RU2686401C1 - Photoelectric method of determining average concentration and average size of dust particles - Google Patents

Abstract

FIELD: measuring equipment.SUBSTANCE: photoelectric method of determining average size and average concentration of dust particles involves converting pulse voltage into light flux, probing the region of the analysed medium with a light beam, separating the light flux, converting said streams into electric signals. Part of the input light flux is diverted to the first photodetector, the signal of which is proportional to the intensity of the light beam at the entrance to the analysed medium, and the second part of the input light flux after passing through the analysed medium is divided into two substreams. First substream is transmitted to a CCD matrix in which the amount of illuminated pixels determines the area of the cross section of the light beam passing through the analysed medium, and the second substream is transmitted to the second photodetector, which signal value is proportional to intensity of the light beam passing through the analysed medium, the path of the beam passing through the analysed medium by the laser range finder is measured, and the obtained signals are digitized and supplied to a computer, where values of the measured parameters are calculated. Process control is carried out by the computer synchronously and cyclically by the trigger signal.EFFECT: invention enables higher accuracy of measuring average concentration and average particle size.1 cl, 2 dwg

Description

The invention relates to measuring equipment.

Industrial applicability of the invention consists in determining the average concentration and average size of dust particles and, in turn, the total share of the respirable fraction of dust causing occupational lung diseases of workers.

Known optical dust meter (US Pat. Of Russia No. 2095792, CL IPC G01N21 / 85, publ. 10.11.1997) for continuous measurement of dust content of gases. The principle of operation of the device is as follows: in the optical dust meter, the first emitter located in front of the working chamber forms the measuring channel and is optically connected to the photodetector through the protective windows of the working chamber, the second emitter located behind the working chamber forms the control channel and optically connected to the photodetector, the third emitter It is located inside the device behind the working chamber and forms an additional control channel and is optically connected to the photoreceiver through a protective window. With the sequential reading of readings from all emitters, the level of dust content in the measuring channel is determined and compared with the data obtained from the control channels.

The disadvantage of this method is the low measurement accuracy.

There is a method for determining the dispersed medium (Shifrin K.S., Moroz B.Z., Sakharov A.N. “Determining the characteristics of the dispersed medium according to its transparency data” - DAN USSR, 1971, t. 199, No. 3, 581-598) on the basis of which the registration device for measuring by the method of fluctuations is compiled (Shifrin K.S. ”Introduction to Ocean Optics”, St. Petersburg: ”Gidrometeoizdat”, 1983 - p. 220-227) selected as a prototype.

The principle of operation of this method is as follows. A parallel beam from a light source, modulated by a modulator, passes through observation windows, cuvettes with the test medium and hits a beam-splitting mirror, which passes the central part of the beam, and sends the rest to the photoreceiver; From the transmitted light, a narrow beam is formed by the diaphragm, which is fed to the photoreceiver. The photodetectors receive signals from the unit, in which electric alignment and subtraction of signals occur, then the difference signal is fed to the amplifier and then to the synchronous detector, the reference signal to which comes from the photodiode. The latter is illuminated by light modulated by a modulator. The spectrum of fluctuations is recorded on the recording unit.

The disadvantage of this method is the low accuracy of measurements of the average size and average concentration of dust particles.

The technical task of the invention is to improve the measurement accuracy of the average size and average concentration of dust particles.

The task is solved by the fact that the photoelectric method of determining the average size and average concentration of dust particles, including the conversion of pulsed voltage into luminous flux, probing the area of the medium under study by a light beam, dividing the luminous flux, converting these fluxes into electrical signals, to improve the accuracy of measurements of the input light the stream is diverted to the first photodetector, whose signal is proportional to the intensity of the light beam at the entrance to the medium under study, and the second hour l input light flux after passing through the test medium is divided into two substreams, the first substream arrives at the CCD matrix, in which the cross-sectional area of the light beam passing through the test medium is determined by the number of illuminated pixels, and the second substream enters the second photodetector, the value the signal of which is proportional to the intensity of a beam of light that has passed through the medium under study is also measured by the path of the beam passing through the medium under investigation by a laser range finder, and Signals are digitized and fed to an electronic computer, where computers calculate the values of measured parameters, and the process is controlled by a computer synchronously and cyclically using a trigger signal.

FIG. Figure 1 shows the change in the special function linking the dispersion with the optical thickness of the system and the average number of particles in the translucent volume.

FIG. 2 shows a block diagram of a device operating in this method.

