Patent GB-165031-A (GB)
Abstract: 165,031. Automatic Telephone Manufacturing Co., Ltd., (Assignees of Wicks, J.). June 17, 1920, [Convention date]. Automatic and semi-automatic exchange systems.-Trunks terminating in connectors H<1> at a number of private branch exchanges are wired to the terminal banks of special second selectors F<1> at the main exchange. The selectors F<1> are different from the second selector F which handle the ordinary traffic; they are associated with special relay sets E<1> and are accessible through first selectors D<2> to a toll operator's position J as well as through first selectors D to main exchange subscribers A - - A<2>. The intermittent ringing current is supplied and controlled at the relay set E<1>, but in the case of a toll call the initiation of ringing is under control of the toll operator's ringing-key. If the wanted P.B.X. subscriber is busy, the calling subscriber or toll operator receives a tone signal and may leave the call in a waiting condition, ringing being initiated when the wanted line becomes idle. The release of the connection is transferred from the control of the toll operator to that of the called P.B.X. subscriber as soon as the latter answers the call. The incoming trunks at a private branch exchange pass through the position of a local operator, who can be called by raising a connector H<1> to its tenth level, and can then release the connector and operate it again to make the desired connection. By depressing a blocking-key at the local operator's position, all calls arriving on a trunk can be directed to the local operator, it being then impossible to complete a connection over the trunk without her intervention. A P.B.X. subscriber to whom connection has been made can signal and converse with the local operator to instruct her to transfer the call to a different department. Some departments at a P.B.X. may have several lines designated by the same number, the connectors H<1> being organized as rotary connectors to make connection with the first idle line of such a series. Outgoing calls from a P.B.X. are made over the same trunks as incoming calls, and can be set up either by the calling subscribers or by the local operator. The line switches of the P.B.X. subscribers give access to selector repeaters, which give access over one level to local connectors, over a second level to information trunks leading to the local operator's position, and over a third level to the main-exchange trunks. The local operator is given general supervision over all calls to or from the main exchange. Ordinary call from main exchange to P.B.X. In response to the first digit, which is such as to signify that a P.B.X. connection is desired, a first selector such as D, Fig. 6, seizes the relay set E' of an idle selector F<1> over terminals 2, 3, 4, Fig. 1, and extends the calling line over wires 70, 71, 72, 73, 62, 63 to the line relay 101, Fig. 2, of the selector F<1>. Relay 101 energizes relay 102, which grounds the wire 9 to mark the trunk busy to other selectors D. A branch of this circuit extends through a low-resistance relay 19 to the terminal 6, so that the trunk is also marked busy to toll first selectors D<2>. The grounding of the wire 9 also energizes relay 20 and the ringing cut-off relay 21. In response to the next digit, which determines to which P.B.X. the call is to be extended, the selector F<1> is raised and rotated in the usual manner to find an idle trunk 120, 122, whereupon the switching relay 100 becomes energized and extends the call to the line relay 205 of the P.B.X. connector H<1>, Fig. 4. Relay 205 is energized in series with the lower winding of an electropolarized relay 15, Fig. 1, which does not respond at this stage. Connector H<1>, Fig. 4. Relay 205 energizes relay 204 which grounds the test wire 164 and lights the busy lamp BL, Fig. 3. The next digit is repeated by relay 101, Fig. 2, to relay 205 and thence to the vertical magnet 214, in series with which the slow-release relay 207 is energized. Relay 207 closes a circuit 231, 229, 240, 289, 290 to energize the ringing cut-off relay 210, which locks up and energizes relay 203 in a circuit 161, 162, 249, 254. The next digit is repeated to the rotary magnet 215 in series with relay 212, which connects the test wiper 274 to the test relay 211. Busy test and signal. If the wanted line is busy the relay 211 is energized and, upon the relapse of relay 212, locks, itself to the test wiper and sends back a busy signal from the machine Q. The calling subscriber may either disconnect himself or may wait until the relay 211 is unlocked by the line becoming idle. Supply of ringing current. If the wanted lineis idle, or when it becomes idle, the switching relay 213 is energized by its lower winding and locks up through its upper winding in parallel with relay 209. Relay 209 reverses the connections of the incoming line with respect to the line relay 205 and wipers 273, 276. The