Fuel ignition control arrangement having a timing circuit with fast reset

Abstract

An arrangement for a direct ignition type fuel ignition system includes a capacitive timing network which enables a flame relay to operate during a trial for ignition interval, energizing a fuel valve to supply fuel to a burner for ignition, and a flame sensing circuit which causes the flame relay and the fuel valve to be maintained operated only if a flame is sensed before the end of the trial for ignition interval. In the absence of a flame, a diode, back biased by the timing signal, decouples the flame sensing circuit from the timing network. When a flame is established, a further diode, back biased by a control signal provided by the flame sensing circuit, decouples the timing network from the flame sensing circuit. In an embodiment wherein the charging time of a capacitor defines the trial for ignition interval, a fast reset circuit provides rapid discharge of the timing capacitor when power is removed from the timing network. In another embodiment, wherein the discharge time of a capacitor defines the trial for ignition interval, a checking relay, energized over normally closed contacts of the flame relay, operates to disconnect the capacitor from a source of charging current and complete a discharge path for the capacitor enabling the timing network to generate the timing signal. The checking relay is prevented from operating, thereby maintaining the system locked out, if the flame relay is operated at the start of an ignition cycle.