JP2003004624A - Particle detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a particle detector in which S/N ratio is enhanced. SOLUTION: In the particle detector where sample gas G to be detected is introduced to a particle detecting region M being formed by irradiating with laser light La and particles contained in the sample gas G are detected by receiving the scattered light Ls from the particles, the sample gas G is admixed with clean gas Ga having a low polarizability before being introduced to the particle detecting region M.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a particle detector for detecting particles contained in a fluid by receiving scattered light generated by irradiating particles with light.

[0002]

2. Description of the Related Art As a particle detecting device, a fluid to be detected is guided to a particle detection area formed by irradiating laser light, and particles contained in this fluid are scattered by irradiating the particle with laser light. It is known to detect light by receiving light.

In recent years, precision electronic equipment has become high-density and high-precision, and its manufacture is performed in a clean environment (for example, a clean room). Therefore, the cleanliness of clean rooms and the cleanliness of liquids and gases used for cleaning and the like are required to be high. To control these cleanliness, lead a large amount of sample at one time to the particle detector,
It is necessary to detect the microparticles in the sample. Therefore,
In order to guide a large amount of sample, it is necessary to increase the cross-sectional area of the flow channel and the particle detection region formed by irradiating the laser beam.

[0004]

However, if the particle detection region is enlarged, the number of molecules of the fluid in the particle detection region increases, and the scattered light emitted by the molecules increases, and as a result, the photoelectric conversion due to the increase in background light occurs. Shot noise of the device increases. Then, the S / N ratio (signal-to-noise ratio) of the electric signal output by the photoelectric device that receives the scattered light is lowered, and it becomes difficult to detect the fine particles.

The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to provide a particle detecting device having an improved S / N ratio. Is.

[0006]

In order to solve the above-mentioned problems, the invention according to claim 1 introduces a fluid to be detected into a particle detection region formed by irradiating light and removes particles contained in the fluid. In a particle detection device that detects scattered light generated by irradiating the particles with the light, a fluid having a low polarizability is mixed with the fluid and is guided to the particle detection region.

According to a second aspect of the present invention, a fluid to be detected is guided to a particle detection region formed by irradiating light, and particles contained in this fluid are scattered light generated by irradiating the particles with the light. In the particle detecting device for detecting by receiving light, the fluid is replaced with a fluid having a low polarizability by using a replacement means, and the fluid having a low polarizability is guided to the particle detection region.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. Here, FIG. 1 is a configuration diagram of a first embodiment of a particle detection device according to the present invention, FIG. 2 is a configuration diagram of a second embodiment of a particle detection device according to the present invention, and FIG. 3 is an electric transfer. It is a block diagram of a degree classifier.

In the first embodiment of the particle detecting apparatus according to the present invention, as shown in FIG. 1, an inlet tube 1 for guiding a sample gas G to a particle detecting region M and a clean gas Ga having a low polarizability are used as a sample. Gas supply unit 2 for supplying to inlet tube 1 for mixing with gas G, sample gas G and clean gas G
a particle detection unit 3 for detecting particles contained in the mixed gas Gm of a, and an outlet tube 4 for discharging the mixed gas Gm of the sample gas G and the clean gas Ga from the particle detection unit 3 to the outside.
And a suction pump 5 for mixing and sucking the sample gas G and the clean gas Ga.

The gas supply unit 2 is a clean gas G having a low polarizability.
a, a cylinder 6 that stores, for example, helium He, a flow rate control valve 7 that adjusts the amount of the clean gas Ga mixed with the sample gas G, and a filter 8. Clean gas Ga
Is mixed with the sample gas G by connecting the pipe 9 to the inlet tube 1. Since the intensity of the scattered light Ls is proportional to the square of the polarizability, even in the case of a gas having a low polarizability, even if the laser La is irradiated, the air whose main polarizability is about 8 times that of helium has the scattered light Ls. Do not emit.

The particle detecting section 3 includes a laser oscillator 10 which irradiates a laser beam La to form a particle detecting region M, a flow path 11 formed by a mixed gas Gm, and a light receiving section 12 which receives scattered light Ls. I have it. The laser oscillator 10 includes a He / Ne laser tube 13 that emits a laser beam La and a He / Ne laser tube 13.
A concave mirror 1 that is installed to face the Ne laser tube 13 with the channel 11 in between and that reflects the laser light La emitted by the He / Ne laser tube 13 and returns it to the He / Ne laser tube 13.
It consists of 4.

