Patent GB-203759-A (GB)
Abstract: 203,759. Siemens Bros. & Co., Ltd., and Christian, D. A. June 9, 1922. Automatic exchange systems; selectors. - In a system provided with means for connecting to ordinary lines or to idle lines of private branch exchange groups, the connectors are provided with an additional wiper and an additional terminal bank, P.B.X. lines and ordinary lines being distinguished independently of the ordinary test circuit. Means are provided whereby if a busy P.B.X. line, other than the first in a group, is called, hunting does not take place. Several modifications are described. Construction of switches. The connectors are Strowger switches provided with an additional terminal bank 7, Fig. 1, arranged above and in front of the ordinary bank. The bank 7 is of metal and is semicylindrical and has 100 tapped holes for the reception of metal or insulating screwed pins, or terminals. The additional wiper may comprise springs adapted to be separated by the pins in the bank or may comprise several springs two or more of which are pressed into contact according to the size of the pins. In another form, two wipers make contact in the ordinary way, with two adjacent terminals at the same time. First arrangement, Fig. 4, in which the additional bank d is grounded and terminals are provided for all ordinary lines and for the last line in a P.B.X. group. When the selector is seized, relay N locks up and relay A energizes slowrelease relay D which causes the lifting magnet HM to operate in response to impulses. At the end of the digit relay D falls back and energizes the switch-over relay G which re-energizes relay D. At the end of the operation of the rotary magnet DM, relay D falls back and completes a holding circuit for relay G dependent on relay PR. If the called line is an ordinary one, wiper d stops on a grounded terminal and relay PR releases relay G but relay T, if the line is idle, locks up to the C-wire before relay G falls back, and releases relay A which removes a short-circuit from relay S and short-circuits one winding of relay TR. Relay S energizes and connects ringing current from the leads 11, 12 to the called line. On the reply of the called substation relay TR locks up and short circuits relay S which completes the connection. In the case of a busy line, relay T does not energize and relay G on relapsing energizes relay TR which sends backs busy tone from the leads 13, 14, releases relay A and locks up dependent on rotary off-normal contact W<2>. If the call is for a P.B.X. group relay PR does not energize but if the first line is idle the call proceeds as before. If it is busy, relay D on falling back completes an interrupter circuit including a contact of the test relay for the rotary magnet and the wipers proceed to hunt for an idle line. When the test relay operates hunting stops, relay G falls back and ringing proceeds as before. If all the grouped lines are busy, relay PR operates when the wiper d reaches the grounded terminal, and the busy signal is sent as with an ordinary line. Release is started by removal of ground from the C-lead by a previous selector. Relay N releases relay T which energizes release magnet RM. Second arrangement, Fig. 5, in which terminals are provided in the extra bank only for the P.B.X. lines except the last. Operation for ordinary calls is similar to that in the first arrangement except that there is no contact of the test relay in the circuit of relay G. Relay D on releasing after the final digit breaks the circuit of relay G. If the call is for the first line of a P.B.X. group, the line is tested when armature d' falls back, armature d<4> falling slightly later. If it is idle ringing proceeds as in the previous arrangement, but if busy relay PR energizes relay G to keep the test relay circuit closed, and completes a circuit for rotary magnet DM which at contact h breaks the circuit of relay PR which open-circuits magnet DM, whereupon contact h closes and relay PR reenergizes. This is repeated until an idle line is found when relay G falls back and ringing proceeds as before. If there are no idle lines, wiper d comes to rest on a bank, relay PR falls back and de-energizes relay G which causes relay TR to give the busy signal as before. In this arrangement the contact h may be omitted, an interrupter being put in the local circuit including contact p<r2>. Third arrangement, Fig. 7, in which the first P.B.X. line of a group is marked with an insulating pin and the last vith a metal one, other lines being unmarked. The extra wiper comprises springs db, dc normally in contact but separated by pins in the bank. The arrangement is generally similar to that shown in Fig. 5, but relay PR has two windings and an additional relay X is put in parallel with the winding 1 when the wiper springs are in contact. Relay X is so designed that it acts as a short-circuit for relay PR. If the first line of a P.B.X. group is called and is busy, the wiper springs db, dc are separated by an insulating pin, relay X is cut out and relay PR energizes and locks up over its winding 2 under control of the test relay. Hunting &c. proceeds as in the arrangement shown in Fig. 5. If there are no idle lines, the metal pin belonging to the last grounds both wiper springs. Relay X pulls up, and releases relay PR and the busy signal is sent as in the arrangement shown in Fig. 5. Preventing hunting if a P.B.X. line other than the first is called. In the last-described arrangement, Fig. 7, if the wipers db, dc come to rest on P.B.X. lines other than the first, no insulating pin is encountered and relay PR remains shortcircuited by relay X. The busy signal is sent as in the case of an ordinary line. In another method in which P.B.X. lines are marked as in the second arrangement, the extra wiper carries a trailing arm adapted to make contact with the preceding adjacent terminal. This arm is connected through a back contact of relay PR to the end of its winding opposite to that to which the wiper is connected so that if the wiper comes to rest on a line other than the first relay PR is short-circuited. Fig. 8 shows a similar arrangement. The first and last lines in a group are marked respectively by a short stud and a blank, and the others have longer studs. The wiper comprises contact springs normally separated as shown. If the wiper comes to rest on the line marked by a short stud, the two lower springs are pressed together and relay PR is energized and hunting proceeds until relay PR releases on the energization of the test relay or on the wiper dd arriving at a blank. If the wiper dd comes to rest on a line other than the first, all three springs are pressed together and relay PR is short-circuited and the busy signal or ringing current sent as in the other arrangements.