Patent GB-909962-A (GB)
Title: Improvements in or relating to automatic telephone systems having selecting stages consisting of cross-bar or like switches
IPC: H01H67/32
Filed: 1959-02-09
Abstract: 909,962. Automatic - exchange systems. TELEFONAKTIEBOLAGET L.M. ERICSSON. Feb. 9, 1959 [Feb. 14, 1958], No. 4455/59. Class 40 (4). In an automatic-exchange having a switching stage utilizing cross-bar or like switches and in which a marker identifies a calling line and controls its extension via free bridges of the switches of that stage, the bridges of at least one sub-stage when operated are held by selfholding means independently of whether a busy connection extends therethrough, and the marker when taken into use applies a potential to all bridges of that sub-stage or those substages which test free, which potential restores the operated ones of those bridges. As illustrated in Figs. 2, 3, a switching stage includes two sub-stages SLA and SLB, two bridges only of each sub-stage being shown. Each bridge has thirteen bar positions, each of the ten digit bar positions having nine contacts, and each of the three auxiliary bar positions, which may all be controlled by one bar, having three contacts. Thus by actuating the contacts at one digit position and one auxiliary position the input of a bridge of sub-stage SLA may be connected to any one of thirty subscriber's lines, or any one of the twenty inputs of the sub-stage SLB may be connected to any one of the thirty outputs thereof. Subscriber " 00 " initiates a call.-Closure of the line loop brings up line relay LR which operates the units relay AO corresponding to the units digit of the calling line and relay AA follows. The relevant tens relay BO then comes up in series with AO, and the calling line is thus identified. Relay BA operates and as the caller is in group 00-29 connected to the first A-switch, it brings up AN1 over front BO, thus connecting the operating and test wires of the SLA-1 switch to the marker. BA also brings up FKA and VKA, of which the former connects negative potential via M 0 -M 9  to the test wires of the bridges whereupon the test relays F 0 -F 9  corresponding to free bridges pull up. The test wire of a busy bridge is connected to positive potential, thus preventing operation of the corresponding F relay. VKA brings up FA which holds the operated F relays, over front contacts of which positive potential via a low-resistance winding of VKA is extended to the hold magnets of all free bridges. Those which are operated are thus short-circuited and restored, whereupon VKA relapses, followed by FA and all except the first of the operated F relays, say FO. FB operates, opens the operating circuits of VKA and FKA, and brings up FC which connects positive potential to the selector relays of SLA corresponding to relays AO and BO, and to those of SLB corresponding to the operated F and AN relays. In the meantime AO has brought up RBL, which connects the testrelays GO-G18 to the test wires of the outgoing lines FURO-FUR18. The free lines have negative potential on the test wire (H back) and the first of the corresponding test relays, say GO, operates and disconnects the others. Relay HK comes up over front contacts of the SLA and SLB select magnets and operates the selected bridges of SLA and SLB over front contacts of FO and GO, respectively. GO also brings up GA which operates relay C of the selected line to extend the connection thereto. Feed relay AU pulls up to the calling loop, thus bringing up holding relay H, which operates the test relay P in series with the caller's cut-off relay BR over the c wire. The subsequent release of LR releases the marker, while P busies the selected line. The choke D connected across the line by the operation of H calls the distant exchange to which the dialled number is repeated by the impulse relay J. When the caller hangs up, AU, H, P and C release in turn, the last relay removing positive potential from the c wire and bringing down BR. Incoming call over line equipments FIR1- FIR19.-On seizure of one of the incoming equipments FIR the operation of its relay B brings up the corresponding G relay, say G19, whereupon GA and the C relay of the equipment follow. GA also brings up NS1 which connects the polarized impulse relay N to the incoming line wires. The first incoming digit is received as successive reversals of polarity and is repeated by N to set relays N1-N6. After the last impulse NS1 relapses, and, before NS2 operates, the corresponding B relay is operated under control of N1-N6 and relay T1 pulls up. Thereafter the operation of NS2 releases N1-N6, and NS1 re-operates, thus releasing NS2 to reconnect N to the incoming line and to bring up T2 in series with T1, thus connecting the N1-N6 contacts to the A relays ready for reception of the second digit. The second digit operates the relevant A relay, NS1 releasing at the end of the digit, but NS2 being held by T2. Operation thereafter is as for an outgoing call. When the caller hangs up, alternating current sent over the incoming line brings up N in the FIR equipment to initiate release. Modification.-Instead of the holding magnets having hold contacts and being released by short-circuit, they may be held by remanence and be released by a reverse current as illustrated in Fig. 4 (not shown). System employing code relay bridge units.- The cross-bar bridge units of Figs. 2, 3 may be replaced by the code relay bridge unit shown in Fig. 5. Operation of code magnets (not shown) cause the corresponding code bars 8 to be displaced horizontally so that recesses 9 therein provide through-recesses 9a below one digital vertical row and one auxiliary row of the contacts 1. When the bridge magnet R is operated attraction of its armature 5 allows the bell-cranks 4 under the selected rows of contacts to be rotated anticlockwise by the springs 10 since the arms 7 of these bell-cranks can pass into the recesses 9a. On the release of bridge magnet 6 the armature 5 is returned by spring 12 and lifts the two bell-cranks 4 concerned, thus lifting the corresponding lifting bars 3 and bringing the contacts 1 of the two vertical rows into contact with the horizontal conductor bars 2. At the same time the arms 7 of the bell-cranks 4 concerned are lifted out of the recesses 9a. Specification 832,865 is referred to.