INDICATING PRESENCE OF A FIRE

Fire indication, derived from a sensor, is tested whether it exceeds a first threshold level; if it does, the signal is integrated in an integrator which has a slow, or long time constant to integrate a rising signal, but a short, rapid time constant to discharge, upon drop of the signal; in one form, the integrator includes a diode in the integration circuit, so that it will discharge an integrating capacitor rapidly, upon drop in signal level exceeding the first threshold. When the integrated signal exceeds a second threshold, an alarm is give. Providing for rapid discharge of the integrated signal prevents false alarms resulting from repetitive short pulses exceeding a first threshold level which, however, do not persist.