GB1396280A - Spark ignition systems - Google Patents

Abstract

1396280 Ignition systems PLESSEY CO Ltd 31 May 1972 [18 June 1971] 28661/71 Heading F1B [Also in Division F4] A spark ignition system comprises an oscillator circuit for generating pulses which are applied to a step-up transformer TR for the production of sparks across spark electrodes SP, a photopositive resistor PC1 which detects the flame resulting from the ignition of fuel oil by the sparks and renders the oscillator circuit inoperative, and a relay RM which is operated in response to the generation of pulses to cause fuel to be supplied to a fuel burner and which is held operated through a circuit including the photopositive resistor when ignition of the fuel has taken place. As shown the oscillator is a relaxation oscillator having a mains supply MS and comprising a capacitor C1 charged through a resistor R1 and normally open contacts TH of a thermostat device and normally closed contacts T 1 of a bi-metal tripping device having an associated heating coil R1. The capacitor C1 charges a capacitor C2 through a resistor R3 until the breakdown voltage of a neon tube device N2 is reached and a triac TRA fires to enable the capacitor C 1 to discharge a pulse through the primary winding P of a step-up transformer TR. A high voltage pulse is thus produced across the secondary winding S 1 and a spark is produced. A flame is thus produced which increases the conductivity of the photo-positive resistor PC 1 and reduces the voltage across the capacitor C2 and prevents the voltage rising to the breakdown voltage of the neon tube device N2. The transformer also has a secondary winding S2 which produces pulses to operate the relay RM. Contacts RM 1 of relay RM close to operate a solenoid fuel oil valve V. The relay RM is held operated while a flame is pre-set by the increased current flow through the photo-positive resistor PC 1. If the igniting sparks fail to produce ignition, the heating effect of the resistor R 1 operates the bi-metal tripping device. This produces a visual indication through a neon tube device N1. In the embodiment of Fig.1, (not shown), the relay (RM) operates the fuel oil pump motor (M). Two embodiments are described which purge the combustion chamber before ignition and after burning. In Fig.2 the fuel oil pump M drives a fan while a capacitor C4 is charged to the breakdown voltage of a neon tube device N3. The oscillator circuit is then connected to the mains supply and the valve V operated. In Fig.3, (not shown), the fuel oil pump (M) motor drive the fan to purge the combustion chamber while a bi-metal device is heated to its operating temperature. The terminal A in the figures is connected to an alarm arrangement.