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Vaisala GMD20 Duct Mount CO2 Transmitter

Vaisala GMD20 Duct-Mount Carbon Dioxide Transmitter are designed for use in Indoor air quality monitoring and HVAC systems. Vaisala GMD20 uses CARBOCAP® ensuring excellent long term stability and reliability.  The sensor is designed to remain inside the duct and in direct contact with the air stream, making the readings more reliable, and the installation leak insensitive. Vaisala define that the GMD20 can be used up to five years between calibrations*. Output options include field selectable 0…20 mA, 4…20 mA or 0…10V output corresponding to 0…2000 ppm CO2.

VAISALA GMD20 Transmitters have been discontinued.  Please phone Fluidic for help with selecting an alternative.

*calibration frequency determined by user and dependant on application


Vaisala GMD20 Duct Mount CO2 Transmitter

  • Measurement range 0…2,000ppm as standard (can be calibrated for higher ranges)
  • Stability: Typically <5% of range per 5 years
  • Operating environment: -5…+45C, 0…85%RH (non condensing).
  • Analogue outputs: (0/)4…20mA and 0….10V
  • Model: GMD20 (blind) or GMD20D with LC display
  • LonWorks interface (Vaisala GML20) and onboard relay (Vaisala GMR20)
  • 24Vac/dc supply voltage
  • 5 year manufacturers warranty
  • Field calibrate using the Vaisala GM70 and GM70A connection cable


CO2 monitoring is an essential part of a healthy office to ensure a fresh air supply.  This is valid now more than ever before since the COVID-19 pandemic and CO2 detectors have been identified by the UK government as an ideal way to monitor building ventilation.

Vaisala GMD20 transmitters utilise 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 temperature and flow dependencies of the sensor are negligible. In addition, the measurement accuracy is not affected by dust, water vapor, and most chemicals.


Fluidic are a recognised partner of Vaisala CEN (Industrial division) for Scotland and the North of England. Our instrumentation engineers are product trained and able to help with instrument selection within the full range of Vaisala HVAC transmitters.  Please call either office for more information (Glasgow 0141 641 5920,  Warrington 01925 572401).


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