| 摘要 |
PURPOSE:To provide long-term high reliability and stability by providing various circuits for compensating the quantity of light of a luminous body, checking operating function and preventing malfunction to the smoke detector of photoelectic scattering light type. CONSTITUTION:The output of a direct light photo detector 2 which receives the direct light from a light emitting element 1 is compared with a reference voltage 19 in a differential amplifier 15. The base current of a transistor 16 is controlled by the difference thus obtained to change the driving current of the ligth emitting element 1, whereby the quantity of light emission is compensated and controlled so as to apply a constant quantity of receiving light determined by the reference voltage 19 to the detector 2. Also, the operation functon is checked by making use of the fact that if, e.g., a twice reference voltage 20 is inputted to a differential amplifier 15 by changing over a switch 18 the quantity of light emission becomes twice. In addition, the malfunction is prevented by holding the signal 25 from a scattering light photo detector 3 as Vh to a memory 30 at a certain time t2, always comparing the value Vs (variable) of the signal 25 up to the set time t3 after several 10 to several 100 mus in a comparator 31 and cancelling the data if the value of 1Vh-Vs1 exceeds the set threshold value Vth even momentarily. |
