Vaisala HMW90
Wall transmitter for humidity and temperature in buildings.
The Vaisala HMW90 is a wall-mounted transmitter that measures humidity and temperature in offices, schools and other buildings. This Modbus RTU template reads all measurements and the error code of the digital HMW95 and lets you set the pressure or elevation used for the humidity calculations from ModbusCloud.
- Protocol
- Modbus RTU
- Connection
- RS485, 19200 baud
- Registers
- 46, read and write
- Brand
- Vaisala
- Key readings
- Relative humidity · Temperature · Dew point · Enthalpy · Error code
- Available commands
- Pressure · Elevation
- Compatible models
- HMW95 · HMW95D
- Last updated
Registers (46)
46 read, 8 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| 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 | ||||
| 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 | ||||
| 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 | ||||
| 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 | hPa | Read and write | |||
| Elevation | m | Read and write | |||
| Pressure Integer | hPa | Read and write | |||
| Elevation Integer | m | Read and write | |||
| Pressure Non-metric | hPa | Read and write | |||
| Elevation Non-metric | Read and write | ||||
| Pressure Non-metric Integer | hPa | Read and write | |||
| Elevation Non-metric Integer | Read and write |
Loading registers…
Send your device list
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 humidity and temperature per room on a dashboard for the facility manager.
- Get an alert when the humidity in an archive, server room or classroom leaves a band you set.
- Keep the history of humidity and dew point to find rooms with condensation risk.
- Watch the error code to see when a transmitter 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 humidity 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.
The non-metric integer values give an error.
The guide prints these registers in two different places. ModbusCloud reads them at the start of the non-metric integer block; if your transmitter answers with an illegal address, use the non-metric float values or the metric values instead.
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.
Mixing ratio and enthalpy are a little off at a high site.
These values depend on air pressure. Write the elevation of the building or the typical pressure; the transmitter then corrects the calculation. Pressure and elevation are linked, so changing one changes the other.
Want to see how it works?
