Patent GB-722764-A (GB)
IPC: F23N5/16
Abstract: 722,764. Controlling burners. SCULLY SIGNAL CO. Sept. 23, 1952 [Sept. 27, 1951; Sept. 9, 1952], No. 23803(52. Class 75 (1) The supply of fuel to a burner is controlled by means responsive to the sounds of a flame produced by the burner and adapted to shut down the fuel supply after a predetermined period if initial ignition does not occur at the burner and/or if the flame is unintentionally extinguished during a period of normal operation. Fig. 4 illustrates a control circuit for a gun type oil burner installation for heating a domestic water boiler in which a microphone 34, Fig. 2, mounted on the firebox door 4 is connected to an amplifier adapted to close a switch 68 when the microphone responds to the sound of the burner flame. The control circuit is energized for starting up the burner when a thermostat 10 located irf the space to be heated calls for heat. The thermal element 54 of the thermostat 10 then bends to engage first a contact 56 and shortly afterwards a contact 58. The contact 58 completes a circuit through the secondary of a transformer T1, having a primary continuously energized from supply lines L1, L2, to energize a relay coil RT which closes contacts CRT1 and CRT2. The circuit established through the contacts CRT2 shunts the contacts 58 to prevent chatter, whilst the contacts CRT1 establish a circuit from the line L1 through a normally closed reset switch, contacts 60, CRF of a thermal time delay switch RF which is closed about 30 seconds after power is applied to the lines L1, L2 by the electrical heating of the bimetallic contact CRF, after which interval the valves of the amplifier are in full operating condition, and thence through wires 62, 64, contacts CTD of a further time delay switch, wire 70, contacts CTS, relay RO, wire 74 to line L1. Actuation of the relay RO closes switches CROI and CRO2. Switch CRO1 energizes a protective relay RP to close contacts CRP1 and CRP2, the latter completing the circuit of the motor 96 driving the burner oil pump, whilst the former energizes a spark ignition circuit through wires 100, 102, contacts CRO2, wire 104, the primary of the ignition transformer T3 and wire 98 to line L2. Normally, the fuel will be ignited and the microphone 34 responds to the sound of the burner flame to close the switch 68. A relay coil RS is then energized through wires 110, 62, contacts CRF, 60, the reset switch, contacts CRT1, and wire 78. The relay contacts CRS1 and CRS2 then close. The contacts CRS1 shunt contacts CRO1 and establish a holding circuit for the relay RP through contacts CRP1. The relay RO is de-energized about six to 12 seconds after combustion begins by the opening of the delay switch CTD. Contacts CRO1 and CRO2 then open, but the pump motor continues to be energized through wire 92, contacts CRP2, wire 84, contacts CRP1, wire 100, and contacts CRS1 and CRT1, whilst the ignition transformer T3 is de-energized by the opening of the contacts CRO2. A further delay switch CTS having a delay period of 10 to 50 seconds is arranged to break the circuit of the relay RO should the switch CTD fail to function. When the required room temperature has been reached, the contacts 56, 58 open to de-energize the relay RT and open switches CRT1 and CRT2 thus breaking the circuit of the pump motor. In the event of flame failure the microphone 34 and associated amplifier will open the switch 68 to de-energize the relay RS and open contacts CRS1 to de-energize the pump motor. In order to restart the system after flame failure it is necessary to open the reset switch for 10 to 15 seconds in order to break a circuit through contacts CRT1 and the primary of the time delay transformer T2, which holds open the thermal switch CTD. The latter is then closed to energize the relay RO whereby the ignition and motor circuits are re-established. An indicating lamp 116 is energized if, during starting up, the burner fails to ignite, so that although the thermostat 10 calls for heat, the switch 68 fails to close. If, however, the switch 68 closes, then the relay RS. actuates the contacts CRS2 to energize a relay coil RL which actuates contacts CRL1 to break the circuit of the lamp 116. Alternatively, if combustion has occurred and is then interrupted, the relay RS is de-energized but the relay RL remains energized through a holding circuit through the contacts CRL2, and the circuit for a further warning lamp 128 is completed through the contacts CRL1. The microphone 34 is mounted within a hood 16 covering the end of a tube 22 extending through the double wall 4 of the firebox and supported coaxially within a casing 20 having apertures 28 for admitting cooling air into the space between the tubes 20, 22. In a modified control circuit the relay RT operates an additional switch which, when the thermostat calls for heat, shunts a resistance in the power supply circuit of the amplifier for reducing the voltages applied thereto by about 10 per cent. when in standby operation. The amplifier illustrated in Fig. 3 comprises (a) four resistance coupled triode amplifiers 140, 142, 144, 146; (b) a degenerative stabilizer for stabilizing the anode voltage on the valves 140, 142 and comprising a triode 148 and associated components; (c) a signal rectifier comprising a triode 150 and associated components; (d) a trigger circuit including triodes 152, 154 and associated components; (e) a time delay circuit comprising triodes 156, 158 and associated components; and (f). a power supply circuit comprising a double diode rectifier valve 160 and associated components. By selecting the values of the coupling and by-pass condensers the amplifier circuit is adapted to have a maximum response to applied frequencies of 20 to 200 cycles, the frequencies of the greatest amplitudes present in the noise of the burner flame. The microphone signal is applied at the points 38', 40<SP>1</SP>, and after amplification is rectified by the valve 150 which acts as a diode rectifier. The rectified signal is applied to the grid of the valve 152 which is non-conducting in the " no signal state, and causes the valve to conduct, thus biasing to cut off the formerly conducting valve 154. When the latter ceases to conduct, the voltage across resistors 194, 196 rises immediately but the maximum voltage applied to the grid of the valve 156, which is also non-conducting in the " no signal " state is delayed for a time determined by the values of the resistor 196 and a condenser 198, after which period the valve 156 conducts to energize the relay coil S and close the switch 68. A modified circuit is described for controlling a system comprising a main burner having an associated pilot burner. A microphone is so disposed as to receive the sounds of both main and pilot burners and is associated with an amplifier connected via two parallel filter circuits to control relays, one filter circuit responding only to the main flame noise and the other only to the pilot flame noise, whereby on failure of either flame the system is closed down. Alternatively, a pair of microphones are connected to a common amplifier, one microphone being responsive only to the sound of the pilot flame and the other only to the sound of the main flame. A further control circuit is described similar to that of Fig. 4, but also including means for closing down the system in the event of a failure of a component of the amplifier circuit such that the relay associated with the amplifier is energized in the absence of a flame at the burner. The control system may be generally applied to gas or liquid fuel burners and may control a fuel valve instead of a fuel pump motor.