Reference
Last revision 2025/12/16
This article explains the laser scattering principle used by PM2.5 sensors to measure air quality, including details on the communication protocol and data analysis methods such as Fourier transform.
Principle
This pm2.5 sensor uses a laser scattering theory. And namely the scattering of laser irradiation in the air suspended particles, while collecting the scattered light at a specific angle, to obtain the scattering intensity versus with time curve. After the microprocessor data collection, get the relationship between the time domain and frequency domain by Fourier transform, and then through a series of complex algorithms to obtain the number of particles in the equivalent particle size and volume units of different size. Each functional block diagram of the sensor portion as shown:
Communication Protocol Description
Serial port baudrate: 9600; Parity: None; Stop Bits: 1; packet length is fixed at 32 bytes.
| Start Character 1 | 0x42(fixed bit) |
| Start Character 2 | 0x4d(fixed bit) |
| Frame Length 16-byte | Frame Length = 2*9+2 (data+check bit) |
| Data 1, 16-byte | concentration of PM1.0, ug/m3 |
| Data 2, 16-byte | concentration of PM2.5, ug/m3 |
| Data 3, 16-byte | concentration of PM10.0, ug/m3 |
| Data 4, 16-byte | Internal test data |
| Data 5, 16-byte | Internal test data |
| Data 6, 16-byte | Internal test data |
| Data 7, 16-byte | the number of particulate of diameter above 0.3um in 0.1 liters of air |
| Data 8, 16-byte | the number of particulate of diameter above 0.5um in 0.1 liters of air |
| Data 9, 16-byte | the number of particulate of diameter above 1.0um in 0.1 liters of air |
| Data 10, 16-byte | the number of particulate of diameter above 2.5um in 0.1 liters of air |
| Data 11, 16-byte | the number of particulate of diameter above 5.0um in 0.1 liters of air |
| Data 12, 16-byte | the number of particulate of diameter above 10.0um in 0.1 liters of air |
| Data 13, 16-byte | Internal test data |
| Check Bit for Data Sum, 16-byte | Check Bit = Start Character 1 + Start Character 2 + ...all data |
Other Supplementary Information
Dimensions
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