Dual channel NDIR sensors contain two IR detectors with narrow bandpass optical filters; one tuned to CO₂ gas absorption at ~4.2 µm (active) and the other at 3.9 µm (reference), unaffected by CO₂ gas concentration. As the sensor drifts over time, the reference channel will experience a change in output due solely to these effects, which can be applied as an offset to the active measurement channel as compensation. In contrast, a single channel NDIR sensor contains only one IR detector and narrow bandpass optical filter tuned to CO₂ gas absorption at ~4.2 µm (active). In this configuration, sensor drift is managed via a calculated offset derived from concentration measurements over an extended period of operation. The sensor’s firmware utilizes a sophisticated statistical algorithm called “automatic background calibration” (ABC Logic™) to determine and apply drift compensation.