Patent GB-746983-A (GB)
Title: Magnetic switching device
IPC: H03K17/81
Filed: 1954-02-17
Abstract: 746,983. Non-contact-making relays; electric selectors. RADIO CORPORATION OF AMERICA. Feb. 17, 1954 [March 2, 1953], No. 4716/54. Class 40(4). [Also in Groups XXXVIII and XL (b)] An alternating signal is selectively applied to one of a number of channels by a magnetic switch comprising a set of saturable cores having separate output coils and a common input coil; the input being effectively coupled by transformer action to an output coil only when the associated core is in a demagnetized condition. Arrangements are described in which switching transients and low-level outputs arising in unselected channels are neutralized. The basic arrangement is shown in Fig. 3 in which a set of magnetic cores 10 have a common signal input coil 20 and individual output coils 16. The switch is controlled by selecting windings 12 coupled with the cores and arranged in series to form four pairs of selecting coils S1, S2-S7, S8. All the cores except one are saturated when one selecting coil in each pair is energized in accordance with a binary code, the unsaturated core providing the transformer link to the wanted output coil. A D.C. bias applied to the input coil 20 may be used to restore the saturated cores to normal. In this arrangement all the selecting coils are energized to open the switch. An alternative embodiment, Fig. 4, utilizes a bias coil 24 which initially saturates all the cores in an " N " direction, and has " P " magnetizing selecting coils S1-S8 arranged to demagnetize a single core when selectively energized. The switch is opened when all the selecting coils are deenergized. Transmission of spurious signals is prevented by the core arrangements shown in Figs. 5 to 7. In Fig. 5 a single core is replaced by identical cores 30, 32, the separate windings constituting the output coil 42 being connected in opposition so that disturbances arising from magnetic changes in the cores are neutralized. As the windings of the input coil 40 are similarly arranged the transformer action is unaffected. Two saturable cores 30, 32 and two further cores 30A, 32A having linear magnetization characteristics are used in the Fig. 6 arrangement. Only the saturable cores are coupled to the bias coil 38, the arrangement of each pair of cores being otherwise similar to Fig. 5. The linear cores are arranged to have like magnetic characteristics to the non-linear cores in the saturated condition. As the input coil 40 is coupled in opposite respects to the pairs of cores 30, 32 and 30A, 32A, low-level signals transmitted by the core pairs when the channel is not selected by coils 34, 36 oppose and neutralize each other in the output coil. When the channel is selected the cores 30, 32 are desaturated and neutralization no longer occurs. In Fig. 7 two pairs of identical saturable cores 30, 32 and 30B, 32B are employed, each pair of cores being saturated to opposite polarities by bias coils 38, 38A. The selecting coils are arranged to magnetize all the cores in the same direction when the channel is selected. As the input and output coils are arranged as in Fig. 6, this embodiment functions in a similar manner. The switch may be used to control the recording of television signals on magnetic tape (see Group XL (b)), the recording apparatus comprising a large number of transducer heads associated with a single tape, Fig. 9 (not shown). Each head is directly coupled to a separate output coil, Fig. 8 (not shown), and the video signals are recorded or reproduced over the switch by a scanning action which necessitates desaturating each switch core in turn in a cyclic time corresponding to the line period. The switch cores may be arranged in a 704 core matrix 70, Fig. 10, controlled by a 22-row and a 32-column set of selecting coils, the coincidence of row and column energization determining the selected core. The video signal is applied to the signal input coil (not shown), which is common to all the cores. Energization of columns and rows is controlled over groups of tubes 72, 74 by 22- and 32-count ring counters 76, 78. A single oscillator 80 drives the counters, the ring counter 76 completing a cycle each line period before stepping counter 78 to the next column. An alternative arrangement is shown in Fig. 11 in which a matrix of cores 82 is arranged in a single plane and selection is by triple coincidence of signals. This arrangement uses three 9- count ring counters 84A, 86A, 88A driven by an oscillator 90 and arranged in a radix-nine system to control 81 X 9 cores over groups of tubes 84, 86, 88. Fig. 12 illustrates one group of sixtyfour cores 100 in a 512-core switch, the remaining seven groups being represented schematically at 64. Two sets of selecting coils are employed, each of 8 coils. One set has its coils S101-S108 separately associated with all the cores in a group while the second set has its coils S111-S118 coupled with eight cores in each group. The arrangement is such that energization of a single selecting coil in each set desaturates eight cores in a single core group against the inhibiting effect of a D.C. bias coil 110. The video signal input from 144 is applied to one of the eight selected cores over an eightcore magnetic switch 140 and an input coil S121-S128, according to the setting of the magnetic switch. Scanning is controlled by a pulse generator 142 which drives switch 140 over a three-stage binary counter 138 and controls the selecting coils over three-stage binary counters 134, 136 and binary to octal converters 130, 132, the arrangement constituting a radixeight system.