Dual wavelength photometric device

Claim 1

A photometric device comprising a photometric optical system for obtaining light outputs each having a predetermined wavelength by transmitting light from a light source to a sample to be measured through different light paths each having a filter, a detector for converting each light output into an electric signal, a switch for deriving first electric signals for one predetermined wavelength and second electric signals for another predetermined wavelength from the output signals of the detector, and a signal treating circuit for treating the first and the second electric signals to obtain a light absorption amount of the sample; wherein one of the light paths comprises a rotating mirror, reflecting mirrors, a first filter for transmitting a first predetermined wavelength and a half-mirror and the other of the light paths comprises the rotating mirror, a second filter for transmitting a second predetermined wavelength and the half-mirror and wherein the signal treating circuit comprises two signal paths and a differential circuit for obtaining a difference between the outputs of both signal paths, each signal path including a sample and hold circuit for maintaining the level of the signal supplied thereto, a high-pass filter, a rectifying circuit and a low-pass filter arranged in a predetermined order, and wherein means are included for synchronizing said switch with the rotating mirror.