If you work in building automation, you will see the Siemens QFM2160 everywhere. It is a rugged duct-mounted sensor that feeds both relative humidity (RH) and temperature (T) to your BMS/PLC — perfect for supply, return, and mixed-air control loops. Here is the quick, field-ready rundown.
What Is It?
The QFM2160 is a duct sensor that measures:
- Relative humidity: 0–100 %RH (capacitive element)
- Air temperature: selectable range (0..50 °C; -35..+35 °C; -40..+70 °C)
- Accuracy: ±3 %RH in the comfort band; typical temp accuracy ±0.3 K at 23 °C
It is part of Siemens' Symaro line and is powered by 24 V AC or 13.5–35 V DC.
What Signal Does It Use?
You can wire it for active voltage or active current outputs — independently for RH and T:
- Humidity output: 0–10 V, 0–5 V, or 4–20 mA
- Temperature output: 0–10 V, 0–5 V, or 4–20 mA (not loop-powered)
- The QFM2160 is a 3-wire device when used with 4–20 mA output
- Temperature measuring range is selectable via onboard jumper
Typical Applications
- Supply/return air control (humidity or temp PID loops)
- Dew-point shift/reference sensing for reheat/dehumidification strategies
- Humidifier safety/limit sensing (steam or atomizing)
- Trending/indication in BMS, and enthalpy/absolute humidity calculations
Power Supply and Wiring Explained
The QFM2160 requires a 24 VAC step-down transformer. The transformer provides low-voltage power to the sensor. Connections from transformer to sensor use:
- Red wire (G): 24 V AC "System Potential" (live)
- Black wire (G0): 24 V AC "System Neutral"
The sensor provides two analog outputs — one for humidity (U1, green wire) and one for temperature (U2, yellow wire) — as active analog signals (0–10 V or 4–20 mA).
Key Dos and Don'ts
- ✅ Always power the sensor with 24 VAC (or DC) — never directly from 220 V.
- ✅ Keep signal wires (U1, U2) separate from high-voltage cables to avoid interference.
- ✅ Use G0 (system neutral) as a common reference between the sensor and controller.
- ✅ Configure the jumpers on the QFM2160 for the desired output range before wiring.
- ❌ Don't share the transformer with noisy loads (contactors, VFDs) unless designed for building automation.
- ❌ Don't leave the G0 (neutral) floating — the analog inputs need a proper reference.
- ❌ Don't short U1/U2 to ground; they must connect only to controller AI inputs.
Conclusion
The Siemens QFM2160 sensor is a reliable choice for measuring both temperature and humidity in duct applications. By supplying the sensor with 24 VAC (G and G0) from a step-down transformer and connecting its two separate signals (U1 for humidity, U2 for temperature) to the controller's analog input module, the BMS/PLC can continuously monitor air conditions for accurate control. When installed correctly — away from condensation, wired with clean signal separation, and scaled properly in the controller — the QFM2160 delivers long-term accuracy and dependable performance in automation projects.
