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Introduction to Laser particle counter and PM2.5 dust detector

50L Particle Counter

Laser particle counters and PM2.5 dust detectors are both instruments that detect particulate matter based on the principle of laser scattering, but their application fields are different. Dust particle counters are used to detect cleanliness levels in dust-free workshops and clean rooms. For example, in industries such as medicine, electronics, precision machinery, color tube manufacturing, microbiology, research institutes, metrology institutes, etc., it is possible to monitor the purification effects and cleanliness levels of workbenches, clean rooms, and purification workshops of various clean levels to ensure that products the quality of. The dust meter is mainly used to measure the atmospheric environment. It is suitable for various environmental research institutions, meteorology, public health, labor hygiene, air pollution research and other fields. The use environment is used in centers for disease control, power plants, chemical manufacturing, health supervision, environmental protection, environmental online monitoring, etc. Why is there such a difference? We can judge by the principles of light scattering of two instruments.
Let’s first introduce a term – aerosol. An aerosol is a suspension system of liquid or solid particles in the air. Fog, smoke, haze, light mist (mist), fine dust and smog are all atmospheric aerosols caused by natural or man-made reasons. They can serve as condensation nuclei for water droplets and ice crystals, absorbers and scatterers of solar radiation, and participate in various chemical cycles. They are an important part of the atmosphere. It can be seen that the PM2.5 and PM10 we call daily are solid particulate matter in atmospheric aerosols. Therefore, dust detectors are also called aerosol detectors. It inhales the aerosol to be measured into the detection cabin through a gas pump, and splits the aerosol to be measured into two parts at the branch. One part is filtered into clean air after passing through a high-efficiency filter, and is used as a protective sheath gas to protect the sensor room. Components are not contaminated by the gas to be measured. Another part of the aerosol directly enters the sensor chamber as the sample to be measured. In the sensor room, the main components are laser diodes, lens groups and photodetectors. During detection, the laser light emitted by the laser diode passes through the lens group to form a thin layer light source. When the thin layer of light is irradiated on the aerosol to be measured flowing through the sensor chamber, it will be scattered, and the scattered light intensity of the light is detected by the photodetector. The photodetector generates an electrical signal after being illuminated, which is proportional to the mass concentration of the aerosol. This is then multiplied by the voltage calibration factor, which is obtained by measuring the specific concentration of aerosol.
The principle of laser particle counter: The particle counter draws the sampling gas through the sampling pump. In the laser room, the sampling gas is irradiated with laser, and the frequency of the flash reflected by the particles represents the number of particles, and the reflected light intensity represents the size of the particles. Since the components in the laser room are not protected by sheath gas, the laser particle counter should be used in a clean environment to prevent damage to the laser sensor. When the measurement area contains loose particles, dust sources, or spray locations, it must be kept at least twelve inches away from the inlet pipe to prevent the above particles and liquid from contaminating the sensor and pipeline.
It can be seen that the laser dust meter (PM2.5 dust detector) not only uses the sheath gas protection function of the clean air path, but also has a more complex internal detection sensor structure, which effectively protects the components from damage by pollutants. Therefore, it can be used for a long time in complex and seriously polluted environments. The dust particle counter (laser particle counter) does not add sheath gas in the gas circuit design, and the detection sensor structure is relatively simple. It can only be classified according to a few particle sizes, and the error is huge when converted into dust concentration (estimate the classification of 8 channels) , the calculation error is greater than 30%; for 2-channel classification, the calculation error is greater than 50%), so particle counting measurements can only be performed in a relatively clean space. If used as a dust concentration measuring instrument, the error will be large.

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