Consider the basis of the method - the method of fluctuations. Measuring transparency allows you to determine the optical thickness of the system. If there are many particles in the beam, then the transparency of the system undergoes noticeable fluctuations. These fluctuations are caused by random movements of particles, and the particles overlap in different ways. Fluctuations contain valuable information about the properties of the dispersed system under study. The dispersion of transparency, in addition to the thickness of the system, depends directly on the number of particles in the object under study, so that a simultaneous measurement of the transparency and dispersion of the medium enables us to determine both the average size and the concentration of particles.

In the course of modeling using the Robins theorem for a dispersed medium consisting of identical spherical particles, projections of the attenuation width of all particles in the illuminated volume onto the cross section of the incident light beam were obtained. As a result of this simulation, the following expressions for the fluctuation method are defined.

Average particle radius:

, (1)

, (one)

where: S _{0 - the} average diameter of the light attenuation by a particle.

The average diameter of the attenuation of light by a particle, having the dimension of the area:

(2)

(2)

where: D is the optical signal dispersion;

S is the cross-sectional area of the light beam;

– интенсивность падающего пучка света;

- intensity of the incident light beam;

τ is the optical thickness of the system;

φ (τ) is a special function linking the dispersion with the optical thickness of the system and the average number of particles in the translucent volume (Fig. 1).

The dispersion of the optical signal (determined on the basis of a statistical analysis of the results of multiple measurements):

, (3)

, (3)

– средняя интенсивность прошедшего через среду параллельного пучка света,Where:

- the average intensity of the parallel beam of light transmitted through the medium,

I _i - the intensity of the parallel light beam transmitted through the medium in the i-th dimension,

N is the number of intensity measurements of a parallel beam of light passing through the medium.

The average intensity of a parallel beam of light passing through the medium:

. (4)

. (four)

The optical thickness of the system is determined using the formula:

. (5)

. (five)

The average particle concentration:

, (6)

, (6)

– длина пути света в исследуемой среде.Where:

- the length of the path of light in the medium under study.

Analysis of expressions (1) - (6) shows that to calculate the average size of dust particles and their average concentration, it is necessary to make a series of measurements of the following parameters:

- the intensity of the incident light beam, i.e. the intensity of the study at the entrance to the test environment;

- the intensity of the light beam passing through the test medium;

- cross-sectional area of the light beam;

- the length of the path of light in the medium under study.

A device operating in this way contains a laser emitter 1, a reflector 2, two beam-splitting mirrors 3, 8, two diaphragms 4, 7, two photodetectors 5, 9, three analog-digital converters 6, 12, 13, laser range finder 10, CCD -matrix 11, computer 14.

Structurally, the optical dust meter consists of transmitting and receiving units. The transmitting unit includes: laser emitter 1, reflector 2, beam-splitting mirror 3, diaphragms 4 and 7, photodetector 5, analog-digital converter 6. The purpose of the transmitting unit is to create an adjustable probe light flux and measure the intensity of this flux at the output of the unit. The receiving unit consists of a beam-splitting mirror 8, a photodetector 9, a laser rangefinder 10, a CCD matrix 11, analog-digital converters 12 and 13, a computer 14.

The receiving unit performs the following functions:

- measurement of the length of the light beam in the investigated volume;

- measurement of the intensity and area of the probing light flux that has passed through the investigated volume of air;

- calculation by formulas (1) - (6) of the average size of dust particles and their average concentration.

The measurement process of an optical dust meter consists of three stages.

At the first stage, a trigger signal is supplied from the computer 14 to the laser range finder 10, which measures the distance to the reflector 2 located in the transmitting unit. The position of the laser rangefinder 10 in the receiving unit is adjusted so that the distance to the reflector 2 is equal to the distance between the centers of the beam-splitting mirrors 3 and 8. Thus, information about the path length in the medium under study comes from the laser rangefinder 10 in the computer 14.

At the second stage, the synchronous cyclic measurement of the following parameters is performed:

- the intensity of the incident light beam, i.e. the intensity of the study at the entrance to the test environment;

- the intensity of the light beam passing through the test medium;

- cross-sectional area of the light beam.

The laser emitter 1 continuously generates a monochromatic luminous flux, which is split into two substreams with the help of a beam-splitting mirror 3.

The first substream received due to reflection from the beam-splitting mirror 3, through the diaphragm 4 enters the photodetector 5. Reading information from the photodetector 5 occurs at the moment when the computer 14 receives the trigger signal in the analog-to-digital converter 6. Read values proportional to the intensity of the light beam at the entrance to the test environment, are recorded in the computer memory 14. The synchronism of the measurement process is achieved by the fact that the analog-digital converters 6, 12, 13 start signal in each measurement cycle comes from the computer 14 o simultaneity.

