| 摘要 |
PURPOSE:To detect a sample tube by a slight variation of the quantity of transmitted light, by providing a feedback means responding to a photodetecting output at the time of passing the sample tube through an optical path. CONSTITUTION:Light sent out from a light emittion element 12 driven by an output of an amplifier 14 to an optical path, is inputted into a differential amplifier 32 and a comparator 52 as a voltage VE by a photodetecting element 22 and compared with a reference electric potential VR and 56 respectively. Further, the electric potential of a point 48 is dropped at the time when VR<VE and the output of the amplifier 14 is dropped and then, the light quantity of luminescence of the element 12 is decreased. Also, charging of a capacitor 46 is increased slowly by an electric current from a resistance 44 only at the time when VR>VE and the charging of the capacitor 46 is continued until it becomes VR=VE. Accordingly, the voltage VE is controlled so as to be equal to the voltage VR does not depend upon the conditions of the elements 12, 22 and the variation of the light quantity accompanied by passing of a sample tube is detected surely. |
