Spectrophotometers with digital processing

Abstract

Monochromatic light emitted from a monochromator is split into two light beams. These light beams are detected by a photodetector and converted into corresponding electric signals after having been transmitted, respectively, through a sample to be analyzed and a reference placed in the respective beam paths. The signal corresponding to the light beam transmitted through the sample and the signal corresponding to the light beam transmitted through the reference are converted into digital signals which are subsequently stored in respective digital storages or memories. The signal corresponding to the light beam transmitted through the reference is compared with a value in a predetermined range. The resultant value is then converted into an analog signal for operating a sensitivity regulator thereby to adjust the sensitivity of the photodetector. Thus, the signal corresponding to the light beam transmitted through the reference (reference light signal) is so controlled as to lie in a predetermined range. From the digital signals stored in the digital memory, ratio between the sample light signal and the reference light signal is arithmetically calculated by a digital processor unit for determining the transmittance of the sample. Since the reference light signal is prevented from significant variation and the calculation of the signal ratio is effected on the basis of digital technique, the measurement accuracy is remarkably enhanced.