PM2.5 sensors, also known as dust sensors or particulate matter sensors, are used to detect the concentration of dust in the air around us, i.e., the PM2.5 value. Aerodynamically, dust particles with a diameter less than 10 μm that can enter the alveoli are generally referred to as respirable dust. Most dust particles larger than 10 μm are deposited through impaction, and when inhaled, most are deposited in the nasopharynx, while dust particles smaller than 10 μm can penetrate deeper into the respiratory tract. Most of the dust deposited in the alveoli is smaller than 5 μm.

    PM10 refers to particulate matter in ambient air with an aerodynamic equivalent diameter of 10 μm or less. PM2.5 fine particulate matter has a small diameter, remains suspended in the atmosphere for a long time, travels long distances, and usually contains a large amount of toxic and harmful substances, thus having a greater impact on human health. PM2.5 can enter the lungs and bloodstream, and if it carries pathogens, it can cause significant harm to the human body, including our respiratory, cardiovascular, and even reproductive systems.

    The working principle of a PM2.5 dust sensor is based on the principle of light scattering. Particles and molecules scatter light when exposed to it, and simultaneously absorb some of the incident light's energy. When a beam of parallel monochromatic light is incident on the particle field being measured, it is attenuated due to scattering and absorption around the particles. The relative attenuation rate of the incident light passing through the measured concentration field can then be calculated. The magnitude of the relative attenuation rate essentially linearly reflects the relative concentration of dust in the measured field. The intensity of the light is directly proportional to the strength of the electrical signal converted from photoelectric signal. By measuring the electrical signal, the relative attenuation rate can be calculated, and thus the dust concentration in the measured field can be determined.

    The PM2.5 sensor is designed to sense dust particles in the air. Inside, an infrared LED and a phototransistor are placed diagonally, their optical axes intersecting. When a dust-laden airflow passes through the intersection of these optical axes, the dust reflects the infrared light, and the intensity of the reflected light is proportional to the dust concentration. Phototransistors enable the detection of light reflected from dust particles in the air, even very small particles such as tobacco smoke. Infrared light-emitting diodes emit light and reflect it when they encounter dust. A receiving sensor detects the intensity of the reflected light and outputs a signal. The concentration of dust is determined based on the intensity of the output signal. The concentration of different dust particles is distinguished by outputting two different pulse width modulation (PWM) signals.

TZH03 Dust Sensor

    Based on the working principle of PM2.5 sensors, they are generally used to help detect air quality. Their main applications are as accessories for air purifiers, fresh air systems, portable instruments, air quality monitors, air conditioners, and consumer electronics.