Carbon dioxide (CO2) is an odorless gas formed during the combustion of carbon-containing materials or metabolic processes of living organisms, e.g. respiration. Excessive CO2 levels can affect concentration and, in extreme cases, lead to unconsciousness. CO2 transmitters are used to control the CO2 value. To control the CO2 value, building automation systems can be used that detect the CO2 concentration via transmitters and readjust the supply air accordingly. A ventilation system equipped with CO2 sensors can thus supply fresh air as needed, ensuring energy-efficient operation of the system while maintaining consistently high air quality. In other applications, such as greenhouses, a high CO2 concentration is required to promote plant growth. In this case, CO2 transmitters are used to regulate the CO2 content to a correspondingly high level.

The CO2 concentration is often measured in rooms that are not permanently but cyclically used by people, such as offices, school buildings or event rooms. In these cases, demand-based ventilation control makes sense, as the fresh air supply should be throttled during periods of low occupancy (e.g. outside of class time) and regulated to full load during periods of high occupancy (e.g. during a class period). This demand-based control saves energy and at the same time guarantees a constant high air quality. In other applications, such as greenhouses or CO2 incubators, CO2 transducers are also used to maintain the value at a certain level.

FSM's CO2 transmitters are based on the NDIR dual beam method. A dual beam NDIR sensor is a non-dispersive infrared sensor with 2 wavelengths and 2 detectors. The concentration of CO2 is measured electro-optically via absorption of a specific wavelength in the infrared spectrum.One detector is set to the 4.2 μm wavelength absorbed by CO2, with the other detector set to a wavelength not absorbed by any gas. This procedure enables auto-calibration of the sensor and ensures optimum long-term stability and insensitivity to contamination in the process.