An Infra-Red Spectrophotometer for Industrial Research

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Abstract
An infra-red spectrophotometer has been designed for the wide variety of problems which arise in an industrial research laboratory. The source of radiation is a Nernst glower, the dispersing unit a 10 × 15 cm sodium chloride prism, and the detector is a compensated thermopile. The output of the thermopile is amplified with a contact modulated amplifier. The installation is comparatively insensitive to mechanical vibration and fast temperature changes. The instrument is enclosed in a vacuum tank to prevent interference from absorption by extraneous gases. Driving motors for prism rotation and slit adjustments are outside the vacuum. Rotary motion is transmitted through the walls of the vacuum tank by means of magnetic drives; this avoids the use of any form of packing gland. Ink-line records of the spectral range from 3 to 15μ can be made automatically in 30 minutes. The instrument is operated semiautomatically for “spot work” in making quantitative analyses after spectral positions and proper calibrations have been made.