The T6615 series Telaire® dual-channel Carbon Dioxide Module. The two channels can be described as a CO2 channel that measures gas concentration and a reference channel that measures the sensor signal intensity. Dual-channel optical system and three-point calibration process for enhanced stability, accuracy and reliability. The T6615 performs periodic self-calibrations using the reference channel. The self calibrations are approximately every 24 hours but can also be initiated by sending a command.