Ultraviolet flame detector for oil and gas burners - DC operated switching tube conducts glow current to control detector relay via thyristor

摘要

Optical flame detector for oil and gas burners comprises a d.c. -operated switching tube (UV-R) which on exposure to UV conducts a glow current for controlling a detector relay (RE) via a thyristor (Th). The switching tube forms part of a self-exciting generator circuit of which the voltage and frequency are adjusted to max. sensitivity and output of the tube. The sawtooth voltage is transmitted to a trigger circuit of which the amplitude and frequency conform to the trigger conditions of the thyristor, independently of the generator circuit. In the quenching stages of the tube, a capacitor (C3) in the generator circuit acts on a storage capacitor (C4) in the trigger circuit which supplies the ignition voltage for a trigger diode (D5) connected to the control electrode of the thyristor.