GB1314255A - High frequency heating device - Google Patents

Abstract

1314255 Control systems for HF heating devices MATSUSHITA ELECTRIC INDUSTRIAL CO Ltd 13 Oct 1970 [18 Oct 1969 20 Nov 1969 8 Dec 1969(2) 29 Dec 1969(3)] 48693/70 Heading H2H [Also in Division H3] A high frequency heating device comprises a high frequency oscillator and an electromagnetic contactor, the electromagnetic contactor being operated by means of a touch switch so as to control the oscillator and hence the heating device. A high frequency oscillator 14 used for energizing a heating apparatus is supplied from an A.C. source 1, 12 by way of an electromagnetic contactor, having normally open contacts 3, 8, and a transformer 5. Closure of a starting switch 13 energizes the coil 16 of the contactor, to close contacts 3, 8, by way of a touch switch 15 to energize the oscillator 14. Touching the electrodes of the touch switch 15 causes the coil 16 to be deenergized to remove the supply from the oscillator 14. The touch switch includes two electrodes 31, 32, a Darlington pair of transistors 27, 28 and a Schmidt trigger circuit 33. Normally the transistor 21 of the circuit 33 is conductive, thus a relay 25 is not energized and the coil 16 of the contactor is energized to supply the oscillator 14. When the electrodes 31, 32 are bridged by an operator's hand, the small current which then flows between the electrodes is amplified by transistors 27, 28 and applied to the transistor 24 in the trigger circuit 33. Transistor 24 then becomes conductive and relay 25 is energized to de-energize coil 16 thus removing the supply from the oscillator. In other embodiments the touch switch comprises one electrode only.