Electronic controller for fluid fuel burner

• Main Authors: NEWBERRY; RICHARD D, WILLIAMS, JR.; ROGER W
• Format: Patent
• Language: English
• Published: 06.03.1990
• Subjects: BLASTING; COMBUSTION APPARATUS; COMBUSTION PROCESSES; HEATING; LIGHTING; MECHANICAL ENGINEERING; REGULATING OR CONTROLLING COMBUSTION; WEAPONS

A primary direct current power source (10) is controlled by a thermostat (8) and a secondary direct current power source (32,34) is independent of the thermostat. A first relay (22) is in circuit with the oil burner motor (4) to energize the same and a second relay (24) is in series with the first and with an alternating voltage source for energizing the ignitor (6) of the furnace. An electronic circuit controls the first relay switch (122) and includes a pair of silicon controlled rectifiers (SCR's) (80,82) connected in series for energizing the first relay. A second electronic circuit includes a pair of interconnected NPN transistors (102,112) for controlling the operation of the second relay switch (124). The first NPN transistor (112) is conductive when the second relay switch (124) is energized and the second NPN transistor(102) is connected to the first to turn "OFF" the same in response to flame being sensed in the furnace. A flame sensing element (30) in the furnace is associated with a control relay (128) for controlling a pair of relay switches, one of which (28) is in series with the SCR's and the other (38) is adapted to energize a redundant pair of time-delay circuits. Each time-delay circuit includes a capacitor (98) and a programmable unijunction transistor (PUT) (94) programmed to breakover at a voltage which is a function of a first predetermined time for charging a capacitor and a resistance in the cathode circuit of each PUT which provides for a second predetermined time for the discharge of the capacitor voltage to hold the second relay (24) "OPEN" by conduction through the second NPN transistor (102). Another electronic circuit includes an NPN transistor (72) and PNP transistor (74) connected to energize the first relay switch (122).