Rotronic HygroFlex HF5A
Humidity and temperature transmitter with exchangeable probes, dew point and other calculated humidity values.
The Rotronic HygroFlex HF5A is a wall-mounted transmitter that measures relative humidity and temperature with an exchangeable probe in HVAC, food, pharmaceutical and other applications. This Modbus RTU template reads humidity, temperature, dew point and the other calculated humidity values, plus CO2 or differential pressure from a matching probe, and lets you set the Modbus address and byte order from ModbusCloud.
- Protocol
- Modbus RTU
- Connection
- RS485, 19200 baud
- Registers
- 43, read and write
- Brand
- Rotronic
- Key readings
- Relative humidity · Temperature · Dew point · Frost point · Wet-bulb temperature · Enthalpy · CO2 concentration · Differential pressure
- Available commands
- Modbus address · Byte order
- Compatible models
- HF5A-D1D · HF5A-D1X
- Last updated
Registers (43)
43 read, 2 write
| Name | Unit | Access | Address (Hidden until you enter your email) | Function (hidden) | Type (hidden) |
|---|---|---|---|---|---|
| Relative Humidity | %RH | Read | |||
| Temperature | °C | Read | |||
| Dew Point Temperature | °C | Read | |||
| Frost Point Temperature | °C | Read | |||
| Wet-Bulb Temperature | °C | Read | |||
| Enthalpy | Read | ||||
| Psychrometric Difference | Read | ||||
| Vapour Concentration | Read | ||||
| Saturation Vapour Concentration | Read | ||||
| Specific Humidity | Read | ||||
| Mixing Ratio | Read | ||||
| Vapour Partial Pressure | Read | ||||
| Vapour Saturation Pressure | Read | ||||
| Volume Mixing Ratio | Read | ||||
| CO2 Concentration | ppm | Read | |||
| Differential Pressure | Read | ||||
| Relative Humidity (Imperial) | %RH | Read | |||
| Temperature (Imperial) | °F | Read | |||
| Dew Point Temperature (Imperial) | °F | Read | |||
| Frost Point Temperature (Imperial) | °F | Read | |||
| Wet-Bulb Temperature (Imperial) | °F | Read | |||
| Enthalpy (Imperial) | Read | ||||
| Psychrometric Difference (Imperial) | Read | ||||
| Vapour Concentration (Imperial) | Read | ||||
| Saturation Vapour Concentration (Imperial) | Read | ||||
| Specific Humidity (Imperial) | Read | ||||
| Mixing Ratio (Imperial) | Read | ||||
| Vapour Partial Pressure (Imperial) | Read | ||||
| Vapour Saturation Pressure (Imperial) | Read | ||||
| Volume Mixing Ratio (Imperial) | Read | ||||
| CO2 Concentration (Imperial) | ppm | Read | |||
| Differential Pressure (Imperial) | Read | ||||
| Device Flags | Read | ||||
| Measurement Flags Value 1 | Read | ||||
| Measurement Flags Value 2 | Read | ||||
| Next Calibration Date | Read | ||||
| Probe Type | Read | ||||
| Probe Serial Number | Read | ||||
| Device Address | Read and write | ||||
| Byte Order | Read and write | ||||
| Serial Number | Read | ||||
| Vendor Name | Read | ||||
| Product Type | 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 humidity, temperature and dew point per greenhouse compartment or production room on a dashboard with 365 days of history.
- Get an email, in-app or webhook alert when relative humidity rises above or falls below the level your crop or process needs.
- Plot the dew point next to the temperature to see when the air comes close to condensation.
- With a CO2 or differential pressure probe fitted, alert on the CO2 level or the room pressure as well.
- Export enthalpy, mixing ratio and vapour pressure as CSV or in a PDF report for climate and energy analysis.
- Change the Modbus address from the portal before you add a second transmitter to the same bus.
Installation
Use the digital version HF5A-D1 and supply it with 18 to 36 V DC on terminals K1-1 (V-) and K1-2 (V+).
Connect RXTX+ (K2-1) and RXTX- (K2-2) to the RS485 data lines of the ModbusCloud Gateway and S-GND (K2-3) to signal ground. Terminate both ends of the bus with 120 ohm.
Keep the defaults, address 247, 19200 baud, no parity, 8 data bits and 1 stop bit, or give each transmitter on a shared bus its own address.
In ModbusCloud, add a Modbus device on the gateway with these settings and import the Rotronic HygroFlex HF5A template.
Check that Vendor Name reads Rotronic and that Relative Humidity and Temperature show plausible values.
Things to watch for
The transmitter does not answer on the RS485 bus. What should I check?
Only the HF5A-D1 has RS485; the HF5A-21 and HF5A-31 have analog outputs only. Check address 247, 19200 baud, no parity, 8 data bits and 1 stop bit. Connect S-GND as well as RXTX+ and RXTX-. If nothing answers, swap RXTX+ and RXTX-, because manufacturers label A and B differently. Terminate both ends of the bus.
Humidity and temperature show huge or tiny numbers. Why?
The transmitter can send its 32-bit values in four byte orders, set in Byte Order. The template expects 0, big endian, which is the factory setting. If Byte Order shows 1, 2 or 3, the readings turn into very large or very small numbers. Set Byte Order back to 0 to fix it.
CO2 or Differential Pressure shows no sensible value. Is something wrong?
No. The HF5A only reports what the connected probe measures. A HygroClip2 humidity probe gives humidity and temperature, and the calculated values follow from those. CO2 and differential pressure need a matching Rotronic probe on a 3- or 4-wire transmitter, and a temperature probe gives no humidity values.
Can I change the Modbus address from ModbusCloud?
Yes, Device Address and Byte Order are writable. After a new address is written, the transmitter replies once on its old address and then switches, so update the address of the Modbus device in ModbusCloud right after. Writing registers in ModbusCloud is off by default and is enabled per gateway on request. The baud rate and other settings are changed with HygroSoft over NFC.
How do I connect several HF5A transmitters to one bus?
Every HF5A ships with address 247. Connect them one at a time, give each a new address in Device Address and only then wire the next one. Keep the same baud rate and parity on every device on the bus, and terminate only the two ends.
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