This document introduces the basic information of Vaisala's GMD20 CO2 sensor, including product features, models, installation methods, electrical connections, etc.
The GMD20 and GMD20D CO2 transmitters are duct‑mounted devices that use Vaisala’s silicon‑based CARBOCAP® sensor technology. The manual describes mounting, electrical connections, power requirements, and optional features such as relay output or LonWorks interface.
Technical data, calibration recommendations, and service information are included, along with accessories, guarantee terms, and safety notes for reliable operation in HVAC and related applications.
| Measuring range | 0‑2000 ppm (nominal), up to 20 000 ppm with recalibration |
|---|---|
| Power supply | Nominal 24 V AC/VDC (18‑30 VDC or 20‑26 VAC) |
| Power consumption | < 2.5 W average, 85 mA typical, 170 mA peak |
| Analogue outputs | 0‑20 mA or 4‑20 mA and 0‑10 V |
| Operating temperature | -5 °C to +45 °C |
| Housing | ABS plastic, IP65 |
The recommended calibration interval is five years for HVAC and related benign applications.
The GMD20 is duct‑mounted using a mounting plate fastened with four screws, allowing the probe distance to be adjusted.
It requires a nominal 24 V AC or DC supply, with the voltage maintained between 18‑30 VDC or 20‑26 VAC.
The transmitter provides analogue outputs of 0‑20 mA or 4‑20 mA and 0‑10 V, and an optional relay output for the GMD20D version.