718,838. Automatic exchange systems. SIEMENS & HALSKE AKT.-GES. July 30, 1952, No. 19320/52. Class 40 (4). In a relay system having a separate relay for initiating the connection of each subscriber to a free trunk, two operating circuits are provided for each such coupling initiation relay, one being used when the subscriber calls and the other when he is called, and a relay in the trunk allotter responds in one of these circuits only, thus indicating the outgoing or incoming nature of the connection to be effected. Local call from T11 to T12.-When the subscriber at T11 takes down his handset, his line relay LR1 responds and brings up An, Kal, and R in the allotter LO (Fig. 2). The operation of R indicates that the call is an outgoing one. Assuming the first intermediate line ZL1 to be free and to have access to a free relay set WR, its coupling relay Qv1 and common relay G pull up over front An and R and lock to An. The test relay Plo comes up in series with Dl, and C1 follows. Relay Plo short-circuits its winding I to busy relay sets WR1-WR6 temporarily. The operation of Cl extends the starting chain to the next free line ZL2-ZLn. With relay set WR1 free, coupling relays K11 and K21 are operated in the preselection couplers VZK (Fig. 2) and VNK (Fig. 3), relay Ug11 coming up in the same circuit. Relay Q1 of the line ZL1 pulls up and operates coupling relay K1 in series with Ugl (Fig. 2). The calling line is thus extended to the relay set WR1 and LR1, K1, Cl, K11, C11 and K21 are held over the third wire, O1 (Fig. 3) and cut-off relay TRI (Fig. 2) coming up in this circuit to busy the relay set WR1 and the calling line respectively. The latter is effected by the connection of Kal to the marking wire tll via high resistance 63. Relay Kal cannot then be operated by the potential normally applied to wire t11 by a final selector, but can be operated by the high potential connected thereto on an incoming trunk call. The relapse of Kal connects the meter Zr in the holding wire. Relays An, R, and Plo fall away and the allotter LO is released. Feed relays A1, B1 (Fig. 3) pull up and C21 comes up in the holding wire. Group selection.-The operation of C21 brings up G1, and a free group register GEW is associated. The first two digits are dialled and are repeated by Al to the digit relay registers in the register, dialling relay VI coming up for the duration of each train. An end-of selection relay Wel (not shown) then comes up to short-circuit resistance 76, whereupon Nl pulls up in series with G1 and locks to C21. Relay G1 is thus short-circuited and test relay F1 is connected up. Provided there is a free connecting line leading to the wanted thousands group, Fl comes up, removes the short-circuit from slow-to-release G1, and operates a coupler in the selector FKDO; which has been pre-selected over lead dg under control of the dialled digits. Assuming final selector relay set ER to be free, Pwrl and C31 operate over their windings I and lock over their windings II, bringing up O11 which busies the relay set ER. The operation of Pwrl also brings up Hrl and releases the register GEW. All group selector outlets busy.-The non-operation of F1 maintains the short-circuit of G1, which eventually releases followed by C21, whereupon K1, K11, K21, C1 and LR1 fall away. Slow-torelease cut-off relay TRI holds to the calling loop after LRI relapses, and engaged tone is reverted to the caller, who hangs up thus releasing TRI. Final selection.-The operation C31 on seizure of the relay set ER connects up Tl which responds to negative battery in a free final register EEW and associates it with the relay set ER. Relay G2 is thus energized in series with resistance 106. Further dialled digits are repeated by Al to A2 and thence to the register relays, dialling relay V2 operating in the usual manner. At the conclusion of dialling, end-of-selection relay We2 (not shown) short-circuits resistance 106, whereupon N2 pulls up and short-circuits G2. Relay N2 completes the text circuit over wire tl2. Called line free.-With the line and cut-off relays LR2 and TR2 back, Ka2 and An (Fig. 2) operate in series with the test relay F2 (Fig. 3). Since R is not operated (this being an incoming call to T12), the Qe relay of a free intermediate line ZL comes up instead of Qv, the lines ZL being allocated in the reverse order ZLn-ZL1. Assuming ZL2 to be the first free line, Qe2 is operated in series with common relay G, and positive battery is applied to wire 144 (Figs. 2-3) to initiate operation of the final selector coupler preselected over lead de. Relay C2 (Fig. 2) pulls up to busy ZL2, and the operation of Q2 brings up coupling relay K2<SP>2</SP> to connect the called line to ZL2. At the final selector the response of F2 prevents the release of G2 and short-circuits S. The final selector switches through to ZL2, test relay Per pulling up to complete the holding circuit over the third wire (157, 158) to hold K2<SP>2</SP>, C2 and Per, and bring up cut-off relay TR2 and line relay LR2. The called line is thus busied and its meter Zr2 connected up. Test relay F2 releases and S pulls up in the holding circuit to switch through the talking circuit, hold U and operate ringing relay V2. Relay S also connects Dr to the incoming side of set ER in place of A2 and B2. When the interrupter LU opens its contact, U is released and V2 is connected to ringing generator S". Release.-When the caller hangs up A1 and B1 fall away, whereupon C21 is short-circuited and opens the holding circuit. Relay Pwrl is released by short-circuit and C31 and Per follow. Cut-off relay TR2 remains held in the called loop and engaged tone' is reverted to the called party until he hangs up. Called line busy.-Relay Ka2 is connected to wire T12 via resistance 165 and, although An operates in the test circuit, F2 remains back. Relay G2 therefore falls away and brings up Br1 (Fig. 3) which releases C31 and Pwrl. Relay C21 relapses and opens the holding circuit, TR1 remaining held to the calling loop so that engaged tone is reverted. Incoming trunk call to subscriber T12.-The set of final selector relays ER is seized by the incoming selector over path FA. Relay C31 responds over wire 185 and locks over 186, a free register is associated and Tl operates as on a local call. The momentary application of negative battery to wire 188 brings up Y which remains held in the holding circuit to denote an incoming trunk call. Called line free.-Test relay F2 responds and the connection is completed as for a local call. Called line busy.-Relay An alone pulls up in the test circuit, but with Y (Fig. 3) up, the operation of U brings up X which applies a high positive voltage through F2 winding II, whereupon F2 and Ka2 are both energized. Assuming that the called subscriber is connected in a local call using ZL1, then T12 is already connected by coupling relay K2<SP>1</SP> to ZL1. Relay K2<SP>2</SP> now connects T12 to ZL2, and Per pulls up. Winding II of relay X (Fig. 3) is then in parallel with either (a) a winding Per II and relay S of a relay set such as ER (if T12 is the called party in the local call), or (b) a winding C21 (II) and relay Cl of a relay set such as WR1 (if T12 is the calling party). In both cases the current in X (II) is insufficient to release this differential relay. Engaged tone is reverted to the trunk operator over transformer Su (Fig. 3) and the windings of A2 and B2. Breaking in by trunk operator.-This is effected by applying negative battery to wire 208 (Fig. 3) thus operating B2 which extends her to the existing local connection. She requests the parties to hang up and if they do so the local connection is released, X relapses and S switches through the trunk call. Forced release of local connection.-If the parties do not hang up, the trunk operator applies positive battery to wire 188 and negative to 208 thus operating A2 and B2. The resulting operation of T1 applies positive battery to both speech wires. If T12 is the called party in the local call this brings up A2 in the local connection and shunts down B2, relay Per (II) thereof is shortcircuited so that X (II) of the trunk connection