| 摘要 |
PURPOSE:To secure high reliability and also, to reduce a consumption of electric current and production cost, by reading an output of a comparison circuit obtained by synchronizing with a luminous pulse in an accumulation circuit at the timing of tailing edge of said pulse. CONSTITUTION:Electric power is supplied to a light emission diode 5, a reference voltage setting circuit 12 and a comparator 15 by a pulse generating circuit 11 by synchronizing in a form of a pulse having about 2-3sec cycle. On one hand, scattered light by smoke which is flowed in a smoke detection part is received by a photodetecting diode 13 and an output of the comparator 15 is read in an FF1 of an accumulation circuit 16 at the time when density of the smoke is exceeded the predetermined density and the light emission of the diode 5 is finished, and a terminal Q becomes an H level. Hereafter, the output of the terminal Q is charged to a capacitor C5 and is read in an FF2 of the succeeding stage delaying about 20-30sec and its terminal Q becomes the H level. Hereby, a thyristor 17 of a switching circuit 2 is turned on through a Zener diode ZD3 and the power source which serves also as signal line between l1 and l2 is short-circuited and a fire alarm is raised. |
