Patent GB-524700-A (GB)
Title: Improvements in or relating to telecommunication exchange systems
IPC: H04Q1/446
Filed: 1939-02-03
Abstract: 524,700. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. Feb. 3, 1939, No. 3654. Convention date, Feb. 12, 1938. [Class 40 (iv)] In a system with alternating-current signalling, the reception of a seizing signal over a junction causes one of a number of impulse-repeating circuits or register-controllers to associate itself with the calling junction. The impulse - repeating &c. circuit receives voicefrequency selecting impulses with the aid of a hot-cathode gas-discharge tube the anode circuit of which is fed with A.C. to make it self-restoring. A similar tube may be made use of by the individual signal receiving circuit. At the end of the connection a releasing signal is received by the individual signal-responsive apparatus and is repeated to the switches. If this signal is received while the common apparatus is connected up, the latter is restored to normal. This apparatus is normally released after it has received a predetermined number of digits. This number may depend on a preliminary signal. In the systems described the selecting impulses are 1,000-cycle currents. The seizing and releasing impulses are in one system 500 cycles and 500 x 20-cycle currents respectively and in the other a brief and a prolonged burst respectively of 2 5-cycle current. First system. Fig. 1. On the reception of a 500-cycle seizing impulse over the junction 0 the hot-cathode gas discharge tube A breaks down and energizes 12 which is followed by 13, 14, 8. The latter starts the hunting-switch R1 of the first idle repeating circuit in search of the junction under control of relays 5, 9. These pull up in series, extend the starting circuit and make the junction non-selectable by other hunting switches. On the termination of the impulse, 12, 13 and 14 fall back, the tube A being made self-restoring by the use of an alternating plate current or being restored by a further signal of another frequency, but 8 remains locked up. Relay 5 engages 6 and connects up the in and out impulsing circuits. These are coupled for the transmission of dialling tone until relay 4 is actuated by the reception of the first digit. Dialled impulses break down the tube L2 which has an A.C. plate supply to make it self-restoring and are thus repeated by relays 1, 2 to the switches ahead and to the relay 3 which remains operated throughout each train and controls a switch R2 which counts the number of digits and after a predetermined number energizes 10 which completes the talking circuit and locks up. Relay 5 falls energizing 7 which marks the repeating circuit busy while R2, which is restored on the relapse of 6, is off-normal. The 500 x 20-cycle releasing signal causes repeated operation of 12, 13 at such a rate that 14 and 15, which are alternately energized and shunted by 13, remain energized and release 16 which thereupon shunts out 8. This releases 10 to release the connection and if received prematurely restores the common apparatus. Second system. Fig. 2. The seizing signal, which is a short burst of 25-cycle current, energizes 17 Which operates relay 8 over the wire c. The releasing signal holds 17 energized long enough to release 18 and relay 8 is thus shunted out over the wire d. The system is otherwise the same as that described above.