SU1516912A1 - Nephelometer for measuring indicatrix of diffusion of aerosols - Google Patents

Abstract

The invention relates to optical instrumentation and can be used in meteorology in the study of atmospheric aerosols. The purpose of the invention is to increase the range of measured scattering angles with a simultaneous expansion of the dynamic range of measured aerosol densities. The nephelometer contains a source of probing radiation, a receiving device, which consists of a mirror and a photodetector, the mirror being inclined 45 ° to the optical axis of the objective and rotated around it by means of a rotation mechanism and an angle position sensor. New is the installation of two light shields located between the radiation source and the mirror in such a way that they overlap a part of the effective light hole of the lens for small scattering angles, while one of the screens is in the geometric shadow of the other screen. This makes it possible to increase the range of measurable scattering angles toward small angles. The sensitivity of the nephelometer is reduced for minimum scattering angle. When the mirror is rotated towards large angles, the overlap of the light aperture with the screens decreases to zero, which compensates for a decrease in the scattering intensity. This contributes to the reduction of the dynamic range of the input signals and the corresponding increase in the dynamic range of the measured aerosol densities. 4 il.

Description

The invention relates to the field of instrumentation, namely to the technique of determining the parameters of aerosols by optical methods, and can be used in meteorology for the study of atmospheric aerosols.

The aim of the invention is to increase the range of measured scattering angles in the direction of small scattering angles with a simultaneous expansion of the dynamic range of the measured aerosols.

Figure 1 shows a diagram of a nephelometer; Fig. 2 shows a receiving device with a rotation mechanism and an angular position sensor, a slit; Fig. 3 is a schematic diagram of a nephelometer, explaining the calculated ratios; Fig. 4 is a screen layout.

The boundaries of the field of view of the receiver are shown by a dotted line.

The nephelometer contains a probe radiation source 1 and a receiver 2 optically coupled

315

among themselves through the scattering volume, the first 3 and second 4 light shields, located between the receiving device 2 and the sources I and crossing the part of the acting opening of the receiving device for small scattering angles.

The receiving device 2 (Fig. 2) consists of a mirror 5, a lens 6, a sliding diaphragm 7 of the field of view, a photodetector 8, a rotation mechanism 9 and an angular position sensor 10, kinematically connected with the mirror 5.

The nephelometer works as follows.

Receiver 2 senses radiation of probe source 1 scattered by aerosol. Scatter radiation is measured for different scattering angles when the mirror 5 (figure 2) rotates by the rotation mechanism 9 around the optical axis of objective 6. The angle position of mirror 5 is determined by sensor 10 angular position. After reflection from the mirror 5, the scattered radiation is focused by the lens 6 on the photodetector 8. The diaphragm 7 forms the angular field of view of the lens 6.

The minimum angle of scattering is 9, the center (Fig. 3) is determined by the position of the received device 2, when the edge of the field of view is near the exit window of the emitter 1. If the receiving device 2 is rotated a little counterclockwise, then the surface of the output one falls into the field of view. source window 1, which is the source of light interference. If the lens diameter is reduced to 6, the minimum angle decreases, but the proportional sensitivity of the nephelometer decreases in proportion to the square of the diameter ratio. Introduced light shields 3 and 4 (Fig. 1) are installed in such a way that they overlap that part of the field of view that is directed to the output window of source 1, i.e. reduces the size of the effective aperture of the lens 6, thereby reducing the minimum scattering angle. Due to the overlap of the field of view, the sensitivity of the nephelometer for an angle of bcz is less important. When you turn the mirror 5 across the clock1 1 stre. gke, the degree of the opening is reduced. and sensitivity

four

nephelometer increases, which compensates for the decrease in the intensity of scattering, typical of almost all aerosols.

The described scheme of the nephelometer and the interaction of its parts help to reduce the minimum scattering angle and decrease the dynamic range of the scattered radiation entering the photodetector, which contributes to an increase in the dynamic range of aerosol densities measured by the nephelometer.

In the layout of shields 3 and 4 (Fig. 4), the optical axis of the source of the probing radiation is denoted as OHI optical axis of the receiving device Op On, directly connecting the working edge of the second screen 4 and closest to the optical axis of the source Oj, 0j, the edge of the input window receiver 2, - BB; Directly, the passage a through the edge of the second screen 4 parallel to the optical axis of the source () SSC AA.

Dependencies determining the position of screens 3 and 4 follow from the following. The following quantities are known (FIG. 3): the distance L from the exit window, the source 1 of the probing radiation to the receiving device 2; the size D of the output window of the source in the plane of measurement of the scattering indicatrix; ; minimum scattering angle as measured by a &lengths; size S is the distance between the AA and BB lines in the plane of installation of the screen 4; size b is the distance from the optical axis of the source to the near edge of the input window of the receiving device 2.

Distance

D

2

tgS

min

Distance

1 L-1, L.-x

tg dAIN

The distance between the mts screen 3 and 4 is a. Mezhl angle, in P11, AA and BB are denoted by o,. Tog for tgoc O / a and

. , b - and / 2

tg T, -

from where

b-G-572

The size O depends on the design and technological features of the nephelometer - on the rigidity of the structure, on (Dimensions, on the accuracy of the alignment of optical elements, on the operating conditions. Size b depends on how much of the light hole of the receiving device 2 can be blocked by screens 3 and 4.

