Duct-mount CO2 sensor with display; 0/2-10-volt (DC) or 0/4-20mA (current loop) output. Stand-alone carbon dioxide (CO2) sensors and controllers are used for determining ventilation necessity with HVAC controllers and to manage amount of fresh outdoor air supplied to maintain acceptable levels of CO2. Models available with LCD that provides sensor readings and status information. Non-Dispersion-Infrared (NDIR) technology used to measure carbon dioxide gas. Gold-plated sensor provides long-term calibration stability. C7232 provides voltage or current output based on CO2 levels. Single Pole, Single Throw (SPST) relay output. Used for CO2-based ventilation control (Demand Control Ventilation (DCV)). Automatic Background Calibration (ABC) algorithm based on long-term evaluation reduces required typical zero-drift check maintenance.