electropolarized relay 15, Fig. 1, is energized by the reversal of current in its lower winding and locks itself by short circuiting the resistance 74 in the circuit of its upper winding, at the same time connecting the feed relay 16 across the line wires in place of its own winding. Relay 209 also de-energizes relay 203, which completes a circuit 164, 229, 248 to energize relay 206, which locks itself, disconnects the line relay 205, and connects relay 200 to the lower tine wire. Relay 200 is energized in series with relay 16, Fig. 1, sufficiently to close its contact 222 to keep relay 204 energized, but the circuit is of too high resistance for relay 16 to respond. Meanwhile the energization of relay 15, Fig. 1, has de-energized relays 20, 21 and caused the energization and locking up of relay 22. The de-energization of relay 21 connects the ringing generator GN to line to ring the wanted subscriber. A tell-tale back-leak is provided by a condenser connected across the contact 46. When the subscriber answers, the ring- ingcut-off relay 21 is energized and locks itself up. The called subscriber is supplied with current through the feed relay 16, which energizes relay 18, which reverses the current in the calling line and short-circuits the lower winding of relay 101, Fig. 2. A relay 202, Fig. 4, in the line circuit is also energized when the called subscriber answers and energizes relay 201, which disconnects relay 200, locks relay 204, and energizes relay 208. Supervisory signals. When the called subscriber disconnects himself, relays 202., 201 become de-energized and the lamp SL, Fig. 3, is lit before the P.B.X. operator in a circuit 160, 243, 223, 230. Relay 200 is again connected to the lower line wire and keeps the release relay 204 locked. Relays 16, 18, Fig. 1, are de-energized and the current in the calling line is reversed again to give a supervisory signal, if desired, at the main exchange. Release. When the calling subscriber disconnects himsell, the relapse of relay 101, Fig. 2, opens the line circuit to release the connector H<1> (the called subscriber being assumed also to have disconnected himself) and energizes a slow-release relay 106, which keeps the wire 9 grounded and the circuit of the release magnet 108 open for a short interval after the relapse of relay 102, so that the release of the selector F<1> is delayed until after that of the P.B.X. connector. Transferring call to third party; control of connector H<1> by P.B.X. operator. The called P.B.X. subscriber can flash the supervisory lamp SL, Fig. 3, by operating his switch-hook. The P.B.X. operator listens in by throwing her key K' to the left, and is told to which other P.B.X. subscriber the call should be transferred. The called subscriber disconnects himself, causing the release of relays 202, 201, with the result that the lower winding of the relay 200 is connected across the incoming line through wire 156 and a contact of the key K<1>. Relay 200 becomes fully energized and locks itself across the line independently of the key K<1>. The operator then throws the key K<1> to the right, severing the line connection, of which the incoming side is bridged through a resistance 170 and the outgoing side through her dial S. The relay 200, being now deprived of current, relapses and de-energizes relay 204, which closes the circuit of magnet 216 to release the connector. When the operator dials the number of the party to whom the call is to be transferred the connector operates as before described, except that the relay 203 is now directly energized by the key K<1>, so that the energization of relay 207 does not energize the ringing cut-off relay 210, and when the switching relay 213 is energized, ringing current is supplied from the circuit 295 instead of from the relay set E<1>, Fig. 1. The operator may either restore the key K<1> at once or wait on the line. If she restores the key, relay 203 is deenergized and energizes relay 206, which disconnects the line relay 205 and connects relay 200 to the lower line wire to prevent the release of the connector. During ringing the supervisory lamp SL is lit in a circuit 164, 268, 257, 253, 228, 160, but when the subscriber answers, the energization of the ringing cut-off relay 210 opens this circuit, and the energization of relays 202, 201 disconnects relay 200. If, on the other hand, the operator waits on the line, the energization of relay 210 when the subscriber answers results in the called line being at first fed with current, through the line relay 205. Afterwards, when the operator restores the key K<1>, relay 203 is de-energized and energizes relay 206, which disconnects the line relay 205, and the called line is supplied with current from the relay set E' in the normal way, the release relay 204 being kept energized by the energization of relays 202, 201. If the wanted third party is busy, the P.B.X. operator gets a busy signal and restores the key K<1>. This