Ventilated psychrometer

From Glossary of Meteorology

ventilated psychrometer

A hygrometer that is artificially aspirated; in this way proper readings can be obtained within about three minutes.

In the case of a naturally aspirated wet bulb, the correct wet-bulb temperature will be attained after approximately 15 minutes provided the water reservoir has about the same temperature as the air. If the water temperature differs substantially from that of the air, it may be necessary to wait up to 30 minutes.