Flame detector circuit for gas fired burner - employs capacitor which discharges across igniter and flame to maintain lamp voltage

摘要

The presence of fire in a gas fired furnace is detected electronically by the ionisation induced between two electrodes by a flame. A burner (3) and an igniter (2) is connected in series with a resistor (10) to prevent shocks when the burner is cleaned. When gas is ignited a capacitor (8) discharges across it to reduce the voltage at a neon lamp (1). A capacitor (4) charges during positive half cycles while during negative half cycles the charge is retained to achieve the lamp striking voltage. A diode (7) assist the diode action of the inner and burner to prevent discharge of the capacitor during the negative half cycles and thus maintain the lamp voltage.