SU1594384A1 - Method of determining size of particles in flow of medium - Google Patents

Abstract

The invention relates to technical physics and, in particular, to methods for the automated determination of particle sizes in process media. The purpose of the invention is to improve the measurement accuracy. The amplitude of each recorded signal is adjusted depending on the distance between the particle's trajectory and the center of the measuring zone, which is determined by measuring the temporal mismatch of the pulses from the attenuation of the luminous flux obtained when the particle passes two sections of the measuring zone that are symmetrical about the optical axis. Before determining the particle size, the amplitude of the attenuation signal is increased, depending on this distance, by a factor of K: K = [(ϕA 2Z / 2λF 2) / SIN (ϕA 2Z / 2λF 2)] 2, where A is the radius of the light-restricting hole

Z is the distance to the center of the measuring zone

λ is the wavelength of the radiation used

F is the focal length of the lens. At Z = 0, the amplitude is not corrected. 1 il.

Description

The invention relates to technical physics and can be used to determine particle sizes and size distribution in laboratory and in production conditions.

The aim of the invention is to improve the measurement accuracy.

The drawing shows a block diagram of a device for implementing the proposed method:

The device contains a laser 1, a collimator 2, lenses 3-5, a capillary 6 for pumping the medium under study, a beam splitter 7, photodetectors 8-10, a double-slit diaphragm 11, a rectangular prism 12, an amplifier 13, threshold devices 14-16, a time meter 17 mismatch, time amplitude converter 18, microcomputer-based calculator 19, which consists of two analog information input modules 20 and 21, a -22 processor, a serial exchange device 23, and a microcomputer system channel 24, 25 26

The method is implemented as follows.

 In the test medium passing at a constant speed through the capillary p 6, a measuring zone is formed.

: l

00 4

dimensions that exceed the maximum size of a piece. The zone is formed by focusing the lens 3 with the light flux from laser-fa 1 expanded by the collimator 2. The zone has parallel limits on the surface of the surface. The luminous flux behind the capillary 6 is divided by the light driver 7 into two streams collected by lenses 4 and 5. They carry out a photoelectric recording of the pulsed signals by the photodetector 8, resulting in a loss of light when the particle crosses the measurement zone. Using lens 5, two slit diaphragms 11e of a rectangular prism 125 of photodetectors 9 and 10, threshold devices 15 and 16, measure 17 time mismatches determine the distance from the trajectory of movement of each individual particle to the center of the measuring zone-v. The distance is found by measuring the temporal mismatch of the pulses obtained by registering the light attenuation signals formed when a particle passes two sections of the measuring zone that are symmetric about the optical axis and located on its trajectory. In the device, the focal planes of objectives 3 and 5 coincide. Signal attenuation from two sites. measure, the full area is distinguished by a double-slit diaphragm .11 .. The attenuation signals are converted into electrical pulses by photodetectors 9 and 10. When the trajectory of motion coincides with the center of the measuring zone, the pulses from the photodetectors are formed simultaneously. outside its center, the pulses have a temporary mismatch, the magnitude of which is proportional to the distance from the trajectory of the particle to the center of the zone. Signals from the photodetectors enter threshold structures CTBA 15 and 16, in which the rows formed vpso- rectangular pulses. Pulses from two threshold devices have a temporary mismatch. On these fronts, the temporal mismatch meter 17 forms rectangular pulses whose durations are equal to the time mismatch between the trajectory of the particles and the center of the measuring zone. Pulse duration

are related to the specified distance by the following relationship:

f

: t.v

Where

/ - i,

z 1 pulse duration; the distance from the center of the measuring zone to the particle trajectory; the distance of the melade by the slit aperture 11, fj is the focal length of the lens 5;

V is the velocity of the particles in the capillary.

