This document describes the features and characteristics of Vaisala's GMW20 series carbon dioxide transmitters, including transmitter types, mounting, electrical connections, power supply requirements, technical data, relays and other accessories, and dimensions.
The GMW20 series transmitters use a silicon‑based CARBOCAP® sensor and are supplied calibrated from the factory. The guide covers basic information, mounting options, electrical connections, and power‑supply requirements for the GMW20, GMW21, and GMW22 models.
Installation steps include drilling a mounting hole, routing power and signal wires through the back plate, and securing the PCB. Electrical connections describe the 24 V supply, selectable voltage or current output, and jumper settings. Power‑supply specifications and recommendations for single‑transmitter or shared‑transformer setups are also provided.
| Sensor type | Silicon‑based CARBOCAP® CO₂ sensor |
|---|---|
| Power supply voltage range | 18‑30 VDC or 20‑26 VAC |
| Nominal supply voltage | 24 V (AC or DC) |
| Current consumption | Peak 170 mA, average 85 mA |
| Default output setting | 4‑20 mA (jumper shorted) |
| Calibration interval | Recommended every 5 years |
| GMW21 dimensions | 80 × 108.5 × 35 mm |
| GMW22 dimensions | 80 × 80 × 35 mm |
The GMW20 is shipped ready for installation onto a standard wallbox or surface mounting; drill a hole, pull wiring through, open the cover, remove the PCB, route the cables, and secure the base with screws.
It uses a nominal 24 VAC/VDC supply with a voltage range of 18‑30 VDC or 20‑26 VAC, and a DC supply is recommended to avoid current peaks.
The transmitter is calibrated at the factory and the recommended calibration interval in normal conditions is five years.