JPH073296Y2 - Vortex detector and vortex detector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a vortex detecting element to which a photoelastic effect is applied and a vortex detector using the vortex detecting element.

2. Description of the Related Art A vortex flowmeter is known in which a Karman vortex in which a vortex generator is arranged is generated in a fluid flow, and the number of Karman vortices generated per unit time is proportional to a flow velocity. As a detection means for detecting a vortex generated in the vortex flowmeter, many methods have been proposed and put into practical use. As one of them, there is a method of detecting a fluctuating pressure generated due to vortex shedding. This fluctuating pressure is converted into an electric signal as a change in strain amount that changes according to the fluctuating pressure of the pressure receiving element, and the pressure receiving element includes a piezoelectric element and an electrostatic capacitance. The detector composed of these pressure receiving elements has a problem that it has a high output impedance and is susceptible to electromagnetic noise. On the other hand, since the photodetector does not receive electromagnetic noise, the photodetection method has recently attracted attention. Among the light detection methods is, for example, the light reflection method. In this, a light reflection plate is embedded in the bottom surface of the recess formed in the vortex generator so as to be orthogonal to the axis of the vortex generator, and light is emitted from the axis toward the light reflection plate. On the other hand, since the bending stress is repeatedly applied to the vortex generator as the vortex is generated, the vortex generator vibrates around the stationary axis, and the vibration causes the light reflection plate on the bottom surface of the recess to rotate and rotate about the symmetry axis. According to this, the projected light vibrates around the axis. Since this vibration is equal to the vortex fluctuation frequency, the vortex is detected by converting the reflected light from the light reflection plate into light intensity. Further, as another method of the light detection method, there is one using photoelasticity. An optical fiber is embedded parallel to the axis of the vortex generator, and the vortex is detected as a change in light intensity due to a stress variation acting on the optical fiber due to a bending variation of the vortex generator.

Problems of the Prior Art In the above-described conventional vortex flowmeter photodetection method, the light reflection type must select the required optical path length in order to increase the photosensitivity, but it is not possible to increase the optical path length. It is easily affected by external vibration and noise is likely to occur. Furthermore, there is a problem that when the temperature changes, especially when the temperature drops below the dew point, dew condensation occurs and the reflectivity is significantly impaired, making detection impossible. In addition, the photoelastic type has a small amount of light in the optical fiber and also has low sensitivity. . In order to improve the sensitivity, it is necessary to increase the optical path length, which is a problem that it is difficult to apply to a small vortex flowmeter.

Means for Solving Problems The present invention is intended to provide a vortex detection element having high sensitivity and excellent S / N in a photoelastic method regardless of a light reflection method having a problem such as dew condensation. A vortex flowmeter provided with a detection element that responds to the vortex fluctuation pressure, detects the fluctuation pressure as a change in an optical amount proportional to the fluctuation pressure, and detects a vortex from the change in the optical amount. A light-conducting thin plate, a light-conducting optical fiber having a light-conducting thin plate and a light-conducting fiber that are fixed to each other at opposite ends on a straight line parallel to the surface of the light-conducting thin plate at a slight distance from each other. The eddy detection element is composed of a light-shielding film which is light-shielding and which surrounds and is integrally surrounded by a light-defective conductor.

