Patent GB-351096-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04M3/40
Filed: 1930-03-25
Abstract: 351,096. Automatic exchange systems. SIEMENS & HALSKE AKT.- GES., Wernerwerk, Siemensstadt, Berlin. March 25, 1930, No. 9564. Convention date, March 25, 1929. [Class 40 (iv).] In an inter-exchange system employing alternating current for impulsing and supervision, the junction FL is coupled at each end to the automatic apparatus and to the A.C. receiving apparatus RE2 through a hybrid transformer Ue4 with a balancing network KL2, so that the receiving apparatus is unaffected by tone currents sent back from the automatic apparatus. The apparatus RE2 comprises a receiving path through a filter F2 tuned to the signalling frequency controlling a relay G2 and a blocking path through a filter F1 which blocks the signalling frequency controlling a relay M2, so that the relay A2 can operate only when the pure signalling frequency is received. Establishment of a connection. To initiate a call, the operator throws the key BS, energizing relays Z, R, U1, 1 in turn, while relay N1 operates momentarily and connects up the generator WO1 to send a preliminary impulse of A.C. over the junction to the receiver RE2 to operate relay G2. Relays A2, 12, H2, V2 respond, and relays C2, T2 energize and lock, while at the end of the impulse when relay H2 falls back, relay E2 energizes. The circuits leading to the selector GW are now in a condition to receive impulses, which are sent under control of the operator's dial, represented by contact nu, from the generator WO1 through the medium of relay N1 to relays G2, A2, 12, H2, V2, and repeated over the a wire at contact 36h2, the b wire being closed throughout each train at contact 84v2. In the case of a busy condition, busy tone current passes through transformer Ue4 to the junction without affecting the receiver RE2. To call the wanted subscriber, the operator presses the ringing key RS, causing a steady flow of A.C. over the junction from the generator WO1, which energizes relays 12, H2, V2, short-circuiting and releasing relay T2. Earth is now connected to the a wire, while the b wire is disconnected, to effect ringing at the connector. Relay X2 energizes, and when the ringing key RS is restored, relay S2 is bridged across the a and b wires and energizes at each pause of ringing current until the subscriber replies, connecting an interrupter RU3 to relay N2, which at each energization connects the generator WO2 to the junction to energize relay A1 (not shown) through the valve receiver RE1, so that supervisory relay S energizes, lights lamp SL and connects up relay X to open the operator's talking circuit. Relay S2 connects up relay Y2 which locks, cuts out transformer Ue4 and extends the talking circuit, which is completed upon the reply of the subscriber by the relapse of sluggish relay B2 also controlled by relay S2. Release. When the called subscriber hangs up, relay S2 re-energizes and causes lamp SL to light as described above. To release the connection, the operator restores the key BS, disconnecting relay Z and sending a preliminary impulse to magnet D, which then interacts with relay K to step the switch aw. Relay G energizes and connects an interrupter RU to relay N1, causing a series of more than 11 impulses to be sent over the junction until the switch aw returns to normal. The impulses are received by the receiver RE2 and are repeated by relay H2 to magnet D2 to step the switch aw2, bw2, which in position 11 closes a circuit for relay P2, which cuts the drive and disconnects relays T2, E2, C2 to effect release of the automatic switches. When impulses cease, relay V2 falls back and disconnects relay P2, and the switch aw2, bw2 moves to normal under control of an interrupter RU2.