Patent GB-187747-A (GB)
Abstract: 187,747. Western Electric Co., Ltd., (Western Electric Co., Inc.). Aug. 10, 1921. Semi-automatic exchange systems.-In a system in which connection between two exchanges is set up over a two-wire trunk, a high-resistance relay bridged across the outgoing end of the trunk produces no effect during the establishment and maintenance of the connection, but upon the release of the trunk at its outgoing end, the relay responds to mark that end of the trunk busy until it is also released at its incoming end. The relay also serves to mark the trunk artificially busy at its outgoing end at the will of the operator. The invention is described with referenceto a semi-automatic system in which an originating operator O connects the calling line with the jack J of a trunk leading to a B-operator O<1> who sets up the wanted number on an impulse register, under the control of which an office selector 6, 7, 8 seizes an idle two-wire trunk 11, 12 ending in a plug P<1> before a terminating operator O<11> at the wanted exchange. The number of the wanted line is transferred to a number-indicating register before the operator O<11> who completes the connection to the wanted subscriber C. Establishment of connection. The energization of the sleeve relay 2 completes a bridge circuit over the polarized supervisory relay 3 across the trunk 4, 5; and upon the seizure of the trunk 11, 12 by the brushes 6, 7, 8 of the office selector, relay 13 energizes over the trunk 11, 12 in series with the relay 14 to energize a slow acting relay 20, the latter closing a locking-circuit over relay 18 which, however, is as yet short-circuited. Relay 14 drives the sender sequence switch 22 into its 16th position in which the battery and earth connections to the trunk 11, 12 over the relay 14 are replaced by a bridged relay 24. Relay 13 relapses and breaks the short-circuit round relay 18 which energizes to complete a new battery and earth connection for relay 13 which re-energizes. Relay 26 lights the assignment lamp 27 whereupon the operator 0" presses the assignment key K<1> individual to the trunk in use, energizing the assignment relay 44 which closes a circuit for a relay 16 to connect the trunk 11, 12 to the conductors 30, 31 over which impulses are then transmitted to determine the setting of the operator's indicator in accordance with the wanted number. The operator O<11> inserts the plug P<1> in the jack J<1> of the wanted subscriber C and the sleeve relay 21 energizing in series with relay 28 locks up relay 18. Relay 28 breaks the locking circuit for the assignment relay 44 which restores relay 16 to connect the trunk 11, 12 directly to the repeating coil 33. Ringing-arrangements; indicating reply of called subscriber. Relay 28 also closes a circuit over lamp 34, which does not yet light, for ring- ing relays 37 which energizes to transmit ringing- current to the called line. When the called subscriber replies, ringing-cut-off relay 35 energizes to break a short-circuit round relay 36 which short-circuits ringing relay 37 to stop the ringing. Supervisory relay 40 energizes over the called line completing a circuit for a relay 17 which reverses the battery connections over the trunk 11, 12 and causes the polarized relay 3 to indicate to the operator O that the called subscriber has replied. Release. When the called subscriber C hangs up, the relapse of supervisory relay 40 de-energizes reversing relay 17 causing a further reversal of current over the trunk 11, 12, the polarized relay 3 giving an indication to the operator O who takes down the calling plug from the jack J. A relay 42 is permanently connected across the outgoing end of the trunk 11, 12 but is of such high-resistance that, during the setting up and maintenance of the connection it does not energize or effect the operation of the other relays. Upon the breaking of the bridge circuit through the low resistance relay 3 when the sleeve relay 2 is disconnected, relay 42 energizes to ground the test terminal 43 to mark the trunk 11, 12 busy until it is released at its incoming end. Relay 13 relapses owing to its series connection with relay 42, de-energizing relay 26 and lighting the disconnect-lamp 34. When the operator 0" removes the plug P<1>, relays 21, 28 release, opening the circuit of relay 18 which causes the deenergization of relay 32 and the removal of the busy condition from the terminal 43. Means for artifically marking any trunk busy. The operator O<11> may insert the plug P' of any trunk into a special make-busy jack similar to J<1>, upon which the relays 21 and 18 respond to energize relay 42 which grounds the terminal 43 as above.