Patent GB-332999-A (GB)
Title: Improvements relating to telephone systems
IPC: H04Q3/00
Filed: 1929-06-04
Abstract: 332,999. Siemens Bros. &. Co., Ltd., and Christian, D. A. June 4, 1929. Automatic exchange systems.-Relates to systems in which several subexchanges are connected to a terminal exchange over omnibus junction circuits. The omnibus circuits may be continuations of physical or phantom circuits from the main exchange and selection of the particular exchange required is effected by the transmission of current reversal impulses over the circuit. At each sub-exchange a unidirectional switch or a relay chain responds to the impulses and selecting apparatus (or a manual board calling signal) is connected up at the exchange required, the circuit being marked busy at all other exchanges on the route. Calling the main exchange is effected by the application of ringing current to the circuit and the system is such that the ringing current does not operate the selecting devices but marks the circuit as busy 'at non- calling stations. Wayside stations may be bridged across the omnibus junctions and a telegraph circuit may be super-imposed as an earthed " ghost " on the phantom circuit. A ring-off signal is given automatically at the termination of the call. Calls between stations at the same junction are set up by the eperatar at the terminal exchange. Specification 328,752 is referred to. Call from terminal to automatic sub-exchange. In the embodiment shown two physical circuits and a phantom extend from the terminal exchange A to a repeater station B, whence three physical circuits extend respectively to two automatic and a manual exchange represented by D1, D2, E1, E2,F1, F2 and C1, C2, C3. To call exchange, say E2, the operator plugs into the jack J3 corresponding to the required junction operating the circuit relay L. Slow relay V pulls up connecting the local battery to the phantom circuit. Polarized relay LP connected to the phantom at station B operates and relay LL pulls up. Relay W which is normally energized is shorted by ll3, and after a slow release pause the relay falls back and VB energizes, locking over vb4 and connecting battery over the circuit to exchanges E1, E2 and C2. The polarized relays LP at each of these exchanges operate, energizing the relays LL (Figs. 2 and 3), and after the normally energized relays W have released V pulls up breaking at v6, the final selector testing circuit at the automatic units (Fig. 2) and energizing busy indicator BI at the magneto unit (Fig. 3).. The plug DP is then inserted in jack DJ3 and the code number of the exchange required is dialled. Relay L falls back at each impulse and make-before-break contacts l1, 12 reverse the current flow over the loop. Polarized relay LP at station B repeats the digits to the omnibus junction and the relays LP at the sub-exchanges respond stepping, at the automatic exchanges, switches SW3. Slow release relay C, which was energized when V pulled up over the home position of SW2, is held during the impulse train over its winding C(II). To call the exchange shown in Fig. 2 the digit 3 is dialled and at the end of the train SW2 is standing on the third bank contact and when C releases D operates extending a loop over a and b to the exchange switches to which further dialled impulses are repeated. At all other exchanges on the junction contact 3 is not connected and as C does not re-operate, further digits have no effect on the apparatus. One arm of the repeating coil is cut out during impulsing, but when the called subscriber replies JS operates re-inserting the coil. Relay JS also energizes Z. When the called party clears JS releases and S operates. During the slow release periods of S and Z ringing current is connected to the junction giving a clearing signal to the operator. When the plug JP is withdrawn relays LP relapse and the circuit is freed for further use. Call to manual sub-exchange., At manual subexchanges (Fig. 3) the first digit train is repeated by relay LL to a relay chain A - - E. The code digit for the exchange shown is 7 and the terminal 7 is connected to 7a, terminals 1-6 and 8-9 are connected to la and texminal 10 to 10a. If 7 impulses only are received relays A, B, D, E are operated and when relay F,. which is held energized during the train, releases, call indicator CI is operated. If any other of the digits 1-9 had been received SS would have operated when F fell back breaking the impulsing circuit. At the end of the conversation a clearing signal is sent back manually over the junction and the withdrawal of the plug at exchange A releases the circuit. Call to wayside station S. To call the station S bridged across the phantom circuit the junction is seized as before and plug RP is inserted in jack DJ3. A large number of impulses are transmitted over the circuit and relay LP at the wayside station responds and single stroke bell B is rung. At the automatic sub-exchanges the switches SW are stepped by the train and, when 10 impulses have been received, relays P operate breaking the impulsing circuits. At manual subexchanges when 10 impulses have been recorded relays SS operate to disconnect the relay chains. Call to terminal exchange. To call the terminal exchange ringing current is connected to the junction. At manual units and wayside stations this is effected manually, at automatic units relay F is energized over the final selector test circuit operating relay S to connect ringing to the junction. The ringing current periodicity is arranged so that relay W at the non-calling exchanges is not released. At the terminal exchange indicator I is operated to indicate a call and relay L is energized over i1 Current is connected to the circuit and relays LP energize to mark' the circuit as busy at the other sub-exchanges. The busy marking remains until the operation at A clears the circuit.