An automatic means for obtaining the spectral-sensitivity characteristics of photosensitive surfaces is described. The radiation from a tungsten filament lamp is divided by means of a monochromator and used to excite the photosensitive surface. Compensation for the variable energy received at different portions of the spectrum (4000 to 12,000 angstroms) is made by a special automatically controlled attenuator, so that the ordinates of the resultant curve may be expressed in response per unit energy. Compensation for the dispersion curve of the monochromator is made so that the abscissa may be calibrated in equal wave-length intervals. The design of a balanced modulator and high gain tuned amplifier necessary to obtain adequate deflection on the cathode-ray tube, on which the curve is traced, is discussed. The total spectral-sensitivity curve can be drawn by means of the automatic curve tracer in 30 seconds. A 909-type cathode-ray oscillograph tube is used, so that the full curve can be seen for several minutes after the curve has been traced.
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