Patent GB-431005-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/00
Filed: 1934-02-02
Abstract: 431,005. Automatic exchange systems. GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, London, COLLYER, J. E., and SCOWCROFT, J., c/o General Electric Co., Stoke, Coventry. Feb. 2, 1934, No. 3445. [Class 40 (iv)] A two-co-ordinate selector has local lines and junctions connected in the same level, the first digit determining whether the call is for a local line or junction, and arrangements being provided for preventing a junction call being connected to a local line and vice-versa. If the first digit signifies a local call, the switch drops back and responds to two further digits, connection to a junction being prevented by a special potential on junction contacts in a bank of the switch. The junctions appear in the earlier positions in a level, and in case of a junction call, a hunting circuit is made in response to the first digit and if all junctions are busy, the switch steps to the 11th position, the test circuit being opened to prevent connection to a local line. P.B.X. facilities are provided, the junction groups being marked similarly to the P.B.X. groups in the P.B.X. bank of the switch. The feed bridge at the selector is cut out on junction calls. Call finder and allotter. Line relay L marks the finder bank LF3 and energizes start relay ST which operates DK in the allotter over common lead 12, wiper PA4 assumed to be standing on the link shown in Fig. 3, and vertical wiper (normal) of the connector. DR now pulls up, makes a self-interrupting circuit for magnet LF of the finder and operates A (upper) in the link circuit where B, BA, C, CC also energize. When the calling line is found, test relay FK in the allotter operates in series with cut-off relay K and energizes switching relay KF which extends the calling loop to OC and A of which OC is differential and remains inert. Line relay L falls back slowly and P in the line circuit pulls up to deal with stand still conditions as will appear later. The operated relays in the allotter relapse and magnet PA, which has also been energized, falls back to step the allotter. If the next link is busy (KF operated), the magnet is stepped on by ground from any idle link on common lead 12 connected to lead 15, an idle link being marked by battery on the normal contact of bank VB. Local calls. On receiving dial tone, the calling party dials a prefatory digit 2 which is repeated by A to series relay C (previously operated) and vertical magnet V, the original circuit of C being opened at the first step. Relays C, CC relapse at the end of the train and W pulls up over the vertical bank to operate the release magnet. The switch drops back and Z, W relapse but as W is slow, MC and WS pull up and lock, the right hand commoned contacts of the vertical wiper being disconnected by WS which also causes re-operation of C, CC. The next digit steps the switch up to the desired level and the subsequent relapse of C, CC operates changeover relay E which also re-operates C, CC and prepares the test circuit over FS4. The last digit steps the rotary magnet R and when C, CC relapse, the line is tested during the release period of E. If the wanted line is idle, H pulls up and as W has been re-operated by the relapse of CC, the wanted line is rung over F and HR operated by H connects back tone from RT. On reply, F trips the ringing, switches through and W, MC fall back slowly in turn, the call being metered over LF4 during the release period of MC. Release. On replacement by the calling party, A, B, BA, F, WS, HR and KF fall back, the release magnet Z energizes and the finder LF homes over LF5. Line busy. H, HR do not operate, and when E has released, BR pulls up to connect busy tone from BT and hold relay B. Incorrect dialling. Assuming that the calling party having dialled a local prefatory digit and a second digit, proceeds to dial a third digit setting the connector on a junction, H, HR pull up as on a local line, but as junctions are grounded in FS3, CC re-operates, sends back NU tone, and releases MC. Metering is not effected. P.B.X. facilities. If the number of the first of a P.B.X. group is dialled, HS operates over the bank SA when CC relapses and makes a circuit for the rotary magnet R in which C re-operates followed by CC which holds E. The magnet interacts with G (lower) until an idle line is found whereupon H operates in series with G (upper) which stops the hunting. If all the lines are busy, the front wiper of the pair at SA runs off the grounded group so that the middle winding of G, no longer shortcircuited, pulls up to open the circuits of the rotary magnet R and C whereupon CC falls back followed by E and BR pulls up to send busy tone. If the number of an intermediate line is dialled, HS is short-circuited over the two wipers of SA and hunting does not ensue. Outgoing calls. Junctions to a main exchange appear in level 9 and junctions to adjacent exchanges may appear in any other level except 2 and 0 which are reserved for local traffic. If the first digit is 9, W pulls up over the vertical bank before the relapse of CC which then operates E over ninth level springs np. HS now pulls up to start hunting by interaction between R and G, over junctions appearing in the first few or all the contacts of level 9, junctions being marked by ground in the P.B.X. bank SA. When an idle junction is found H pulls up and, as WS is not operated, SW operates to disconnect the feed bridge and switch directly through to the junction. All relays are now de-energized except SW, H and HR which are held over FS4 from the outgoing repeater. To call the manual board at the main exchange, O is dialled instead of 9 so that C, CC do not relapse at the end of the 9th impulse. W is operated as before on reaching level 9 and switches over the tenth impulse from the vertical magnet to MC which locks up. The switch hunts as before but when SW switches through, a battery signal is sent forward over the third wire to the outgoing repeater which signals over the junction to route the call to an operator. Calls to other exchanges are directed over levels 6 and 7, E being operated over the vertical bank to initiate hunting. As shown, levels 1, 3, 4, 5 and 8 are spare, and if any one of these digits is dialled, CC is held over the vertical bank and the relapse of C connects N.U. tone. All junctions busy. Similar operations ensue as for an all lines busy condition in a P.B.X. call. As however WS is not operated on junction calls, rotary magnet R and relay G interact when BR operates, to step the switch to the 11th position in which contacts s operate an overflow meter and hold G. Restricted service. Subscribers with restricted service have their meters SM connected to battery instead of to ground, and consequently CB, Fig. 3, pulls up and locks when the connector goes off normal. If level 7 is barred, CB holds CC over the vertical bank and N.U. tone is given as previously described. When a call is made to an operator (level 9), CB connects up a different (low resistance) battery signal to the outgoing third wire to warn the operator and CC is also held to return N.U. tone. Incoming calls, toll break in. Both-way junctions terminating in repeaters are used, and an incoming call starts up a finder LF as in a local call. In a toll call the operator on receipt of the busy flash signal, momentarily grounds the calling loop to unbalance OC while holding A. Relays F and H pull up to connect with the busy line and D operates over its lower winding. If the busy party accepts, he hangs up, whereupon HR pulls up in series with the cut-off relay, and releases BR which connects D to the called line. As the called party has hung up, D falls back and reverses the current in the calling line to signal the operator who again momentarily grounds the loop to operate OC to release F which has been held by HR. The relapse of F re-operates W to ring the wanted line, and the re-operation of D on the reply of the called party again reverses the battery feed to signal the operator. Stand still release. If dialling is delayed, TM is operated by a battery pulse over TS and holds to battery over TH. Subsequently, a ground pulse over TP releases B and the link so that the cut-off relay K is released, but slow release relay P holds over the calling loop and engages the connector multiple until the loop is opened. A similar condition arises if the calling party fails to restore after the called party has hung up, the release of D starting the forced release in this case.