GB1388057A - Combustion control apparatus - Google Patents

Abstract

1388057 Burner controllers ELECTRONICS CORP OF AMERICA 20 June 1972 [21 June 1971] 28884/72 Heading F4T [Also in Divisions G1 and H3] Combustion control apparatus has a photoconductive flame sensor 65 connected in shunt with a regulated voltage source 10, a flame relay 94 and fail-safe circuitry responsive to sensor 65 for operating relay 94; the fail-safe circuitry comprising an amplifier 66, 54, 74, a fail-safe means for monitoring the regulated voltage source and having a source of standard voltage 58, an alternating voltage source applied as an additive component to the standard voltage applied to a base electrode of solid state device 16, the regulated voltage being applied to the emitter of device 16, whereby device 16 alternately conductor and is cut-off in operative mode and assumes a single state in inoperative mode, a fail sage capacitor-diode rectifier circuit 28 responsive to an output signal at the collector of device 16 so that circuit 28 produces a voltage signal level that is substantial in said operative mode and negligible in the inoperative mode, and means for applying said voltage signal level so that the amplifier is enabled and disabled in response to the substantial and negligible values respectively, the monitoring means assuming the inoperative mode upon failure of any non-resistive component thereof. The A.C voltage to the base of transistor is derived from transformer 61 via resistor 62, or by means of a secondary winding of a further transformer connected between resistor 20 and bus 38, Figs. 1, 2 (not shown). The signal at transistor 16 collector passes directly, or via a second transistor 50, to a D.C. blocking capacitor 30 in circuit 29. Photo-cell 65 is responsive to infra-red and gives a signal fluctuating with the flame predominantly at about 10 Hz, this signal being amplified by band-pass amplifier comprising transistor 66, 54 and passed via Darlington pair 75, 76 to an output transistor 74 which is arranged to conduct when transistor 82, in a boot-strap circuit, is non-conducting and vice versa, a capacitor 84 discharging through transistor 74 and charging through transistor 82 and inductor 91, which blocks signals substantially higher than 10 Hz. The varying voltage on capacitor 84 is rectified by diodes 89, 90 to charge capacitor 90 and thereby energize flame relay 94. It is stated that, except for short circuits in the resistors and inductor, all failures of components of the circuit of Fig. 3, result in de-energization of relay 94, even when the supply line voltage fluctuator at the predominant 10 Hz flame fluctuation frequency.