GB1026199A - Electric time relay device - Google Patents

Abstract

1,026,199. Valve relay-operating and delayedswitching circuits. ELECTROLUX A.B. Nov. 16, 1962 [Nov. 17, 1961], No. 43384/62. Headings H3P and H3W. A timing circuit comprises a capacitor charged by a grid-controlled valve so as to define a first time period, the capacitor being discharged at the end of the time period and recharged when required so as to define a second time period. A circuit is described for controlling the magnetron of a microwave oven. Terminals 27, 28 are connected to an alternating voltage supply at the same time as the filament of the magnetron is energized. Capacitor 2 begins to charge via valve 1, the charging time being dependent upon resistors 8, 9, 10 and capacitor 6 connected in the grid, cathode circuit feedback from cathode to grid tending to reduce the charging rate. After about two minutes, capacitor 2 is charged sufficiently to energize the control relay 5 which also energizes an auxiliary relay 3. Capacitor 2 is now discharged via contacts 15 and the coil of relay 5; capacitor 6 is discharged via resistor 12 and contacts 20. Once the auxiliary relay 3 has been energized, push-button 14 may be operated so as to energize an operating relay 4, contacts 25 of which supply HT to the magnetron. Capacitor 2 now begins to recharge via valve 1, the charging time being dependent on capacitor 6 and resistors 7, 9, 10 in the grid/cathode circuit. When capacitor 2 has charged sufficiently to energize the control relay 5, the operating relay 4 becomes released, disconnecting the H.T. from the magnetron. Resistors 8, 7 may be variable to permit respective adjustment of the first and second time periods.