Patent GB-1262947-A (GB)
Title: Burner control apparatus
IPC: F23N5/20
Filed: 1969-05-29
Abstract: 1,262,947. Controlling burners. ELECTRONICS CORP., OF AMERICA. 29 May, 1969 [17 June, 1968], No. 27171/69. Heading F4T. Burner control apparatus for use with a fuel burner installation having a combustion chamber, a fuel flow control 28 and an ignition control 26 comprises four timing circuits containing respectively unijunction transistors 50, 70, 90 and 110. Operation commences when switch 14 is closed, thereby energizing damper control 22 and main control relay 20. This relay closes contacts. 20-1, to energize blower 16, and also closes contacts 20-2. When air flow has been established in the combustion chamber, flow switch 16-1 closes. If at this stage detector 62a generates a spurious flame signal, indicating a fault in the installation, transistor 86 becomes conducting and energizes flame relay 82. Contacts 82-2 are thereby closed to complete a current path to coil 44. This in turn opens contacts 44-1, de-energizing the circuit, and closes contacts 44-2 to sound an alarm. If there is no spurious flame signal, the sequence of timing operations commences. The first timing circuit, containing transistor 50, controls a first, or pre-purge, timing interval (T1, Fig. 3, not shown). When the potential on capacitor 52 exceeds that on the emitter of transistor 50, the capacitor discharges through this transistor to energize the coil 60. When this happens contacts 60-1 open; contacts 60-2 close, completing a holding circuit for coil 60; contacts 60-3 close, energizing the second and third timing circuits; contacts 60-4 open, deenergizing damper control 22; contacts 60-5 close, energizing pilot fuel control 24 and ignition control 26; contacts 60-6 open, cutting off transistor 86 from the power supply; contacts 60-7 open; and contacts 60-8 close. At this stage, pilot fuel is flowing and ignition control 26 is operating, but since transistor 86 is not energized, detection of ignited pilot fuel will not result in energization of relay 80 and consequent shut-down of the installation. The second timing circuit, containing transistor 70, is energized when contacts 60-3 close and controls a second timing interval (T2). When a portion of the corresponding relay 82 is energized thereby energizing the fourth timing circuit, contacts 82-1 open; contacts 82-2 close; contacts 82-3 open to de-energize the ignition control; contacts 82-4 close to energize transistor 86 and thereby provide a holding circuit for coil 82 if flame is present; and contacts 82-5 close. The third timing circuit, containing transistor 90, is also energized when contacts 60-3 close and controls a third timing interval (T3), longer than the second. When the relay 98 is energized, contacts 98-1 open; contacts 98-2 close, providing a holding circuit for coil 98; contacts 98-3 close; and contacts 98-4 close to initiate fuel flow into the combustion chamber, where the fuel is ignited by the pilot flame. The fourth timing circuit, containing transistor 110, is energized when coil 82 is energized and controls a fourth timing interval (T4). When transistor 110 becomes conducting, transistor 120 is rendered non-conducting and coil 60 is de-energized. Accordingly, contacts 60-1 close; contacts 60-2 open; contacts 60-3 open, deenergizing the second and third timing circuits; contacts 60-4 close, re-energizing the damper; contacts 60-5 open, de-energizing the pilot control; contacts 60-6 close; contacts 60-7 close, establishing a holding circuit for coil 98; and contacts 60-8 open. Should flame failure occur after main fuel flow has started, transistor 86 will cease conducting and coil 82 will be de-energized. Thus, contacts 82-1 close to energize lock-out actuator 44. Contacts 44-1 open, disabling all the relays and their associated controls, and contacts 44-2 close, energizing the alarm 18. Should air flow cease at any time, switch 16-1 opens to deenergize the relays and shut down the installation in a safe condition.