Patent GB-187208-A (GB)
Title: Improvements in or relating to telephone systems
IPC: B60Q1/26
Filed: 1922-08-24
Abstract: 187,208. Automatic Telephone Manufacturing Co., Ltd., (Assignees of Richardson, R. G.). Oct. 11, 1921, [Convention date]. Automatic exchange systems. - Where five groups of ten trunks terminate in non-numerical switches, for connecting any trunk to an idle trunk of an outgoing group of thirty trunks, the non-numerical switches are divided into ten groups of five, the different trunks of an incoming group being led to switches in different groups. Each group of five switches gives access to only three outgoing trunks so that the switches may be of very simple construction, each switch consisting, for example, merely of a group of three relavs. The numbers stated above are of course only by way of example. In the system described the groups of incoming trunks are from the tenth levels of different groups of group selectors, and the thirty trunks to which they are given access lead to another exchange. From an inspection of Figs. 1 and 2 it will be observed that the first trunk from the first group of selectors leads to the first non-numerical switch in the first sub-group, the second trunk to the first switch in the second sub-group, and so on, whereas the first trunk from the second group of selectors leads to the second switch in the third sub-group, the second trunk to the second switch in the fourth sub-group, and so on. This slip is carried out all down the line in order that the traffic shall be evenly divided among the sub-groups. The system is described in greater detail with reference to Figs. 3 and 4 wherein is shown a non-numerical relay switch E<3>, Fig. 3, having access to three exchange trunks X, X<1>, X<2>, Fig. 4, over repeaters F, F<1>, F<2>. When all the trunks X, X<1>, X<2> are engaged all the non-numerical switches E<3> having access to them are marked non-selectable by the permanent earthing of a common lead 90, Fig. 3, by a relay group RG, Fig. 4, associated with the outgoing trunk subgroup and controlled by circuits over the contacts or additional relays 105, 105<1>, 105<2> in the repeaters F, F<1>, F<2>. A modified form of nunnumerical relay switch in which the trunks are preselected is described with reference to Fig. 5. Operation of non numerical switch E<3>, Fig. 3. Assuming that a trunk in the sub-group served by the switch E' is idle and that a group selector (not shown) engages the trunk 38, 40 terminating in this switch, the response of the line relay 50 earths the holding wire 39 and also a common wire 90 which marks busy all the non-numerical switches in the sub-group to which the switch E<3> belongs thereby preventing simultaneous calls in the same sub-groups. A series circuit is also completed for a switching relay 51 and the lower winding of a connecting relay 54 associated with the first trunk 76, 78, and a point between these relays is earthed over armatures 55, 59, 63, 67, 72. The switching relay 51 is thus short-circuited but the relay 54 locks up over its upper winding and connects the test wire 77 of the first trunk to the relay 51. If this trunk is busy the relay 51 remains short-circuited and the connecting relay associated with the second trunk 79, 81 is energized over the armature 74 and its lower winding, locks up, and connects the test wire 80 to the switching relay 51. If this trunk also is engaged the last trunk 82, 84 is tested in a similar manner. In the present case it is assumed that the first trunk 76, 78 is idle so that when the test wire 77 is connected to the switching relay 51 the latter is energized. The test wires 77, 39 are thereby connected together over armatures 59, 60, earth is removed from the common conductor 90, and the trunk conductors 38, 40 are extended to the repeater F, Fig. 4, over the trunks 76, 78. Repeater F and operation of relay group RG. The repeaters F, F<1>, F<2>, are of standard design and operate in known manner to re-transmit dialling impulses over the two-wire trunks X, X<1>, X<2>. They are, however, provided with additional slow-release relays 105, 105<1>, 105<2> which are energized as long as the associated repeaters are in use, and control the circuits of the relays in the group RG. On the energization of the relay 105 when the trunk X is the only one in use, a circuit is completed over armature 122 for the relay 131 which is immediately interrupted by the response of a marginal relay 133 in a circuit including the resistances 123<1>, 123<2> in parallel. Assuming that a seccnd trunk X<1> in the same sub-group is taken into use, the circuit of the marginal relay 133 by the energization of the re'ay 105<1> is made to include only the resistance 123<2>, with the result that the armature 138 relapses and completes a circuit for the relay 131. If now a third non-numerical relay switch in the same sub-group is taken into use, the relay 130, Fig. 4, energized on the grounding of the common conductor 90 by the line relay, is locked up over armatures 134, 135, and holds the common conductor 90 earthed and does not relapse on the response of the switching relay of the non-numerical relay switch, in order that should another call come in all the relay switches in the subgroup will test busy. The energization of the relay 105<2> in the repeater F<2> associated with the last trunk X<2>, completes a circuit at armature 121<2> for the relay 132 which de-energizes relay 131 and replaces the earth on conductor 90 at armature 135, by earth on its own armature 136. Upon a trunk falling idle the relapse of relay 132 energizes relay 131 and breaks the circuit of relay 130, the armature 134 falling away from its contact slightly before the armature 135 makes contact in order to prevent the relay 130 from again locking up over the armature 135. Release. De-energization of the line relay 102 when the calling party hangs up, restores the repeater F and the distant exchange apparatus in known manner. Disconnection of earth from the release conductor 77 causes the relapse of the relays 51, 54 of the switch E<3>, which is thereby restored to normal, and de-energizes the switching relays of preceding switches which release as in standard practice. Operation of modified non-numerical switches H, H<1>, H<4>, Fig. 5. Each switch comprises three relays 210, 211, 212 for.connecting an incoming trunk 201, 203 to any one of the three out-going trunks 275, 277 &c. The initial circuit of each relay extends through a chain circuit over contacts of the other relays of the same switch and contacts of the relays in other switches associated with the same outgoing trunk. Assuming that the switch H is taken into use by a group selector and that all the switches and all the outgoing trunks are idle, on the trunk 201, 203 being seized, earthing of the test lead 202 connects earth to a common conductor 292 over the armatures 216, 223, 225, thereby (1) earthing the test leads of the other switches in the same subgroup over corresponding armatures to prevent simultaneous calls, and (2) completing a chain circuit over armatures 218, 224, 226, conductor 294, and armatures 221, 232, 252, for the connecting relay 210, similar chain circuits extending from the test conductors of other idle switches through the relays therein associated with the same trunk. Relay 210 in pulling up, breaks the circuit of the other relays, locks up over armature 219, extends earth at armature 217 to conductor 290, transfers earth from conductor 292 to the test wire 276 of the seized outgoing trunk at armature 216, and extends the calling line to the trunk 275, 277 over armatures 215, 222. The battery indicated in the left-hand corner of Fig. 5 is also disconnected at armature 221 from the windings of the relays 210, 244 &c. associated with the first trunk, and connected to conductor 286, in order that when another call comes in the relays 211, 245 &c. associated with the second trunk 273, 280 will pull up. The relay used for extending this second call transfers earth from the conductor 290 to the conductor 291 and battery from the lead 286 to the lead 288. If a third call now comes' in the relays 212, 246 &c. associated with the last trunk 281, 283 pull up, the relay of the switch seized transferring earth from the conductor 291 to the common conductor 292, thereby earthing the test wires of all the switches in the sub-group and preventing further calls from coming in. Since battery is connected to the armature 252 the first trunk is always given preference over the second and the second preference over the third, but the work may be distributed more equally over the trunks by associating working contacts with the armatures 277, 243 &c. of the relays of last trunk, joining these contacts by a conductor connected to the armature 252 and providing either a manual switch operated by an attendant for transferring battery potential from one to another of the armatures 252, 255 &c. as desired, or a master switch for transferring the potential from one armature to the next upon the extension of each call.