Patent GB-234151-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/62
Filed: 1923-12-21
Abstract: 234,151. Western Electric Co., Ltd., (Deakin, G.). Dec. 21, 1923. Semi-automatic exchange systems.-In a private branch exchange in which the same finder switches LF are employed in establishing both outgoing calls to and incoming calls from the main exchange., the latter being effected under the control of the P.B.X. operator by the depression of keys 7, 40 individual to the incoming trunk 32, 33 and the wanted line 1 respectively, the switch LF is prevented from starting its operation if the wanted line is busy. The depression of key 40 also lights a common busy lainp 42. If the wanted line is idle the switch LF hunts under the control of a fourth wiper 18, and when the line is found, lamp 42 is lit and the operator releases the keys 40, 7 and rings the subscriber 1 who is provided with two bells to differentiate between local and main exchange calls and with a key 2 by which his apparatus may be disconnected from the local apparatus and connected to the main-exchange terminals 10, 11. A lamp 39 remains lit until the called subscriber replies so that if a call is unanswered, the operator is informed and can release the connection. The conductors 32, 33 of the trunk are normally disconnected from the wipers 15, 16 at the contacts of a relay 23 which operates to complete the talking connection, when the calling line has been found in the case of an outgoing call and when the called subscriber has replied and an operator's key 26 has been restored in the case of an incoming call. The operation of relay 23 also disconnects the operator's equipment so as to prevent any interference with or interruption of the conversation. A special tone signal is given to a calling P.B.X. subscriber if all the outgoing trunks 32, 33 are engaged. An outgoing call may also be established by the operator and then transferred to a P.B.X. subscriber. Outgoing call established automatically. When the calling subscriber throws key 2 and removes his receiver, line relay 3 energizes relays 6, 8 which completes circuits for the stepping magnets 14 of idle finders. When the calling line is reached, cut-off relay 4 energizes over its left-hand winding in series with test relay 19 and resistance 20, the test relay locking up over contacts of relay 22 to mark the calling line busy. The cut-off relay locks up over both its windings in series to prevent double connections. The opening of the back contact of relay 19 inserts relay 23 in the stepping circuit whereby magnet 14 can no longer operate, but relay 23 energizes to switch through the connection, to disconnect the operator's equipment and the ringing relay 24 and to energize a relay 22 which transfers the locking circuit of relays 4, 19 to the left-hand armature of relay 23. Relay 29 now energizes over the talking conductors and operates relay 30 which maintains relay 23 energized. All outgoing trunks busy. In this case the relays 22 of all the trunks complete a chain circuit for a relay 5 which disconnects direct battery from line relay 3 and inserts a high-resistance relay 36. Line relay 3 is unable to energize, but relay 36 energizes to connect up a buzzer 35 which transmits a busy tone to the calling subscriber. Incoming call. Ringing current transmitted over the trunk 32, 33 operates a relay 37 which locks up over key 25 and extends ground to light lamp 38 and to operate a relay 21 which prevents the seizure of the finder LF for an outgoing call. The P.B.X. operator throws a key 25 which unlocks relay 37 and extinguishes lamp 38, and connects her set OTS across the incoming conductors 32, 33. Relay 28 and lamp 39 are also operated over key 25 and are maintained energized over release key 34 and a back contact of relay 22. The operator, having communicated with the calling party, restores key 25 and depresses a key 40 individual to the wanted subscriber, and if the cutoff relay 4 is energized, relay 41 energizes to light lamp 42. The operator having informed the calling party that the wanted line is engaged, releases the trunk 32, 33 by operating key 34. If, however, lamp 42 does not light, the operator depresses keys 40, 7 simultaneously, thereby completing a circuit from the left-hand back contact of relay 41 for stepping magnet 14, connecting the cut-off relay 4 to the test terminal 13, and the second test wiper 18 in series with relay 43. (If the wanted line had been busy, the operation of relay 41 over key 40 would have prevented the closure of this circuit.) When the wanted line is found relay 43 operates, opens the stepping circuit and connects up the test relay 19 which operates to mark the line busy as before. The operation of the cut-off relay 4 energizes relay 41 which lights lamp 42 to notify the operator that she may release keys 40, 7. Keys 26, 27 are now thrown and relay 24 operates to connect ringing current to the wanted line. With key 27 restored, the reply of the called subscriber energizes relay 29 in series with the coil 51. The operator then restores key 26, whereupon relay 24 releases and relay 23 energizes to switch through the connection and operate relay 22 as before. Relay 28 is now unlocked and lamp 39 is extinguished. If the call remains unanswered, the operator releases the connection by depressing keys 34, 7. Outgoing call established by operator. The key 25 of any trunk is thrown, and if the line is idle, lamp 39 will light up and relays 28, 21 will operate. The throwing of key 34, if the main exchange is of automatic type, removes a shunt circuit and places the trunk directly under the control of the operator's dial. When a desired connection has been obtained it may be transferred to a P.B.X. subscriber in the same way as if were an incoming call, as described in the preceding paragraph. Night arrangements. By throwing a key 60 any line 1 mav be disconnected from the local apparatus and directly connected to a main exchange trunk.