Carbon Dioxide Sensor - Nondispersive Infrared (NDIR) CO₂ Sensors

Nondispersive Infrared (NDIR) CO₂ Sensors

NDIR sensors are spectroscopic sensors to detect CO₂ in a gaseous environment by its characteristic absorption. The key components are an infrared source, a light tube, an interference (wavelength) filter, and an infrared detector. The gas is pumped or diffuses into the light tube, and the electronics measures the absorption of the characteristic wavelength of light. NDIR sensors are most often used for measuring carbon dioxide. The best of these have sensitivities of 20–50 PPM. Typical NDIR sensors are still in the (US) $100 to $1000 range. New developments include using Microelectromechanical systems to bring down the costs of this sensor and to create smaller devices (for example for use in air conditioning applications). NDIR CO₂ sensors are also used for dissolved CO₂ for applications such as beverage carbonation, pharmeceutical fermentation and CO₂ sequestration applications. In this case they are mated to an ATR (attenuated total reflection) optic and measure the gas in situ. Another method (Henry's Law) can be also be used to measure the amount of dissolved CO₂ in a liquid, if the amount of foreign gases is insignificant.