SU1404900A1 - Method of measuring fractional particle-size composition of aerosols - Google Patents

Abstract

The invention relates to measurement instrumentation, in particular to devices for the optical control of the dispersed composition of microparticles in a gas medium, and can be used, for example, in the control of the environment. The goal is to increase the sensitivity and accuracy of measurements by increasing the intensity of light in the volume being analyzed. The microparticles carried by the gas flow are probed by a highly diverging laser beam, which is formed using a focusing lens. The analyzed volume is placed on the optical axis of the probe laser beam in the vicinity of the overshoot region. The light scattered by a microparticle is recorded by a photodetector located at a certain angle to the direction of the probe beam. Passing through the analyzed volume, the particle crosses the diverging probe beam of light and is successively illuminated by rays coming at different angles to the axis of the probe beam. The time dependence of the signal of the photodetector is reflected. It depends on the angle of the indicatrix scattered within the divergence of the laser beam. The analysis of the time dependence of the electric signal allows to draw a conclusion about the type of scattering indicatrix and, therefore, about the size, shape, refractive index and internal structure of the particle. This establishes the fractional dispersion composition i of the sample being analyzed. Due to the concentration of the light energy in the analyzed volume, located near the zone of the overlap of the probing light, the scattering signal detected by the photoreceiver is increased, which makes it possible to increase the sensitivity and accuracy of measurements. 1 il. to 4

Description

The invention relates to a measuring and control technology, in particular, to optical devices for controlling the dispersed composition of microparticles in a gaseous environment, and can be used for controlling the environment.

The purpose of the invention is to increase the sensitivity and accuracy of measurements by increasing the intensity of the probing radiation in a counting volume.

The drawing shows a block diagram of a device implementing the method.

The device contains a laser radiation source 1, a focusing lens 2, a flow chamber 3 with a nozzle 4, a countable volume 5, a field diaphragm 6 forming a lens 7, a photodetector 8 and a recording unit 9,

The device implements the method as follows.

The focusing lens 2 forms, on the optical axis of the laser source 1 of radiation, a zone 10 of overbing of the probing light beam. The microparticles, together with the gas flow, enter the flow-through optical chamber 3 after 4 and intersect the equivalent volume 5, which is dispersed by the laser beam after the transfer. When a particle is illuminated by a laser beam, a secondary scattering flux appears. Part of the flux extending at an angle to the beam axis enters the field diaphragm 6 and the forming lens 7 is directed to the photodetector 8. The latter produces an electrical signal proportional to the power of the recorded light flux, which enters the registration unit 9 Passage through the countable volume, the particle intersects the diverging beam and is successively illuminated by the rays going at different angles to the axial beam 11. Therefore, the time dependence of the signal arriving at block 9 of the recording reflects the spatial th angle dependence indikatris-

The scattering is not within the limits of the divergence of the laser beam. The analysis of the time dependence of the electrical signal allows one to draw a conclusion about the type of the indicatrix of scattering and, therefore, about the size, shape, refractive index and internal structure of the particle. In this case, the fractional dispersion composition of the sample is determined.

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15 20

25 30 5 0 5

0

The radius p of the probe beam, depending on the distance k from zone 10 of the overburden, is expressed by the relation

Ro (.

where rd- is the radius of the probe beam in

zone 10; t

 - probing wavelength

radiation. Laser radiation at a distance

X from the zone of traffic, where x is the river.

is a spherical wave propagating from a point source located in the overshoot region. In this zone of the diverging laser beam, the necessary distance from the over-banding zone 10 to the center of the countable volume can be found from the relation

l-t-.

where d 2p is the length of the countable volume along the direction of the flow of particles. The possibility of applying the focusing of laser radiation into a small counting volume causes an increase in the sensitivity of measurements. In addition, a reduction in countable volume allows more concentrated suspensions to be analyzed.

Claims (1)

Invention Formula A method for measuring the fractional dispersion composition of aerosols, which involves sensing the flow of aerosols with a laser beam inclined to the direction of propagation of the probe beam, characterized in that, in order to increase the sensitivity and accuracy of measurements by increasing the radiation intensity in a counting volume, the probe laser beam focuses on distance L to the center of a countable volume, determined from the ratio t - 0 - 2TG where PO is the radius of the probing laser beam in the region of its center of focus; extent of counting volume along the direction of the flow of aerosols; probing radiation wavelength. and the scattered radiation is recorded at an angle to the direction of propagation of the probing laser beam, which exceeds its divergence angle after focusing. eleven