Patent GB-797433-A (GB)
Abstract: 797,433. Controlling burners. TEDDING- TON INDUSTRIAL EQUIPMENT, Ltd. May 24, 1956 [May 25, 1955], No. 15106/55.. Class 75(1) In an electrical control apparatus for a liquid fuel burner comprising an electromagnetic-relay-controlled ignition device I, an electromagnetic-relay-controlled fuel pump motor P and a thermal switching means Ha actuated by an electrical heating element He and operable after a predetermined delay period to disconnect the electric supply in the event of the burner failing to ignite, means are provided for adjusting the current through the heating element He so as to vary the delay period. The electromagnetic relay IR controllinig the ignition device I is connected in series with the heating element He and a variable resistance Vr is connected across the heating element and the ignition relay IR with its movable slider connected to their junction. The variable resistance Vr is in series with a resistance r1 which prevents short circuiting of the ignition relay IR and with a second resistance r2 which reduces the voltage drop across the heating element. At starting a master switch T is closed by a thermostat to connect the low voltage secondary winding of a transformer TR to the ignition relay IR and to the heating element He. The two contacts IRb close to supply mains voltage to the ignition device I and the contact IRa closes to connect the low transformer voltage to the fuel pump relay PR which closes contacts PRa to energize the fuel pump motor P from the mains. If ignition occurs a flue thermostat opens cold contacts Fa to deenergize the ignition relay IR and the heating element He. The flue thermostat also closes hot contacts Fb which form, with contacts PRb closed by the pump relay PR, a holding circuit for the pump relay PR so that the supply of fuel is continued. If ignition does not occur the flue thermostat cold contacts Fa remain closed and the heating element He after a delay actuates the bimetallic element of the thermal switch Ha to open contacts Ha1 and deenergize the control circuits and energize an alarm L. The thermal switch is reset manually by a button B. If flame failure occurs the hot contacts Fb of the flue thermostat open immediately to stop the fuel pump P and after a delay the cold contacts Fa close to start ignition. The modified circuit shown in Fig. 2 brings the thermal switch Ha into operation to de-energize the control circuits in the event of the hot contacts Fb of the flue thermostat sticking in closed position on flame failure. In this event when the cold contacts Fa close current flows through additional changeover contacts IRc controlled by the ignition relay IR to a resistor BR of negative temperature coefficient of resistance and to the heating element He which eventually actuates the thermal switch. An additional contact on the pump relay PR connects hot contacts Fb to a lead SC when the pump relay is de-energized so that the ignition relay is short circuited whilst the hot contacts Fb remain closed. At starting the ignition relay IR and the heating element He are energized through an additional contact PRc on the pump relay PR. The resistor BR is in parallel with the ignition relay IR but its initial resistance is high and does not fall sufficiently rapidly to prevent operation of the ignition relay IR. Specification 661,924 is referred to.