How does optical design affect instrument time stability?

As an example of the difference in time stability between the configurations, the fluctuations in measurement values over time (drift) were compared using a single-beam instrument (blue line) and a double-beam instrument (red line). The top figure shows the results from placing the single beam and double beam instruments in the same room and using each to obtain time-course measurements for one hour at 5-second intervals. The double-beam instrument had less time variability than the single-beam instrument.

This means the double-beam system provides more stable measurement values than the single-beam system. The single-beam system requires waiting until the light source and detector stabilize, performing frequent blank corrections to minimize such time variability. A summary of single-beam and double-beam characteristics is shown in the table at bottom.