Patent GB-518241-A (GB)
Title: Improvements in or relating to teleprinter exchange systems
IPC: H04L12/06
Filed: 1938-08-19
Abstract: 518,241. Teleprinter exchange system. STANDARD TELEPHONES & CABLES, Ltd., HARTLEY, G. C., and HYDE, G. A. M. Aug. 19, 1935, No. 24479. [Class 40 (iii)] A machine for transmitting a predetermined permutation teleprinter code comprises two commutators, a first commutator with contacts preconnected for given signals and messages and a second commutator rotating in synchronism with the first for successively completing polarized relay circuits for a brief period during the closing period of each successive contact of the first commutator. The contacts of the first commutator may be controlled by a keyboard or perforated tape to set them for the desired message codes. In the form shown in Fig. 3, the first commutator is a single motion selector switch of the type used in telephone exchanges and comprises in effect eight banks of contacts 19 with their respective wipers AS1 .. 4, and BS1 .. 4. The second commutator has a conducting sector A carried by an insulating sector B and connected to a slip ring. A brush SRB connected to earth bears on the slip ring, and conducting brushes BAS1 .., BBS1 .. spaced one-eighth of a circumference apart are adapted to contact with the sector A in turn. These brushes BAS1 .. and BBS1 .. are connected respectively through polarized relays BU, UN, PE, C1, C2 to the wipers AS1 .., BS1 .. which are staggered relatively to each other to compensate for the circumferential spacing of the brushes. Some brushes and wipers are not required for the particular purpose illustrated and are therefore unconnected, and one wiper BS4 is connected to earth. The two commutators are geared together so that the disc B makes 3,000 revs. per minute and the wipers AS1 .., BS1 .. make 60 sweeps a minute ; hence each contact 19 is covered by a wiper for 20 milliseconds and a brush makes contact with sector A for 5 milliseconds during the same period. The devices shown in this figure are connected by leads SC, PU, TO and the leads on the left of the figure to a teleprinter exchange system as described in Specification 498,416. A full cycle of signals requires two complete sweeps of the wipers. During the first sweep, front contacts x5, x6, x7 are open, the wipers AS1, BS1, AS2 are therefore ineffective, the wiper BS4 sends to teleprinter through lead PU a message to prepare for reception, and wipers BS2, AS3 send spacing and marking signals through relays C1, C2. This preliminary period is needed to give time to the motor of the teleprinter to reach its normal speed. At the end of the sweep, wiper BS4 sets relays X, Y in operation, whereby contacts x5, x6, x7 are closed to connect wipers AS1, BS1, AS2 to their relays, and contacts x1, x2, and xr1 .. 4 are reversed. During the second sweep of the wipers, the coded messages are sent out by the wipers AS1, BS1, AS2, BS2, AS3, the codes marked "Figs" and "D" making up the "who arc you signals." Near the end of the sweep, wiper BS4 sends a signal through line TO that transmission is at an end ; then wiper BS4 sets relay Z in operation, whereby relays X, Y are de-energized; and finally wiper BS4 cuts off relay Z and all parts are again in starting position. In addition, the wiper BS4 serves to send supervisory lamp flashing signals through lead SC. In a modification, tne selector switch constituting tne first commutator is replaced by a bank of contacts controlling cams on a shaft geared to the shaft of the commutator disc A.