JP3615140B2 - Particle detector - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention particularly relates to a particle detector that detects particles contained in a sample gas using laser light.
[0002]
[Prior art]
As a conventional particle detector, as shown in FIG. 4, a flow path 105 is formed between the laser medium 101 constituting the laser resonator 100 and the reflecting mirror 102 to allow a gas to be detected to pass from the inlet 103 to the outlet 104. A plate member 106 is disposed between the laser medium 101 and the flow path 105 and between the reflecting mirror 102 and the flow path 105, and the pin hole 107 through which the resonating laser light La and the purge gas Pa of clean gas pass is formed in the plate. What was formed in the member 106 is known.
[0003]
The pinhole 107 is an opening having a size that allows only the resonating laser beam La to pass therethrough. The purge air Pa is blown to the laser medium 101, the reflecting mirror 102, and the vicinity thereof in order to prevent the laser medium 101 and the reflecting mirror 102 from being contaminated by dust or mist contained in the gas to be detected. It is a clean gas. Reference numeral 109 denotes a purge air introduction port.
[0004]
As described above, the plate member 106 having the pinhole 107 disposed therein is disposed in the case 108. The resonating laser beam La is irradiated to the gas to be detected through the pinhole 107, but the laser medium 101 and the reflecting mirror are disposed. This is because the scattered light S generated by the laser medium 101 and the reflecting mirror 102 when the laser beam La resonates with the plate 102 is prevented from entering the detection unit (light receiving unit) by the plate member 106.
[0005]
[Problems to be solved by the invention]
However, in the conventional particle detector, the laser beam La used for particle detection passes through the pinhole 107 and passes through the purge air introduction port 109 into the case 108 and goes out to the outlet 104 together with the gas to be detected. Since some purge air Pa passes, the laser beam La is disturbed in the pinhole 107 due to the flow of the purge air Pa, and this becomes optical noise, which reduces the signal-to-noise ratio (S / N ratio) of particle detection. is there.
[0006]
The present invention has been made in view of such problems of the prior art, and its object is to improve the signal-to-noise ratio of particle detection by suppressing light disturbance caused by the flow of purge air. It is an object of the present invention to provide a particle detector capable of detecting minute particles.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the invention according to claim 1 uses particles of laser gas that resonate in a laser resonator to spray particles contained in a sample gas while blowing clean gas purge air onto a laser medium or a reflecting mirror. In the particle detector to be detected, in addition to the laser beam formed on the plate member and the pinhole through which the purge air passes, a passage through which the purge air passes to the outlet is provided in the plate member or the wall of the case .
[0008]
According to a second aspect of the present invention, in the particle detector according to the first aspect, the passage provided in the plate member is a vent hole.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings. Here, FIG. 1 is a schematic sectional view of a particle detector according to the present invention, FIG. 2 is a schematic sectional view of the same, and FIG. 3 is a sectional view of another embodiment of a plate member.
[0010]
As shown in FIG. 1, the particle detector according to the present invention has a laser medium 3 constituting a laser resonator 2 and a reflecting mirror 4 arranged in a case 1 so as to face each other, and an intermediate between the laser medium 3 and the reflecting mirror 4. In addition, a flow path 7 for allowing a gas to be detected to pass from the inlet 5 to the outlet 6 is formed, and further, plate members 8 and 9 are respectively provided between the laser medium 3 and the flow path 7 and between the reflecting mirror 4 and the flow path 7. It is arranged.
[0011]
As the laser medium 3, a solid-state laser such as a ruby laser or a YAG laser, or a gas laser such as a helium neon laser or a carbon dioxide laser is used. The laser resonator 2 includes an excitation light source (not shown) that excites the laser medium 3.
[0012]
Further, purge air inlets 10 and 11 for supplying clean gas purge air Pa into the case 1 are provided on the wall surface of the case 1 near the laser medium 3 and the reflecting mirror 4. In addition, 12 is a particle | grain detection area | region where the laser beam La and the flow path 7 cross | intersect.
[0013]
Further, as shown in FIG. 2, a light receiving portion 13 that receives scattered light generated in the particle detection region 12 when irradiated with the laser light La is provided inside or outside the case 1. 2 is a schematic configuration diagram of the particle detector viewed from the direction of the flow path 7 shown in FIG. 1 (outlet 6 side), and illustration of the inlet 5 and the purge air introduction ports 10 and 11 is omitted.
[0014]
The light receiving unit 13 is installed at a location that faces the particle detection region 12 in a direction orthogonal to the resonating laser beam La and does not interfere with the flow path 7 formed by the gas to be detected from the inlet 5 to the outlet 6. Yes. The light receiving unit 13 includes a condenser lens 14, a photoelectric conversion element (for example, a photodiode, a phototransistor, etc.) 15, and the like, and outputs an electric signal corresponding to the intensity of scattered light in the particle detection region 12.
[0015]
The plate members 8 and 9 are formed with pinholes 16 through which mainly resonating laser light La and vent holes 17 through which clean gas purge air Pa passes. The vent hole 17 is a simple hole such as a circle or a rectangle that opens perpendicularly to both surfaces of the plate members 8 and 9. A plurality of vent holes 17 are provided at positions where there is no possibility that the scattered light S generated by the laser medium 3 and the reflecting mirror 4 directly enters the light receiving unit 13 by the laser light La.
