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Air-Conditioning-Generated Noise in a Near-Infrared Spectrometer Caused by Fluctuations in Atmospheric Water Vapor

Volume 41, Number 7 (Oct. 1987) Page 1248-1250

Davies, A.M.C.; Grant, A.


Near-infrared (NIR) spectrometers should be operated in temperature-controlled environments; however, these kinds of facilities are not generally available in most UK laboratories. Although we took delivery of a Neotec Mark I NIR spectrometer in 1982, it was not possible to install it in a permanent home with a temperature-controlled atmosphere until late in 1984. This was a small laboratory (3 m × 4.7 m with a total volume of 45 m3) which was cooled by a "split"-system, direct-expansion, airconditioning unit operating on refrigeration type 22 with a temperature range of 8 to 12°C. The system maintained the set temperature of 23°C to ±1°C except when overloaded by the presence of several workers. The spectrometer was subjected to monthly checks of wavelength accuracy and noise level, carried out with the use of standard system programs delivered with the instrument. In the spring of 1985 we reported to the company that the system was exceeding the specification for noise levels.