Patent GB-678503-A (GB)
Title: Party-line telecommunication system
IPC: H04Q3/58
Filed: 1948-04-30
Abstract: 678,503. Automatic exchange systems. COMPAGNIE INDUSTRIELLE DES TELEPHONES. April 30, 1948 [Aug. 7, 1947], No. 11844/48. Class 40 (iv). A junction between an automatic switching centre and an exchange is terminated by synchronously stepped switches, the outlets of the switch at the exchange end leading to the line equipments and the call finder-final selector multiple positions individual to the subscribers served by the switching centre. If out of step, the switches are automatically brought into corresponding positions. The switching centre uses the exchange battery and as shown, the switching centre is provided with two junctions. Outgoing call from switching centre, Fig. 3. Closure of the caller's loop A, B connects earth over rectifier RD<SP>2</SP> to the wire A<SP>1</SP> of the first choice junction A<SP>1</SP>, B<SP>1</SP>, or if the line switch is positioned on the caller's line the earth is supplied over rectifier RD<SP>3</SP>. If the junction A<SP>1</SP>, Bl is busy, the starting earth is applied to the wire A<SP>2</SP> of the second choice junction A<SP>2</SP>, B<SP>2</SP> over rectifier RD<SP>2</SP> or RD<SP>5</SP>. Relay 10 at the exchange, Fig. 1, operates and brings up relays 12, 13, 14 in a control circuit, Fig. 2. When the coupling switch X<SP>4</SP> of the control circuit finds the junction, say A<SP>1</SP>, B<SP>1</SP>, it is stopped by the release of 14. Relay 16 operates, followed by 22 which energizes the magnet X<SP>3</SP> of the exchange switch, completes a circuit for 23 and applies positive battery to the wire B<SP>1</SP> to energize the magnet X<SP>1</SP> of the line switch over a rectifier RD<SP>4</SP>. Relay 23 releases 22 to connect negative battery to the wire B<SP>1</SP> so that 1 is energized over the rectifier RD3 and X<SP>1</SP> releases; X<SP>3</SP> also releases, the junction switches X<SP>1</SP>, X<SP>3</SP> thus being stepped in unison by the interaction of relays 22, 23. A pair of corresponding outlets of X<SP>1</SP>, X3 are used as check positions, earth being applied in these positions to contacts A, S of X<SP>1</SP>, X<SP>3</SP> respectively. When the exchange switch X<SP>3</SP> arrives at the check position, relay 21 disconnects the switch magnet X<SP>3</SP> until 20 operates as a result of Xl arriving at the corresponding position, whereupon relays 21, 20 release in turn. When X<SP>1</SP> finds the calling line, a circuit is completed for 17 over make contacts of relay 1 and the line loop. Relay 3 pulls up, followed by 5 which connects it to the calling loop. Relay 19 operates in series with relay 8 in the exchange line equipment. Relay 10 falls back and releases the control circuit. The digits are repeated by relay 3, and 4 operates for the duration of each digit. Relay 6 responds to the current reversal when the called party answers. Incoming call. Earth applied to the exchange wire B operates a start relay 11 which marks the free junctions to the required switching centre. Relays 12, 13 14 in the control circuit pull up and when X<SP>4</SP> finds a free junction 13 releases to energize 15, whereupon relays 22, 23 interact to step switches X<SP>1</SP>, X<SP>3</SP>. When the wanted line is reached, relay 18 operates 7, followed by 1, 5. Relay 8 energizes in series with 19 and disconnects 11 so that the control circuit is released. When the called party answers, 7 falls back to reverse the line wires and 3 operates.