An automatic slit drive has been constructed for a single-beam infrared spectrometer, using two helical potentiometers in a servosystem. The output of generator potentiometer is heavily loaded causing its output voltage function to curve sharply with displacement. This reduces the number of taps per prism to two. Evaluation of circuit parameters is described, and values are listed for prisms of calcium fluoride, sodium chloride, potassium bromide, and cesium bromide, used in double pass. A simple modification permits selection of several different energy levels. The resulting curves of spectrometer output vs frequency are constant.
D. F. EGGERS JR. and M. T. EMERSON, "Automatic Slit Drive for Infrared Spectrometers," J. Opt. Soc. Am. 50, 11-11 (1960)