Patent GB-495800-A (GB)
Title: Improvements in or relating to teleprinter exchange systems
IPC: H04L12/18
Filed: 1937-05-21
Abstract: 495,800. Telegraph exchange systems. STANDARD TELEPHONES & CABLES, Ltd. (Haigh, L. B., and Clemens, P. J.) May 21, 1937, No. 14181. [Class 40 (iii)] Certain substations in an automatic exchange system can broadcast a message and obtain an acknowledgement of the receipt of the message. Connecting individual sub-stations. To originate a call, a key SK is operated, or the offnormal contacts of the dial are actuated, Fig. 3 (not shown). This closes a loop across the a, b wires and operates a relay Lr. If the selector switch is in the normal position, a relay Onr operates, connects itself to the c wire and operates a relay Lbr. The latter makes the calling line busy to other selectors by disconnecting the d wire of the incoming line IL from a relay Cor and battery. It also breaks the original circuit for energizing the relay Onr and leaves it connected to battery over a relay Msr, which connects up the teleprinter motor M and maintains the substation loop when the key SK is released. When the motor starts, the subscriber actuates the dial which releases the relay Lr to operate a stepping magnet SM and a slow-release relay Lmr, which remains operated during the train of signals. When the wipers rest on the contacts of the called line, if this is free, battery is connected in series to relays Cor and Tr in the called line circuit. The relay Tr short-circuits its high-resistance winding and completes a circuit for the relay Hr, which breaks the circuit of the relay Onr, releasing the relay Lbr, but operating the relay Cr. The latter locks the relay Hr, which locks the c wire of the called line in series with the relay Msr which connects up the motor. A transmission circuit shown in thick lines is now closed between the two lines. If the called line is busy, the relay Tr is prevented from operating, and a sluggish relay Dr breaks the circuits of the relays Onr and Msr over the c wire. The relay Onr' releases the relays Lbr and Dr in turn. The former closes a homing circuit for the selector SM. During the homing operation, the relay Lmr prevents testing of the lines over which the wiper is passing, and, when the selector reaches its home position, releases, and the calling line is again free. At the end of a communication the connection is released by a key RK or by the automatic opening of contacts SW if no signals have been transmitted for a certain interval. Originating a broadcast call. The starting key SK is operated as described above, and the subscriber then dials his own number (1 as shown). When the relay Lmr releases, the relay Tr and a relay Arl, Fig. 2, are operated in series over the d contact of the selector. The latter relay disconnects a relay Ar2 from the d wire of a line OL to another substation which can broadcast messages. The relay Cr, when operated as described above, operates a relay Sr1 over the d wiper and changes it to its marking contact. The relay Arl also operates a relay Ahr which connects battery to the relay Bcr of each subscriber entitled to receive broadcast messages. If the line is already engaged, the c wire is opened and the connection released. The caller types T to cause the relays Sr1, Sr2, Sr3, Sr4 to change to their space contacts S. This operates momentarily relays Gr1., Gr2, Gr3, which close a circuit for the relay Hr in each line circuit receiving broadcast messages. When a relay Hr is operated, battery is removed from the corresponding arc terminal of a selector SMV, and the control of battery to the terminal corresponding to the calling line is transferred to a relay Er. When the caller transmits signals, the relay Sr1 repeats them to the relays Sr2, Sr3, Sr4, each of which retransmits them to six lines in parallel. Acknowledgement of reception. Each subscriber releases his key RK, which releases the relay Hr to reconnect battery to the corresponding arc terminal on the selector SMV. The line circuit remains busy owing to the continued operation of the relay Bcr. When all subscribers have acknowledged, the relay Er releases. To verify collectively the receipt of acknowledgement signals, the caller throws his key AK. Relays Br, Kr place the selector SMV under the control of the dial, and the lamp AL glows owing to the battery on the terminal N of brush a. The caller dials his number, and, if all subscribers have acknowledged, the lamp AL glows, because battery has been connected to the appropriate terminal by the relay Er. To verify acknowledgement by a particular line, the caller dials that number. The caller can also advance the selector SMV step by step.