Patent GB-1398575-A (GB)
Title: Spark ignition system for a plurality of gas burners
IPC: F23Q3/00
Filed: 1972-09-29
Abstract: 1398575 Ignition systems for gas burners RANCO CONTROLS Ltd 14 Sept 1973 [29 Sept 1972] 45213/72 Heading F1B [Also in Division F4]  A spark ignition assembly for a plurality of gas burners comprises a respective timing circuit, R2- Cl to R5-C4, Fig. 2, for association with each burner, a pulse generating circuit Q1, C5, P1 connected to all the timing circuits and operative to generate voltage pulses when any one of the timing circuits is operative, and spark ignition means L1 to L4 energized by the voltage pulses to produce sparks simultaneously at spark gaps G 1 to G4 which in use are located in the flames of respective burners, gaps G1 to G4 having connections I 1  to I 4  to the respective timing circuits and each said connection being operative to inhibit the respective timing circuit in response to the decrease in resistance of the spark gap when a flame is present at the corresponding burner. Switches S1 to S4 are closed when respective gas cocks supplying gas to respective burners are opened. Thus if S1 is closed, for example, C1 charges through R2 to a voltage at which Cl discharges via diode D2 to trigger neon N1 thus causing thyristor Q1 to discharge C5 through transformer primary P1 whereby multiple secondaries L1 to L4 give sparks at all gaps Gl to G4. Sparking continues at a rate determined by the R2-C1 time constant and neon N2 flashes out in synchronism. When ignition at the first burner occurs N2 stays on and the resistance at gap G 1 decreases and forms with L1 and connection I 1  an effective shunt across Cl thus inhibiting the first timing circuit by preventing Cl charging sufficiently to trigger N1. The other timing circuits remain uninhibited until the corresponding burners are ignited. If the flame of any turned-on burner goes out the resistance at the corresponding spark gap increases whereby, the switch S1 to S4 remaining closed, the corresponding timing circuit becomes operative and sparks are produced at all gaps until the extinguished burner reignites. Manual over-ride of the spark-inhibiting means may be provided by closure of a manual switch (S5), Fig. 3 (not shown), to connect a further timing circuit (R 8), (C 6) via diode (D6) to neon N1. Automatic over-ride for all or selected burners may be provided for a predetermined time after commencement of operation of the corresponding timing circuits by providing for each selected burner a two-way switch S6, Fig. 4, in place of switch S 1 &c., the switch S6 being in the position shown in Fig. 4 when the associated gas cock is closed whereby C6 is discharged. When the cock is opened Cl charges through a first path R2, D7 and through a second path C6, R10. The second path is effective for said predetermined time which terminates when C6 is fully charged. The circuit effectively gives a low initial charging resistance for C1 such that the fall in voltage across Cl when ignition occurs at Gl is insufficient to cause quenching of neon N 1 whereby a succession of sparks are produced irrespective of ignition occurring, until C6 is charged. Self-heated or separately heated, positive temperature coefficient charging resistors may alternatively be used to produce time-dependant charging resistances. Reference is made to Specification 1240957.