Patent GB-394772-A (GB)
Title: Improvements relating to automatic telephone systems
IPC: H04Q3/58
Filed: 1932-03-21
Abstract: 394,772. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., Caxton House, Tothill Street, London, LONG, D. P., 3, Ingleby Way, Chislehurst, Kent, and PATTERSON, W. G., 68, Eltham Road, Lee, London. March 21, 1932, No. 8325. [Class 40 (iv).] In a satellite exchange, a single-motion switch SMS which gives access to main-exchange junctions and local switches is associated on the initiation of a call with an idle one of a plurality of common discriminating circuits each comprising a single-motion digit switch DS 1 .. 8 responsive to from one to four digits. If the call is local, the main-exchange junction first taken into use is released and the discriminator switch controls the switch SMS by marking. The switch SMS has two sets of wipers and each wiper is double-ended with the ends engaging successively with different rows of contacts. Each discriminating circuit comprises two finder-switches P1 .. P16, Sl .. S16, of which the first hunts for a calling link and the second is then set to the same position. Connection to idle discriminator. When the link is seized, relay WS operates over wipers 13, 9, and the incoming test wire p, completing circuits over contacts of normally-energized relays GP for start relays SS in the first.idle discriminating circuit in each of two sub-groups of such circuits. Relay SS energizes the latch magnet LMP of finder P1 .. P16, and when the calling link is reached relay TA operates in series with relay K (i). During the hunting operation relay WS remains held by ground applied to the wire p over contacts k3, h3, h2, k2, and the calling loop. Relay TA operates TB which connects up impulse relay A, and relays B, C (i), operate releasing TA. Magnet LMS of finder S1 .. S16 is now energized and the second finder rotates until wipers P1, S1 occupy corresponding positions when TA again energizes. Starting- circuit arrangements. Normally, relay GP controlling the starting circuit in each discriminator is energized over its winding (ii) and the normal contact of wiper P1. When the starting relay SS operates, GP commences to release but its release period is long enough for the finder P1 .. P16 to move once round its bank. As soon as the finder moves off normal, relay FX operates releasing SS which connects the two differentially-wound windings of GP in series so that the relay continues to release. The arrangement is thus such that the starting circuit will be extended to the next discriminating circuit after the end of a definite time-interval corresponding to the release period of GP under all circumstances and even if the circuit seized is faulty. This feature forms the subject-matter of Specification 394,775. Seizure of main-exchange junction. Relay B completes a circuit over wiper P7 for latch magnet LM of switch SMS and connects the test relays TP, TS over contacts l1, l7, two of the marking banks P9 .. S6, S7 .. S16, wipers 15, 13 to test wipers 11, 9. Testing over both banks occurs simultaneously and when an idle junction is found relay TP or TS operates, followed by PT or ST which completes an outgoing loop over wipers P4, P5. If idle junctions are found by both test wipers simultaneously relay TP is given the preference since it disconnects ST, and PT disconnects TS. Relay PT if operated energizes the wiperswitching relay WS over wiper P15. If all junctions are busy, the switch continues to the last terminals in the second part of the bank when relays TS, LA, operate and dialling tone is transmitted from lead DT. Discrimination. Impulses dialled are repeated by relay A to the main exchange and to magnet DSM, relay C releasing at the end of a digit. If the first digit dialled is such that it is not yet determined whether the call is local, the contact engaged by wiper DS4 is j umpered to terminal E so that relay E operates to move the digit switch to its-second normal position in readiness for another digit. Similar operations may take place after the second and third digits, relay X being operated after the second so that discriminating bank DS5 is connected up for the third and fourth digits. Relay X also changes over marking leads in banks DS2, DS3 so that different outlets may be marked for the digit O as a first and as a third digit, the single digit O being used for calls to an operator. When it is definitely established that a call is local, relay L operates over a jumpered connection from bank DS4 or DS5 to terminal LE, PP, or RL, to open the outgoing loop and release the main-exchange connection. If the jumper is to terminal PP indicating that the connection will go over the second part of the bank of switch SMS i.e. the dotted portion, relay PP operates in series with L connecting up magnet LM and changing over the connection to relay TS so that this relay will test for ground instead of battery and will operate over wiper P14 to stop the switch at the beginning of the second part of the bank. On a subsequent digit determining the wanted local group relay R (i) operates over terminal R connecting up magnet LM. Relays TP, TS test simultaneously over wipers 11, 9 (or 12, 10), in the groups of terminals marked in banks 15, 13 (or 16, 14), by wipers DS3, DS2, over two of the banks P9 .. S16. If the digit which determines that a call is local also determines the group required, connection is made to terminal RL and relays L (ii), R (ii), both energize. When an idle outlet is found, relay ST or PT completes a circuit for relay H which switches through. If all outlets are busy the switch SMS moves to the last contacts of the dotted bank when relay LB operates in series with TS and connects up busy tone BS (or NU tone of the group is a dead group in which case relay SL operates over bank DS8). If the number dialled indicates a main-exchange connection, relay M operates over terminal M connecting up relay H which switches through. If, however, no idle junction has been found so that switch SMS has moved to the end of the bank as described in a previous paragraph busy tone BS is supplied over contacts la 5, m 2. The transmission forward of a discriminating signal over wiper DS7 or DS6 and terminal FS, and the operation of the circuit in response to the receipt of no impulses or of a single accidental impulse take place in a manner similar to that described in Specification 378,585.