The FGD 3 Infrared Carbon Dioxide Gas Detector incorporates the latest generation of compact sensors incorporating infrared technology for the accurate detection of Carbon Dioxide concentrations over various ranges up to 100% volume. The detectors use the industry standard 4-20mA current loop to convey the gas levels detected to a control unit. This means that under zero gas conditions 4mA is drawn from the supply, and under full scale gas conditions 20mA is drawn from the supply. The current varies linearly for gas levels between zero and full scale. The detector heads use a three-wire connection. While the loop current supplies the power required by the detector head electronics within the detector head, a second supply must be provided to power the infrared sensor and its associated circuitry.