....the probe is equipped with a silicone membrane making it possible to isolate the volume of the measuring chamber from the liquid medium in which the probe is immersed. Only the gases pass through the side walls, so once the sensor is immersed, the partial pressures of CO₂ equalize between the middle and the internal volume of the sensor.
An optical sensor is placed inside, it uses the principle of non-dispersive infrared absorption (NDIR). The CO₂ molecules present in the measurement chamber absorb some of the infrared radiation emitted by the sensor. The radiation attenuation is therefore directly proportional to the amount of CO₂. This partial pressure measurement must be coupled by the values of temperature and atmospheric pressure to calculate the concentration of dissolved CO₂ in mg/l ...... .