Patent GB-179188-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1922-04-28
Abstract: 179,188. Automatic Telephone Manufacturing Co., Ltd., (Assignees of Wicks, J.). April 28, 1921, [Convention date]. Addition to 165,031. Automatic and semi-automatic exchange systems.-The trunks connecting an automatic main exchange to a private branch exchange are divided into two groups, those of the first group being accessible only to toll selectors and serving to establish toll calls, while those of the second group carry the ordinary traffic and are also available for toll connections if all the trunks of the first group are busy. In the system illustrated there is only a single toll trunk X, connected to the first set of terminals of a particular level of the toll second selectors E, the subsequent terminals being wired to trunks Z of the second group, which are also connected through repeating sets F to the same level of the ordinary second selectors. When a toll connection is to be extended to the P.B.X. the trunk X is seized, if idle, by the selector E, and the toll operator sends ringing current to line to signal the P.B.X. operator, who completes the connection by means of the toll connector H'. If. however, the trunk X is busy, the selector E seizes an idle trunk of the series Z and apprises the toll operator of this fact by sending back a tone signal. The toll operator may then either dial the last two digits to complete the wanted connection through the connector H, or she may dial the digit O to raise the connector H to its tenth level to call the P.B.X. operator, who then releases the connector and operates it herself to complete the connection. The P.B.X. operator mav have thrown a blocking-key, to prevent the establishment of incoming calls without her assistance. In such case, if a trunk Z is seized at the main exchange, a call signal is immediately energized at the P.B.X. operator's position. When the P.B.X. operator goes off duty, she may operate the toll connector H' to make connection. with a particular substation, to which all night calls over the toll trunk X are extended. The trunks Z serve also for calls from the P.B.X. to the main exchange, the local connectors having access to them on their tenth levels. Establishment of toll call over special trunk X; signalling P.B.X. operator. The toll operator, by means of her dial S, Fig. 1, operates a first selector D to select an idle toll second selector E, which is associated with a relay set RG. The trunk wires 29, 31, Fig. 1, are normally connected through wires 78, 79, Fig. 2, and 73, 76 tc the line relay 100, Fig. 3, which immediately becomes energized and energizes the release relay 101, which grounds wires 30, 74. The next digit operates the vertical magnet 125 of the selector E in the usual manner, and the series relay 102 momentarily grounds the wire 75 to energize the ringing cut-off relay 37, Fig. 2, which locks itself to the grounded wire 74. At the termination of the digit, the wipers are stepped into engagement with the terminals of the trunk X, and assuming this trunk to be idle the switching relay 105 is energized. The terminal engaged by the auxiliary wiper 131 is grounded in the case of the trunk X, though not for other 'trunks, so that a circuit is now closed over wire 72 to energize relay 32, Fig. 2, which connects a feed relay 35 across the right-hand condenser of the repeating coil T in place of the normal bridge circuit through relay 33. Relay 32 also energizes relay 34, which locks itself to wire 74 and reverses the incoming trunk connections, so as to energize a polarized cord relay 10, Fig. 1, which lights the supervisory lamp L. The operator now transmits ringing current to energize relay 36, which unlocks relay 37, which connects a ringing generator to the outgoing trunk to energize relay 300, Fig. 5, which locks itself and lights the call lamp L<1>, Fig. 4. Operation of toll connector H' by P.B.X. operator. The P.B.X. operator answers by throwing to the right a listening key K<2>, Fig. 4, which bridges a relay 301, Fig. 5, across the trunk X, thereby energizing the ringing cut-off relay 37, Fig. 2, which connects the trunk circuit to the feed relay 35, which locks the relay 100, Fig. 3, and disconnects it from the incoming trunk 29, 31. The polarized relay 10, Fig. 1, is thus deenergized and extinguishes the lamp L. In the meantime the relay 301, Fig. 5, has locked itself and unlocked relay 300, so as to extinguish the call lamp L<1>. The P.B.X. operator, having ascertained the wanted number, throws a key K<3> which lights a busy lamp L<3> and energizes relays 220, Fig. 4, and 302, Fig. 5. Relay 302, which is the release relay of the toll connector, lights the supervisory lamp L<2>, Fig. 4. Relay 220 connects the operator's dial S<1> over wire 263 to the connector impulse relay 303, and the connector is set on the wanted line in the usual manner. If the line is busy, the test relav 308 is energized, locks itself under control