[0016]
The gas to be detected by the particles forms a flow path 7 from the inlet 5 when a suction pump (not shown) connected downstream of the outlet 6 sucks the gas in the case 1.
The particle detector according to the present invention has the same configuration as the conventional particle detector shown in FIG. 4 except that the air holes 17 are formed in the plate members 8 and 9.
[0017]
The operation of the particle detector according to the present invention configured as described above will be described. Laser light La that resonates between the laser medium 3 and the reflecting mirror 4 is generated. This laser beam La passes through the pinhole 16.
[0018]
Further, when purge gas Pa, which is a clean gas, is supplied into the case 1 from the two purge air inlets 10 and 11, the purge air Pa is sprayed mainly on the laser medium 3, the reflecting mirror 4 and the vicinity thereof, and then mainly vent holes. Pass through 17 and exit to outlet 6. A part of the purge air Pa passes through the pinhole 16 and escapes to the outlet 6.
[0019]
In this state, the gas in the case 1 is sucked by the suction pump, whereby the gas to be detected from the inlet 5 flows into the case 1 to form the flow path 7. Then, the particle | grain detection area | region 12 is formed because the laser beam La and the flow path 7 cross | intersect.
[0020]
If particles are contained in the gas, scattered light is generated in the particle detection region 12, the light receiving unit 13 receives the scattered light, and particles contained in the gas from the level of the electrical signal corresponding to the intensity of the scattered light. Can be confirmed.
[0021]
Here, the purge air Pa blown to the laser medium 3 and the reflecting mirror 4 and the vicinity thereof is mainly discharged through the vent hole 17 and the gas to be detected from the outlet 6.
[0022]
Accordingly, since the purge air Pa passing through the pinhole 16 is less than that of the conventional particle detector, fluctuations in the intensity of the laser beam La caused by the purge air Pa passing through the pinhole 16 are reduced. As a result, it is possible to prevent a decrease in the signal-to-noise ratio of particle detection caused by fluctuations in the intensity of the laser light La.
[0023]
In the above-described embodiment, in addition to the pinhole 16, as a passage through which the purge air Pa passes through the plate members 8, 9, a simple circular or square shape that opens perpendicularly to both surfaces of the plate members 8, 9 is used. A pore 17 was employed.
However, the scattered light S generated by the laser medium 3 and the reflecting mirror 4 does not directly enter the light receiving unit 13 through the air holes formed in the plate members 8 and 9, and the purge air Pa hardly passes through the pinhole 16. Any structure that can smoothly exit to the outlet 6 may be used.
[0024]
Therefore, the passage through which the purge air Pa passes through the plate members 8 and 9 is not simply the vent hole 17 that opens perpendicularly to both surfaces of the plate members 8 and 9, but as shown in FIG. Can also be formed on the plate members 8 and 9.
[0025]
Further, as shown in FIG. 1 or FIG. 2, purge air Pa supplied into the spaces 19 and 20 formed by the case 1 in which the laser medium 3 or the reflecting mirror 4 is disposed and the plate members 8 and 9 is supplied to the outlet 6. As a passage through which the purge air Pa is blown to the laser medium 3 or the reflecting mirror 4, a passage led to a space 21 formed by the plate members 8 and 9 and the case 1, for example, a space formed in the wall portion of the case 1. A passage (not shown) that communicates the spaces 19 and 20 with the space 21 may be used.
[0026]
【The invention's effect】
As described above, according to the first aspect of the present invention, in addition to the pinhole, a passage through which purge air passes to the outlet is provided in the wall of the plate member or case, so that the amount of purge air passing through the pinhole can be reduced. Since the degree of fluctuation of the resonating laser beam is reduced, the signal-to-noise ratio in particle detection can be made sufficiently high, and particles having a relatively small particle size can be accurately detected.
[0027]
According to the second aspect of the present invention, the amount of purge air passing through the pinhole is reduced with a simple configuration that merely forms a vent hole in the plate member provided with the pinhole, and the degree of fluctuation of the resonating laser beam. The signal-to-noise ratio in particle detection is sufficiently high, and particles with a relatively small particle size can be detected accurately.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of a particle detector according to the present invention. FIG. 2 is a schematic sectional view of a particle detector according to the present invention. FIG. 3 is a sectional view of another embodiment of a plate member. ] Cross-sectional view of schematic configuration of conventional particle detector [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Case, 2 ... Laser resonator, 3 ... Laser medium, 4 ... Reflecting mirror, 5 ... Inlet, 6 ... Outlet, 7 ... Channel, 8, 9 ... Plate member, 10, 11 ... Purge air introduction port, 12 ... Particle detection region, 13... Light receiving portion, 16... Pinhole, 17, 18 .. vent hole, 19, 20, 21 .. space, La .. laser beam, Pa.

Claims (2)

The laser formed on a plate member in a particle detector that detects particles contained in a sample gas while blowing clean gas purge air onto a laser medium or a reflecting mirror using laser light that resonates in the laser resonator In addition to a pinhole through which light and the purge air pass, a particle detector is provided with a passage through the outlet of the purge air in the plate member or case . The particle detector according to claim 1, wherein the passage provided in the plate member is a vent hole.

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