Dust particle counter and PM2.5 dust detector

Both dust particle counters and PM2.5 dust detectors use the principle of laser scattering for particle detection, but their application fields are different. The dust particle counter is used to detect the cleanliness level in dust-free workshops and clean rooms. In industries such as medicine, electronics, precision machinery, color tube manufacturing, microbiology, research institutes, metrology institutes, etc., the purification effect and level of various cleanliness levels of workbenches, purification rooms, and purification workshops are monitored to ensure product quality. The dust meter is mainly used to measure the atmospheric environment and is suitable for various environmental research institutions, meteorology, public health, labor health, air pollution research, and other fields. The usage environment is applied to centers for disease control, power plants, chemical manufacturing, health supervision, environmental protection, online environmental monitoring, and so on. Why is there such a difference? We can judge by the principle of light scattering using two instruments.
Let's first introduce a term - aerosol. Aerosol is a suspension system of liquid or solid particles in the air. Fog, smoke, haze, light fog (haze), fine dust, and smoke are all atmospheric aerosols caused by natural or human factors. They can serve as condensation nuclei for water droplets and ice crystals, absorbers and scatterers of solar radiation, and participate in various chemical cycles, making them an important component of the atmosphere. From this, it can be seen that the PM2.5 and PM10 we commonly refer to are solid particulate matter in atmospheric aerosols. Therefore, dust detectors are also known as aerosol detectors. It sucks the aerosol to be tested into the detection chamber through a gas extraction pump, and divides it into two parts in the branch flow. One part is filtered into clean air through an efficient filter, which serves as a protective sheath gas to protect the components in the sensor room from being contaminated by the gas to be tested. The other part of the aerosol, as the sample to be tested, enters the sensor chamber directly. In the sensor room, the main components are laser diodes, lens groups, and photodetectors. During detection, the laser emitted by the laser diode is first used to form a thin layer surface light source through a lens group. When a thin layer of light is irradiated on the aerosol to be measured passing through the sensor chamber, it will generate scattering, and the scattered light intensity is detected through a photodetector. The photoelectric detector generates an electrical signal after being illuminated, which is proportional to the mass concentration of the aerosol. Then multiply by the voltage calibration coefficient, which is obtained by measuring specific concentrations of aerosols.
The principle of laser particle counter: The particle counter extracts the sampled gas through a sampling pump. In the laser chamber, the sampling gas is irradiated by a laser, and the frequency of the flash reflected by the particles represents the number of particles, the intensity of the reflected light, and the size of the particles. Due to the lack of sheath gas protection for the components in the laser chamber, the laser particle counter should be used in a clean environment to prevent damage to the laser sensor. When there are loose particle materials, dust sources, and spray at the measured place, it must be kept at least 12 inches away from the inlet pipe to prevent the above particles and liquids from polluting the sensor and pipeline.
It can be seen that the laser dust detector (PM2.5 dust detector) not only adopts the sheath gas protection function of the clean gas path, but also has a more complex internal detection sensor structure, effectively protecting the components from damage from pollutants. Therefore, it can be used for a long time in complex and heavily polluted environments. The dust particle counter (laser particle counter), due to the absence of sheath gas in the gas circuit design and the relatively simple structure of the detection sensor, can only be classified according to a few particle sizes. When converting to dust concentration, the error is huge (estimating the classification of 8 channels, the calculation error is greater than 30%; the classification of 2 channels, the calculation error is greater than 50%), so particle counting measurement can only be carried out in relatively clean spaces, If used as a dust concentration measurement instrument, the error is large.