Double Relays: The CO2 controller can be connected to the CO2 regulator or generator and the exhaust fan simultaneously. WORK1: The CO2 regulator or generator; WORK2: The air extractor. Programmable: The controller has adopted the NDIR sensor to obtain an accurate CO2 ppm level, equipped with 2 display windows to show the current measured CO2 concentration value and the set CO2 concentration value simultaneously, supports CO2 calibration and high/low CO2 concentration alarm. Easy to Use: Comes with everything you need to start the CO2 system, no more complicated installation, the controller will automatically turn the CO2 generator or regulator and the fan on/off according to your settings. Multiple Uses: Widely applied in ventilation systems, building control equipment, and HVAC.