Dwyer RHPX
Humidity and temperature transmitter for ducts, rooms and outdoor air with dew point and enthalpy.
The Dwyer RHPX is a humidity and temperature transmitter that measures air in ducts, rooms and outdoors for building management and HVAC control. This Modbus RTU template reads humidity, temperature, dew point, absolute humidity, enthalpy and error flags and lets you set the sensor offsets and display units from ModbusCloud.
- Protocol
- Modbus RTU
- Connection
- RS485, 9600 baud
- Registers
- 19, read and write
- Brand
- Dwyer
- Key readings
- Relative humidity · Temperature · Dew point · Absolute humidity · Enthalpy · Error flags
- Available commands
- Humidity offset · Temperature offset · Display units
- Compatible models
- RHPX · RHPX wall mount · RHPX duct mount · RHPX large enclosure
- Last updated
Registers (19)
19 read, 4 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| Relative Humidity | %RH | Read | |||
| Temperature C | °C | Read | |||
| Temperature F | °F | Read | |||
| Dew Point C | °C | Read | |||
| Dew Point F | °F | Read | |||
| Absolute Humidity | g/m³ | Read | |||
| Absolute Humidity lb per Million ft3 | Read | ||||
| Enthalpy kJ per kg | Read | ||||
| Enthalpy BTU per lb | Read | ||||
| Error Flags | Read | ||||
| Humidity Offset | %RH | Read and write | |||
| Temperature Offset | °F | Read and write | |||
| Humidity Display Unit | Read and write | ||||
| Temperature Display Unit | Read and write | ||||
| Device Name | Read | ||||
| Model Number | Read | ||||
| Serial Number | Read | ||||
| Firmware Version | Read | ||||
| Date Code | Read |
Loading registers…
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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 supply air humidity, temperature and dew point on a ModbusCloud dashboard.
- Send an email alert when relative humidity in a clean room or archive leaves the band you set.
- Keep 365 days of humidity history as evidence for a museum or data centre.
- Use enthalpy of outdoor and return air to check the free cooling decision of an air handling unit.
- Alert on the error flags to catch a failed or missing sensor.
Installation
Mount the transmitter in the duct, on the wall or under a shield outdoors, away from coils and fans.
Set the address with DIP switches 1 to 8, switch 9 on for Modbus, and switch 10 on at the end of the bus.
Connect B+, A- and RS485 GND to the ModbusCloud Gateway with shielded twisted pair and power the transmitter with 14 to 35 Vdc or 10 to 32 Vac.
In ModbusCloud, add a Modbus device with the address of the transmitter and import this template; it picks up the bus speed from the first requests.
Check that humidity and temperature come in and match the display or a reference meter.
Things to watch for
Why does the transmitter not answer after I changed the bus speed?
The RHPX learns baud rate, parity and stop bits from bus traffic once after power-up. Switch the power off and on again after a change, so it detects the new settings from the next requests.
Why does it not answer on address 0 or above 247?
Modbus addresses must be between 1 and 247. The default DIP setting gives address 127. Check that switch 9 is on for Modbus, otherwise the transmitter talks BACnet.
What does the temperature offset do?
The holding registers for humidity and temperature offset shift the reading, by up to 3.5 %RH and 5 degrees F. Write a small value after comparing with a calibrated reference, and leave them at 0 otherwise.
Why do I see an error flag?
The flags show an invalid address, a sensor out of range, a sensor error, a missing sensor or invalid settings or memory. A sensor error usually needs the probe checked or replaced.
Want to see how it works?