Example FIG. 1 is a schematic explanatory view of a vortex detection element of the present invention,
(A) The figure is a perspective view showing the structure of the optical path of the main part photoelastic
The figure (b) shows a sectional view taken along line XX of the figure (c), and the figure (c) shows a plan view. In the figure, 1 is an extremely thin optical conductor, for example 0.2 m, which receives vortex fluctuation pressure and detects light as a change in light quantity.
It is a glass plate or acrylic plate of about m. Although the shape shown in the figure is rectangular, the shape is not limited to this, and it may be circular as long as it is a photoconductor thin plate that receives photoelasticity. In the illustrated rectangular plate, the light introduction and derivation parts are the end faces 1 ₁ and 1 _{2 of} each rectangle.
I am trying. 2 ₁ and 2 ₂ are optical conductor fibers, which are a plurality of glass optical fibers or resin optical fibers 2 _1a to 2 _1n , 2
_2a consists to 2 _2n, 2 ₁ of one end the end portion A of the light source (not shown), also of 2 ₂ not shown end B is connected to the photoelectric converter, each other end a plurality of optical waveguide fibers 2 _1a ,
2 _1b, ..., 2 _1n and _{2 2a, 2 2b, ...,} 2 2n is that each relative to the optical conductor sheet 1 is arranged in parallel planar. 3 ₁ is a fixed plate of one of the optical conductor fiber for fixing remain parallel optical waveguide fibers of each said at holding plate. When the holding plate 3 ₁ and the thin optical conductor plate 1 are joined together, for example, with a joined optical conductor, the optical coupling loss is prevented, and a change in state in space, such as instability in light transmission such as dew condensation, is prevented. be able to.
However, if the above-mentioned object can be achieved by the method of assembly, etc., this junction light guide is not always necessary,
In the figure, an example without a junction light guide is shown. 6
Is a flexible light-shielding film which is a light-defective conductor and is made of a flexible resin, and surrounds the main part of the light detection shown in FIG. 7 is a protective tube, which is a light guide fiber 2 ₁ , 2 ₂
Is to be inserted and protected to be bonded to the light shielding film 6. 5 ₁ , 5
Reference numeral ₂ denotes a light-transmitting film that protects the light guide thin film 1 when the light guide thin plate 1 is surrounded by the light shielding film 6, and a material having a smaller refractive index than the light guide thin plate 1 is selected. Vortex sensing element which is constructed as the Jo, (a) as shown in FIG, the end face 1 _1, 1 a vortex variable pressure ΔP
_{When 2} is received by the fixedly arranged photoconductor thin plate 1, it is elastically deformed in the direction of the arrow, which is the direction of action of the vortex fluctuation pressure ΔP, and the photoelastic effect causes a change from the light source A side to the detection B side. The amount of light decreases. Since this change in the light amount is due to the vortex fluctuation, it can be converted into an electrical signal as a vortex signal by the change in the light amount.

FIG. 2, shows another embodiment, 8 is a polarizer, arranged in parallel between the holding plate 3 ₁ and the light conductor sheet 1, linearly polarized light from a light source A side. 9 quarter-wave plate, 10 is arranged in parallel between each successively to the optical conductor sheet 1 and the holding plate 3 ₂ in the analyzer, as in the embodiment of FIG. 1, is shielded by the light shielding film 6 Although the light guide path is integrally formed with this, it is omitted in the drawing. Light linearly polarized by the polarizer 8 is the light guide thin plate 1
After being incident on the 1/4 wavelength plate 9 and circularly polarized by the 1/4 wavelength plate 9, the light is detected by the analyzer 10. However, when the light guide thin plate 1 receives the vortex fluctuation pressure ΔP, light rotation occurs and It becomes elliptically polarized light, and the light passing through the analyzer 10 undergoes a change in the amount of light according to the pressure, and the vortex signal can be detected as described in FIG.

FIG. 3 shows an embodiment of the vortex flowmeter equipped with the above-mentioned vortex detector. (A) is a horizontal sectional view taken along the line YY in (b), and (b) is a flow direction in (a). It is the XX sectional view seen from Q.
In the figure, reference numeral 11 is a main body of the vortex flowmeter, which has a rectangular cross section in which the upstream side is enlarged and the downstream side is a parallel flow path. Reference numeral 12 is a grid-like body that rectifies the flow by a rectifying grid, and 13 is a vortex generator, which is shown as a typical triangular section. Reference numeral 100 denotes a vortex detecting element of the present invention, which is disposed on the side surface near the vortex generator 13 on the downstream side of the main body 11 and on the same surface as the side surface so as not to disturb the flow. Reference numeral 14 is an outer casing that forms an empty chamber 15 on the rear surface of the vortex detection element 100, and 16 is a conduction path for applying a static pressure equal to that in the main body 11 to the empty chamber 15, with the main body sandwiching the vortex generator 13. 13
Are disposed on both side surfaces of. In the above vortex flowmeter, the vortex detection element 100 is arranged parallel to the main body 11 and so as not to project from the inner wall surface, so that excellent S / N can be detected without disturbing the fluid. Since the vortex detection elements 100 on both sides receive vortex fluctuation pressure in the same direction on the paper surface, each vortex signal is synchronously doubled.

