States that conventional hygrometers do not function well in harsh environmental conditions such as high pressure, high temperature, liquid aerosols, occasional water submersion, high flow velocity or corrosive carrier gas. Discusses a humidity-measuring technique involving differential infrared measurements wherein the sample probe is a beam of light rather than a physical contact sensor. States this device can be immersed in water without failure or loss of calibration, has a wide dynamic range, and has a 0.05 second response time. Presents field and laboratory data.

KEYWORDS: Hygrometers, humidity, measuring, instruments