The working edge of the screen 4 is a source of scattered light. The stray light, which could have penetrated the receiver, propagates in a cone, bounded by the dotted lines BB and CC. Screen 3 overlaps these rays. If the working edge of the screen 3 is below the BB line, then scattered light enters the receiver, if the edge is above the AA line, then it enters the probe beam and becomes a source of scattered light. The optimum position of the edge is in the middle between the AA and BB lines, which corresponds to the distance from the optical axis of the source

D 5 D li. 2 2 2

The technical effectiveness of a nephelometer compared to limestone is illustrated by examples. Let the dimensions of the known nephelometer be the same as the one proposed. The minimum scattering angle is for a known 8 ° 30. In the proposed nephelometer, when measuring, the minimum scattering angle is 4 ° 50, while the sensitivity is reduced by a factor of 8, which compensates for an increase in the scattering intensity at this angle. When the mirror 5 is rotated, the effective aperture of the lens 6 increases, the sensitivity of the nephelometer increases accordingly, and, starting at angle 15, the light shields 3 and 4 cease to block the light opening of the lens 6.

If, in the known, the optimal angle of dispersion is 4 50 by decreasing the diameters of the source and the objective, then the sensitivity of the nephelometer is reduced for all angles.

ten

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dissipation is not 9.7 times. A decrease in the diameters also leads to a decrease in the scattering volumes, as a consequence, to an increase in the errors caused by the heterogeneity of the density and structure of the aerosol.

The use in the proposed optical nephelometer scheme of two or more light shields provides, in comparison with the known, an increase in the range of measured scattering angles due to a decrease in the mini-low scattering angle and an expansion of the dynamic range of measured aerosol densities due to a decrease in the dynamic range scattered radiation arriving at the photodetector.

Fo, rmula invention

A nephelometer for measuring the indicatrix of dispersion of aerosols containing a source of probe radiation optically coupled through a diffusing volume to a receiver consisting of successively along the optical radiation of the mirror, lens, sliding diaphragm of the field of view and photodetector, a rotation mechanism kinematically connected with a mirror and a sliding diaphragm and an angle position sensor, kinematically connected with the mirror, the mirror being set at an angle of 45 to the optical axis of the lens, distinguishing In order to increase the range of measured scattering angles with a simultaneous expansion of the range of measured aerosol densities, at least two light shields are installed between the mirror and the source of probing radiation, intersecting a part of the light hole of the receiving device, while the first screen is set to distance 1 from receiver equal to S

, - - :: s

tg0MHH

where D is the size of the output window of the source of probe radiation In the plane of measurement of the scattering indicatrix; the empirical value is equal to the distance between the straight line.

S.

conducted through the edge of the second screen parallel to the optical axis of the source, and the straight line connecting the edge of the second screen and near the optical axis of the source, the edge of the input window of the receiver, in a plane. the settings of the first screen, with the value o being in the range of values from 0.0005 L to 0, od5, L; L is the distance from the source to

receiving device;

0 min. Minimum recorded angle of scattering,

the working edge of the first screen facing the optical axis of the source is located at a distance of

(D -) / 2 from it, the.-Second screen is located between the first screen and the source at a distance a from the first screen, equal to

ffl

K-S- -)

where b is an empirical value, is equal to the distance from the optical axis of the source to the edge of the input window of the receiver close to it, lying in the range of values from 0.005 L to 0.05 L,

at the same time, the working edge of the second screen is parallel to the working edge of the first screen and is located at a distance D / 2 from the optical axis of the source.

FIG. 2

is he

Fig it

Claims (1)

A nephelometer for measuring the aerosol scattering indicatrix, containing a probe radiation source optically coupled through a scattering volume to a receiving device consisting of a mirror, a lens, a sliding diaphragm of the field of view and a photodetector sequentially located along the optical radiation, a rotation mechanism kinematically connected to the mirror and sliding diaphragm and an angular position sensor, ki, nematic associated with the mirror, the mirror is mounted at an angle of 45 * ¹ to the optical axis of the lens, differing in order to increase the range of measured scattering angles while simultaneously * expanding the range of measured aerosol densities, at least two light shields are installed between the mirror and the probe radiation source, which overlap part of the light opening of the receiving device, while the first screen is installed at a distance of 1 from the receiver equal to 50 d + - ^S 40 where D is the size of the output window of the probe radiation source in the plane of measurement of the scattering indicatrix; an empirical value equal to the distance between the straight line drawn through the edge of the second screen parallel to the optical axis of the source and the straight line connecting the edge $ of the second screen and the edge of the input window of the receiving device closest to the optical axis of the source in the plane. setting the first screen, while the value of 8 is in the range of values from 0.0005 L to 0.005 .L; L is the distance from the source to the receiver; fifteen Θ min is the minimum recorded scattering angle, and the working edge of the first screen facing the optical axis of the source is located at a distance of 20 (D - #) / 2 from it,> the second screen is located between the first screen and the source at a distance from the first screen , equal to where b is an empirical value equal to the distance from the optical axis of the source to the edge of the input window of the receiving device nearest to it, lying in the range of values from 0.005 L to 0.05 L, while the working edge of the second screen is parallel to the working edge of the first screen and is put at a distance D / 2 from the optical axis of the source.