PHOTOMETRIC DEVICE

PURPOSE:To compensate the temperature drifts of light detecting elements and amplifiers, and to increase the S/N of a measurement signal by providing a light detecting element which receives radiation, a light detecting element which does not receive it, and operational amplifiers which amplify their output signals in the same housing. CONSTITUTION:A photodetection part 18 is constituted by arranging the light detecting element 13 which receives the radiation from a material 10 to be measured and the light detecting element 15 for temperature compensation which is shielded from the radiation in the same housing 14, so they have the same operation temperature. Then the output signals of the elements 13 and 15 are amplified by the operational amplifiers 16 and 17 of the same constitution arranged in the same housing 14. Then the difference between their amplification output signals is found by a differential amplifier 21 to cancel and remove the temperature drifts of the elements 13 and 15 and the temperature drifts of the amplifiers 16 and 17. Further, signal lines 19 and 20 are connected to the amplifiers 16 and 17 having low output impedance, so no external noise is picked up. The state of the material 10 to be measured is detected with high accuracy and the accuracy of, specially, a turbidimeter up to three digits below the decimal point can be secured.