Spectrophotometer

Claim 1

A spectrophotometer comprising: means for generating a beam of electromagnetic radiation, said beam comprising a range of wavelengths of said radiation; wavelength selector means disposed in the path of said beam for providing transmission of a narrow wavelength band within said range of wavelengths of said radiation; means connected to said wavelength selector means for causing said wavelength selector means to scan continuously through said range of wavelengths, whereby sequential transmission of different narrow wavelength bands of said radiation can be provided; chopper means disposed to receive any one of said narrow wavelength bands of radiation, and being operative to direct said one narrow wavelength band of radiation alternately through a reference cell and a sample cell; signal generating means disposed to receive radiation that has been transmitted through said reference and sample cells, said signal generating means being responsive to said transmitted radiation to produce a pulse train signal, the number of pulses in said pulse train being representative of the ratio of the intensities of the radiation transmitted, respectively, through said reference and sample cells, said signal generating means also producing a first signal representing when a number of pulses in said pulse train corresponding to a unity ratio is achieved and a second signal representing the end of said pulse train; difference detection means responsive to the occurrence of said first and second signals for determining deviations from unity for the ratio represented by the number of pulses in said pulse train; storage means operable in a calibration mode to store information characteristic of any deviations from unity for said ratio detected by said difference detection means, and operable during a sample analysis mode to retrieve said stored information; and correcting means operatively connected to both said storage means and said signal generating means so as to produce a correction signal characteristic of said stored information when radiation is being transmitted through said sample cell, and to apply said correction signal to said signal generating means to modify said pulse train signal so that said pulse train signal, as so modified by said correction signal, is representative of the effect of material in said sample cell on the intensity of said radiation.