718,746. Automatic exchange systems. SIEMENS & HALSKE AKT.-GES. July 21, 1952, No. 18424/52. Class 40 (4). In an automatic telephone system employing relay selectors, a discriminator at a local exchange releases the local register in response to digits signifying a main exchange call, and connects a junction to the main exchange to the link circuit of the pre-selection stage associated with the calling party. Subsequent digits dialled are repeated over the junction to the main exchange. General operation, Fig. 1.-When the subscriber Tln calls, operation of a relay in his relay set TR causes the control circuit LO to associate a free first intermediate line l.ZL with the calling line by means of line coupler LK. A pre-coupler VK extends the connection to a free set of selection relays WR, and coupler ZEK associates a free register ZE with the selection relays. Local call.-After registration of the called number in register ZE, the common marker LEF marks the called line relay set TR, whereafter it is connected by a line coupler LK with a free fourth intermediate line 4.ZL which is connected via a final intermediate coupler EZK and a final selection pre-coupler EVK to the set of selection relays WR seized by the calling party. Coupler ZEK, marker LEF and register ZE are then released. Call to main exchange.-When the caller dials "O", registration of this digit in the register ZE causes a signal to be reverted to the set of selection relays WR, and thence to the control circuit LO which initiates connection with a main exchange junction via coupler VLK, a feed bridge being provided in the repeater Ve. VK, WR, ZEK, and ZE are released. Detailed operation, Figs. 3, 4, 5.-When the subscriber Tln12 calls, operation of line relay Lrl brings up relay P1 of the calling line and common relays R and An. The last relay operates the Qv relay of the first free intermediate line 1.ZL, e.g. Qv1 of line 1.ZL1, and common relay G. Assuming that the set of selection relays WR1 is free the control circuit test relay Plo pulls up over back ug2, and is followed by Cl (which allots the next free intermediate line 1.ZL), and by Q1 (which operates the coupling relay K1 to extend the calling line to intermediate line 1.ZL1) and blocking relay Ugl. The operation of Ugl releases Qvl followed by Plo and Q1, whereupon Ug1 itself relapses. Relays C1, K11, and C11 also operate and 1.ZL1 is extended to relay set WR1. The holding circuit extends from the calling subscriber's line circuit over the c wire to relay O1 in relay set WR1. Cut-off relay T1 pulls up in this circuit, releases P1 and connects it in the marking wire from the marker LEF (Fig. 4). Relays A1 and Drl pull up to the calling loop, followed by V1. Relay O1 also operates in the holding circuit, allots WR2 for the next call, and brings up T2. A free register, e.g. ZE1, is seized by operation of K21 and C21 which lock up in series with G2 and N, the last named relay remaining down. Call to main exchange.-Dialled impulses are repeated by Al to A2 in the register ZE1, V2 coming up for the duration of the train. If the digit "O" is dialled, it results in the operation of relay Do over contacts of the "O" tens register relay (not shown). Providing no other register is at that time controlling the setting of a selector, test relay Pzel comes up, and locks in series with Sp. Relay A2 is released and resistance 63 is short-circuited, whereupon relay N pulls up and locks up with U1. The resulting operation of UR1 initiates the switching to a junction to the main exchange (Fig. 5) by bringing up Wl (Fig. 3). Providing the junction Uel is free (R5 up), coupling relay Kvl pulls up, and K11 relapses due to reversal of current in the c wire. Relay C5 (Fig. 5) comes up in the operating circuit, and the connection holding circuit extends to 05 (Fig. 5). The local exchange equipment ahead of control circuit LO1 I is released, and the feed relays A5, B5 in the junction repeater (Fig. 5) pull up. Operation of F5 locks up R5 in series with S5, so that the junction is switched through. Subsequent dialled digits are repeated by A5 over the a wire of the junction, V5 opening this wire on the local exchange side of the repeating contacts during signalling. Release is under the control of the calling party. Local call.-The register ZE1 receives two digits (hundred line exchange) after which We1 (Fig. 4) is operated, bringing up Pzel. The subsequent operation of N and G2 connects up F1 which tests the called line and the connection is established.