Loose CO2 sensor on the Maxi Controller can be connected. This sensor also controls the CO2 generator or CO2 pressure reducing valve. The sensors make use of the Dual-Beam NDIR technology which ensures an unprecedented calibration. Similar CO2 sensors are single beam and therefore must be calibrated regelmatif. Dual-Beam sensors are two sensors in one of which the probe is corrected by the 2nd sensor periodically. Because the 2nd sensor only 5 minutes per month is not active aging and there will be no drift on.