The second substream, which is part of the luminous flux of the laser emitter 1 passing through the beam-splitting mirror 3 and diaphragm 7, after passing through the test volume of air enters the beam-splitting mirror 8. A part of the second sub-stream passing through the beam-splitting mirror 8 is projected onto the CCD matrix 11. Information from the CCD matrix 11 enters the analog-to-digital converter 12, and then into the computer 14, where the number of illuminated pixels of the CCD matrix 11 determines the cross-sectional area of the light beam, edshego through the test medium. A part of the second substream reflected from the beam-splitting mirror 8 is fed to the photodetector 9. An analogue signal from the output of the photodetector 9, whose value is proportional to the intensity of the light beam transmitted through the medium under study, is converted into analog-digital converter 13 and in discrete form enters the computer 14. The intensity of a beam of light passing through the medium under study is measured in order to determine the dispersion of the optical signal using formulas (3) and (4).

At the third stage, on the basis of the measured data, the values of the average size of dust particles and their average concentration are calculated. Since the calculation of the dispersion of the optical signal is made according to statistical data, it is necessary to repeatedly measure the intensity of the light beam passing through the medium under study. This is achieved due to the fact that the analog-to-digital converter has a cyclical nature of work. The computer 14 synchronizes the cycles of analog-to-digital converters 6, 12 13 and provides a specified number of cycles of their work, after which the average values of the intensity of the incident light beam and the intensity of the light beam transmitted through the test medium are calculated. Then, using formulas (1) - (3) and (5) - (6), the computer calculates the values of the average size of dust particles and them. average concentration.

The computer, when operating in cyclic mode in each cycle, performs the following actions:

1) determines the cross-sectional area of the light beam;

2) organizes N cycles, consisting of the following commands:

- gives to analog-to-digital converters 6,12 and 13 start signal,

- receives signals from analog-digital converters,

- writes the received data to memory arrays.

3) calculates the average value of the intensity of the incident light beam;

4) calculates the average value of the intensity of the beam of light passing through the test medium;

5) calculates the dispersion of the optical signal;

6) calculates the optical thickness of the system;

7) determine the value of the special function connecting the dispersion with the optical thickness of the system and the average number of particles in the translucent volume;

8) calculates the average width of the particle attenuation of light;

9) calculates the average radius of the particles;

10) calculate the average particle concentration;

11) displays the average particle radius and average particle concentration.

The calibration of the optical dust meter is made in two stages.

At the first stage, the readings of the laser rangefinder are equal to the length of the path of the light in the medium under study. To do this, the transmitting and receiving units are placed at a specified distance from each other. This distance is measured with a caliper, and the laser rangefinder, mounted on the rail in the receiving unit, is moved to a position where the readings of both instruments will coincide.

At the second stage, the calibration coefficients are determined when measuring the total concentration and the average size of dust particles. To do this, a closed cloud of turbulent air creates a cloud of dust with specified parameters, where the transmitting and receiving units of the optical-electronic dust meter are placed. Then measure the average concentration and average size of dust particles and calculate the values of the calibration coefficients by dividing the actual value of the parameter by its measured value. Calibration coefficients are added to formulas (1) and (6).

Thus, the considered method, in contrast to the known, allows to obtain a higher accuracy of measurement of the average concentration and particle size. The average size of dust particles allows you to determine the level of the respirable fraction and to predict the occurrence of occupational diseases in various industries, depending on the dust load received by the body.

Claims (1)

A photoelectric method for determining the average size and average concentration of dust particles, including the conversion of pulsed voltage into luminous flux, probing the area of the medium under study by a light beam, dividing the luminous flux, converting these fluxes into electrical signals, characterized in that part of the input luminous flux is diverted to the first photodetector the signal of which is proportional to the intensity of the light beam at the entrance to the studied medium, and the second part of the input light flux after passing through the black The test medium is divided into two substreams, with the first substream arriving at the CCD array, in which the cross section of the light beam passing through the test medium is determined by the number of illuminated pixels, and the second substream arrives at the second photodetector whose signal is proportional to the intensity of the light beam passed through the test medium, the path of the beam passing through the test medium by the laser range finder is also measured, and the received signals are digitized and fed to the electronic ychislitelnuyu machine where calculation is made of the measured values of the parameters, the process control is carried out electro-computing machine synchronously and cyclically for launch signal.

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