Patent GB-169285-A (GB)
Abstract: 169,285. Automatic Telephone Manufacturing Co., Ltd., Savin, J., and Mercer, R., (Automatic Electric Co.). June 23, 1920. Automatic a n d semi-automatic exchange systems and apparatus.-A switching device is energized to attract the attention of an operator when a non- privileged subscriber makes connection with certain lines. In the system described, privileged automatic subscribers can obtain direct connection to a main exchange over trunk lines, but on a non-privileged subscriber making such a call the operator at the branch exchange is signalled and further extension of the connection prevented until allowed to proceed by the operator. The line switches C, Fig. 2, of non-privileged subscribers are provided with a fourth wiper '67, which, on the line being extended to an idle group-selector D, is earthed over armatures 65, 66, and causes the energization of a discriminating relay 77, which transfers the test circuit from the test wiper 74 to a fourth wiper 75 of the selector D. On an idle trunk being engaged, a relay 60, Fig. 3, is energized to actuate a signal 65 at the branch operator's position and hold up the call. In an alternative arrangement, the line switch C and selector D are of standard construction, but privileged and non-privileged subscribers dial to different levels when calling the main exchange. The bank contacts of the trunk lines of both levels are multipled together, but the private bank contact of the level of privileged subscribers is connected as contact 48, Fig. 3, whilst the private bank contact of the level of non-privileged subscribers is connected as contact 37. Connection of non-privileged subscriber to main exchange. The line switch C extends the call in the usual manner, and on coming to rest on an idle trunk leading to a group selector D the switching and line relays 70 and 68 are momentarily energized simultaneously, and a circuit completed for the discriminating relay 77 over the armatures 65, 66. The relay 77 locks up over armature 78 and at its armature 79 transfers the test circuit to an additional wiper 75. Impulses dialled by the subscriber operate the vertical magnet 32 in known manner to step the wipers up to the level in which terminate the trunks leading to the main exchange, and the rotary magnet 33 operates to rotate the wipers until an idle trunk is engaged. If a line is busy earth is found on contact 48 over the armatures 63, 47. On an idle trunk being found, the lowresistance relay 60 responds to cause the illumination of a lamp 65 at the branch exchange and break the circuit cf the switching relay 49, before the relay 45 responds subsequent to the energization of line relay 38 and release relay 40. The branch operator then inserts the answering plug P<1> of her cord circuit O in the jack J<2> to ascertain the subscriber's requirements, and short-circuits the relay 60 by depressing a key K. The relay 49 is thereby energized and extends the call to the main exchange over contacts 50, 51 through the repeater windings 52, 54. A circuit is completed for the relay 15 which lights a lamp 19 at the main exchange. On the calling subscriber hanging up, de-energization of the line relay 38 is followed by the relapse of relays 40 and 45. Earth is removed from test contact 48 to permit the release of the switches C and D, but the trunk is immediately made busy again over contacts 55, 46, 43 by the response of the polarized relay 53, the short circuit about which is removed at the armature 41. Relay 53 completes a locking circuit for the switching relay 49. On breaking the short-circuit across the relay 53, the current through the relay 56 is sufficiently reduced to cause it to relapse and give the operator a disconnect signal. All circuits are then restored to normal by the removal of the plug from the jack J<1>. Connection of a privileged subscriber to the main exchange. Armatures 65, 66 and wiper 67 are omitted from the line switches of privileged subscribers or alternatively earth is disconnected from the armature 65. The call is extended in the usual manner by a line switch C and group selector D, but the test circuit remains connected to the wiper 74 so that on the selector finding an idle trunk the relay 60 is not energized, and the call is extended direct by the switching relay 49 without the intervention of the branch exchange operator. Calls to main exchange operator by branch operator. The .insertion of the calling plug P into the jack J actuates a signal 4 at the branch exchange, puts a busy potential on the sleeve of jack J<2>, and the test contacts 37, 48 in the banks of the group selectors D, and energizes the relays 9, 15, and 23. The polarized relay 9 lights a lamp 16 in the branch operator's cord circuit, relay 15 causes the response of the lamp 19 at the main exchange, whilst the relay 23 disconnects the relays 22 and 24 from the trunk circuit. The insertion of the main operator's plug in the jack J<1> retires the signal at 19 and reverses the current in the relay 9, thus extinguishing the lamp 16. The branch operator gives the required number and the connection is extended in the usual manner. Removal of the main operator's plug from the jack J<1> again reverses the current in the relay 9 and gives a disconnect signal. Calls to branch operator by main exchange operator. The insertion of the calling plug into the jack J<1> and the projection of ringing current over the line energizes the bridged relay 24, which lights the call lamp 26 at the branch operator's position, who inserts her answering plug P<1> in the jack J, thereby engaging a polarized relay 27 which operates a supervisory lamp in a similar manner to the lamp 16. By means of a two-way key K a calling device 28 may be connected to either the calling or answering side of the cord circuit O.