Carbon dioxide sensor

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.

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. Most are used for carbon dioxide, because no other sensing method works reliably for this gas. New developments include using MEMS to bring down the costs of this sensor and to create smaller devices (for example for use in air conditioning

Chemical CO₂ Sensors

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^.

Applications

• Since the danger of fires comes mostly from its quickly spreading CO₂ output, these sensors can be used to detect fire and certain other air related problems safely without false alarm.
• 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.
• In applications where direct temperature measurement is not applicable NDIR sensors can be used. The sensors absorb ambient infrared radiation (IR) given off by a heated surface.