Patent GB-307398-A (GB)
Title: Improvements in automatic telephone exchange systems
IPC: H04M3/60
Filed: 1929-03-04
Abstract: 307,398. Telefonaktiebolaget L. M. Ericsson. March 6, 1928, [Convention date]. Automatic and semi-automatic exchange systems.-In a small automatic exchange, such as a private branch exchange, one or more of the sub-stations are provided with simple equipment for setting up calls incoming from a maih exchange and also, if desired, outgoing calls. Outgoing calls are, however, normally set up without the assistance of an operator at such a substation. These sub-stations are provided with telephone apparatus, preferably of the desk-settype, and with signal lamps, keys and relays for connecting the set across an incoming junction or a trunk leading to a non-numerical switch giving access to the numerical selectors. This switch acts as a call-finder on out-going calls. If the P.B.X. is furnished with more than one such sub-station, arrangements are provided for transferring all calls, or waiting calls, or calls over one or more groups of junctions, from one substation to another. Completion of a connection is dependent on the disconnection of the operator's telephone set from the line. Incoming calls from manual or automatic main exchange. Relay IR is operated by calling current over junction HL, locks over its upper winding, and lights the call lamp AL1 at sub-station A1. The operator momentarily depresses key SKI to operate relays AR1, BR1 which lock up over the switch-hook H01 from which the receiver has been removed. Relay GR energizes and connects operator's set to the junction, completes the circuit of supervisory lamp KL1, and releases IR to extinguish lamp AL1. After ascertaining the wanted number, operator depresses key DK1 to energize relay DR1 which transfers her set from the junction to a line leading to a hunting switch V, the junction being looped at contacts 13 of DR1. Relay ER pulls up, closes an additional circuit over ER16 for lamp KL1, and energizes PR so that, OR operates and locks up, and PR falls back. An additional circu.t for GR is completed at OR23, and relay NR pulls up over OR24 to connect an inductive resistance RD to line L2. When relay DR1 connected operator's set through to the switch V. line relay LR completed a circuit for magnet DM over interrupter IM, and also a test-circuit over the third wiper Kc. When an idle outlet has been found, relay SR switches through and operator receive dialling tone. Line relay LR holds over inductance RD. The operator sets up the connection to the wanted party, and, if he is free, releases key DK1 and replaces her receiver so that DR1, AR1, BR1 fall back and the connection from ihe junction HL to the called party is completed over condensers 31, 32, the junction being bridged by relay HR. When the called party replies. OR pulls up over the loop and at CR40 removes the short-circuit around FR (lower) so that this relay operates, and locks over its upper winding. Relay ER falls back and lamp KL1 is extinguished. Normal release. When the called party replaces his receiver, relay CR falls back followed by FR, OR, GR and also NR which opens the holding circuit for line relay LR over inductance RD. Busy release: called party fails to reply. On receipt of the busy signal, operate depresses key BK1 and, as BR1 has not been released, relay CR pulls up and effects the changes following the reply of the called party. Key BK1 is then restored to release CR with the results previously described, and the operator disconnects herself by restoring key DK1 and replacing her receiver. If lamp KL1 remains alight indicating that the called party has failed to reply, release is effected in the same manner, but operator must first depress key SKI to re-operate relays AR1, BR1 in order that key BK1 may operate CR. She may also communicate with the calling party. Disconnection of operator from junction without replacement of her receiver. This facilitates the work of the operator during busy periods and is effected by the depression of key SKI of the next calling junction. A low resistance path over common resistance R1 and the relays BR1, AR1 of the next junction is now closed, so that relays BR1, AR1 of the present junction do not receive sufficient current and fall back. Calls from PBX to main exchange. A circuit over 39 is established for relay RR at switch V which hunts for the calling line under the control of test relav SR and the fourth wiper Kd. Line relay LR and relay CR pull up when SR switches through, and PR energizes to operate OR and then relapses. Relay GR now pulls up over OR23 to complete the connection to the junction. Outgoing calls may also be effected by calling the operator who connects herself to the junction by depression of key SKI as for an incoming call. The operator ascertains which junctions are busy by depression of key KK to light all lamps KL1 of such junctions. Distribution of calls to operators. A second sub-station A2 may be provided with apparatus for setting up calls to and from the main exchange. Depression of key KBK by operator at A1 operates relay KR which connects up the lamps AL2, KL2 at sub-station A2. Relay TR operates in. parallel with lamp AL2 on arrival of a call, and disconnects lamp AL1. the operator at A2 then setting up the connection under the control of relays AR2, BR2, DR2 whose functions correspond to those of AR1, BR1, DR1. The operator at A1 may switch over a particular call by depressing key MBK and the key SK1 of the calling junction. Relay MR pulls up followed by TR which connects up lamp AL2. Lamp KL2 is not connected up so that supervision remains with the operator at A1. All unanswered calls may be transferred by momentary depression of key KBK, and by providing such a key for eachgroup of junctions, calls incoming over any group or groups may be transferred to A2.