GB994355A - Microwave oven control - Google Patents

Abstract

994,355. Control systems for microwave ovens. TAPPAN CO. Dec. 28, 1962 [June 14, 1962], No. 48891/62. Heading H2H. [Also in Division H5] The filament heating circuit of the magnetron 19 of a microwave oven is held energized for a predetermined period following the completion of a cooking period. Fig. 2 shows a control circuit in which the supply to the magnetron filament from terminals 23, 24 is connected via a normally-open switch 25 which is closed by energization of a relay coil 55 supplied from terminals 28, 29 through a rectifier 36. This energization is effected by opening and closing the oven door whose arm, Fig. 1 (not shown), momentarily closes a switch 18 thereby shortcircuiting a resistance 52 and connecting coil 55 across terminals 28, 29, operation of another switch 45 controlled by the relay effecting permanent connection of the coil 55 after the switch 18 has opened. Actuation of switch 45 allows the charging of a capacitor 40 through a resistance 41 so that after a predetermined time a neon bulb 42 is lit and its illumination alters the resistance of a photo-electric cell 56 to de-energize the coil 55 and open switches 25, 45. Upon expiration of the cooking period, which may be selected by a push-button timer, the oven door is opened and closed, thereby actuating the switch 18 to short-circuit the capacitor 40 and thus reset the timing circuit, which thereupon operates as described above to maintain the magnetron filament energized for the predetermined time. Such resetting also occurs if the oven door is operated before the expiration of the cooking period or the predetermined period subsequent thereto. In a modification, Fig. 3 (not shown), the capacitor 40 is short-circuited by a switch controlled by a second relay coil connected between the rectifier 36 and a fixed contact of the switch 18. Alternatively, the second relay coil may form one arm of a bridge network across whose output is connected to the first relay coil, the switch 18 having only two fixed contacts, Fig. 4 (not shown). In another modification of the circuit of Fig. 2, the switch 18 comprises a conductive slide which is reciprocated in response to movement of the oven door and connected so that the capacitor 40 is short-circuited by operation of the switch 45 upon de-energization of the relay coil 55, Fig. 5 (not shown).