Weather station and outdoor monitoring setups depend on stable air temperature and humidity signals that can be wired directly into loggers, controllers or Modbus networks. The HD9008 series provides microprocessor-based transmitters in compact single-block form, available as combined RH/temperature or temperature-only versions depending on the model.
Humidity is measured with a capacitive polymer sensor, chosen for good linearity, fast response and long service life. Temperature is measured by a Pt100 element, with the Pt100 resistance variation converted into a linear output signal. The standard operating range is -40...+80 °C and 0...100%RH, with RH accuracy specified as ±1.5 % (0...90 %RH) and ±2 % (90...100 %RH) at 15...35 °C.
Integration choices cover common field needs. Select two-wire 4...20mA outputs (HD9008TRR), a 4...20 mA temperature-only version (HD9008T7AC), or RS485 MODBUS-RTU (HD9008T7S). The probe housing provides ingress protection (IP) IP65 and is designed for outdoor installation, including compatibility with multiple radiation shields such as the HD9007A options.
Capacitive sensor with hygroscopic polymer dielectric provides linear humidity measurement and fast response.
Pt100 element converts resistance change into a linear temperature output signal.
HD9008TRR provides two 4...20 mA outputs for RH and temperature. HD9008T7AC provides 4...20 mA temperature output only. HD9008T7S provides RS485 MODBUS-RTU temperature output.
For RH models, 4 mA (or 0 Vdc) corresponds to 0% RH and 20 mA (or 1 Vdc) to 100% RH.
Recommended mounting with sensor facing downwards to reduce dust deposit on the filter, and use of shielded cable in noisy environments.
MODBUS models support RS485 address 1 to 247, with typical max bus length up to 1200 m depending on baud rate and cable characteristics.
