An Automatic Recording Spectrophotometer

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Abstract
A National Technical Laboratories Model DU Quartz Spectrophotometer has been converted into an automatic recording spectrophotometer by (a) utilizing the monochromator with unchanged optics, (b) introducing a common motor drive for the wave‐length and all mechanical parts, (c) dividing the exit beam into two parts by a beam‐splitter, (d) using a ``blank'' absorption cell in one beam and a ``sample'' absorption cell in the other, (e) placing an amplifier photo‐tube in each exit beam to measure the transmitted light, (f) amplifying the photo‐tube signals with linear cathode‐follower type d.c. amplifiers, (g) recording the ratio of the amplifier outputs as percent transmission of the ``sample'' relative to the ``blank'' as a function of wave‐length on a ratio potentiometer strip‐chart recorder, (h) providing for automatic monitoring of the monochromator slits to maintain constant energy in the ``blank'' light beam, and (i) providing a ``correction device'' for automatic correction of all errors due to mis‐matching in the relative intensities of the beams from the beam‐splitter, in the transmission characteristics of the absorption cells, and in the spectral sensitivity characteristics of the photo‐tubes. The instrument which has been developed has considerably greater resolution than the original spectrophotometer, has completely automatic high speed operation which permits recording of the spectrum from 4000 to 2000 angstroms in less than 15 minutes, and has an accuracy of transmission measurement very nearly equal to that obtainable with the original manual instrument.

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