Patent GB-297696-A (GB)
Title: Improvements in synchronising means for printing and like telegraphs
IPC: H04L5/18
Filed: 1927-06-20
Abstract: 297,696. Beatty, W. E., (Bell Telephone Laboratories, Inc.). June 20, 1927. Type - printing telegraphs; synchronous movements.-In a printing telegraph system using the 5-impulse code and adapted for periodical automatic reversal of the direction of working, the synchronism-correcting means is controlled by the signals through a correcting distributor ring which, like the receiving ring, can be rotated manually through a small angle in relation to the sending distributor ring at the same station, to allow for such factors as line lag. The system described is a 5-channel multiplex system in which signals from the transmitter station A, Fig. 1, pass through a land line 6 to a repeater station B, Fig. 2, and thence through a cable 103 to a receiver at station C, Fig. 3, or vice versa. In both directions of working the pace is set by the transmitter; thus the distributors at A -and B may tend to run slightly faster than those at C, and when A is transmitting the differential gear 313, Fig. 3, applies forward corrections to the distributors at C, while when C is transmitting the differential gear 20, Fig. 1, applies backward corrections to the distributors at A. Specification 165,783 is referred to. Arrangement for two-way working. In the situation shown in the drawings the station A, Fig. 1, is sending. Impulses are emitted by the transmitter 2 through the distributor 1 and land line 6 to the receiving distributor 100 at station B, Fig. 2, and thence to storing relays 101, which control the retransmitting distributor 102. The latter sends impulses through cable 103, amplifier 300 at station C, Fig. 3. line relay 301 and receiving distributor 302 to printer 303. The synchronizing distributor 8 at A is out of action, and synchronism is effected at C by the signals through the synchronizing distributor 310. Periodically. however, the cam switches 5, Fig. 1, 104, 104', Fig. 2, and 322 (controlling switch 348), Fig. 3, operate, approximately at the same movement, to reverse the direction of working. The impulse transmitter 320 at station C, Fig. 3, then sends through the transmitting distributor 321, cable 103, amplifier 105 at repeater station B, Fig. 2, line relay 106, land line 6, and receiving distributor 3 to the printer 4 at station A, Fig. 1. At the same time the synchronizing circuits are rearranged so that station C controls the synchronizing relay 109 at station B, and so through land line 12 controls the corrector relay 10 at station A. Synchronization of repeating with sending station. The repeater station B is synchronized with the sending station A by the direct control of its motor 110 by impulses received from distributor 18 through the landline 16. Synchronization of receiving with sending fitation under normal conditions. It is assumed that station A runs slightly faster than station C. The switch 316 at station C is therefore set as shown so as to connect in circuit the forward correcting relay 314 and to disconnect the backward correcting relay 315, while at station A the switch 40 is set as shown so as to connect in. circuit the backward correcting relay 32 and disconnect the forward correcting relay 31. Under these conditions, when station A is sending, the signals which actuate the time relay 301, Fig. 3, also actuate the synchronising relay 304. When positive impulses are received the situation is as shown in Fig. 3, and the condenser 336 is charged by batteries 351, 352. When, however, the change occurs in the polarity of the received impulses, the armature 304a rocks and so causes the armature 306a to rock. The condenser 336 then discharges through the brush 337 and a segment of the correcting distributor 310. If the brush lies on an odd-numbered segment 335, the synchronism is satisfactory and the condenser discharge passes through to earth through battery 353. If, however, the brush 337 has lagged sufficiently to discharge the condenser through an even-numbered segment 345, battery 356, and earth, the winding 339b of relay 339 is energized, the armature 339c is rocked, and an impulse-from batteries 354, 355, energizes the magnet 314, which actuates the pawl 340 and so rotates the worm 341 one step. The pinion 342, carrying the parts 357 of a differential gear 313, is thus rotated, and the shaft 343, which drives the distributors, is thereby advanced slightly with respect to the motor shaft 344. Energization of the magnet 314 diverts the circuit at 814a so that winding 339a becomes energized by batteries 356, 358, and the armature 339<c> is restored in preparation for the next change from positive to negative line-impulse. When the direction of working is reversed, a similar series of operations takes place through the synchronising distributor 8 and differential gear 20 at station A, but in this case the switch 40 is so set as to cut out the magnet 32 and to bring in the magnet 31 which. when operated, retards the brushes one step in relation to the driving motor. Initial phase-corrections. When the direction of working is reversed so that synchronism is now governed by station C, a loss of synchronism of definite amount occurs owing to time lag and the accumulation of phase error during the short interval occupied by the automatic operation of changing over the connections. It is shown that this loss of synchronism can be remedied by adjusting the relative position of the transmitting ring at station A and the synchronising ring at the same station. Facilities are therefore provided for adjustment to an extent at least equivalent to one distributor segment. Correct phasing is established by repeated trial and error, under conditions illustrated in Fig. 4 (not shown).