QFM31... is a duct sensor for measuring relative humidity (high precision) and temperature. It uses a capacitive humidity measurement principle, has an operating voltage of AC 24 V or DC 13.5.35 V, and a signal output of DC 0.10 V/4...20 mA, for relative humidity and temperature. It is suitable for HVAC applications with high requirements for relative humidity measurement accuracy and response time, and the measurement range covers the entire humidity range of 0...100%.
The QFM31 series duct sensors from Siemens are designed for high‑accuracy relative humidity and temperature measurement in HVAC applications. The manual describes the sensor’s capacitive humidity principle, temperature measurement ranges, and the available DC 0‑10 V or 4‑20 mA output signals.
Installation guidelines cover mounting the sensor in the middle of a duct, required clearances from steam humidifiers, wiring recommendations (shielded twisted pair, cable length limits), and safety considerations such as using a SELV transformer and maintaining IP65 protection. This manual is written in Chinese.
| Working voltage | AC 24 V ±20 % or DC 13.5‑35 V |
|---|---|
| Humidity measurement range | 0‑100 % RH |
| Temperature measurement ranges | ‑35…+35 °C, 0…50 °C, 0…70 °C |
| Humidity accuracy | ±2 % RH |
| Temperature correlation | ≤ 0.05 % RH/°C |
| Time constant | ≈ 20 s (air flow) |
| Output signal (humidity) | DC 0‑10 V or 4‑20 mA |
| Output signal (temperature) | DC 0‑10 V or 4‑20 mA |
| IP protection rating | IP65 |
Use shielded cable, route signal and power lines as twisted pairs, keep cable lengths within the allowed range, and follow EMC guidelines in noisy environments.