Patent GB-757025-A (GB)
Title: Improvements in automatic telephone exchange systems
Inventor: JOHNSON BENJAMIN BERTIE
IPC: H04Q3/00
Filed: 1953-06-15
Abstract: 757,025. Automatic exchange systems. TELEPHONE MANUFACTURING CO., Ltd. June 10, 1954 [June 15, 1953 ; July 23, 1953], Nos. 16473/53 and 20532/53. Class 40 (4)' An exchange is equipped with means whereby extra subscribers or extra traffic can be handled readily by the addition of equipment, the additional line growth units or traffic growth units being self-contained. Fig. 1 shows the invention schematically and Fig. 2 shows the essentials of the switch construction. Crossbar switches of the type described in Specification 728,892 are used. Ten subscribers' lines are connected to each bridge of the switch, SLO1- SLO5 to the lower and SLO6-SL10 to the upper contacts in bank C1 Operation of one of the finger magnets FM1-FM5 interposes a corresponding finger f1-f5 between the corresponding contact bank and an armature which is then operated by magnet AR to close the contact bank, the upper or lower contacts thus connecting to the trunk according to whether a further finger magnet FMch has or has not operated contact Cch. As shown in Fig. 1, a system serving twenty subscribers has two " line growth units " each with four bridges, the uppermost three connected to primary outgoing trunks such as POG11-POG13 and the lowermost three to primary incoming trunks such as PIC12-PIC14. The primary trunks are connected by similar cross - bar switches to secondary trunks SOG, SIC, respectively, which are connected to connections CA1 which can take into use register controllers CA. To meet a demand for more subscribers' lines, additional line growth units may be installed, while if the traffic demands additional secondary trunks and connectors may be installed. Operation, Figs. 5-9. Connection from subscriber SL18 to subscriber SLO6. When subscriber SL18, Fig. 9, closes his loop relay L13/18, which serves both SL13 and SL18, pulls up to energize GB, Fig. 5, and all finger magnets FM3 in line growth unit 2. If SL13 had called the operation would have been similar except that BSA would have energized also to energize finger magnets FM6 as well as FM3. Assuming that the first outgoing trunk is busy so that LB5 is already energized, circuit is made over conductor 2 to energize finger magnets FM5 in the secondary outgoing cross-bar switch, Fig. 6. At the same time, assuming that connector CA1 is idle, circuit is made over conductor 4, Figs. 5, 7, to energize TA and T. Circuit 5 is then energized to operate cross-bar bridge magnet OTB11 which engages finger f5 to close contacts c11. This earths the P wire of the selected primary outgoing trunk POG and over contact c6, Fig. 5, of the line growth unit energizes cut-off relay K18 of the calling line. K18 releases line relay L13/18 to restore FM3 but the finger f3 is held by bridge SRU22. L13/18 also restores TA to direct the next call to the connector CA2. Relays A and B in connector CA1 now operate. In known manner one of the registers RC1, RC2 is taken into use, registers the called number and marks appropriate leads. Thus, in the example, the register marks the appropriate tens and units wires 7, 8 to energize MA and all finger magnets FM1 in line growth unit 1. MA energizes all the finger magnets, say FM3, corresponding to the first idle secondary incoming trunk in the secondary incoming switch, Fig. 8. The register meanwhile,marks wire P1 to energize magnet ITB11, 1, which locks up to wire H and closes contacts c11<1>. Contacts c11<1> energize magnet LB4 to operate the armature of the lowermost bridge in line growth unit 1, so that contacts c4 close to energize the cut-off relay of the called line SL06. As soon as the connection is thus established, the register restores MA and the finger magnets, the connection being held over wire H. For a units digit 1-5, the register also marks wire 9 to operate the change-over contacts previously described.