Patent GB-281725-A (GB)
Title: Improvements in circuit arrangement for automatic telephone exchanges
IPC: H04Q3/00
Filed: 1927-12-05
Abstract: 281,725. Merk, F. 'Dec. 4, 1926, [Convention date]. Semi-automatic exchange systems.-In systems in which the same final selectors are used for local and for toll calls, the whole of the operations following the selection of the wanted line take place automatically for both types of call, and are such that for a toll call, if the wanted line is idle ringing and through-connection take place, if the wanted line is busy with a local call throughconnection only. is effected, whilst if the wanted line is engaged in another toll call, neither ringing nor through-connection is effected. The operations in the case of a toll call are controlled by an extra test relay, which 'is connected in response to a special signal automatically transmitted from the toll-operator's position. The invention is described with reference to a system comprising a number of local exchanges in which internal calls are established over call finders LF and final selectors FS, Fig. 1, calls between two local exchanges are set up by an operator at a central " allotting " exchange, Fig. 3, over junctions L1, L2, whilst toll calls are established by a special toll operator, Fig. 2. The operator at the " allotting " exchange is called from a local exchange by setting the final selector to a particular position. The selectors used are constructionally of the type described in Specification 275,255, in which a first set of impulses sent to the magnet H effects the selection of a set of wipers which are then tripped by the magnet S. a second set of impulses through the magnet H effecting the selection of the wanted line. Release is effected by passing further impulses through the magnet H, which lifts the wipers to the top of the bank, from which they fall to normal under gravity. Call between two local exchanges. A call incoming over junction L2 for a subscriber in the exchange shown in Fig. 1 is answered by the operator; Fig. 3. who inserts the right-hand plug of her cord in the jack of junction L1 leading to the final selector FS<1>. Fig. 1, thereby operating relays A, B, A3, followed by R, VII. VIII. Impulses from dial contacts i are repeated by relay A to magnet H. At the end of the digit, relays VII, VIII fall back slowly, transmitting an intermediate impulse to tripping magnet S. The impulses of the second digit are also repeated by relay A to magnet H, relays VII, VIII energizing at the first break and releasing relay R. At the end of the digit relay PI is connected to the test wiper CII, and if the wanted line is idle, relay PI operates, holds VIII, and connects up ringing current. A " free signal " fs informs the calling subscriber that the line is free. When the called subscriber replies, relay Q operates, releasing VIII. PI, and switches through. Relay Y releases relav A and removes a short circuit from the right-hand winding of relay Q, which locks itself to the test wire. When the called party hangs up, the release of relay Y lights lamp SL, and when the, operator takes down the plugs, the selector is restored to normal by a circuit over interrupter U and magnet H. If the wanted line is busy, relay PI does not operate, and a busy tone bs is connected through the left-hand windings of relays A, B, to inform the operator. Toll call. A call coming in over a toll line L3 is answered by the toll operator, Fig. 2, who controls the final selector FS<1> in the same way as described above, with the exception that at the end of the last digit, a dial contact z de-energizes, relay B. If the wanted line is engaged, the relapse of relay VIII after PI has failed to respond connects up the second test relay PII. If the existing call is local, relay PII responds, locks itself in series with the left-hand winding of relay Q, which switches through, re-energizes relay B, and short-circuits the right-hand winding of Q, thus connecting positive battery directly to the test wiper to mark the line busy to all calls. The called party may flash lamp SL to recall the toll operator, or by moving her switch hook up and down, thus intermititently energizing relays A, A2. If the wanted line is engaged in a toll call, relay PII does not respond and busy tone is transmitted as before. If the wanted line is idle, relay PI operates and connects up ringing-current as for a local call. When the called subscriber replies, the operation of Q releases VIII, so that PII operates and causes direct battery to be connected to the test wiper as before. The Specification as open to inspection under Sect. 91 (3) (a) comprises also a similar system described with reference to drawings not supplied. This subject-matter does not appear in the Specification as accepted, but forms the subject-matter of divided Specification 307,389.