RU2691978C1 - Optical dust meter - Google Patents

Abstract

FIELD: ventilation and air conditioning.SUBSTANCE: dust meter can be used for control of ventilation equipment, as well as for determination of total fraction of dust respirable fraction causing professional pulmonary diseases. Dust detector has a light source, two beam splitters, two diaphragms, two photodetectors, a laser range finder, a reflector, a CCD matrix, three analogue-to-digital converters and an electric computer. Light flux reflected from the first beam-splitting mirror is transmitted through the first diaphragm to the first photodetector, and the transmitted through the first beam-splitting mirror and the second diaphragm arrives at the second beam-splitter mirror. Portion of the light flux transmitted through the second beam-splitter mirror is projected onto the CCD matrix, and reflected from it is transmitted to the second photodetector. Laser range finder measures distance between centres of beam-splitter mirrors. Two photodetectors and CCD matrixes are connected to a computer via three analogue-to-digital converters.EFFECT: high accuracy of continuous measurement of average concentration, as well as determination of average size of dust particles in the medium under study.1 cl, 2 dwg

Description

The proposed device relates to the measurement technique.

The invention can be used in industry to determine the average concentration, to control the ventilation equipment of an enterprise by the dust factor, as well as to determine the average size of dust particles and, in turn, the total fraction 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 invention: in the optical dust meter, the first emitter is 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 is located behind the working chamber, forms the control channel and is optically connected to the photodetector, the third emitter is located inside the device behind the working camera, forms an additional control channel and is optically connected to the photodetector through a protective window, with all the emitters made with the possibility of alternating inclusion.

The disadvantage of this device is the low measurement accuracy.

The optical absorption dust meter is known (Klymenko A.P., Korolev V.I., Shvetsov V.I. Continuous monitoring of the dust concentration. Kiev: “Technique”, 1980- p. 62-65). The principle of operation of the device is as follows: the light from the source is formed in two streams. One of them is sent to the gas duct with the measured dust-gas medium and, with the help of a system of mirrors, passes through the switch of channels and is perceived by the photo-receiver. The second luminous flux passes through a reference channel, which is filled with a dust-free gas mixture, its composition is similar to the exhaust gases of a particular industrial enterprise. The luminous flux that has passed the reference channel, with the help of a system of mirrors, hits the channel switch and is perceived by the same photodetector. The signal from the output of the photodetector enters the amplifier, then to the separation unit of the measuring signal and the comparison signal, then to the logarithm device, the measurement results are recorded by the measuring device.

The disadvantage of this device is the low measurement accuracy.

Known optical dust meter for the ventilation control system of the enterprise (US Pat. Russia No. 2210070, IPC G01N15 / 02, publ. 10.08.2003) selected as a prototype.

An optical dust meter for an enterprise ventilation control system that contains a light source that is connected in series and optically connected to the input of a light beam separation device, the first output of which is connected in series and optically connected to the first protective window, the measuring channel, the second protective window and the first signal-processing device; the second output of the device for dividing the luminous flux is serially connected and optically connected to the reference channel, which is filled with a gas-free mixture of dust that is similar in composition to the flue gases of a particular industrial enterprise, the second input of the signal processing device, characterized in that the light source is powered by a pulsed voltage source as well as additionally introduced a dust control device for the protective window, which is optically connected to the protective window in the measuring channel, the output of which o is the input for the control device, the output of which is connected to the blowing device that blows the viewing windows, a temperature control device is also introduced, the output of which is connected to the input of the signal processing device, in addition, to reduce the dusting of the protective windows, the heating window of the viewing windows is introduced associated with heating elements located in the viewing windows.

The principle of operation of the device is as follows:

The functional-pulse sweep generator supplies a pulsed voltage to a source of light radiation, optically connected to the input of a luminous flux separation device, the main purpose of which is to direct the separated light streams to the measuring and reference channel.

Pulsed light radiation passing through the measuring channel is attenuated by dust and enters the photodetector located in the electrical signal processing device.

Pulsed light radiation passing through the reference channel changes slightly and enters the photodetector of the reference channel located in the electrical signal processing device.

The inspection window dust control device controls the blowing device with cleaning brushes specially attached to the fan blades automatically approaching the viewing windows when the fan is running.

The disadvantages of this device is the low measurement accuracy.

The optical scheme and the block diagram of a recording device for measurement by the fluctuation method (Shifrin K.S. “Introduction to Ocean Optics”, St. Petersburg: ”Gidrometeoizdat”, 1983 - p. 225), selected as a prototype, is known. The principle of operation of the registration device for the specified 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 device 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 accuracy of continuous measurement of the average concentration, as well as the determination of the average size of dust particles in the studied environment.

The task is achieved by the fact that the optical dust meter contains a light source, a beam-splitting mirror, a diaphragm, two photodetectors. To improve measurement accuracy, it additionally contains a laser range finder, a reflector, a second aperture, a CCD matrix, a second beam-splitting mirror, three analog-digital converters, a computer (computer), and a laser emitter is used as the light source.

FIG. Figure 1 shows a special function that relates the dispersion to the optical thickness of the system and the average number of particles in a translucent volume.

Figure 2 presents the block diagram of the device in accordance with the invention.

The device 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, a laser range finder 10, a CCD 11, a 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 operation of the described device is based on the so-called fluctuation method. 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.

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 proposed optical dust meter, based on the method of fluctuations, improves the accuracy of determining the average concentration and average size of dust particles to predict the occurrence of occupational diseases in various industries, depending on the dust load received by the body.

Claims (1)

Optical dust meter containing a light source, a beam-splitting mirror, a diaphragm, two photodetectors, characterized in that it additionally contains a laser range finder, a reflector, a second diaphragm, a CCD matrix, a second beam-splitting mirror, three analog-to-digital converters, an electronic computing machine, and the luminous flux from the light source, reflected from the first beam-splitting mirror, through the first aperture enters the first photodetector, the light flux that passes through the first beam-splitting mirror, and the second di the fragment enters the second beam-splitting mirror, part of the luminous flux transmitted through the second beam-splitting mirror is projected onto the CCD matrix, and part of the light flux reflected from the second beam-splitting mirror enters the second photodetector, while the laser rangefinder measures the distance to the reflector equal to the distance between the centers of the beam-splitting mirrors, and the information from the two photodetectors and the CCD matrix is fed through three analog-to-digital converters to an electric computer.

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