Relative Humidity

The sensor measures the relative humidity in the air duct via its capacitive humidity sensing element whose electrical capacitance changes according to the relative humidity of the ambient air.

The electronic measuring circuit converts the sensor’s signal to a continuous 0 to 10 Vdc or 4 to 20 mA signal, which corresponds to 0 to 100% relative humidity. In the range 0 to 9.5 V or 4 to 19.2 mA ( 0 to 95% rh), the signal is linear to the measuring accuracy given in the Specifications section, resulting in an effective measuring range of 0 to 95% rh.


The sensor measures the temperature in the air duct via its sensing element whose electrical resistance changes according to the temperature of the ambient air.

Depending on the type of sensor, this change in resistance is converted either to an active 0 to 10 Vdc or 4 to 20 mA output signal corresponding to a temperature range of −40°F to 158°F (−40°C to 70°C); –31°F to 95°F (35°C to 35°C); or is provided as a passive output signal ( −31°F to 140°F [−35°C to 60°C]).

Sensing Elements, Synthetic Resistance Output

Figure 1. 1000 ohm Platinum.

Figure 2. Siemens 1000 ohm Nickel.

See document 155-748 for more information about QFM2160U.