GB1318597A - Microwave ovens - Google Patents

Abstract

1318597 Control systems for microwave cooking apparatus DYSONA INDUSTRIES Ltd 17 Oct 1970 49426/70 Heading H2H The power output of a magnetron used in a microwave cooking apparatus is controlled by repeatedly switching the H.T. supply to the magnetron ON and OFF whilst simultaneously controlling the power input to the magnetron filament. Closure of an oven control push button switch 2 causes a filament transformer 1 to be energized over a contact A2 of a relay A, the filament being supplied from the secondary winding at a high level since only a part of the primary winding is energized. Simultaneously a time delay device 11 is energized and after a predetermined time-to allow the filament to become heated-completes a circuit to a push button switch 5 by way of door and cover switches 12, 13, 14 and contact T1 of a timer T. Closure of the push button switch 5 energizes the relay A and a relay B by way of a bimetal switch 6. Relay B operates to close contact B1 thus energizing a transformer 9 supplying H.T. to the magnetron and relay A operates to close a self holding contact A1 and changes over contact A2 thus de-energizing the magnetron filament. Passage of current through the heater 6c of the bimetal switch 6 causes the bimetal element 6a to flex to de-energize the relay B thus opening contact B1 to remove the H.T. from the magnetron. The heater 6c then cools and the cycle repeats, the average power output from the magnetron being determined by the ON/OFF switching ratio of the bimetal switch 6. This is adjustable by means of a manual control on the switch 6 which control is also arranged to close a contact 10 which causes the filament transformer 1 to be re-energized at a low level should the power output of the magnetron be adjusted to a level less than say 40% of the maximum value. The closure of the push button switch 5 also starts a timer T which, after a set time, causes contacts T1, T2 to change over thus operating a buzzer 15 and de-energizing relays A and B to remove the H.T. supply and returning the filament transformer to the high, standby, level of energization. The pattern of energization of the filament transformer can be set as desired according to the type of magnetron used in the apparatus. Auxiliary apparatus such as motors 3, 7 and indicating lamps 4, 8 are incorporated.