Solid state ignition control

Abstract

A control arrangement for a fuel ignition system having pilot and main valves in which the energization of the operate windings of the pilot and main valves, which are connected in series, is controlled by a silicon controlled rectifier. The SCR is enabled at the start of each ignition cycle by trigger pulses provided by a pulse generating circuit and when enabled, the SCR provides a shunt circuit path around the main valve winding permitting the pilot valve winding to be energized at its operating level effecting pilot valve operation and preventing the main valve from operating. When a pilot flame is provided, a capacitor of a flame sensing network is charged by flame rectified current, generating an inhibit signal for the pulse generating circuit which causes the SCR to be cut off, interrupting the shunt path to allow the main valve winding to be energized, effecting main valve operation. A trial for ignition timer diactivates the pilot valve and locks out the system if the pilot fuel fails to be lit before the end of a trial for ignition interval, the ignition timer being rendered ineffective in response to disabling of the SCR when a pilot flame is sensed. In one embodiment, the ignition timer comprises a time delay relay which is resettable by cycling the thermostat contacts open and closed. In another embodiment, the ignition timer comprises a thermal cutout switch mounted on the pilot valve and heated by the pilot valve operate winding.