Improved Infrared Absorption Spectra Hygrometer
- 1 January 1958
- journal article
- research article
- Published by AIP Publishing in Review of Scientific Instruments
- Vol. 29 (1), 36-42
- https://doi.org/10.1063/1.1716000
Abstract
An infrared hygrometer is described which utilizes a light beam as the principal sensing element. Composed of two narrow bands of infrared radiation, this beam traverses a 12‐in. path through a sample atmosphere containing the humidity concentration to be measured. Wavelength isolation is by means of germanium narrow band‐pass interference filters. One band, centered near a wavelength of 2.60 μ, is subject to attenuation by water vapor, the other located near 2.45 μ is not. Thus the ratio of transmitted band energies is sensitive to the concentration of water vapor in the path. This ratio is effectively maintained at unity through use of a servo‐operated glass wedge which moves to compensate for energy unbalance caused by changes in absorbing vapor. Wedge position is given electrical significance through use of an appropriate transducer, calibrated in terms of vapor density, grams per cubic meter. Included in the design is a dry‐gas purge standardization system whereby periodic checks of the zero point enable compensation for drift factors. Because of the potential use of the method in airborne applications, the instrument was used in tests to determine the character of pressure effects. These showed that vapor concentration (W), total pressure (P), and partial pressure (p) of water vapor, may be related to fractional absorption (A): Conditions under which other, simpler relations may be used are discussed.
Keywords
This publication has 5 references indexed in Scilit:
- Infrared Transmission of Synthetic Atmospheres* II Absorption by Carbon DioxideJournal of the Optical Society of America, 1956
- INFRARED ABSORPTION HYGROMETERMonthly Weather Review, 1953
- Long Optical Paths of Large ApertureJournal of the Optical Society of America, 1942
- Pressure Effect on Infra-Red AbsorptionPhysical Review B, 1940
- The Spectroscopic Determination of Aqueous VaporThe Astrophysical Journal, 1912