Update: 2020-06-03 16:28 Source: LUFTMY
PM2.5 refers to fine particles with aerodynamic equivalent diameter less than or equal to 2.5 microns in ambient air.This kind of fine particulate matter mainly comes from the soot emission in industrial production, automobile exhaust in daily life, cooking fume emission, forest fire in natural disasters and so on.The smaller the diameter of the fine particles, the deeper they enter the respiratory tract, and thus can cause great harm to human health.
At present, there are 5 kinds of PM2.5 testing methods and working principles of PM2.5 sensors
PM2.5 test method
I. Infrared method
The infrared method detects PM2.5 according to the principle of light dispersion. The infrared light emitting diode produces reflected light when it encounters dust. The highly sensitive photoelectric receiving sensor detects the intensity of reflected light and outputs a signal.The output current of the detector is proportional to the detected light intensity. The output electricity of the sensor flows through the amplifier and is amplified, and then processed by the processor for correction. Finally, the digital PWM signal pulse is output, or the dust concentration value is output through the IIC data interface.
Ii. Beta ray method
Beta ray instrument is based on the attenuation principle of Beta ray. Ambient air is inhaled by the sampling pump into the sampling tube and is discharged after the filtration membrane. The particles settle on the filtration membrane.
Three, the microoscillation balance method
The microoscillation balance method USES an oscillating hollow conical tube in the mass sensor and a replaceable filter film is installed at the oscillating end. The oscillation frequency depends on the characteristics of the conical tube and its quality.When sampling air flow filter film, the particles in it are deposited on the filter film, and the change of the mass of the filter film leads to the change of the oscillation frequency. Then the mass of the particles deposited on the filter film is calculated through the change of the oscillation frequency, and then the mass concentration of the particulate mark at that time period is calculated according to the flow rate, on-site environmental temperature and air pressure.
Iv. Weight method
The principle of the grainy method for PM2.5 detection is to extract quantitative volume air at a constant speed through samplers with certain cutting characteristics, so that PM2.5 and PM10 in the ambient air are trapped on the filter film of known mass. The concentration of PM2.5 and PM10 is calculated based on the difference in quality of the filter film before and after sampling and the sampling volume.It must be noted that the volume of denominator in the unit ug/m3 of particulate matter measurement should be the volume under standard conditions (0℃, 101.3kPa), and the volume under measured temperature and pressure should be converted into the volume under standard conditions.
V. Laser method
Laser method to detect pm2.5 concentration, LUFTMY recommended LD07 laser pm2.5 dust sensor module, the particle sensor using Mie Mie spherical particle scattering principle, namely the laser sensor using laser the light scattering in the suspended particles in the air, the photoelectric detector in a certain way within the scope of collecting scattering intensity, will receive the scattering intensity linear converted into voltage, and then into a data processing system, data processing system according to the program in advance according to the Mie scattering theory for data processing, it is concluded that the equivalent grain size of particles of different size particles per unit volume and quantity.
How the PM2.5 sensor works