Patent GB-221474-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1924-05-01
Abstract: 221,474. Automatic Telephone Manufacturing Co., Ltd., (Assignees of Ray, A. J.). Sept. i7, 1923, [Convention date]. Automatic and semi-automatic exchange systems; phantom-circuit systems.-Pairs of two-way inter-exchange trunk circuits between a manual exchange and an automatic exchange are phantomed to provide additional one-way trunk circuits from the automatic exchange to the manual exchange. The phantom and physical trunks are arranged in the banks of the automatic switches having access to them, in such an order that when making a call from the automatic to the manual exchange, an idle physical trunk is only seized if all the phantom trunks are busy. Call from automatic exchange to manual exchange over a one-way phantom trunk circuit. A group selector E, Fig. 1, is raised in known manner to the level in which the manual exchange trunks terminate, and is then stepped round to an idle trunk. Assuming that the first phantom trunk 73<1>, 74 is idle, on the response of the switching relay 10, a line relay 61 and slow release relay 62 in the repeater R', Fig. 2, are energized. A slow-release relay 60, which is energized for a short time over the holding wire 20, closes a circuit for a slow-release relay 71, which for a short interval bridges a ringing current generator across the conductors 73<1>, 74. This ringing current is induced in the right-hand windings of the repeating coil RC', Fig. 3, and passing over the phantomed trunks X, Y, is induced across the repeating coil RC<4> to operate a supervisory drop signal 86 at the manual operator's position. A portion of the ringing current also passes over the conductors 89, 90 and 89<1>, 90<1>, to impedance coils 42, 42<1> and line relays 40, 40<1>, but the windings of the coils 42, 42<1> act cumulatively to impede this current, whilst the windings of the line relays 40, 40<1> oppose one another in this circuit and prevent the operation of these relays. The operator inserts the plug of a cord circuit into the jack J, and completes the connection in well-known manner. When the calling subscriber hangs up, the relays 61, 62 relapse and the relay 71 is momentarily energized to project ringing current over the phantom trunk and give the operator a disconnect signal. The automatic switching apparatus restores in known manner. Call from automatic exchange to manual exchange over a two-way physical trunk circuit. If the trunk X is the first idle trunk, the three phantom trunks associated with the first three contact sets in the selected level of the switch E being busy, when the wipers engage the fourth contact set and the switching relay 10 pulls up, the line and release relays 56, 31 of the repeater R associated with the trunk X energize, and a circuit is closed for a reversing relay 50. Prior to the response of relay 31, the slow-release relays 43, 45 are momentarily energized, and ringing current is induced over the repeating coils RC, RC<3>, Fig. 3, to actuate a supervisory drop signal 77. The operator inserts an answering plug into the jack J<1>, thereby closing at springs 76 a circuit which includes the line relay 40, Fig. 2, impedance coil 42', and a polarized relay 78, Fig. 3. Owing to the energization of the reversing relay 50, the polarized relay 78 does not respond, but the line relay 40 is operated, completes the talking circuit at armature 74, and energizes a slow release relay 37. The operator then completes the wanted connection. When the calling party hangs up, the relays 56, 31, 50 de-energize, the relay 50 reversing the current over the trunk X back to normal and causing the response of the polarized relay 78, which lights a disconnect lamp L. The automatic switching apparatus restores in known manner, and when the operator withdraws her answering plug from the jack J<1>, the relays 40, 37, 78 are de-energized and the lamp L is extinguished. Call from manual exchange to automatic exchange over a two-way physical trunk circuit. The operator inserts the plug of her cord circuit into the jack J<1> of an idle trunk, thereby completing a circuit for the line relay 40 and the polarized relay 78. The line relay 40 energizes relay 37, which marks the trunk X busy by grounding the test wire 7, completes a circuit for the upper winding of a polarized relay 34, and closes a bridge 48, 93, 87, 36, 33, 88, 94 across the outgoing conductors 93, 94 including the lower winding of the relav 34. The windings of the relay 34 oppose one another and the relay remains inert. The closure of the bridge causes a line switch C, Fig. 1, to operate in known manner and select an idle trunk to a first selector at the automatic exchange. The operator now throws a key K to connect her sender S across the trunk X, and dials the wanted number. thereby causing interruptions in the circuit of the line relay 40, which at armature 74 opens the bridge across the outgoing conductors to actuate the automatic switching apparatus. The windings of the impedance coil 42 are differentially connected as regards the dialled impulses, which are thereby not unduly impeded. Having dialled the wanted number, the operator restores the key K, again connecting the polarized relay 78 across the trunk. The relay 78 responds and lights the lamp L. When the called subscriber replies, the back-bridge relay of the connector reverses the current over the conductors 3, 4, the polarized relay 34 pulls up, and energizes the reversing relay 50, which reverses the current over the trunk X, causing the relay 78 to relapse and extinguish the lamp L. On the calling subscriber hanging up, relays 34, 50 relapse, and the polarized relay 78 again operates and lights the lamp L. The operator then withdraws the plug from the jack J<1> and all the apparatus is restored to common use.