| 摘要 |
PURPOSE:To prevent the malfunction due to both an external light and an electrical noise removing affection to the frequency, which is caused by a change of temperature, by controlling both an oscillating circuit of a modulating oscillator and a tuning circuit of a selective amplifier by means of the same mechanical vibrator. CONSTITUTION:A fixed frequency oscillator 2 is operated by a pulse signal from the square wave oscillator 1 to provide a modulated pulse signal of a frequency f1 that is determined by the mechanical vibrator 3, a modulated pulse light ray is emitted from the light emission element 4. When no smoke is present in the room, the light receiver element 5 provides no output. On the other hand, when smoke enters the room due to a fire, the light ray from the element 4 is scattered, a modulated pulse signal of a frequency f1 is produced by the element 5 and is fed to the selective amplifier 8 through the preamplifier 6 and the delay circuit 7. The tuned frequency of the amplifier 8 is controlled by the vibrator 3, and when the output level of the amplifier 8 reaches a fixed value, a fire alarm is provided to the output of the device through the switching circuit 9. |