0

0

five

0

five

u

five

Square pulses from meter 17 arrive during amplitude converter 18, the amplitude of the signals at the output of which is proportional to the distance between the trajectory of the particles and the center of the measuring zone. These signals are fed to the analog input module of the calculator 19. The attenuating signals amplified in the amplifier 13 are fed to the analog input module 20. The attenuation signals also enter the threshold device 14, the trigger level of which is higher than the noise level. The threshold device generates pulses that serve to control the operation of the modules 20 and 21 of the anomaly input. The module and the analog input convert the amplitudes of the input signals into codes that are transmitted through the system channel 24 to the processor 22, and the information is transmitted to the processor only if there are control pulses from the threshold device 14. The analog-digital conversion in the modules the analog input is gated with pulses from generator 25. In the calculator, the amplitude of each registered and measured attenuation signal is increased, depending on the distance between the trajectory of the particle and the center of the measuring zones, and this dependence is inversely proportional to the distribution function of the intensity of the light flux in the direction of its propagation. Indeed, the amplitude of the attenuation signal U is proportional to the square of the radius of the particle r and the intensity I, of the illuminating light flux at the particle detection point:

and, with 1, r2,

where c is the proportionality coefficient.

Since the amplitude of the measured signals should not depend on the location of the particle, but should be associated only with its size, the amplitudes of the signals from parts of the same size passing through the center of the measuring zone and outside it should be the same:

X1; G2

J

Where

1o the intensity of the light flux in the center of the measuring zone;

K is the gain of the signal from particles passing outside the center of the measuring zone.

It is known that the intensity distribution along the axis of the focused flow is described by the extrusion

 / V

G. / ffafz V

. I; if2 /

de L is the wavelength of the radiation used;

Z - dissipation to the center of the measuring zone .; a - radius limiting flow

holes;

f is the focal length of the lens. Consequently, the signal gain ratio is

2: 7 / 5Ha2712

Tg-G / /

sin

2Af2

Thus, the law of variation of the measured signals is the reciprocal of the distribution function of the intensity of the light flux in the direction of its propagation. After this operation, the signals from the particles do not depend on the distance between the trajectory of movement and the center of the measuring zone.

The distance r enters the calculator 19 in the form of an amplitude with a time-amplitude converter 18. With the help of the calculator, the sizes of the particles are also determined by the increased amplitudes of the signals. The most simple particle sizes are found by the tabular method.

The device is pre-calibrated against reference latexes. Particle sizes are listed in the table, respectively

the amplitude signals from them. The particle sizes are determined by the corrected amplitudes. The number of particles in the flow of the medium is determined. The time interval in the various ranges- (the boundaries of the ranges are set in advance) is displayed on the display 26, to which information is transmitted through the device 2 of the serial exchange.

The proposed method has a higher accuracy due to the exclusion of measurement errors associated with the effect of irregularity of the illumination of particles in different parts of the measuring zone along the direction of propagation of the illuminating radiation and, therefore, with the mismatch of the amplitudes of the measured signals.

Claims (1)

Invention Formula 25 thirty The method of determining the size of particles in the flow of the medium, including the formation of probe radiation in the test flow of the measuring zone, surpassing the maximum particle size, photoelectric recording of pulse signals resulting from the attenuation of the luminous flux at the intersection of the particles, the measurement zone, determining the particle size from signal amplitudes, about 35 l and h and y with the fact that, in order to increase the accuracy of the measurements, the distance from the trajectory of movement of each in the compartment is additionally determined nosti particles to center izmeri40 tion zone by measuring temporal mismatch pulses the formation. two portions of the measuring zone that are symmetrically located with respect to the optical axis during the passage of the particle, and before determining the particle size, increase the amplitude of each attenuation signal, depending on this distance, K times: G Ga2 Z /. Fa2 Z × 2TR-G 50 2 / lf2 G. where a is the radius of the hole restricting the luminous flux; Z is the distance to the center of the measuring zone; f (- dpina wave of radiation used; f is the focal length of the lens. Yu