Patent GB-363309-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1930-09-10
Abstract: 363,309. Automatic exchange systems. POLLAK, J. E., 20, Holborn, London.- (Siemens & Halske Akt.-Ges.; Siemensstadt, Berlin.) Sept. 10, 1930, No. 27085. [Class 40 (iv).] In a system employing two-conductor junction circuits, release is initiated by a signal from the outgoing end, the junction being marked busy until a signal is received from the incoming end indicating that the apparatus there has been released. The signals may consist of pulses of either alternating current or direct current, in the latter case the initial junction operation is effected by increased current flow over one lead whilst release is controlled by increased flow over the other. In addition, for a predetermined time after release, a guarding device is operative to prevent false reseizure of the incoming selector by cable discharges. When the selector 1GW (Fig. 1) seizes the circuit shown, C1 operates over winding (1), contact 1r being closed. Winding ( 111 ) of normally energized relay R is shorted and the additional current flow over the b wire is sufficient to energize C2 (to battery on wire c). Relay C2 looks, switches the circuit through, and releases R which completes the through talking connection. When the calling subscriber hangs up C1 in Ue releases connecting ringing over W1 to energize B at the distant exchange. Relay A pulls up to battery over R (1) and locks over W2, shorting C2 which relay releases. Relay C2 effects the release of the succeeding switches. So long as the succeeding selector is off-normal, battery on wire c shorts B and this relay falls away, bringing down A. When the next switch is fully restored, low resistance battery on c enables B to re-energize and, as C2 and A are both down, an increased current flows over the a junction wire to energize winding (I) of R. Relay R cuts off the ringing current from the b wire, locks over windings II and III in series and at 1r recompletes the testing circuit for the selector 1GW. The system shown in Figs. 2 and 3 uses alternating current for all signals. When the system is normal relays N1 (Fig. 2) and N2 (Fig. 3) are energized hence 4n1 is closed and 5n2 is open. When the junction VL is seized over 6w1, C2 energizes, C3 pulls up and A1 energizes. C3 also closes a circuit to energize V1 and W1 pulls up. W1 breaks the circuit of A1 but during its energized period the generator WQ1 sends alternating current to energize F2 and H2 pulls up. Relays C4 and E operate and lock, and N2 releases. The impulse trains are repeated over the junction by A1 as alternating current pulses and F2 responds repeating the impulses via H2 to the magnets of the succeeding selectors. When the calling subscriber hangs up C2, C3, V1 and W1 fall back, the release of C3 breaking the circuit of N1 to open the testing circuit to C2 and energizing A1 to connect the alternating current generator WQ1 to the junction, the pulse terminating when Wl, which is shorted on the release of V1, falls back. Relay F2, at the incoming end, energizes, H2 operates, and C4 releases. When the pulse ceases H2 de-energizes, E falls back and S operates. Relay S connects the generator WQ2 to the junction to operate F1. S remains energized until the incoming selector regains its normal position, when off-normal contact 3k closes allowing N2 to operate and S releases. At the outgoing end relay F1 completes a circuit for R which opens another point in the circuit of N1, retaining the busy marking at 4n1. During the period between the release of A1 and the operation of F1, the circuit of N1 is held open by slow relay X. When the incoming selector is fully restored the pulse terminates, Fl releases and N1 re-operates, removing the busy marking. When S at the incoming station operated, Z pulled up breaking the circuit of H2. It may happen that after the guarding current is removed from the line, cable discharges energize F2 but, instead of H2 re-operating to re-engage the selector, Z is held up until the discharges cease. Z also guards the selector if A1 should be energized by the release of A before C1.