The HD9008…and HD9009… series are single block RH and temperature (or only RH or only temperature) microprocessor transmitters, temperature configurable.
They are available in different versions:
- HD9008TRR: 2-wire with 4…20 mA output for RH and temperature
- HD9008T7AC: 2-wire with 4…20 mA output (only temperature)
- HD9008T7S – HD9008T17S: with RS485 MODBUS-RTU output
- HD9009TRR: 0…1 V standard voltage output (other ouputs available on demand) for RH and temperature
SENSORS
The humidity sensor is a capacitor which dielectric is made up by an hygroscopic polymer. As water dielectric constant is approximately 80, you’ll get a strong change in capacity as the humidity content of this polymer changes. The advantages of this kind of sensor are: good linearity, insensitivity to temperature changes, fast response time and long-lasting life. The sensor temporary looses its accuracy if some condensation develops on its surface (the transmitted value is higher than the real one because of an increase in effective capacity).
The temperature sensor is a Platinum resistance thermometer (100Ω @0°C). The Pt100 resistance variation is transformed into a current or voltage signal, linear to temperature.
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