of the release relay 302, and sends back the usual busy signal. If the line is idle, the switching relay 310 is energized and ringing current is supplied, a tell-tale back-leak being transmitted through the condenser 394. When the subscriber answers, the ringing cut-off relay 307 and supervisory relay 305 are energized, the latter serving to extinguish the lamp L<2> and to energize a selflocking relay 304. When the P.B.X. operator restores the keys K<2>, K<3> the original circuit 262 of the release relay 302 is opened, but the latter, together with the busy lamp L<3>, is locked by relay 303, which is kept energized over the circuit 263, 222. Current is fed to the line A through the relay 35, Fig. 2. Re-signalling the P.B.X. operator; re-ringing the called subscriber. The toll-operator, by sending ringing current to line, can energize relay 36, Fig. 2, to unlock relay 37, which retransmits ringing current over the trunk X. The supervisory relay 305, Fig. 5, is adjusted to respond to this current to flicker the lamp L<2>. The toll operator can thus call the P.B.X. operator into conversation to inform her, for example, that the called subscriber has neglected to hang up his receiver after the calling subscriber has disconnected himself. The same means is applicable for re-ringing the called subscriber if he disconnects himself prematurely. Supervisory signals; release. When the called subscriber disconnects himself, the de-energization of the feed relay 35, Fig. 2, re-connects the incoming trunk 29, 31 to the line relay 100, Fig. 3, so that the polarized relay 10, Fig. 1, is again energized and lights the lamp L. The toll operator releases the selectors D, E by taking down the cord O. The release of the connector H<1> is under control of the P.B.X. operator, who is apprised of the called subscriber's disconnection by the lighting of the lamp L<2> when the supervisory relay 305 de-energizes. When the key K<2> is thrown to the left to open contact 222, relay 303 is de-energized and unlocks relay 302, which closes the circuit of the release magnet 338. Establishment of toll call over ordinary trunk Z. If the special trunk X is busy the toll selector E continues its rotation until it seizes an idle or crdinary trunk Z. In this case,. since the terminal 139 is not grounded, the relay 32, Fig. 2, is not energized, so that the trunk Z is bridged through the upperwinding oi the electropolarized relay 33, and the line relay 277 of the connector H is energized in this circuit. Over the terminal 139 the toll operator ge a a special tone signal from a machine- TM to infcrm her that the connection has been extended over an ordinary trunk. She may then transmit further digits, which are repeated by relay 100, Fig. 3, over the trunk Z, to the line relay 277 of the connector H, which selects, tests, and rings the wanted line in known manner. The reversal of current in the trunk Z when the subscriber answers energizes theelectropolarized relay 33, Fig. 2, which energizes the self-locking relay 34, to reverse the current in the trunk 29, 31, and also energizes relay 35, which disconnects the relay 100, Fig. 3, from the incoming line as before described. After conversation, when the called subscriber disconnects himself, the current in the trunk Z is again reversed. and the relay 100, Fig. 3, is re-connected to the incoming line, so that the polarized relay 10, Fig. 1, becomes energized and lights the lamp L. The whole connection, including the connector H, is released when the toll operator takes down the cord O. Alternative method, involving the intervention of the P.B.X. operator. Alternatively the toll operator may dial the digit O to raise the connector H to its tenth level, on which a contact 287 is closed to light the call lamp L<6>, Fig. 4. The P.B.X. operator answers by throwing her listening key K<7> to the right, thereby grounding the wire 252 and energizing relay 220, which connects the dial S<1> to a high-resistance relay 205, the circuit of which is completed over wire 251 and tl e rotary magnet 286. Relay 205 energizes a slow-release relay 206, which locks the relay 205 and disconnects it from wire 251. The kev K<7> also closes a circuit 255 for the reversing relay 276, to light the toll operator's supervisory lamp L, Fig. 1. After ascertaining the wanted number, the P.B.X. operator momentarily throws a release key K<4> to the right, to remove ground from wire 254, so as to de-energize relay 278, Fig. 5, to release the connector H, and then calls the wanted subscriber by means of her dial S'. The impulses are repeated by relay 205 over wire 251 and operate the connector H in the usual manner. Operation when the P.B.X. operator has thrown her blocking key K<5>. This has the effect of introducing a resistance 212 in the circuit 254, which prevents the energization of the vertical' magnet 299 but not of the release relay 278. When the trunk Z is seized at the main exchange the relays 277, 278 become energized and the l