JPH0226176B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a light scattering suspended particle counting method, and more particularly to a light scattering suspended particle counting method that utilizes the thermophoretic phenomenon of a sample aerosol to generate a concentration deviation.

Light scattering particle counters are commonly used to measure air cleanliness in environments such as clean rooms equipped with special dust removal air conditioning equipment. As shown in Figure 1, the principle is that a sample aerosol S to be measured flows out from a nozzle N into a beam-shaped irradiation light L, and the light scattered by individual particles is converted into a photoelectric conversion element. This is to detect and count the electrical signals as electrical signals, and optical systems with various configurations have been proposed and put into practice in this case.

By the way, in environments where a high degree of air cleanliness is required, such as in the VLSI manufacturing process, the number of particles in a unit volume of air is extremely small, so the number of particles detected is a significant value as a measurement value, that is, a small number. friend
To reach 100 samples, a large number of samples must be introduced into the device. From this, if the inner diameter of the nozzle N that jets the sample air into the irradiation area T is constant and the flow rate of the sample air is unchanged, a long measurement time will be required, and if you try to obtain a measurement time in a short time, The flow velocity becomes high and laminar flow cannot be maintained. As another means, if the inner diameter of the nozzle N is increased, the width of the irradiation light beam L must also be increased. In other words, if W _A is the diameter of the sample air flow that is approximately equal to the inner diameter of nozzle N, and W _L is the width of the irradiated light beam L, W _A < W _L must be satisfied in order to detect all particles without missing them. Must be. Therefore, it is difficult to maintain the luminous flux density unless a powerful light source is used.

This invention solves the above-mentioned problems. That is, when a temperature gradient exists in an aerosol, the kinetic energy of the medium gas molecules is greater on the high temperature side than on the low temperature side, so the collision energy of molecules with particles is also greater on the high temperature side, and the particles receive a force directed toward the low temperature side. Utilizing this thermophoretic phenomenon, particles in aerosol, which are almost uniformly dispersed in the air, are locally concentrated (concentration biased), making it possible to quickly measure dust concentration in highly clean air using the light scattering method. The object of the present invention is to provide a method that allows measurement of a large amount of sample aerosol.

A further object of the present invention is to solve the problem that when detecting extremely small particles with a particle size of about 0.1 μm, the light scattered by gas molecules in the irradiation region approaches the light scattered by particles, making measurement difficult.

Next, the present invention will be explained with reference to an embodiment in FIG. The sample aerosol S introduced by keeping the tube wall at a temperature higher than the ambient temperature
A temperature gradient is applied in an axially symmetrical manner. Then, among the medium gas molecules constituting the sample gas flow, the kinetic energy of the medium gas molecules at the periphery is made larger than the kinetic energy of the medium gas molecules around the axis, thereby reducing the collision energy of the medium gas molecules with floating particles around the axis. collision energy. As a result, suspended particles contained in the sample gas stream are concentrated around the axis of the sample gas stream due to a phenomenon in which they are collected around the axis of the sample gas stream (ie, a thermophoretic phenomenon). In this way, the irradiation light beam only needs to be applied to the portion S _T of the sample aerosol S shown by the diameter w A that is offset from the axis center of the sample aerosol _S , and the amount of light required is much smaller than the amount of light used to irradiate the sample flow shown by the diameter W _A . S _A
indicates the area of the sample aerosol that does not contain dust particles. Therefore, the configuration of the optical system can be simplified and the power of the light source can be reduced, which has many advantages.

Furthermore, particles with a diameter of about 0.1 μm can be detected accurately by eliminating interference caused by light scattered by gas molecules.

As described above, the present invention facilitates the detection of extremely fine particles in environments requiring a high degree of cleanliness by simple means, and has significant industrial benefits.

[Brief explanation of drawings]

FIG. 1 is a perspective view for explaining the principle of a conventional method, and FIG. 2 is a perspective view of an embodiment for explaining the present invention. S: Sample aerosol, S _T : Sample aerosol portion biased to the axial center, S _A : Sample aerosol portion without dust particles, N: Nozzle, H: Heating element.

Claims (1)

[Claims] 1. A sample gas flow is caused to flow out from a nozzle into an irradiation light beam, and when floating particles are included in the sample gas flow, scattered light scattered by the floating particles is transmitted to a photoelectric conversion element. In the light scattering suspended particle counting method, which converts the sample gas into an electrical signal and counts the number of suspended particles contained in the sample gas based on a change in the electrical signal, the sample gas flow is discharged from the nozzle. By heating the periphery of the sample gas flow, an axially symmetrical temperature gradient is applied to the sample gas flow. It is characterized by making the kinetic energy of the sample gas flow larger than the kinetic energy of the medium gas molecules in the peripheral part to collect the suspended particles in the sample gas flow around the shaft by thermophoresis, and converging the irradiation light beam on the peripheral part of the shaft. A light scattering suspended particle counting method. 2. A light scattering suspended particle counting method, characterized in that a peripheral portion of the sample gas flow is heated by attaching a heating element to the nozzle.