FIG. 4 shows an embodiment in which the flow tube is circular, 20 is a circular tube, 21 is a vortex generator, 24 is a vacant chamber for accommodating the vortex detecting element 100 in the central portion of the vortex generator 21, and 22 and 23 are The vortex fluctuation pressure ΔP is applied to the vortex detection element 100 by the pressure introduction hole that connects the vacancy chamber 24 and the side surface of the vortex generator 21. Only one vortex detection element 100 is required.
The S / N can be improved by removing the minute fluctuating pressure by the integration effect of providing 4.

Effect As described above, according to the vortex detector of the present invention, since the vortex signal conversion is performed by light detection, there is no electromagnetic noise received near the vortex flowmeter, and the optical lever that applies light reflection is used in the light detection method. Instead of directly receiving pressure, it is possible to obtain an excellent S / N vortex signal without being affected by external vibration. Moreover, the light is not from the photoelasticity using the fine optical fiber as in the prior art, but from the optical conductor fiber arranged on the line, and the amount of light is increased because it receives pressure as a surface, so the vortex signal becomes significantly large and stable. The optical vortex signal can be obtained at low cost.

[Brief description of drawings]

FIG. 1 is a vortex detection element of the present invention, in which (a) is a perspective view of essential parts, (b) is a sectional view taken along the line XX of (c), (c) is a plan view, and FIG. FIG. 3 shows another embodiment, and FIGS. 3 and 4 are views showing a vortex flowmeter equipped with the vortex detecting element of the present invention. 1 ... Light guide thin plate, 2 ₁ , 2 ₂ ...... Light guide fiber, 3 ₁ , 3 ₂
... Holding plate, 6 ... Shading film, 8 ... Polarizer, 9 ... Quarter wave plate, 10 ... Analyzer.

Claims (4)

[Scope of utility model registration request] 1. A detecting element of a vortex flowmeter for detecting a fluctuating pressure due to a vortex as a change in an optical amount proportional to the fluctuating pressure and detecting a vortex from the change in the optical amount, wherein the fluctuating direction is perpendicular to a plane. An optical conductor thin plate for receiving pressure, an optical conductor fiber arranged opposite to both end faces parallel to the surface of the optical conductor thin plate, the optical conductor thin plate and the optical conductor fiber made of a non-translucent flexible material. And a light-shielding film that integrally surrounds the vortex detection element. 2. A polarizing plate on the light-incident side and a quarter-wave plate on the light-exiting side are provided between the optical conductor fiber and the thin optical conductor plate, respectively. The eddy detection element described. 3. A vortex flowmeter body comprising a vortex generator and a flow tube having a rectangular cross section in which the vortex generator is arranged in axial symmetry, and a thin optical conductor plate for receiving the fluctuating pressure in a direction perpendicular to a plane. A light-shielding film that integrally surrounds the light-conducting thin plate and the light-conducting fiber with a non-light-transmitting flexible material, the light-conducting fibers being disposed so as to face both end surfaces parallel to the surface of the light-conducting thin plate. And a vortex detecting element disposed on the same surface as the tube wall on the tube wall of the flow tube near the vortex generator, and the vortex detecting element is formed on the other surface of the vortex detecting element. A vortex detector characterized in that an empty chamber communicating with the pipe is provided. 4. A light guide thin plate for receiving the fluctuating pressure in a direction perpendicular to the surface, light guide fibers arranged opposite to both end faces parallel to the face of the light guide thin plate, and a non-translucent material. A through-hole is formed in a through-hole that penetrates the vortex generator in a direction perpendicular to the flow, and has a vortex detecting element formed of a flexible material and a light-shielding film that integrally surrounds the optical-conductor thin plate and the optical-conductor fiber. A vortex detector characterized in that the vortex detecting element for closing the vortex is arranged in parallel to the surface of the vortex detecting element and the flow direction.