RU2006824C1 - Method of analysis of impulse pairs in photoelectric aerosol counters - Google Patents

Abstract

FIELD: measurement technology. SUBSTANCE: flow of particles is illuminated by light beams with intensity ratio depending on ratio of diameters of these beams; intensity of broad beam is set lower than that of narrow beam. EFFECT: facilitated procedure. 2 dwg

Description

 The invention relates to measuring technique and can be used to determine the characteristics of dispersed media in the chemical industry, meteorology, medicine, and for controlling dustiness of gases and liquids.

 The known method [1] for a similar purpose, consisting in the fact that the particle flux is illuminated with two light beams spaced apart in the direction of the flow by a predetermined amount, pairs of pulses are scattered by the particles of light, one of the pulses is recorded in each pair, by which the sizes are judged and particle concentration.

 In this method, the particle flux is illuminated with two semi-circular beams, for the formation of which, in particular, an axicon with a small refracting angle is used. This type of optical design requires fairly accurate alignment, and therefore the method [1] is difficult to implement.

 The closest technical solution is a method for measuring the size and concentration of suspended particles [2], which consists in the fact that the particle flux is illuminated with two light beams of different diameters spaced in the direction of the flow by a predetermined amount, pairs of pulses scattered by light particles are separated, separated by a time interval determined by beam spacing, and in each pair, pulses are recorded corresponding to the passage of particles through a wide beam, the amplitudes of which do not exceed the amplitudes of the pulses corresponding to Oleta particles through a narrow beam, which is judged on the size and concentration of particles.

 Since the volumetric analysis rate in this method depends on the particle size, the disadvantage of the method [2] is the noticeable error in determining the concentration of particles and their size distribution function.

 The aim of the invention is to reduce measurement errors due to the formation of sharper boundaries of the counting volume.

 The goal is achieved in that the particle stream is illuminated by light beams with a ratio of intensities determined by the ratio of the diameters of these beams, and the intensity of the wide beam is set lower than the intensity of the narrow beam.

 In FIG. 1 shows a block diagram of a device for implementing the method; in FIG. 2 - the cross section of the beams (a) and the type of intensity profiles I (x) of these beams (b).

 The device (Fig. 1) contains a illuminator 1 (for example, laser), a circuit 2 for the formation of two light beams passing through the stream 3 of the studied particles, a light trap 4, a lens 5, a photographic successor 6, and an analysis unit 7 (including an analog key, a comparator, a logic element) And, two single vibrators and an OR logic element and pulse analyzers).

 The device operates by the proposed method as follows.

пучка меньшего диметра 2σ₂превосходит интенсивность I

первого пучка в некоторое число Краз, где К определяется отношением σ₁/σ₂ и видом профиля интенсивности (фиг. 2бв). Для гауссова профиля интенсивности К = 2,25, если σ₁/σ₂ = 3. Оба пучка проходят через поток 3 исследуемых частиц и гасятся ловушкой 4. Рассеянный частицами свет объективом 5 собирается на фотоприемник 6. При этом каждая частица, пролетая через оба пучка, формирует пару фотоэлектрических импульсов, разделенных временным интервалом T = l/v. Блок 7 анализа обеспечивает выделение из всей совокупности выходных импульсов фотоприемника лишь пар импульсов, разделенных временным интервалом не менее Т. В каждой из выделенных пар измеряются амплитуды соответствующих импульсов и выделяются первые импульсы в каждой паре (соответствующие пролету частиц через широкий пучок), амплитуды которых не превосходят амплитуды второго импульса той же пары (соответствующей пролету частицы через узкий пучок). Амплитуды выделенных первых импульсов блоком анализа регистрируются, при этом о размерах частиц судят по амплитудам зарегистрированных импульсов, а о концентрации - по средней частоте повторения упомянутых импульсов.Scheme 2 forms from the light beam of illuminator 1 two light beams having diameters 2σ ₁ and 2σ ₂ in the region of the particle stream 3, respectively, and spaced apart in the direction of flow (each velocity is equal to v) by l (Fig. 2a). Intensity I

a beam of a smaller diameter 2σ ₂ exceeds the intensity I

the first beam in a number of Kraz, where K is determined by the ratio of σ ₁ / σ ₂ and the type of intensity profile (Fig. 2BV). For a Gaussian intensity profile, K = 2.25, if σ ₁ / σ ₂ = 3. Both beams pass through a stream of 3 particles under study and are quenched by a trap 4. The light scattered by the particles with lens 5 is collected by a photodetector 6. In this case, each particle passing through both beam, forms a pair of photoelectric pulses separated by a time interval T = l / v. Analysis unit 7 ensures that only pairs of pulses separated by a time interval of at least T are extracted from the entire set of output pulses of the photodetector. In each of the selected pairs, the amplitudes of the corresponding pulses are measured and the first pulses in each pair (corresponding to the passage of particles through a wide beam) are extracted, the amplitudes of which are not exceed the amplitudes of the second pulse of the same pair (corresponding to the passage of a particle through a narrow beam). The amplitudes of the extracted first pulses by the analysis unit are recorded, while the particle sizes are judged by the amplitudes of the recorded pulses, and the concentration is judged by the average repetition rate of the mentioned pulses.

As can be seen from FIG. 2b, in the considered method, only particles flying through both beams within a certain region of 2X _about are recorded (regardless of their size). Thus, the formation of sharp boundaries of the counted volume is achieved by the optoelectronic path, which ensures the independence of the volumetric analysis rate from the particle size and, accordingly, reduces the measurement errors. (56) 1. USSR author's certificate N 1173265, cl. G 01 N 15/02, 1985.

 2. USSR author's certificate N 857812, cl. G 01 N 21/85, 1981.

Claims (1)

 METHOD FOR ANALYSIS OF COUPLES OF PULSES IN PHOTOELECTRIC METERS OF AEROSOLS, consisting in the fact that the particle flux is illuminated by two light beams of different diameters spaced apart in the direction of the flow by a given amount, pairs of pulses scattered by light particles separated by a time interval defined by the spacing register pulses corresponding to the passage of particles through a wide beam, the amplitudes of which do not exceed the amplitudes of pulses corresponding to the passage of particles through a narrow beam, over which m is judged on the size and concentration of particles, characterized in that, in order to reduce errors, the particle stream of the illuminating beam of light with the intensity ratio determined by the ratio of diameters of these beams, the beam intensity is set at the wide-intensity narrow beam.

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