In the flow path 11, the mixed gas Gm of the sample gas G and the clean gas Ga, which are particles to be detected, is sucked by the suction pump 5 connected to the downstream side of the outlet tube 4, so that the mixed gas Gm is introduced into the inlet tube 1. Formed from the outlet tube 4 to the outlet tube 4. Laser light La
The part where the flow path 11 intersects with the particle detection region M.

The light receiving section 12 has a condenser lens 15 for condensing the scattered light Ls generated in the particle detection region M, and a photoelectric element 1 such as a photodiode for photoelectrically converting the condensed scattered light Ls.
When the mixed gas Gm contains particles, the scattered light Ls by the laser light La with which the particles are irradiated in the particle detection region M is received, and an electric signal corresponding to the intensity of the scattered light Ls is output. .

The operation of the first embodiment of the particle detecting device according to the present invention configured as above will be described. The sample gas G to be detected and the clean gas Ga are mixed in the inlet tube 1 to form a mixed gas Gm, and this mixed gas Gm is guided to the particle detection region M by the suction pump 5.

In the particle detection region M, the mixed gas Gm is irradiated with the laser light La, but the amount of scattered light Ls emitted by the mixed gas Gm is smaller than that of the sample gas G alone.

Therefore, since the background light generated by the mixed gas Gm is suppressed to a low level, the level of shot noise of the photoelectric element 16 such as a photodiode can also be lowered. As a result, the S / N ratio of the particle detecting device can be improved.

In the second embodiment of the particle detecting apparatus according to the present invention, as shown in FIG. 2, a classifier 21 for replacing the sample gas G containing particles to be detected with a clean gas Ga having a low polarizability. A sampling tube 22 for guiding the sample gas G to the classifier 21, a gas supply unit 23 for supplying the clean gas Ga to the classifier 21, an inlet tube 24 for guiding the clean gas Ga to the particle detection region M, and the clean gas Ga. A particle detecting section 25 for detecting particles contained in the outlet tube 26 for discharging the sample gas G or the clean gas Ga to the outside.
27 and suction pumps 28, 29 for sucking the sample gas G or the clean gas Ga.

The classifier 21 is a device for mixing a large amount of clean gas with a sample gas and taking out particles in a certain particle size range contained in the sample gas together with a part of the gas by using a physical law. Degree Classifier (Differential Mobility Analyz
er), diffusion method (diffusion battery method) classifier and inertial method (impactor method, cyclone method) classifier etc. can be applied.

The gas supply unit 23 and the particle detection unit 25
Has the same structure as the gas supply unit 2 and the particle detection unit 3 shown in FIG.

When an electric mobility classifier is used as the classifier 21, as shown in FIG. 3, particles in the sample gas G are charged by passing through the neutralizer 30, and the sample gas G containing the charged particles is charged. Are introduced between the outer cylinder member 31 and the inner cylinder (center rod) 32 from the upper side surface of the outer cylinder member 31. Then, the sample gas G merges with the clean gas Ga having a low polarizability passing through the inside of the sample gas G without being disturbed and flows down.

The central rod 3 is driven by the high voltage power source 33.
Since the voltage is applied to 2, the particles charged with the opposite polarity to the central rod 32 are attracted toward the central rod 32. Therefore, only particles having an electric mobility corresponding to the applied voltage are taken out together with the clean gas Ga replaced with the sample gas G from the sampling slit 34 provided below the center rod 32. On the other hand, the sample gas G and the extra clean gas Ga are discharged to the outside through the outlet tube 26.

The particle diameter Dp of the particles taken out together with the clean gas Ga by the electric mobility classifier is obtained by the following equation. Dp = (2CcpeLV) / (3μQcln (R2 / R
1))

Here, Cc is a correction coefficient of Cunningham, p
Is the number of charges, e is the elementary charge, μ is the viscosity coefficient of the sample gas G,
Qc is the flow rate of the clean gas Ga, R1 is the radius of the central rod 32, R2 is the inner radius of the outer cylindrical member 31, V is the applied voltage, L
Is the distance from the introduction portion of the sample gas G to the sampling slit 34. Therefore, the particle diameter Dp of the particles that can be taken out together with the clean gas Ga by the electric mobility classifier
Can be controlled by the applied voltage V.

