GB255162A - Improvements in or relating to high frequency heating apparatus - Google Patents

Abstract

255,162. Burch, C. R., Davis, N. R., and Metropolitan-Vickers Electrical Co., Ltd. April 18, 1925. No Patent granted (Sealing fee not paid). Induction furnaces.-The effective load presented by an induction furnace or heating apparatus to a high - frequency generator is rendered adjustable, for example by providing variable coupling between the valve circuits and the load circuit when a thermionic generator or amplifier is employed. The adjustment may be made automatically by a relay in the plate supply circuit of the valve. As shown in Fig. 2, the coil 10 of the load circuit 10, 11 has tappings 12 any one of which may be selected for connection through the blocking condenser 14 to the plate of the generating or amplifying valve 15. The tappings may alternatively be taken from points between a number of condensers connected in series in the oscillatory circuit 10, 11. In a modification, shown in Fig. 4, two condensers 11<d>, 11<c> are connected in the oscillatory circuit, and a seriesparallel switch 19 is provided. The switch 19 may be arranged to adjust simultaneously the inductance or capacity of the grid circuit, or to adjust the frequency of a separate generator. The tappings may be provided on a choke coil 21, Fig. 8, connected across the plate circuit of the valve 15, and the oscillatory circuit may ba connected to the adjustable switch arm. The choke coil 17 in the plate supply circuit mav be tapped, for adjustable connection to the oscillatory circuit 10, 11, the additional choke 21 being dispensed with. The load on the generator may be adjusted by varying the mutual induction between the induction coil 10 and the body to be heated; for example, the body may be movable relatively to the coil.