Patent GB-976853-A (GB)
Abstract: 976,853. Controlling burners. ELECTRONICS CORPORATION OF AMERICA. Dec. 5, 1961 [Jan. 13, 1961], No. 43583/61. Heading F4T. [Also in Division G1] The Specification describes a circuit for the automatic lighting of an oil burner and for the closing down of the burner in the event of ignition or flame failure. The flame of a gas pilot burner or the main burner is detected by a photo-cell 95 or by a flame rod 97. When a flame is present a rectified current flows through the flame detector and produces a net negative charge on the plate of the condenser 107 connected to the detector. The voltage across the condenser is applied to the grid and cathode of a triode valve 113, and causes the valve, when a flame is present, to be non-conducting. Consequently no bias voltage is developed across a resistance 135 and a second triode 125 conducts to energize a flame relay 143 in its anode circuit. During the first five seconds of the starting cycle and before an ignition circuit 61, including a transformer and a pilot fuel valve, is energized a flame signal is simulated to check the operation of the circuitry associated with the flame detector. This simulated signal consists of a bias voltage developed across a condenser 127 by half cycles of current flowing from one end 159 of a transformer 25 through the condenser 127, the grid cathode path of the first triode 113 and a resistance 177 back to the other end of the transformer 25. The transformers 11, 25 are connected to the supply so that end 159 of transformer 25 is positive when the anode of the first triode 113 is negative. The discharge of condenser 127 through resistances 101, 129 during alternate half cycles, when the anode of triode 113 is positive, is negligible. A timer motor 37 actuates all the contacts shown as arrow heads in the Figure and these contacts are in the condition shown when the timer motor is in its start position. In the start position the two transformers 11, 25 are energized through contact 39 but the flame relay 143 and a control relay 171 are not energized and the contacts operated by them are then as shown in the Figure. The starting sequence is initiated by closing a control switch 155 to apply the simulated flame signal to the first valve 113. In consequence the second valve 125 conducts to energize the flame relay 143 which closes contact 185 to energize control relay 171 which closes contact 89 to energize a burner motor 87 and the timer motor 37. After three seconds the timer motor opens contact 39 and closes contact 31 but since these contacts are shunted by closed contacts 81, 89 the circuit is not affected. After five seconds from the start the timer motor opens contact 153 to remove the simulated flame signal and closes contact 181 in series with the heater 179 of a thermal lockout switch 69. The bias charge on condenser 127 leaks away at such a rate that after just over one second the second triode 125 is cut-off and the flame relay 143 is de-energized. Just before this occurrence at six seconds of timer motor rotation contact 167 is opened to remove the shunt current path across the heater 179. The latter therefore begins to heat up and the current therethrough maintains the control relay 171 energized. At nine seconds of timer rotation contact 35 opens but does not affect the circuit since flame relay switch 93 in parallel therewith is again closed. At twelve seconds of timer rotation contact 35 recloses and contact 63 closes but again the circuit is not affected. At fifteen seconds contact 45 closes to energize the ignition circuit and the pilot flame is established. The flame relay 143 therefore becomes energized. At twenty-five seconds of timer rotation contact 167 again closes and since flame relay contact 185 is now closed the heater 179 of the lock-out switch is shunted. At the same time contact 47 opens and contact 49 closes. The main fuel valve 51 is then energized through contact 45 and flame relay switch 55. If at this stage flame relay 143 becomes de-energized half cycles of current flow through the heater 179 to the junction of a resistance 133 and a condenser 131 to produce a bias voltage on the condenser which prevents the second valve 125 from conducting. After thirty-five seconds of timer rotation contact 63 opens to extinguish the pilot flame. Flame relay is now maintained energized by the detection of the main flame. After forty-five seconds contact 33 opens to stop the timer motor 37. When the heat demand is satisfied the control switch 155 opens and de-energizes control relay 171. Contact 81 opens to shut the main fuel valve 51 and contact 91 closes to start the timer motor 37 through contact 31. The burner motor 87 continues to run. After five seconds of timer rotation (i.e. fifty seconds from its start position) contacts 45 and 49 open and contact 47 closes and after a further five seconds contacts 153 and 33 close and contact 181 opens. These changes produce no changes in operation. After a further five seconds (i.e. sixty seconds of timer rotation) contact 31 opens to de-energize the burner motor 87 and the timer motor 37 and contact 39 closes. The timer motor has now made a complete cycle and is back at the start position. If power is interrupted prior to the opening of contact 39 three seconds after the start the normal sequence proceeds when the power is resumed. If power is interrupted after three seconds from the start relay 171 cannot be re-energized when power is resumed since contact 39 and switch 81 are both open. The burner motor 87 will be re-energized through contact 31 and timer motor 37 will be reenergized through contact 31 and switch contact 91. The timer motor then runs to the start position. If a false flame signal is given during the checking period flame relay 143 remains energized when contact 153 opens at the end of five seconds. When contact 167 closes a second later the heater 179 heats up and the bimetallic element of the lock-out switch 69 opens contact 71 to de-energize transformer 25. The burner motor 87 remains energized and the timer motor rotates to the start position. The lock-out switch 69 must be re-set manually. If flame failure occurs flame relay 143 becomes de-energized and opens switch 55 to deenergize the main fuel valve. Heater 179 heats up since the shunt path provided by flame switch contact 185 is removed and lock-out occurs a minute later. Timer motor 37 is again energized and rotates to the start position.