Fire alarm based on UV detector - uses cold-cathode discharge tube with shift-register for discrimination between signal and noise

摘要

The flame detector consists of a transistorised h.v generator comprising an oscillator and voltage doubler circuit to supply the required potential to a cold-cathode type discharge tube which is used as the detector element. The tube responds to ultra violet radiation from an open flame. The monitor stage itself comprises a first 4-bit shift register with signal input connected to the cathode of the tube. The register is wired so that it gives an output when three successive pulses appear at its input. It is reset to zero by an astable multivibrator. The output is connected to a second similar shift-register whose reset input is driven from a flip-flop. Its output is conected to an alarm circuit.