1967 年 36 巻 11 号 p. 894-902
A digital densitometer for presenting the peak densities of spectral lines on photographic plates, which works in conjunction with a photoelectric digital comparator previously developed, is con-structed to complete a fully automatic digital densitometer comparator. The measurement of the optical densities is carried out in parallel with the comparator operation by means of a logarithmic analog-to-digital converter including a ratio circuit. In the converter, the exponential shaped voltage of which peak height is proportional to the reference light intensity is compared with the sampled voltage corresponding to the light flux passing through the center of spectral line image. The pulses generated in the exponential function generator and the voltage comparator are re-spectively used as the start and stop commands for a conventional linear analog-to-digital converter. The overall accuracy of the densitometer is better than one percent in a density range up to 2 (O.D.). The instrument can also provide two modes of operation, one of which is a manual mode for taking the density at any point of the plate and the other is a semi-automatic mode for presenting the density profile of the spectral line both in digital forms.