Patent GB-962645-A (GB)
Title: Improvements in or relating to telephone systems
Inventor: PARIS HOWARD VAREY
IPC: H04Q3/00
Filed: 1960-03-02
Abstract: 962,645. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO. Ltd. Feb. 6, 1961 [March 2, 1960], No. 7312/60. Heading H4K. In a line concentrator arrangement having a remote unit associated with an exchange unit over a plurality of links less than the number of lines served, a link is preselected at the exchange and an associated bridge magnet of a cross-bar switch at the remote station being held by battery over the loop from the exchange, the loop being monitored thereat for fault conditions. When a remote line is in the calling condition, a signal is sent over the link to the exchange which thereupon reverts a signal over the link to the remote unit to initiate the connection of the calling subscriber to the link. At the exchange the link terminates on a linefinder for connecting to appropriate line circuits, the finder being homed only when preselection of the link takes place. Construction of cross-bar switch.-The switch has select and bridge magnets, and for actuating a cross-point a bridge magnet is energized and then a select magnet. The bridge magnet is then released and traps the mechanism of the select magnet which may now be de-energized and at the same time completes the cross-point connection. The connection is thus maintained without any current flow and off normal contacts associated with the select magnet are held operated. Release of the cross-point is effected by re-operating the bridge magnet. Operation of satellite. Pre-allocation of main exchange link.-The main exchange sends - ve battery over wire CW4 to charge a large electrolytic condenser C2. This provides the local negative supply LNS for the satellite and wherever a conventional battery source is shown in the satellite diagrams the source used in fact is the source LNS. Normally, the main exchange supplies alternating current over control wires CW1 . . . CW3 to maintain RA ... RF operated, and this causes CR to operate provided condenser C2 is charged. The main exchange determines which link is to be preallocated and signals its identity by releasing one or more of RA ... RD by interrupting half cycles of various polarities on the control wires. This releases CR and operates LM in series with either LMB or LMA according as RD is released or not. The combination of relays RA, RB, RC and LMA or LMB determines the identity of the link in a contact tree MRC over which a corresponding bridge magnet such as 1BM is operated. Relay SB operates over contacts of 1BM. Further contacts of 1BM extend the link to a loop comprising the upper winding of 1BM and the right-hand winding of differential relay DC. The loop at this time receives - 100V and earth over the - and + wires from the main exchange and this holds 1BM and operates DC. Relay AR follows in this circuit to break the original operating circuit for 1BM. The main exchange now restores full A.C. over wires CW1 ... CW3 so that all relays RA ... RF are again operated. This releases LMB, LM and re-operates CR which releases SB. The link is now ready to take a call in either direction. Call originated by subscriber on satellite.- The subscriber's line loop (say of subscriber No. 1) operates line relay 1LR. This connects earth from dc3 via rectifier MR1, a chain, relay IF, resistance R10 and the left-hand winding of DC to the loop over the link to the main exchange. This unbalance causes changes in the main exchange culminating in the insertion of a resistance in the +leg of the link. The consequent reduction of current in the right-hand winding of DC causes the currents in its windings to balance so that DC releases. Earth is now connected to the link loop via dc3, d2 and chain relays IF, 1G and this combination of relays, indicative of the identity of the calling subscriber operates. The F and G relays open the circuits of corresponding combinations of relays RA ... RF, the corresponding halfcycles being suppressed in the control wires CW1 ... CW3, the main exchange then operating to maintain these half-cycles suppressed. In this case RA and RE release. Relay CR is now released and relay SMA (one of six relays SMA ... SMF) is operated over an RD, RE, RF contact tree in series with SM. The latter energizes relay D and the select magnet 1SM associated with the calling subscriber over contacts of RA, RB, RC and SMA. Relay D releases 1F, 1G and 1LB. The main exchange now disconnects the holding potentials connected to the loop and operate magnet 1BM releases to complete the cross-point connection and to hold the select magnet off normal springs operated to maintain 1LR disconnected from the subscriber's lines. Magnet 1BM releases D, SMA and AR which prevents another subscriber from initiating a call until another link is proallocated. SMA releases 1SM. After a suitable interval the exchange restores the A.C. (both half-cycles) to all the wires CW1 ... CW3, so that all of RA ... RF are again operated, CR comes up and SM releases. When C2 is again sufficiently charged up the exchange preallocates a fresh link as described above. Call from main to satellite exchange.