Cryogenic hygrometer

From Glossary of Meteorology

cryogenic hygrometer

A special type of chilled mirror hygrometer capable of measuring very low frost points.

These low temperatures at the mirror are attained by evaporating low boiling point or cryogenic fluids. This strong cooling capability allows cryogenic hygrometers to maintain reasonable response times even at low frost points. Cryogenic hygrometers are used for airborne humidity measurements from aircraft or balloons, but also in semiconductor industries for monitoring very dry environmental conditions needed in manufacturing processes.