Patent GB-637145-A (GB)
Title: Improvements relating to automatic telephone and like selective systems
IPC: H04M3/08
Filed: 1948-02-06
Abstract: 637,145. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., and LONG D. P. Feb. 6, 1948, No. 3592. [Class 40 (iv)] In an automatic telephone system, a calltracing arrangement comprises a test device connected to the known end of a set-up connection, and automatic switching apparatus which hunts for the one required among all such possible connections, applying an operating potential to each in turn until the required set-up connection is found and the test device operates. As described, a test relay T is connected to a final selector FS, and automatic switching apparatus hunts for the line finder F connected to the said final selector FS by a through private wire shown at the top of the diagram, the holding relays HL, HA, HB, HF having been operated. To start the tracing, a plug TJ is moved from the top and middle to the middle and bottom contact springs of its jack and a key ENG is then operated, replacing holding earth FSW by a connection to earth through a rectifier MRA and a relay HP, which is part of equipment REQ common to all the final selectors on a rack.. HP operates to prepare a circuit for a coupling relay TC which is then energized by closing a key TK, thus operating a supervisory lamp SY and a start relay S and connecting the through private wire to earth through the test relay T and a rectifier MRB which prevents flow of current from ordinary battery. S brings up SR which completes a circuit for a latch magnet FA to start a uniselector, positive battery being applied over a wiper FA1 to the private wire of each line finder in turn. Relay RA operates, followed by BR which prevents the operation of any further coupling relays TC by disconnecting battery from their operating windings (II). Relay NR operates when an offnormal contact FAN2 opens, bringing up relay NS and releasing SR. When the uniselector returns to normal, NR releases followed slowly by NS, a circuit being first closed and then opened to advance a sequence switch CS one step, thus replacing wipers FA1, FA5 by another pair. SR once more operates, and the hunting continues. This process is repeated, if necessary with further uniselectors FB, FC, until the required through private wire is reached by one of the wipers such as FA1 over which positive battery is applied. The test relay T then operates to energize a high-resistance relay TB, releasing the latch magnet and stopping the wipers, and to operate a relay TA which disconnects the positive battery from the through private wire. A lamp PLF is lit over a contact SFT and wiper CS5, a lamp PRQ is flashed to indicate the rack or small group of racks containing the required line finder F, a lamp PSQ shows the suite of racks concerned, and a lamp PG flashes to indicate that the line finder F is the one required. If, through a fault, relay T is not energized when all the uniselectors FA, FB, FC have operated and the sequence switch CS has completed twelve steps, then the release of NR causes relays NS, TA to operate over their windings (II) and wiper CS3, disconnecting positive battery from wiper CS7 and holding relay SR inoperative. Interrupted earth is applied from a line IEW over wiper CS9 to flash a supervisory lamp SY. When the key ENG is restored at the end of a call-tracing operation, all the switches home and the equipment returns to normal. According to the Provisional Specification, the plug TJ and keys ENG, TK may be restored without releasing the relevant coupling relay TC which is held until released by any one of a number of multipled release keys distributed over the exchange equipment; also the positive battery applied as an operating condition over wiper CS7 may be replaced by A.C.