Patent GB-164147-A (GB)
Abstract: 164,147. Automatic Telephone Manufacturing Co., Ltd., Carter, W. R., and Mercer, R. March 6, 1920. Automatic exchange systems.-For the provision of "conference" facilities, the leads of privileged subscribers, before passing to the automatic switching apparatus, pass through a switching device, which, on a certain number allotted to conference calls being dialled, operates to disconnect the automatic switching apparatus and connect the subscriber's leads to an auxiliary line in which the usual busy arrangements are eliminated. The Figure shows the application of the invention to a private automatic exchange in which, between the leads 11, 12 of a privileged subscriber A and the line switch C, is inserted a polarized switching relay 13 for establishing connection to the conference line 14. On removing the receiver at substation A to make a conference call, the line relay 15 of the line switch C is energized over the resting contacts of armatures 18, 19 and the upper winding of the relay 13, which, however, only operates when both its windings are excited to assist one another. On the response of the line relay 15, the lower winding of the switching relay 13 is energized to oppose its upper winding, and the switch C operates in the usual manner to extend the line to an idle first selector E. A certain leyel, say the tenth, of the first selector is allocated for conference calling, and upon the subscriber dialling the appropriate digit " o," the wipers of the selector E are stepped up in well known manner to the tenth level, and the rotary magnet 50 then operates to step them on to the first set of contacts. As a number of parties would be ringing up the conference number at about the same instant, the first private contact may be earthed, in which case the wipers are rotated in the usual manner until an unearthed contact is reached and the switching relay 33 energized. A circuit is thereby closed for a relay 54 multipled to the corresponding bank contacts of the other selectors, and the current through the upper winding of the switching relay 13 is reversed, causing the response of this relay, which locks up over the calling line, and extends the latter to the conference line 14 over the armatures 63, 61. The circuit of the relay 54 is broken at the armatures 18, 19, and the removal of earth from the test contact 60 results in the release of the line switch C and the selector E as in general practice, the private normal 26 being re-connected to earth over the armatures 62, 16. Speaking current is supplied to the subscriber A over the relay 13, and condensers 64, 65 are inserted to maintain the feeding current for different parties independent. Condenser 64 also provides a shunt path for speech currents across the upper winding of relay 13 when the line is used for ordinary calls. As the relay 54 is only energized momentarily, it is only necessary to provide such relays for the first two or three contacts of the selected level, but the Provisional Specification states that relays may be provided for all the contacts in the level, in order that ten simultaneous calls may be dealt with. The Provisional Specification also states that a high voltage battery may be arranged to effect the operation of the switching relay 13, or a rotary switch arranged to seek the line calling and effect its transfer to the conference line. According to another modification described in the Provisional Specification, upon any particular set of contacts being seized bv the selector E, a relay may be arranged to reverse the feeding current from the line relay of the switch associated with the seized contacts and thereby reverse the current in the calling line.