A Spectrophotometer for the Direct Determination of Sample Extinction by Simultaneous Measurement at Multiple Wavelengths and Application of Allen's Correction

A spectrophotometer for the direct determination of sample extinction by simultaneous measurement at three wavelengths and application of Allen's correction has been developed. White light is passed, first through a blue heat filter, and then through the sample and finally through a trichromator which selects the required three wavelengths. These wavelengths illuminate the base region of three FPT 100 type photo diodes which operate as linear transducers converting the incident light intensity to a current which is converted to a voltage in head amplifiers. A computation sub-unit together with a logarithmic amplifier generate the function required for the Allen correction, and the corrected extinction value is displayed digitally on neon display tubes.