Patent GB-750901-A (GB)
Title: Improvements in or relating to automatic telephone systems
IPC: H04Q3/00
Filed: 1953-03-24
Abstract: 750,901. Automatic exchange systems. LEICH ELECTRIC CO. March 24, 1953 [June 25, 1952], No. 8056/53. Class 40 (4). A dual purpose link circuit, which can be used subject to minor modifications either with a group selector or a connector, each of the relay type, comprises means for registering digits, means for selecting ringing codes for party lines, battery feed and supervisory relays and means for disconnecting a call after it has been taking place for more than a predetermined period. System employing finder-connecter links only. In this case the connections marked C 'but not those marked S are completed in Fig. 17. Allotting of link and operation of line-finder. The line relay LR operates to the calling subscriber's loop connecting together a tensindicating lead TN and a units indicating lead U1. This brings up the appropriate one of five relays T1 . . . T5 and one of two relays TE1, TE2 in a combination indicative of the tens digit (say T1 and TE1). Priority in the case of simultaneous calls is given to a line in the group operating TE 1 and within the group the priority' is determined by a chain circuit containing contacts of T1 . . . T5. The latter brings up UG1, UG2 which includes a pair of relays, say U1, UE1 out of U1 . . . U5, UE1, UE2 indicative of the units digit in the circuit of the tens relays. UE1 brings up TT, UE1, TF1 in series. Links are seized over a chain circuit (F1, F0) of contacts of link relays X which are released as the link is taken into use and remain released until all the X relays are released. This removes earthfrom the lead RT to release relay RS (Fig. 9) which grounds lead RS to bring up the X relays in all idle links to render them available for selection. RS is then restored by earths reverted on RT by the free links. Relay UF1 connects ground through the chain circuit to the lead F1 of the first available link to bring up the allotter magnet AR of the finder thereof (Fig. 15). TF1 in combination with T1 grounds the appropriate bar 10 of the tens allotter bank, so bringing up the tens relay 10 of the finder and UF1 in combination with U1 grounds the appropriate bar 1 of the units allotter bank so bringing up the finder units relay 1 so that the calling line is now connected to the link. The ground on F1 also brings up C to connect up dial tone. The calling subscriber's loop brings up A and hold relay B follows. Ground is now reverted on the test wire T to hold the line relay LR and bring up the cut-off relay CO the latter releasing the allotter, whereupon the finder allotter magnet is released and also the chain relay X to allot the next free link to the next idle call. All links busy. If all links are busy RS remains released and inserts relay OMF in the operating circuit for T1 . . . T5 so that when a call arrives T1 . . . T5 remain down but OMF operates, locks over lead FOA and energizes an overflow meter. The ground on FOA is briefly disconnected at one second intervals to permit OMF to release when the calling subscriber hangs up but prevents faulty operation of the meter should the subscriber attempt to dial. Operation of allotter under fault conditions. If a faulty line fails after a prescribed time to complete its connection with a link, e.g. due to failure of its CO relay, the normally operated TG is short-circuited by one of T1 . . . T5 and releases followed by the normally operated TH. TG in releasing causes the identity of the calling line to be registered as different combinations of relays 1T ... 5T, 1U ... 5U. These relays operate in such a manner as to alter the point of entry of the T1 . . . T5 and U1 . . . U5 chains (and if necessary give TE2 and UE2 preference over TE1, and TE2 respectively) to give the faulty line least priority in seizing a link. Relay TH releases T1 . . . T5, TE1, TE2, U1 . . . U5, UE1, UE2, TF1, TF2, UF1, UF2 and TT whereupon TG re-operates followed by TH. The allotter circuits is now normal except that some of 1T . . . 5T, IU ... 5U are operated. The calling line repeats its attempts to obtain connection until the caller hangs up, but meantime if another subscriber makes a call he gets priority when next TH releases. If two lines are faulty they make alternate attempts to make connection. If CO fails to operate due to the seized link being faulty the relays IT . . . 5T, 1U . . . 5U operate as before but at the next attempt a different link will be seized due to the X relay of the previous link having been released. If failure in the guard chains occurs, say, over contacts of T1 then calls from groups 20-50 will not obtain connection. However, calls in such groups will automatically shift the point of entry of the chain so that calls in subsequent groups can obtain connection so that ultimately only the associated 20's group will be adversely affected. Similarly faulty contacts of relays IT . . . 