JPS6158765B2 - - 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 flow meter or a current meter, and in particular,
The present invention relates to a Karman vortex flowmeter or current meter that utilizes a mechanical modulation device for light passing through a fiber optic element.

More specifically, as a light modulation method, conventionally,
Electro-optic light modulation, which utilizes the rotation of the plane of polarization by applying an electric field to a single crystal, and acousto-optic light modulation, which uses piezoelectric phenomena to change the refractive index of the medium, have been put into practical use in optical communications. The present invention relates to a current meter or flowmeter 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.

(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 specifically explained with reference to the drawings.

FIG. 2 is a diagram showing the basic structure of the mechanical light modulation device. In FIG. 2, ₁₁₁ is the core of the input optical fiber 11, ₁₁₂ is the cladding of the input optical fiber 11, ₁₂₁ is the core of the output optical fiber 12, 12
₂ designates the cladding of the output optical fiber 12, respectively. Input optical fiber 11 and output optical fiber 12
are continuous and identical, and the cladding part of the same optical fiber element is peeled off by length L, and total reflection is generated in the peeled part by a material with a higher refractive index than the cladding material. Prevention material 1
8 is covered with a coating, for example.

Here, of the light from the input optical fiber 11, only the light 19 parallel to or very close to the fiber axis reaches the core ₁₂₁ of the output optical fiber 12. This light amount is approximately 1/100 of the input optical fiber light amount.
or less light intensity. Since most of the light is not parallel to the fiber axis, it comes into contact with the inner wall of the total reflection prevention material 18 while passing through the distance L. The refractive index of the total reflection prevention material 18 _{is 2} or 1.
2 is larger than ₂ and close to that of the core, so the light that hits the inner wall of the total reflection prevention material escapes to the outside of the fiber core as shown by reference numeral 20 without being totally reflected.

Now, when the input optical fiber 11 is fixed and the angle θ of the output optical fiber 12 is oscillated at θ=θmsinωt, the amount of transmitted light is as shown in FIG. 3b. Third
Waveform A in Figure b is when the refractive index of the total reflection prevention material 18 is large and the coating width L is long, resulting in a sharp pulsed light quantity, but since the absolute value of the passing light quantity is small, it is not suitable for signal processing. A large degree of amplification is required. Waveform B is the most preferable since the coated portion has an appropriate refractive index, degree of blackening, and width L. Waveform C is the case where the cladding of the optical fiber is not peeled off, and there is almost no loss of light due to bending.

The anti-total reflection material 18 does not necessarily need to be coated, and may be fixed using a mold or the like. Further, its outer diameter does not need to be the same as that of the cladding. Furthermore, as shown in Figure 2, it is not necessary to completely peel off the cladding in a section of length L, but only locally.
It is clear that the same effect can be obtained even if multiple parts are peeled off and coated with a total anti-reflection material.

Since the core of the input/output optical fiber is continuous, the above-mentioned optical modulation device has advantages such as no alignment operation required and no deterioration over time. In addition, in this optical modulation device, the above-mentioned patent application
Like the invention described in the specification of No. 154814, since a capillary tube is not necessarily required, the manufacturing process is generally easy. There are many applications that do not require protection with metallic capillaries. In such a case, the present optical modulation device is more suitable than the invention described in the above specification. Similar to the invention described in the above specification, if the core of the portion to which the anti-total reflection material is fixed is stretched thinly, light is modulated by slight bending. If the core is cut at right angles to the axis at the right end of L in FIG. 2 and a mirror is attached to this surface, a portion of the light from the core ₁₁₁ will be reflected by the mirror and return to the core ₁₁₁ again. It is clear that this returning light is modulated by the bending angle.

Now, conventional devices of this type that utilize Karman vortices include those that detect Karman vortices thermally, those that detect them as differential pressure, and those that detect them using ultrasonic waves.
There are methods that magnetically detect vibrations of the tail blade caused by vortices, and methods that use piezoelectric elements or strain gauges to measure the alternating force that acts on the vortex generator as a reaction to the generation of the Karman vortex. 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 50 mm.
The minimum value is about mm.

(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. and a vibrating tail fin such that there is no cladding entirely or partially along the axial direction of the optical fiber at a connection portion between the vortex generator and the oscillating tail fin or in the tail fin. A light modulation device formed by attaching a total anti-reflection material to a portion where the cladding does not exist is provided, and the portion to which the anti-reflection material is attached is elastically deformed by the vibration of the tail wing to adjust the amount of light passing through the optical fiber. It is characterized by modulating.

(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 flowmeter. 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 within 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. The mechanical light modulator shown in FIG. 2 is disposed between the vortex generator 35 and the tail 38, as shown, so that the covered portion of the anti-total reflection material 18 is located in the constriction 39 between them. has been done. As a result, the amount of passing light is modulated due to the bending (elastic deformation) of the attached part of the total reflection prevention material 18 due to the vibration of the tail 38.

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 the plastic material, polyacetal resin, polypropylene resin, fluororesin, etc. are advantageous in terms of appropriate elastic modulus and 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.

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 modulation portion may be formed within the tail fin instead by forming the entire tail fin to be soft and bendable.

In addition, although the optical fiber has a circular cross-sectional shape,
It does not necessarily have to be circular; oval, square, etc. will have the same effect and effect. The only difference is that the circular 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, 11 ₁ , 12 ₁
...Core, 11 ₂ , 12 ₂ ...Clad, 2,1
2... Output optical fiber, 3... Shutter, 18...
... Total reflection prevention material, 30 ... Pipe, 32 ... Flange, 33 ... Ring-shaped gasket, 34 ... Bolt, 35 ... Karman vortex generator, 36 ... Connecting body, 37 ... Karman vortex, 38 ... ...Tail, 39...
...neck part, 41...window.

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. The optical fiber is formed by completely or partially not having a cladding for a certain length along the axial direction of the optical fiber, and by adhering a total anti-reflection material to the part where the cladding does not exist. A Karman vortex flowmeter characterized in that a light modulation device is provided, and the amount of light passing through the optical fiber is modulated by elastically deforming the anti-reflection material attached portion by vibration of the tail. 2. The Karman vortex flowmeter according to claim 1, further characterized in that the core of the modulation portion to which the total reflection prevention material is attached is thinly stretched. 3. The Karman vortex flowmeter according to claim 1, further characterized in that one end of the modulating portion to which the total reflection prevention material is attached is cut at right angles to the axis and a reflecting mirror is attached thereto. 4. The Karman vortex flowmeter according to claims 1 to 3, further characterized in that the Karman vortex generator is formed long and a plurality of vibrating tail blades are installed on the vortex generator.