How PM2.5 sensor and CO2 sensor work.

1. How does the PM2.5 laser sensor work?

The AirVisual Node/Pro uses a light scattering laser sensor for PM2.5 measurements. How it works is that within the sensor's measuring 'chamber', a laser light beam is shone onto particles, and this light is then irradiated in all directions from these particles (scattering). A light detector (or 'photometer detector') then measures all of this scattered light, and from this, the sensor can calculate the concentration of particles within the chamber. In this way, the sensor is able to detect near microscopic particles ranging from 0.3μm to 2.5μm. The sensor in the AirVisual Node/Pro also has a small fan to ensure a constant flow of air through the measuring chamber.

Each reading reported from the sensor is calibrated by a special algorithm which takes into account external temperature and humidity values.

infographic of sensor reading

2. How does the IR CO2 sensor work?

The CO2 censor is composed of an infrared (IR) lamp, a reflective gas cell, and IR filtered detectors. The IR lamp sends waves of light towards the IR filtered detectors, which can measure how much IR light reach them. While the IR light goes through the cell, CO2 modules absorb lights of certain wavelength (shown in the graph). Thus, the number of CO2 modules in the cell can be calculated by comparing the amount of light IR lamp radiated and the amount of light detectors received.

IR Lamp infographic

CO2 transmission graph

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