GB1379644A - Control circuits for oil and gas fired burner assemblies - Google Patents

Abstract

1379644 Burner control circuits LANDIS & GYR AG 4 July 1972 [15 July 1971] 31192/72 Heading F4T A control circuit for an oil or gas fired burner comprises an igniter 9, an electromagnetic control means 23 for controlling fuel flow to the burner, and a flame relay 6 arranged to be deenergized when a flame is present, relay 6 having a set of contacts 19 which when the relay is energized pass current to control 23 via a first path including a positive temperature coefficient resistor 27, the current initially being sufficient to pull in control 23 but then dropping, due to heating of resistor 27 by the current therethrough, to a value below the hold-in current of control 23, contacts 19 passing current to control 23 via a second path 26 when the relay 6 is deenergized and the second path supplying a current which is only sufficient to hold-in control 23 but not to pull it in. Current is passed to the circuit via a controller 3 responsive to a demand for heat. A motor 4 supplies air to the burner and, in the case of oil burners, drives a liquid fuel pump. Control 23 may be the coil of a relayhaving contacts operating a solenoid fuel valve, or may be the coil of said valve. On start-up relay 6 is energized and closes a contact S to energize a high voltage igniter 9, giving sparks at electrodes 12, 13, and energizes control 23 via resistor 27. When a flame 14 is sensed relay 6 is deenergized to switch off igniter 9 and change make-before-break contacts 19 over to the holdin current path comprising a resistor 26. If ignition does not give rise to a flame, current continues to flow to control 23 via resistor 27 for a limited time after which resistor 27 has heated to a state in which the current is not sufficient to hold in control 23 thus interrupting fuel supply. If the flame is extinguished during operation then amplifier 21 again energizes relay 6 to energize igniter 9 and the circuit operates as above in accordance with whether or not the flame is restored. If control 23 is a relay, further contacts may be incorporated in a lead 28 to motor 4 and igniter 9 to thereby also switch off said motor when relay 23 is cut out. The flame may be sensed either by ionization currents to electrode 12 or by a visible or ultra violet light sensor. The operating coil of control 23 may be a D.C. type, a rectifier being placed in series therewith.