Trend Duct Humidity / Temperature Sensor, externally mounted relative Humidity and Temperature Sensor for HVAC Systems. The certified 2% high accuracy versions offer excellent linearity and is stabile over a wide humidity range (10 to 90 %RH), the temperature range is: 0...40C. The Externally mounted sensor is fitted with a weatherproof shield to avoid solar, rain and wind effecting the sensor. This sensor was removed from a working system recently during upgrade work when the Trend System was being replaced for a different manufactures system.