Patent GB-1080243-A (GB)
Title: Improved burner control system
Filed: 1965-02-02
Abstract: 1,080,243. Flame monitoring devices. SARCO CANADA Ltd. Feb. 2, 1965 [Feb. 5, 1964], No.4491/65. Heading G1A. [Also in Division F4] An electronic system for controlling the starting up and safe operation of a burner comprises a signal conditioner 34 which at starting sends a positive pulse to a bi-stable memory unit 36 which then applies a negative voltage to an AND gate 38 to start a clock pulse generator 40 connected to four bi-stable timing units 41, 44, 46, 48 connected in series as a binary counter and each adapted to pass on pulses at half the frequency of its input pulses, transistor switches 49, 50, 52, an amplifier switch 54 and a series of relays 140, 142, 146, 76, 148. The system provides a preliminary purge period, an ignition period, a continuous run period of indefinite duration and a post purge period. The signal conditioner, Fig. 3 (not shown), is supplied with -130V, -6V and +6V from a power unit 32 and on application of the supply a positive reset pulse flows from a capacitor 34. 19 through four semi-conductor diodes 34.13, 34.14, 34.15, 34.16 to the four bi-stable timing units 41, 44, 46, 48. When a control switch 57 is closed to start the burner the -6V supply passes current through the detector relay 76 and a diode 34.1 to ground and a positive going voltage step is taken off a capacitor 34.19 and transmitted to the memory unit 36. The memory unit 36 and the bi-stable unit 41, 44, 46, 48 are identical and each comprises a standard bi-stable transistorized multi-vibrator, Fig. 4 (not shown), driven by a positive going voltage step. An output of the memory unit changing from zero to negative voltage is taken by a lead 90 to an AND gate 38, Fig. 5 (not shown) comprising three semi-conductor diodes having a common cathode lead. The lead 90 is connected to the anode of one diode; leads 92, 94 lead from the other two anodes to relay operated switches 88 and 58. The clock pulse generator 40 comprises a transistorized squaring amplifier followed by an inverter circuit, Fig. 6 (not shown). A potentiometer 40.8 controls the frequency. Each transistor switch 49, 50, 52 comprises a transistor 49.1, Fig. 8 (not shown), functioning as an emitter follower and a second transistor 49.10 functioning as an inverter amplifier. A negative signal input to the first transistor 49.1 causes saturation of, the second transistor 49.10. The amplifier switch, Fig. 9 (not shown), comprises a transistor 54.21 arranged as an emitter follower and a second transistor 54.25 arranged as an amplifier. Operation The application of power to the conditioner 34 results in a reset pulse being emitted to the binary bi-stable units, 41; 44, 46, 48 to set each unit in the start position. The closing of the control switch 57 starts the cycle by energizing the detector relay 76 and causing the signal conditioner 34 to send a positive going voltage step to the memory unit 36. The latter develops a negative voltage which is applied via lead 90 to the AND gate 38 which therefore releases the clock pulse generator 40 provided the other two gate inputs via leads 92, 94 are negative or are disconnected. The pulse generator 40 then produces pulses which are fed to the four binary bistable units, 41, 44, 46, 48 in series. The detector relay 76 closes a switch 160, Fig. 2, to energize a fan motor 10 through an alarm switch 166 and actuates a modulating control, if provided, to its "high-fire" position. The clock pulse generator operates at one half cycle per second and therefore thirty-two seconds after closing the control switch the output 48.1 of the last bi-stable unit 48 changes from 0 to -6volts, thus saturating the transistor switch 52 so that current flows therethrough to energize the fan motor relay 146 through a switch 126 now closed by the detector relay 76. The motor relay 146 then closes a switch 178, Fig. 2, providing an alternative circuit for the fan motor 10 and closes a switch 174 thus connecting the "low fire" terminal 172 and disconnecting the "high fire" terminal 173. A switch 74 actuated by the motor relay 146 provides a holding circuit for the motor relay 146 through the signal conditioner 34 and also opens the startup circuit to the detector relay 76. The latter however is maintained energized by the conducting transistor switch 52. After a further thirty-two seconds the last bi-stable unit 48 opens the transistor switch 52 de-energizing the detector relay 76 and