GB1223057A - Improvements in or relating to electrical control circuits for burners - Google Patents

Abstract

1,223,057. Controlling burners. ELECTRONICS CORP. OF AMERICA. 31 May, 1968 [22 June, 1967], No. 26164/68. Heading F4T. [Also in Division G1] In a burner control system which includes a pilot fuel control 35, a main fuel control 36, an ignition control 34, a timer motor 30 to provide an initial purge period, an ignition period and a combustion interval, and a flame detector 26 sensitive to ultraviolet radiation, the circuit includes means responsive to the flame detector and normally has monostable characteristics so that there is an indication of flame only when the flame detector senses a flame condition, the system including an arrangement for converting the flame detector responsive circuit to a bistable mode in which flame continues to be indicated after the detector provides a transient flame condition signal during the initial period but returning the circuit to monostable condition prior to the ignition period to check the flame sensor and its circuitry for false indications of flame, a safety circuit shutting down the system in safe condition when a flame signal is provided for a predetermined interval of time during the said initial period. Detector 26 is of the Geiger-Muller type and is coupled by a resistor 60 to an inductor 62 having output lines 64, 66 coupled through diodes 68 to provide an input signal to a controlled rectifier 24. A mode conversion circuit connected across the controlled rectifier includes a resistor 108, capacitor 110 and timer contacts 30-13, the flame sensor circuitry being converted from monostable to bi-stable mode when at seven seconds the contacts 30-13 close. A purge cycle continues for twenty six seconds and then contacts 30-13 open to restore the circuitry to its monostable mode. If a flame signal is generated during this purge interval the flame relay remains energized whether the signal is transient or continuous. Current flows in a lock-out heater 32 of magnitude sufficient to open contacts 32-1 after a short time to de-energize control relay coil 20 and to close contacts 32-2 and signal an alarm. Contacts 20-3 are opened so that no ignition sequence may be initiated. The timer motor circuit is completed however and the timer motor runs until contacts 30-1 open at sixty seconds and the system is reset in a safe condition but cannot be restarted until switch 32 is manually reset. If no false flame signal is generated during the bi-stable mode interval and ignition takes place the combustion cycle continues until the call for heat is terminated by the opening of switch 16. Flame failure causes lockout heater 32 to be energized so that the system is locked out.