Patent GB-716464-A (GB)
Title: Arrangement for automatic control of resonance in high frequency electric apparatus
IPC: A61N1/40
Filed: 1952-07-11
Abstract: 716,464. Control of D.C. motors. SIEMENSREINIGER-WERKE AKT.-GES. July 11, 1952 [July 12. 1951; July 23, 1951], No. 17598/52. Class 38(3) [Also in Group XXXV]  In an automatic system for maintaining resonance in the work circuit of a high-frequency heating or treatment apparatus, a motor arranged to drive a tuning reactance continuously towards its resonance value, is reversed in direction soon after the resonance value has been reached. A control voltage varying in value according to the degree of mistuning, is sampled at short intervals and is applied to a motor-reversing relay in such a way that whilst the tuning is approaching resonance no effect is produced, but when resonance has been passed the reversing relay is operated. The control voltage may be derived as the difference between the voltages created across resistors connected respectively in the grid and anode circuits of the high-frequency generator. In Fig. 1. the tuned anode circuit GK of the oscillator valve G is coupled to circuit BK comprising a variable condenser C, driven by a motor M, and terminals 1, 2 for connexions to the treatment electrodes. The control voltage ST, varying with the degree of mistuning of the work circuit BK, is derived through a filter SG from two resistors Ra, Rg traversed respectively by the anode and grid currents. This voltage is applied to the grid circuit of a valve V; Fig. 3 to charge a condenser Ci intermittently through a resistor R whenever a contact i is closed by a cam N driven by the motor M. Consecutive voltage pulses are thus produced on the grid, in the positive sense when approaching resonance, and in the negative sense when receding. These pulses are differentiated in the anode circuit to provide sharp pulses st of opposed sign, which are applied to a gas-filled triode GT in the motor reversing circuit, Fig. 5. When the applied pulses st are of negative sign (approaching resonance), the triode is unaffected. The positive pulse occurring when resonance has been passed fires the triode and energizes a relay S. One of its contacts s2 is thrown over to connect a charged condenser Cp across a polarized relay P which thereupon reverses the contact p to short the motor-reversing relay MR. and thus reverse the direction of the motor M. The relay S also opens a contact s1 in its own circuit, thus extinguishing the triode GT and allowing contact s2 to return to the position shown. As contact p retains its new position, the condenser Cp is now charged from the potential divider Sp in the opposite sense. Reversal of the motor M having carried the tuning beyond resonance, another positive pulse st is applied to the triode GT with the result that the condenser Cp discharges in the opposite direction through the relay P and throws the contact p back to the position shown. The tuning is thus oscillated to a small degree on either side of resonance. In a modified motor-reversing circuit, Fig. 8, the pulses st are applied in parallel to the grids of two gas triodes Th1, Th2 the anode circuits of which include respectively field windings F1, F2 for forward and reverse running of the motor armature M. The two triodes have their cathodes coupled by a resistor RK, and their anodes connected by a condenser. Vacuum valves may be employed in the known flip-flop circuit instead of the gas triodes. motorreversing relays replacing the field coils F1, F2.