energizing the ignition relay 142 through switches 74, 126. A holding circuit for the ignition relay comprises a switch 114 actuated by the ignition relay and a transistor switch 49 which closes when the transistor switch 52 opens, being energized by the second anti-phase output 48.2 of the last bi-stable unit 48. The ignition relay energizes the solenoid valve 14 of a pilot burner and an ignition transformer 12. If the pilot burner ignites a flame scanner 125 switches on the amplifier switch 54 to energize again the detector relay 76. The flame scanner 125 is a semi-conductor element having a high resistance which becomes conductive when light impinges thereon or an ultraviolet detector in which ultraviolet radiation causes ionization of an inert gas. Eight seconds after the energization of the ignition relay 142 the second bi-stable unit 44 closes the transistor switch 50 and the relay 140 for opening the fuel valve 16 (Fig. 2) of the main burner is energized via a switch 202 actuated by the ignition relay 142 and a switch 208 actuated by the detector relay 76. A holding circuit for the main valve relay 140 comprises a switch 59 closed by the relay. At the end of the thirty two second period following the energization of the pilot valve and the ignition transformer the last bi-stable unit 48 opens the transistor switch 49 to de-energize the ignition relay 142 thereby disconnecting the pilot valve 14 and the ignition transformer 12 and switching the modulator control to an automatic position. The other output 48.1 from the fourth bi-stable unit 48 at the same instant closes the transistor switch 52 and a ground signal is transmitted through a switch 88 and lead 92 to the gate 38 thereby arresting the clock pulse generator. This is the operating position. Shutting down the burner. When the control switch 57 is opened the main valve relay 140 is de-energized by the signal conditioner and closes the main fuel valve 16. But a holding circuit is provided for both the detector relay 76 and the fan motor relay 146 by the closed transistor switch 52 and the switch 88. The latter also discontinues the ground signal to the gate 38 so that the clock pulse generator 40 is released. After a thirty-two second post purge period the transistor switch 52 is opened and the detector relay 76 and the motor relay 146 are de-energized. Also the other output 48.2 from the last bi-stable unit 48 closes the transistor switch 49 and a ground signal is passed through switch 114 to the memory unit 36 and in consequence the memory unit switches back to its original condition thus blocking gate 38 by a ground signal and stopping the clock pulse generator 40. The entire control circuit is now in its original condition. Closing the control switch 57 during the post purge period will not start the cycle since the switch 74 is open and prevents the signal conditioner from developing the operating signal for the memory unit 36. If the pilot does not ignite within the eight second period following the energization of the pilot valve and the ignition transformer the alarm relay 148 is energized instead of the main valve relay 140 by the detector relay switch 208 and actuates switch 166, Fig. 2, to de-energise the burner controls and energize a horn 18 and a light 20. The alarm relay also operates a switch 58 which causes the signal conditioner 34 to deenergize the main valve relay 140 as in shutting down the burner using the control switch 57. The switch 58 also connects the lead 94 of the gate to ground thereby stopping the pulse generator. When the armature of the alarm relay 148 is reset manually the starting sequence starts automatically. If flame failure occurs after the ignition period the detector relay 76 is de-energized by the flame scanner 125 and the switch 208 de-energizes the main valve 140 but the latter de-energization is delayed 150 milli-seconds by a capacitor 152 so that the switch 59 can energize the alarm relay 148 through the switch 208. False light impinging on the scanner 125 or a shorted scanner causes energization of the alarm relay. An open scanner results in the same condition as flame failure. In the event of momentary power failure the reset circuit of the signal conditioner 34 automatically resets the control sequence to its startup position at the restoration of power and commences re-cycling the burner system. In a modification Figs. 11, 12 (not shown) the relays have three sets of single throw double-pole switches in place of four sets as in Figs.1, 2.