The duct-mounted Vaisala CARBOCAP^® Carbon Dioxide Transmitter Series GMD20 are specially designed for demand-controlled ventilation (DCV). They are easy to install and require no maintenance. The GMD20 transmitters use the silicon-based Vaisala CARBOCAP^® Sensor. The simple structure and reference measurement capabilities make this Single-Beam, Dual-Wavelength NDIR sensor extremely stable and reliable. The CO₂ concentration is measured inside the duct without risks for leaks or wrong flow direction affecting the measurement. In addition, the measurement accuracy is not affected by dust, water vapor and most chemicals.