Patent GB-999903-A (GB)
Title: Improvements in or relating to fuel burner control apparatus
IPC: F23N5/20
Filed: 1962-01-30
Abstract: 999,903. Controlling burners. HONEYWELL Inc. Jan. 30, 1962 [Jan. 30, 1961], No. 3495/62. Heading F4T. [Also in Division G1] In an electrical control apparatus for a burner comprising a main control relay 11 actuating contacts 13 . . . 17, a timer motor 44 actuating contacts A . . . H and a time delay bi-metal switch that opens contacts 23 to deenergize the main control relay 11 if a flame is not established within a predetermined ignition period, the coil 12 of the main control relay 11 and the heater 22 of the bi-metal switch 20 are connected in series during a purge period of forty seconds preceding the ignition period and the impedances of the coil 12 and the bimetal heater 22 are such that the main control relay 11 is actuated but the energization of the heatet 22 is insufficient to actuate the bimetal switch. Open circuiting of the heater 22 during the purge period thus de-energizes the main control relay. At the end of the purge period the timer motor closes contacts G to connect the heater 22 to the secondary winding 62 of a transformer 60. The energization of the heater 22 is then sufficient to actuate the bimetal switch during the ignition period if ignition does not occur. The bi-metal switch is reset manually. A flame detector 25 is operated by a photo-cell. Fig. 1 (not shown), responsive to a pilot burner flame during the ignition period and to the main burner flame during normal running and in the presence of a flame closes contacts 36, 37 and opens contacts 38. The latter de-energize the heater 22. The sequence of operation of the contacts A . . . H by the timer motor 44 is shown in Fig. 3, each dark bar indicating the closed condition of the respective contacts and the remaining unbarred section indicating the open time of the contacts. The contacts A . . . H may be operated by cams. Fig. 2 shows the contacts and switches in the standby condition corresponding to the zero time point in Fig. 3. If now a starter button is depressed current flows from the line 27 through the start switch, the contacts A, the contacts 38, the heater 22, the winding 62 of the transformer 60, the contacts 23 of the bi-metal switch, the main control relay coil 12 and the line 63 to the line 28. The main control relay therefrom closes contacts 14, 15, 16 and opens contacts 17. The closed contacts 16 energize the timer motor 44 and the winding 41 of a further relay 40 which closes a switch 42 to energize a fan 56 to supply air to the fire-box. After five seconds, timer motor opens contacts A and closes contacts B. During the purge period which lasts for forty seconds the closed contacts 38 of the flame detector relay are in series with the main control relay coil 12 so that a component failure indicating a flame when in fact no flame is present de-energizes the main control relay 12 and the contacts 15 open to prevent energization of either a main fuel valve 57 or a pilot fuel valve 52. At the end of the purge period contacts C and G close. Contacts C energize the pilot valve 52 and an ignition transformer 54, and contacts G connect the heater 22 of the bi-metal switch to the secondary winding 62 of the transformer 60. If ignition occurs the flame detector opens contacts 38 to de-energize the heater 22 of the bi-metal safety switch and closes contacts 36, 37. At the fifty second time point contacts D close to energize the main fuel valve 57 and contacts H and contacts E open to transfer control to the contacts 37 and 36 of the flame detector. During the time period from fifty to eighty seconds both the pilot burner and the main burner are in operation but at the end of this period contacts C open to close down the pilot burner and de-energize the ignition transformer. At the one hundred and five second point contacts F open to stop the timer motor. This is the running position. On depressing a stop button the main control relay 11 opens its contacts 15 to de-energize the main fuel valve 57 and closes its contacts 17 to re-start the timer motor 44. The relay 40 remains energized to maintain the fan 56 operating, for a post-purge period. Contacts D and G open and contacts E close at the one hundred and ten second point; contacts A, F, H close at the one hundred and fifteen second point; and contacts B open at the one hundred and twenty second point to stop the timer motor. All the contacts are now in the start position.