hygromètre infrarouge

OBS: L'un des meilleurs hygromètres, mais aussi le plus coûteux, mesure sur un trajet optique de l'ordre du mètre le rapport d'une raie d'absorption intense de la vapeur d'eau dans l'infrarouge moyen à celle d'une bande très voisine non absorbée.

CONT: A particularly sensitive and accurate type of hygrometer has been developed in recent years by the Instrument Division of the U.S. Weather Bureau. The device, known as the infrared hygrometer, employs a beam of infrared light projected through the air to a photo-electric detector. Two separate wave lengths of light are used; one is absorbed by water vapor and the other passes through undiminished. The ratio of the infrared light transmitted by the different wave lengths is a direct indication of the amount of water vapor in the light path.