Double-beam spectrophotometers noise

One source of noise of ihls type is the slow drift in the radiant output of the source. This type of noise can be called source flicker noise (Section 5B 2). The effects of nuctuations in the intensity of a source can be minimized by the use of a constani-voUagc power supply or a feedback system in which the source intensity is maintained at a constant level. Modern double-beam spectrophotometers (Sections I3D-2and I3D-3) can also help cancel the effect of flicker noise. With many instruments, source flicker noise does not limit performance. 

Early UV-Vis and IR spectrophotometers, back in the 1950s, were big clunkers that usually had double-beam monochrometers to compensate for opti-cal drift and electronic noise They were slow and only moderately sensitive. Improvements in optical and electronic technology have reduced the necessity for double-beam optical systems that reduce, the energy of the transmitted beam. Modem single-beam instruments are smaller faster, more sensitive, and more economical than the older versions. But double-beam instruments still provide the optimal stability and the choice depends on your need. All modem dispersive IR instmments are single beam. 

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