A carbon dioxide sensor or CO2 sensor is an instrument for the measurement of carbon dioxide gas. The most common principles for CO2 sensors are infrared gas sensors (NDIR) and chemical gas sensors. Measuring carbon dioxide is important in monitoring indoor air quality and many industrial processes.
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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.[1] The best of these have sensitivities of 20-50 PPM.[1] 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 insitu.
Chemical CO2 gas sensors with sensitive layers based on polymer- or heteropolysiloxane have the principal advantage of a very low energy consumption and can be reduced in size to fit into microelectronic-based systems. On the downside, short- and long term drift effects as well as a rather low overall lifetime are major obstacles when compared with the NDIR measurement principle[2].
For air conditioning applications these kind of sensors can be used to monitor the quality of air and the tailored need of fresh air, respectively.
CO2 sensors are also able to determine how many people are in a room and then adjust the air conditioning accordingly. ui