744,098. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd. May 26, 1954 [Aug. 25, 1953], No. 23380/53. Class 40 (4). In an automatic exchange having a plurality of stages of crossbar switches, one stage is a line finder/final selector stage having groups of subscribers' lines each multipled across a plurality of its bridges; originating and terminating trunks are connected to the bridges of that stage and are multipled across all the bridges of the second and third stages respectively; battery feeding relay sets are connected between corresponding bridges of the second and third stages; and registers, for controlling the setting up of corinections, are connected to other bridges of the second stage. The embodiment described is a 100-line private automatic exchange using seven 12 X 10 crossbar switches. The eleventh and twelfth select magnets of each switch are used as auxiliary magnets and are designated AM1 and AM2. Line finder/final selector. This consists of the four switches LF/FS1 to LF/FS4, which are arranged to provide ten switching units (each of four bridges), in each of which the individual contacts of corresponding crosspoints controlled by select magnets SM1 to SM10 are multipled together. Ten subscribers' lines are connected to the ten inlets of each unit, and the units are grouped in pairs, each pair being associated with four originating and four terminating trunks which are connected to the crosspoints controlled by AM1 and AM2 respectively. Thus any of the twenty subscribers 11 to 20, served by bridges BR1 to BR8 of LF/FS1, may be connected to any of the four originating trunks OT1 to OT4. Such a connection would be effected, preferably under control of equipment common to all line finder/final selectors, by the operation of AM1, the select magnet relevant to the calling line, and that bridge magnet of the switching unit serving the calling line which is appropriate to the trunk concerned. For connections to the terminating trunks TT1 to TT4, AM2 is operated instead of AM1. Originating connecting stage. The twenty originating trunks OT1 to OT20 are connected two to each of the crosspoints controlled by SM1 to SM10 in bridge BR1 of switch OCSA, and are multipled across all the bridges of OCSA and OCSB which constitute this stage. In each bridge the contact appropriate to AM1 is strapped to that of AM2, and the two switches are used for double group working to provide a 20 X 20 co-ordinate arrangement, the bridges of which may be connected to local transmission equipments, registers and outgoing relay sets, provided according to traffic requirements. As shown, ten local transmission equipments LTE1 to LTE10 are provided, each extending directly to the corresponding bridge of the terminating connecting switch TCS, and incorporating battery feed and call supervisory arrangements together with tone and ringing current supply. Bridges BR1 to BR4 of OCSB are connected to registers REG1 to REG4, and BR7 to BR10 to outgoing relay sets ORS1 to ORS4 associated with junctions to exchanges EA and EB. Terminating connecting stage. The twenty terminating trunks TT1 to TT20 are connected to the first bridge of the single switch TCS of this stage, one pair of trunks to each crosspoint relevant to SM1 to SM10, and are multipled to all the bridges. This stage also employs double group working. Preferred method of operation. When a call is initiated, a start signal is sent to the LF/FS common control equipment (not shown) which effects the operation of the select magnets corresponding in position to the calling line, and of the magnets AM1, in all LF/FS switches, followed by the operation of the bridge magnet required to extend the calling line to an idle originating trunk. The LF/FS control equipment also sends a signal to cause operation of the select magnets in OCSA and OCSB appropriate to that trunk, and the magnets AM1 or AM2, respectively, according as the trunk appears at the left- or right-hand half of the double crosspoints. Bridge magnets associated with an idle transmission equipment and an idle register, respectively, are then operated by control equipment (not shown) common to the originating connecting stage. Dial tone is reverted and the select and auxiliary magnets of the LF/FS and originating connecting stage are released. Local call. The digits dialled are stored in the register and simultaneously transferred to the LF/FS control equipment wherein the last two digits cause the operation of the select magnets corresponding to the position of the wanted line, and of the magnets AM2, in all LF/FS switches. The tens digit determines the group of four bridges serving the wanted line, and an idle terminating trunk serving that group is chosen and the appropriate bridge magnet operated. The LF/FS control equipment then causes the operation of the select and auxiliary magnets appropriate to that trunk in switch TCS, whereupon the register operates the bridge magnet of TCS associated with the transmission equipment taken into use. The select and auxiliary magnets of LF/FS and TCS are then released, as are also the register and its associated bridge magnet in OCSB. The transmission equipment rings the called line and reverts ringing tone to the caller, ringing being tripped and the connection switched through in known manner on the reply of the called party. Outgoing calls. On the reception of a first digit " 3 " or " 4 " indicative of a call to exchange EA or EB, the register seizes an idle outgoing relay set leading to the relevant exchange and causes the select and auxiliary magnets of switches OCSA and OCSB appropriate to the originating trunk in use to be reoperated, followed by the bridge magnet appropriate to the outgoing relay set. Seizure of this relay set causes the originating connecting stage control equipment to release the transmission equipment and the register, together with their associated bridge magnets. Subsequent dialled digits are repeated over the junction. Incoming calls. These would be catered for by associating incoming junctions with the LF/FS switches in place of some of the subscribers' line circuits. Specification 555,614 is referred to in the Provisional Specification.