-With a link circuit pre-allocated as before, the exchange suppresses appropriate half-cycles in leads CW1 ... CW3 to release a combination of relays RA ... RF, say RD, RE, RF, indicative of subscriber member 48. CR releases to bring up SM in series with SMF one of six relays SMA ... SMF determined by the RD ... RF combination. Relay SMF in combination with the RA ... RC relays determines the operation of select magnet 48SM in series with relay D. When, at the main exchange a finder associated with the link is connected to the incoming call the exchange opens the supply to the link loop to release magnet 1BM to operate the cross point. Relays AR, D, SMF and magnet 48SM release whereupon another link is pre-allocated as described above. Operations at main exchange. Pre-allocation of link to satellite.-On initial going into service CWF operates and all the PT relays associated with the links are operated either to battery from the line circuits or P-wires or from relay CCE if the finders FA, FB are homed. DL also operates and alternating current is applied via relays ERA ... ERF to the control wires and these are operated by one or other of the halfcycles of the alternating current. Relays ERC, BF follow the latter connecting charging battery for condenser C2 in the satellite over wire CW4. This charging current operates BFM which releases when the condenser is charged up, followed by CWF and DL. The latter completes a circuit for K in series with the drive magnet and K operates. In later operations when some of the links are busy this fact is indicated by the PT relay being unoperated. Earth at pb4 shunts relay K and provides a drive circuit for the magnet LKADM which thus steps until a free link is found whereupon K operates as above and the switch stops. Relay K operates OL which connects - 100V to relays A and DF. Relay K also earths wipers LKA2 ... LKA5 to bring up a combination of one or more relays E1G ... E8G indicative of the identity of the chosen link. These relays suppress combinations of +ve or - ve half-cycles from the A.C. supplied by source ACS to control wires CW1 . . . CW3, thereby signalling the link identity to the satellite. Corresponding ones of relays ERA ... ERD are also released. Relay ECR is thereby released and either ELA or ELB come up in series with CO, depending on ERC, ERD. The selected link is determined over a contact tree of relays ERA ... ERC and ELA, ELB and over this circuit relay H in the link circuit operates in series with ED. Relay H releases PT to busy the link, and connects relays A and DF across the - and + wires of the link, thereby extending - 100V and earth to the satellite which thereupon loops the line to bring up A. Release of PT operates HA which homes the finders FA, FB, whereupon PT re-operates over its left-hand winding and removes a shortcircuit from DL which operates and energizes the allotter magnet LKADM. This releases K and LKADM releases to step the allotter off the link in question. Relay K releases the relays E1G ... E8G, CO and ELB. Relay CO restores the A.C; over the control wires any of the released relays ERA ... ERD being reoperated. Relay ECR now operates and ED releases. The exchange is now ready for a call in either direction. Call originated by subscriber (No. 1) at satellite.-When the satellite unbalances the link loop DF operates, followed by SU. This inserts resistor R14 in the + leg to release DC in the satellite as previously described. Relay SU also disables EU to prevent response to a call in the other direction at this time. The satellite suppresses combinations of + and - half-cycles over control wires CW1 ... CW3 to signal the calling subscriber's identity, so that, say, ERA, ERE release. The ERD, ERE, ERF settings bring up relay ESA (one of six such relays ESA . . . ESF determined by the combination in question) in series with CO. The subscriber's line circuits at the main exchange are accessible over two line finders FA, FB, so that if any of ESD, ESE or ESF had been operated, a switching relay SW is operated to bring in finder FB instead of FA. In either case CO comes up to ensure that such of the ERA ... ERF relays which release cannot re-operate. Relay ESA in combination with the settings of ERA ... ERC marks the subscriber's line circuit by putting battery on the FA8 terminal. Relay ERE de-energizes ECR and when this eventually releases B operates to release SU and cause the finder FADM to step. SU removes resistance R14 from the + wire of the link. Relay B operates ON. When the marked line circuit is found T operates over PAS and brings up E and stops the switch. Relay E removes the - 100V from the - wire of the link to release the bridge magnet at the satellite. Relays A, BF release, followed by CO, ESA, H and OL. Relay CO enables ERA, ERE to reoperate, followed by ECR and B, ESA