Patent GB-946840-A (GB)
Title: Improvements relating to automatic telecommunication switching systems
Inventor: WARMAN BLOOMFIELD JAMES
IPC: H04Q3/00
Filed: 1961-08-02
Abstract: 946,840. Automatic exchange systems. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. July 16, 1962 [Aug. 2, 1961], No. 28097/61. Heading H4K. A subscriber's line circuit, Fig. 1, comprises a resistance Rs2 which when the loop L is closed presents a positive start potential to a gate CG and a two-step cut-off relay KA/KB which is controlled from the primary switch PS and in the event of a permanent calling condition becomes partially energized and presents a negative start potential to a gate PG. The line circuits are interrogated in turn by a scanning circuit, Fig. 2, which applies scanning pulses to the pairs of gates CG, PG by way of combining gates GX, GY, GX<SP>1</SP>, GY<SP>1</SP>, the pulses being distributed by a circuit CC comprising counters C, B, A. The scanning circuit may cater for 1600 lines, and in a larger exchange several such circuits would be provided under the control of an auxiliary pulse distributing circuit UC. On the occurrence of a calling condition, a scanning pulse applied to GX produces an output from GY which opens gates G6, G8 with the result that scanning is stopped. A pulse on wire rl by way of gate G13 causes seizure of a register, and when a signal is returned over wire pl the identity of the calling line is sent thereto together with a signal on wire cgl to indicate a calling condition. To this end binary marking signals Gci, Gbi, Gai are fed by way of gates to converters Coc, Cob, Coa, Fig. 4, which provide code signals on a number of wires, e.g. 2-out-of-7 in the case of Coc and 2-out-of-5 in the case of Cob, Coa. In addition, further signals may be provided from UC through a converter Cou. The register becomes connected to the calling line over a train of switches including PS and then returns a step-on signal over wire sl to the scanning circuit, but scanning is not resumed until the gate CG is reclosed by the full operation of relay KA/KB to earth on wire PL. Assuming that the call is set up in the normal manner, when release occurs the earth on wire PL is replaced by negative potential and KA/KB is fully released. If, however, the calling subscriber fails to dial, after a time the seized apparatus is released and earth is removed from wire PL but is not replaced by negative potential. In consequence relay KA/ KB releases only partially since a fresh circuit is made over ka1, kb1, and negative potential is presented to the gate PG. If the line loop is no longer closed, a scanning pulse applied to GX<SP>1</SP> produces an output from GY<SP>1</SP> which opens gates G7, G8 and operations ensue similar to those in the case of a calling condition, except that a signal is sent to the register over wire pgl instead of cgl. As a result, negative potential is applied to wire PL to restore the line circuit to service. On the other hand if the line loop is closed at this time so that both gates CG, PG are open there is no output to gate G8 from G6, G7, the scanning circuit does not operate as for a detected line and the line circuit remains out of service. The form of the pulse distributing circuit CC is more fully described with reference to Fig. 3 (not shown). The exchange may comprise a number of switching ranks, each consisting of cross-point arrays preferably using reed relays. The connections between 3 such switching ranks are illustrated in Fig. 5 (not shown). Specifications 483,525 and 916,633 are referred to.