those described above, but all such modifications and changes are included within the scope of the present invention. be.

[Brief explanation of the drawing]

Figures 1a, b, and c are diagrams explaining the principle of a conventional mechanical light modulation method; Figure 2 is a diagram explaining the principle of a mechanical light modulation device used in the present invention; Figures 3a,
b is a diagram for explaining the operation of the optical modulation device shown in FIG. 2, FIG. 4 is a sectional view showing an embodiment of the Karman vortex flowmeter according to the present invention, and FIG. 5 is a diagram on the right side of FIG. 4. 6 is a sectional view taken along the line 6--6 of FIG. 4 and viewed in the direction of the arrow, and FIG. 7 is an enlarged sectional view of the light modulation portion. 1, 11... Input optical fiber, 2, 12... Output optical fiber, 3... Shutter, 14... Capillary tube, 15, 16... End face of optical fiber, 30...
Pipe, 32... flange, 33... ring-shaped gasket, 34... bolt, 35... Karman vortex generator, 36... connection body, 37... Karman vortex,
38... tail, 39... waist, 41... window,
42...Modulation space.

Claims (1)

[Claims] 1. A system comprising a Karman vortex generator disposed perpendicular to a fluid flow and a vibrating tail mounted on the downstream side of the Karman vortex generator, and a connection between the vortex generator and the vibrating tail. first and second optical fibers are inserted into the pores of the elastic body in the section or the tail, and the end surfaces of the first and second optical fibers are separated by a certain distance so that no optical fibers exist. A Karman vortex flowmeter characterized in that a light modulation device having a light modulation space is provided, and the amount of light passing between the optical fibers is modulated by elastically deforming the modulation space by vibration of the tail. 2. The Karman vortex flowmeter according to claim 1, further characterized in that the elastic body is a capillary tube made of metal or plastic material. 3. The Karman vortex according to claim 1 or 2, further characterized in that a transparent liquid or solid whose refractive index matches the refractive index of the core of the optical fiber is sealed in the light modulation space. Flowmeter. 4. The Karman vortex flowmeter according to claim 1 or 2, further characterized in that a lens or a rod lens is inserted in the light modulation space. 5. Claim 1 further characterized in that the light modulation space is compressed to narrow the light path.
The Karman vortex flowmeter according to item 1 or 2. 6. The Karman vortex flowmeter according to claim 1 or 2, further characterized in that the optical modulation space is expanded to narrow the circular cross-sectional area of the optical path. 7. The Karman vortex flowmeter according to claim 1 or 2, further characterized in that a reflecting mirror is inserted at one end of the light modulation space. 8. The Karman vortex flowmeter according to claim 1 or 2, further characterized in that the end face of the second optical fiber is inclined with respect to the fiber axis. 9. The Karman vortex flowmeter according to claims 1 to 8, further characterized in that the inner wall of the light modulation space is blackened. 10. The Karman vortex flowmeter according to claim 1, further characterized in that the Karman vortex generator is formed long and a plurality of vibrating tail blades are installed on the vortex generator.