5T can be shown to be self-correcting. If a faulty contact exists in the X relay chain (F1 ... F0), a failure to establish a connection operates some of relays 1U . . . 5U which shifts the point of entry into this chain. Prefix digit. Relay A repeats the prefix digit to the registering relays 1 . . . 5 and relay C releases at the end of the train to ground lead GS via relays G and H to the marker (Figs. 11, 11a). The links are divided into two groups which may seize the marker by the operation of GA or GB, each of these relays in operation disabling the other, GA having preference if simultaneous attempts are made to seize the marker from both groups. Each group is provided with a chain circuit over contacts of the link relays G which ensures the impossibility of seizure of the marker by more than one link and allocates the order of priority in the event of simultaneous attempts by links of the same group to seize the marker. When the marker is free its relay GA (or GB) operates over GS to the calling earth from the link, and inserts its low resistance winding into the circuit to bring up G and H in the calling link (or the first calling link if there are more than one). Relay H brings up R in the link, connects leads P1, P2 to contacts of the digit register 1 . . . 5 and grounds SN indicating that a prefix selector is to be made, thereby bringing up SA, SB and start relay GM in the marker. The digit is transferred over leads P1, P2 as described below to operate combinations of marker relays N1 . . . N8 and GR follows opening leads GS over which seizure of the marker takes place. If the digit 2 or 9 (the latter prefix being reserved for coin boxes) indicating a local call is received N1 ... N8 ground lead 2H which is connected over contacts of SA to lead HS to bring up S in the link circuit. This ground also unbalances a bridge circuit containing relay GS which operates to release the marker. Relays G, H in the link thereupon release followed by 1 . . . 5 and C re-operates. Tens digit. The first impulse releases R to reclose the locking circuit for the registering relays 1 . . . 5. Relay T is also operated by relay 2 after the first impulse and locks. The digit is registered as before on relays 1 . . . 5 after which C falls back. The marker, when free, is connected up as previously described, but this time with T up TN is grounded to bring up TA, TB indicating that a tens selection is to be made. The marker relays N1 ... N8 ground one of the tens bars 10 . . . 00 in accordance with the tens digit and TA grounds AC to operate the connector allotter magnet AR which connects the tens coils to their appropriate bars for operation in accordance with the marking applied. The tens coil locks to lead LKC and extends direct ground thereto which is effective over lead RC to unbalance GS in the marker which is thereupon released. In the link circuit G, H, AR and 1 . . . 5 release and C re-operates to insert U into the holding circuit of S and T in which all three are then held. Units digit. This is registered like the tens digit and the marker is again seized, but this time with U operated UN is grounded to bring up UA, UB to indicate that a units selection is to take place. UA, UB connect the marking provided by N1 ... N8 to the units bars and a units coil is operated in a manner similar to the tens coil and the marker again released. When H in the link circuit releases S now falls away. The connector is now through to the wanted line circuit. Party digit and busy test and ringing. The party digit is registered on 1 ... 5 and when C releases, E tests the line during the slow release of T. If the line is free E operates and grounds the test wire to operate the line and cut off relays LR, CO. The ringing circuit provides a set of 5 different ringing codes or frequencies operable during alternate periods of the ringing cycle. Brief ground impulses are applied alternately over RS1, RS2 and one of these (according as 5 is or is not operated) operates F which subsequently locks to RH for the rest of the ring- ing period. Two ringing codes in alternate cycles are applied to each of leads R17, 56, 28, 40, 39 the appropriate ringing code being applied in accordance with the digit registered on 1 . . . 5. Parties 1 . . . 5 may be rung on the - ve line and parties 6 . . . 0 on the + ve line by connecting an interrupter lead not shown, which is grounded prior to each ringing cycle to 15N, so that ringing normally goes out over the - ve line but when 5 is up (i.e. for 6 . . . 0) R is operated to connect the ringing current to the + ve line. The opposite arrangement can be obtained by connecting the interrupter lead to 15P. Alternatively odd or even numbers can be rung on one or other of the + or - lines by connecting the interrupter lead to ODN or ODP. If the calling party answers while F is up, T operates over the loop releasing F which then releases T. Back bridge relay D then comes up to the called subscriber's loop and speech ensues. If F is down when the called subscriber answers D operates directly. If the called line