Patent GB-191001050-A (GB)
Title: Improvements in Telephone Switchboards.
IPC: H04M5/04
Filed: 1910-01-15
Granted: 1911-01-12
Abstract: 1050. Aitken, W., and British Insulated and Helsby Cables. Jan. 15. Exchange systems.-Private branch exchange systems are arranged so that microphone current for local connexions is supplied by a local battery, but for exchange connexions is supplied by the battery at the main exchange. Connexions with the exchange, and in some cases the inter-connexion of the extension lines, are effected by manually-operated multiple-contact switches, which are retained in their operated position by a magnet in the microphone circuit, so that the c o n - nexion is automatically released when the receiver of the extension line is replaced. Fig. 1 shows a common -battery system, with an electro - magnetic multiple-contact - switch CS in connexion with the exchange line A, B, and with the usual cord-circuits for interconnecting the extension lines A<1> B<1>, A<2> B<2>, A<3> B<3>, A<4> B<4>. The exchange line is bridged by a condenser j and calling-indicator m, which is returned to normal by the depression of the operator's listening-key k. The lines A, B are connected respectively to the outer contacts a, b of the switch CS, the moving contacts c, d, of which are connected to the extension leads, and also in the normal position of the switch to the local jacks V ... V<3> and indicators t<2> ... t<5>. The extension station 4, for example, is connected to the main exchange by depressing the switch CS in position 4, whereupon current from the exchange flows over the line B magnet g (shunted by a condenser or non-inductive resistance h), contact a in position 4, spring c, extension line A<4>, B<4>, spring d, contact b, and line A back to the exchange. The magnet g retains the switch CS in its operated position, until its circuit is broken when the receiver is replaced at the end of a conversation. The operator's speaking-set j, r, p, q receives current from the main exchange or from the local battery w<1>. A similar system is described in which magneto calling is used. In another system, electro magnetic multiple-contact switches are used also for interconnecting the extension stations, the switch associated with extension line 1 being used to connect that line with the lines 2, 3, and 4, the switch for line 2 being used to connect that line with lines 3 and 4, and the switch for line 3 to connect lines 3 and 4 only. The operator's listening-key is of a similar type, so that she can connect herself to all the extension lines. Connexions with the main exchange are made as shown in Fig. 1. In a modified system having two exchange lines, each such line has a switch of the above-described type, to which the extension lines are connected in parallel. Similar switches are also associated with each extension line, and are provided with transfer circuits so that, by depressing. the keys associated with both the calling and the called lines, the two lines may be connected together by a transfer circuit. When an extension line is connected to the main exchange, the exchange switch and the line switch must both be operated, the latter serving to cut out the local indicator. The Provisional Specification refers to arrangements for connecting the exchange line to a greater number of extension lines than can be assembled on one switch. In one arrangement, a switch is provided for each group of subscribers, and a connexion is established by depressing the plungers of both switches. In another arrangement, the exchange leads are connected to a master key, which can be moved in several directions, each direction connecting with a separate multiple. contact switch. Specifications 15,819/08 and 2057/10 are referred to.