The operation of the second embodiment of the particle detecting apparatus according to the present invention constructed as above will be described. The sample gas G containing particles to be detected is guided to the classifier 21 via the sampling tube 22, and the clean gas Ga is supplied to the classifier 21 by the gas supply unit 23.

Then, due to the action of the classifier 21, a clean gas Ga containing particles having an electric mobility corresponding to the applied voltage V is obtained.
Are guided to the particle detection unit 25 via the inlet tube 24. On the other hand, the sample gas G and the excess clean gas Ga are discharged to the outside by the suction pump 28 via the outlet tube 26.

In the particle detection region M, the clean gas Ga is irradiated with the laser light La, but the quantity of scattered light Ls emitted by the clean gas Ga is smaller than the quantity of scattered light Ls in the case of the sample gas G.

That is, the waveform of the output signal of the photoelectric element 16 when the sample gas G is guided to the particle detection region M as it is is that the intensity of the scattered light Ls by the sample gas G is high as shown in FIG. The shot noise level of the photoelectric element 16 is also close to the intensity of the light Ls scattered by the particles.

On the other hand, the waveform of the output signal of the photoelectric element 16 when the sample gas G is replaced with the clean gas Ga having a low polarizability by the classifier 21 and guided to the particle detection region M is as shown in FIG. The intensity of the scattered light Ls due to the clean gas Ga having a low polarizability is low, and accordingly, the level of the shot noise of the photoelectric element 16 is also lower than the intensity of the scattered light Ls due to the particles.

Therefore, the background light can be suppressed to a low level by replacing the sample gas G with the clean gas Ga, so that the level of shot noise of the photoelectric element 16 such as a photodiode can be lowered. As a result, the S / N ratio of the particle detecting device can be improved.

Further, by mixing the sample gas G with the clean gas Ga having a low polarizability or by replacing the sample gas G with the clean gas Ga having a low polarizability, a large amount of the sample gas G flows at one time. Therefore, even if the particle detection region M is enlarged, the light amount of the background light is not increased and the scattered light L by the particles is increased.
Since the intensity level of s can be made higher than the noise level, it becomes possible to detect fine particles in the sample gas G.

[0031]

As described above, according to the first aspect of the present invention, the fluid having a low polarizability is mixed with the fluid to be guided to the particle detection region, so that the background light can be reduced and the S / N ratio can be reduced.
The ratio can be improved.

According to the second aspect of the invention, since the fluid is replaced with a fluid having a low polarizability and is guided to the particle detection region, the background light can be reduced and the S / N ratio can be improved. .

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment of a particle detection device according to the present invention.

FIG. 2 is a configuration diagram of a second embodiment of a particle detection device according to the present invention.

FIG. 3 is a block diagram of an electric mobility classifier.

FIG. 4 is a waveform diagram showing an output signal of the photoelectric element when the sample gas is directly guided to the particle detection region.

FIG. 5 is a waveform diagram showing an output signal of a photoelectric element when a sample gas is replaced with a clean gas having a low polarizability by a classifier and led to a particle detection region.

[Explanation of symbols]

2, 23 ... Gas supply unit, 3, 25 ... Particle detection unit, 21 ...
Classifier (replacement means), G ... Sample gas, Ga ... Clean gas,
La ... laser light, Ls ... scattered light, M ... particle detection region.

Claims (2)

[Claims] 1. A fluid to be detected is guided to a particle detection region formed by irradiating light, and particles contained in the fluid are detected by receiving scattered light generated by irradiating the light with the particles. In the particle detecting device, the fluid is mixed with a fluid having a low polarizability and is guided to the particle detecting region. 2. A fluid to be detected is guided to a particle detection region formed by irradiating light, and particles contained in this fluid are detected by receiving scattered light generated by irradiating the light with the particles. In the particle detecting device according to the present invention, the fluid is replaced with a fluid having a low polarizability by using a replacement means, and the fluid having a low polarizability is guided to the particle detection region.