Patent GB-533347-A (GB)
Title: A synchronising system particularly applicable for telegraph distributors
IPC: H04L7/00
Filed: 1939-10-31
Abstract: 533,347. Synchronous movements ; valve generating circuits ; automatic control systems. STANDARD TELEPHONES & CABLES, Ltd. Oct. 31,1939, No. 29051. Convention date, Nov. 16, 1938. [Classes 40 (iii) and 40 (v)] [Also in Groups XXXV and XXXVI] The frequency of a source of current driving the apparatus to be synchronized, e.g. a telegraph distributer, is determined by an impedance network, and is controlled, on lack of synchronism occurring, by making an immediate and temporary change in the network in the required direction, this being supplemented by a small permanent change in the same direction. The current driving the motor at 50 c.p.s. is derived, by repeated frequency division, from a valve oscillator generating 100 k.c.p.s., the controlling crystal circuit including a condenser and inductance, either of which may be cut in to produce a temporary change in frequency, and a variable condenser which can be moved in either direction to produce a small permanent change. Synchronizing circuits ; valve oscillator. The motor 17, Fig. 2, is driven by a relay 20 supplied at 50 c.p.s. as described later. At each change' from spacing to marking current, relay 15 discharges a condenser 21 over one or both windings of relay 25. If synchronism is perfect, both windings are energized without result. If there is lack of synchronism, relay 15 energizes relay 28 or 29 and if this continues a thermial slow-acting relay 32 or 33 energizes relay 34 or 36 which in turn energizes relay 26 or 27, Fig. 5. The train of relays ensures that 26 or 27 is only energized on a definite lack of synchronism, and not by random impulses such as static. The relay 26 or 27 temporarily removes a short-circuit around an inductance 43 or condenser 45, and causes a motor 38 to move slowly a variable condenser 46 in a corresponding direction, to make a small but permanent change. The inductance 43 and condensers 45, 46 are associated with crystal 44 in a frequency-determining bridge feedback circuit of the pentode oscillator 50, as described in Specification 510,379. Frequency-reduction circuits. The frequency of 100 kc. produced by pentode 50 is reduced in stages to 20 kc., 4 kc., 2 kc., 1 kc., 500, 250, to 50 which is used to drive the motor 17, Fig. 2. The reduction in frequency is effected by crystal bridges acting as modulators and in some cases as frequency multipliers. In Fig. 6, current of frequency 100 kc. is led over wire 70 via the mid-point of transformer 72 to one diagonal of the crystal bridge 74, the other diagonal of which is connected through a transformer 73, tuned to 20 kc., to the amplifier 75, the output circuit 82, 83 of which is tuned to 20 kc. and connected to one diagonal of a crystal bridge 77, functioning as a frequencymultiplier, its other diagonal being connected to the transformer 72 tuned to 80 kc. The currents of 20 kc. produced in circuit 82, 83 are converted by bridge 77 to a frequency of 80 kc. which modulate at bridge 74 the currents of 100 kc., the difference frequency 20 kc. being thus sustained in the output of valve 75. The circuit on the right of Fig. 6 is similar and reduces the frequency to 4 kc. A somewhat different circuit is shown in Fig. 7 for successively reducing the 4 kc. to 2 kc., 1 kc., 500, 250. The current of 4 kc. is led over to circuit 102, 103 to one diagonal of a crystal bridge 106 (acting as a. modulator), the other diagonal being connected to the amplifier 99, the output circuit 110 of which is tuned to 2 kc. and connected by coil 111 to both diagonals of bridge 106, which modulates the currents of 4 kc. and 2 kc. thus sustaining the frequency 2 kc. in the output of valve 99. This output is supplied over leads 113, 114 to one diagonal of a crystal bridge 117, the other diagonal of which is connected to the amplifier 99, the output circuit of which includes a circuit 120 tuned to 1 kc. and connected via winding 124 to both diagonals of bridge 117, which modulates the currents of 2 kc. and 1 kc. thus sustaining the frequency of 1 kc. in the output coil 123. The circuits on the right of Fig. 7 are similar and reduce the frequency from 1 kc. to 500 and then to 250. The frequency of 250 is reduced to 50 by a circuit Fig. 8 (not shown), similar to that of Fig. 6, and the current of frequency 50 is amplified and used to drive the motor 17, Fig. 2. A current of frequency 300 may be produced by intermodulating by a bridge rectifier the currents of frequencies 250 and 50, Fig. 8 (not shown).