Vaisala GMW90
Wall transmitter for CO2, temperature and humidity in buildings.
The Vaisala GMW90 is a wall-mounted transmitter that measures CO2, temperature and, on R models, humidity in offices, schools and meeting rooms. This Modbus RTU template reads all measurements and the error code and lets you set the pressure or elevation used for CO2 compensation from ModbusCloud.
- Protocol
- Modbus RTU
- Connection
- RS485, 19200 baud
- Registers
- 50, read and write
- Brand
- Vaisala
- Key readings
- CO2 concentration · Temperature · Relative humidity · Dew point · Error code
- Available commands
- Pressure compensation · Elevation
- Compatible models
- GMW95 · GMW95D · GMW95R · GMW95RD
- Last updated
Registers (50)
50 read, 8 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| CO2 Concentration | ppm | Read | |||
| Relative Humidity | %RH | Read | |||
| Temperature | °C | Read | |||
| Dew Point | °C | Read | |||
| Dew/Frost Point | °C | Read | |||
| Dew Point Depression | °C | Read | |||
| Wet Bulb Temperature | °C | Read | |||
| Absolute Humidity | g/m³ | Read | |||
| Mixing Ratio | g/kg | Read | |||
| Enthalpy | Read | ||||
| CO2 Concentration Integer | ppm | Read | |||
| Relative Humidity Integer | %RH | Read | |||
| Temperature Integer | °C | Read | |||
| Dew Point Integer | °C | Read | |||
| Dew/Frost Point Integer | °C | Read | |||
| Dew Point Depression Integer | °C | Read | |||
| Wet Bulb Temperature Integer | °C | Read | |||
| Absolute Humidity Integer | g/m³ | Read | |||
| Mixing Ratio Integer | g/kg | Read | |||
| Enthalpy Integer | Read | ||||
| CO2 Concentration Non-metric | ppm | Read | |||
| Relative Humidity Non-metric | %RH | Read | |||
| Temperature Non-metric | °F | Read | |||
| Dew Point Non-metric | °F | Read | |||
| Dew/Frost Point Non-metric | °F | Read | |||
| Dew Point Depression Non-metric | °F | Read | |||
| Wet Bulb Temperature Non-metric | °F | Read | |||
| Absolute Humidity Non-metric | Read | ||||
| Mixing Ratio Non-metric | Read | ||||
| Enthalpy Non-metric | Read | ||||
| CO2 Concentration Non-metric Integer | ppm | Read | |||
| Relative Humidity Non-metric Integer | %RH | Read | |||
| Temperature Non-metric Integer | °F | Read | |||
| Dew Point Non-metric Integer | °F | Read | |||
| Dew/Frost Point Non-metric Integer | °F | Read | |||
| Dew Point Depression Non-metric Integer | °F | Read | |||
| Wet Bulb Temperature Non-metric Integer | °F | Read | |||
| Absolute Humidity Non-metric Integer | Read | ||||
| Mixing Ratio Non-metric Integer | Read | ||||
| Enthalpy Non-metric Integer | Read | ||||
| Error Code | Read | ||||
| Error Code Non-metric Block | Read | ||||
| Pressure Compensation | hPa | Read and write | |||
| Elevation | m | Read and write | |||
| Pressure Compensation Integer | hPa | Read and write | |||
| Elevation Integer | m | Read and write | |||
| Pressure Compensation Non-metric | hPa | Read and write | |||
| Elevation Non-metric | Read and write | ||||
| Pressure Compensation Non-metric Integer | hPa | Read and write | |||
| Elevation Non-metric Integer | Read and write |
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If a device is not in the library yet, we build the template for free as soon as we have the register data.
Use cases
- Show CO2 and temperature per room on a dashboard for the facility manager.
- Get an alert when the CO2 level in a classroom or meeting room stays above a threshold you set.
- Keep the CO2 and humidity history to check whether ventilation keeps up with occupancy.
- Watch the error code to see when a measurement module needs service.
Installation
Set the protocol switch to Modbus, choose the baud rate and parity and set a free address with the address switches.
Connect D+, D- and ground to the RS485 port of the ModbusCloud Gateway and terminate the last device on the bus.
In ModbusCloud add a Modbus device with the same address and serial settings and import this template.
Check that CO2 and temperature come in with plausible values, and set the elevation of the building if it is far above sea level.
Things to watch for
The transmitter does not answer. What should I check?
Check that the protocol switch is on Modbus and that the address switches match the address in ModbusCloud. With the baud rate on automatic the transmitter needs traffic on the bus to find the speed; set a fixed rate if your bus is quiet.
Humidity values show NaN or -32768.
Humidity, dew point and the other humidity values only exist on R models such as the GMW95R. On a GMW95 these registers return the not-available value.
Floating point values look wrong but the integer values are fine.
The transmitter sends the low word of a float first. The template already reads it that way; if you copied registers to another system, swap the words there or use the integer registers.
The CO2 reading is a little off at a high site.
CO2 measurement depends on air pressure. Write the elevation of the building or the typical pressure; the transmitter then corrects the CO2 value. Pressure and elevation are linked, so changing one changes the other.
Want to see how it works?
