Patent GB-717728-A (GB)
Title: Automatic control of energy transfer from an electrical source to a load
IPC: G05F1/00
Filed: 1952-09-10
Abstract: 717,728. Automatic control of electrical energy transfer. SONTHEIMER, C. G. Sept. 10, 1952, No. 22722/52. Class 38(4) Automatic control of electrical energy from a source (such as an oscillator S, Fig. 1, and transmission line 2) to a load L (such as a high-frequency heater) is effected by separate adjustment of two or more reactances 4, 6 forming part of network T. When, e.g. the matching is incorrect, the sense of the mis-match is determined by making continuous incremental and individual variations of both reactances, either in alternate time relation, Fig. 1, or at different rates, Fig. 10, and the resulting changes in the energy reflected by the matching-device are used to control motors 34, 36 for adjusting both reactances 4, 6 in a compensatory sense. In Fig. 1, the in cremental changes in the shunt capacities 4, 6 of the matcher T are effected by a motor 32 which drives switch arms 14, 22 past diametrically - opposed quadrantal contacts 15, 14 to insert and remove small capacities 8, 18 in parallel with the respective capacities 4, 6. The resulting changes in the matching varies the energy reflected from the network T towards the source S, and a directional coupler D diverts the reflected energy to a rectifier R, whose alternating output is applied in push-pull to the grids of two pairs of valves 38, 42. The anodes of the valves 38 are connected to each other and through a field winding 82 of the motor 34, and switch contacts 84, 26 to a positive anode supply 86. The arm 26 is driven by the motor 32, and contact is made with the quadrant 84 to render the anodes of valves 38 positive whilst the capacity 8 is connected. Similarly the valves 42 have their anodes positive whilst the capacity 18 is in circuit. A mains supply is coupled in push-pull to the valve cathodes, and current flows to the field winding 82 through that valve of the pair 38 which has the more positive grid, thus driving the motor 34 and the condenser 4 in the direction to correct the mis-match. The other field winding 88 receives quadrant current from the supply mains through a condenser 92. The other condenser 6 is similarly adjusted by the motor 36 under the control of the valve pair 42. In a modification circuit, Fig. 3 (not shown), the switched condensers 8, 18 of Fig. 1 are replaced by rotary variable condensers, driven continuously by an induction motor supplied by the mains, and with their moving vanes displaced by 90 degrees. Input current is supplied from the mains to the valve pairs 38, 42 in quadrature, and from the rectifier R in pushpull, the output of the respective valve pairs 38, 42 controlling the direction of rotation of the respective motors 34, 36 for separately adjusting the condensers 4, 6 of the matching network T. The matching network T may take alternative forms, such as a single fixed shunt capacity and two series variable inductors; or a variable shunt capacity and a variable series inductor, Figs. 4 and 5 (not shown). In another form, the line 2 terminates in a variable inductive coupling to a closed circuit comprising a variable capacity and an inductor with tappings feeding the load, Fig. 6 (not shown). The matching element may comprise a co-axial stub which is variable in length by a sliding plunger, and is adjustable lengthwise of the coaxial line 2, Fig. 7 (not shown). In all cases two separate adjustments are provided. In a modified arrangement, Fig. 8, the directional coupler 196 responsive only to reflected energy is supplemented by a further coupler 198 responsive only to energy proceeding towards the load L. Their respective outputs are rectified at 202 and 204 and fed to an amplifier whose output is proportional to the ratio of the incident and reflected energy, and is used to control the adjusting motors. This ratio is not affected by variations of the actual power transmitted, but only by variations in the impedance of the'load L as modified by the network T. If squarelaw rectifiers are employed at 202, 204 their differential output is proportional to the net power delivered to the load L, and is used to control the adjusting motors when maximum power consumption in the load is desired, Fig. 9 (not shown). In a further modification, Fig. 10, the increments to the matching condensers 232, 234 are supplied by continuous rotation of dielectric disks 242, 248 between the plates 236, 238, 246 of shunt condensers. The disks have different numbers of teeth, so that one supplies variations at, say, 300c/s and the other at 450 c/s. The reflected energy picked up by the coupler D is detected in the rectifier 264, and the output at 300 and 450 c/s is passed through an amplifier 288 to a filter 294 which selects, say, the 300 c/s wave. This is further amplified at 296 and fed through a cathode-follower stage 302 to an output transformer 310 whose centre-tapped secondary is connected across the grids of balanced valves 336, 338. The cathode circuits of these valves include a winding 344 on a permanent magnet 346 the gap of which is traversed by a ferromagnetic toothed disk 348 applying voltage at 300 c/s to the cathodes. The anodes are connected to the ends of the primary coil of an output transformer 354, the centre tap of which is connected to a positive voltage B+ through a mains supply transformer 362. The anode current of one of the valves 336, 338 will predominate over that of the other valve according as the insertion of the teeth of the disk 248 has increased or reduced the mismatch at the network T. The output current at mains frequency is amplified in the push-pull stage 368, 372 and is fed to a field winding 382 of a motor 384 which adjusts the condenser 234 in the direction to correct the mis-match. Simultaneously, the 450 c/s current is selected in a similar valve circuit 282, whose output at X, Y supplies a motor 394 for correcting the adjustment of the matching condenser 232. A rectifying valve 314 fed from a secondary coil on the transformer 310 supplies AGC voltage to the grid of the amplifier 288.