| 摘要 |
PURPOSE:To enable accurate smoke sensing while a key switch is turned on by quickly charging the capacitor of an integrator at a time constant shorter than that of the integrator and having the output from the integrator coincident to the light receival output signal at the charging time. CONSTITUTION:A luminous element 6 is driven by pulses of a pulse oscillator 8 and another luminous element 10 sends an output to a point (a) in accordance with rate at which light is scattered by smoke. The light receival output signal which is shaped in the form of dc supply voltage by both an amplifier 11 and a sample hold circuit 12 is sent to a point (d). An average of dc voltages accord ing to the thickness of smoke at the point (d) is determined by the integrator which consists of a resistor 4 and a capacitor 3. By providing a diode 5, the capacitor is instantaneously charged so that a voltage at the point (e) of the integrator becomes the voltage at the point (d) within a short period. As a result, even if the output of the luminous element is increased because a person smokes a cigarette immediately after a power source is thrown, the output at the point (e) will exceed that at the point (d) so that sensing of smoke can be enabled. |
