Electronic fire detection circuit - avoids false alarms by monitoring waveform shape of detected parameters over suitable period

摘要

An electronic circuit in more than one form for use processing the analogue signal from a basic transducer and for monitoring the waveform of this signal to avoid false alarms is used. The circuit finds the first and second derivatives of the waveform with respect to time, and if this is always positive over a certain period, triggers the alarm system. A detailed circuit for dealing with a temperature dependent waveform of this type consists of an amplifier (A) a shaping network (D, F, D, L) and a transistor switch (SW). The circuit can be applied to a thermocouple transducer (TP). A similar circuit for application to temperature dependent diodes (D1) and for application to ionization detection chambers, for smoke detection and for application to ionization detection chambers, for smoke detection (CH1, CH2) may be used.