Patent GB-331223-A (GB)
Title: Improvements in or relating to automatic or semi-automatic telephone systems
IPC: H04Q3/42
Filed: 1929-03-18
Abstract: 331,223. Standard Telephones & Cables, Ltd., (Hatton, W., Vriendt, C. de, and Rousseau, E. J.). March 18, 1929. Divided on 331,204. Automatic exchange systems.-A selector circuit for use at a satellite comprises two or more switches in parallel one of which gives access to junctions and local lines and the other or others to local lines only. Two systems are described. In the 1st, a connector comprising 3 100-point switches is provided the particular one to be used in a local call being determined by a signal sent back from discriminating apparatus temporarily associated with the junction seized initially. In the other system, 2 50-point switches are used and no selective signal is necessary. 300-line circuit, Fig. 1. When the call finder PF finds the line, Ltr, Ar pull up and switch Ps<1>, the wipers of which are shown hunts for a junction under control of Jtr. Jtr is followed by Mcr, Lbr, Er. Ltr falls back but Ar is held. 'The subscriber's loop is now switched metallically through to the junction and if the call is non- local, nothing further happens in the circuit. If the call is local, discriminating apparatus associated with the junction removes the test potential from the c-wire and connects full or weak ;ground or nothing to the metering wire a. Jtr, Mcr fall back, and Har, Hbr the latter of which is marginal test for the condition on the d-wire in accordance with which Ps1 is to remain connected up or to be replaced by Ps2 or Ps3. The relapse of Mcr puts a feed bridge in the talking circuit and the line relay Asr releases Ar, hulds Lbr and repeats the next 2 digits to the registers SM1, SM2. As soon as the tens register goes off-normal the selected selector begins to hunt for the selected tens group under control of Str. Dialling relay Lmr at the end of the tens digit energizes Hsr, Rcr in parallel the former connecting up the drive for SM2 and when Jtr stops the selector Ucr pulls up to change the marking from S11I1 to SM2. Jtr is held over the normal and 1st terminals in the a-bank of SM2 but if the units digit is greater than 1 falls back to drive the selector on. When Lmr falls at the end nf the digit, Esr releases Hsr. In the interval between the operation of Esr and relapse of Hsr the test circuit is made over Ftr. If the line is idle Ftr switches the talking and test wires through so that both cut-off relays are held in series with Lr. Ringing current goes out over Rgr, which, when the called party replies releases Rcr to complete the talking circuit whereupon Csr pulls up. 100-line circuit, Fig. 2. Relays Ltr, Ar, Jtr, Mcr, Lbr, Er, are operated as in the previous system during the finding of the call and the selection of a junction. Ltr falls back. If the call is local Jtr is released by the discriminating device, Mcr also falls back to insert the feed bridge and Asr releases Ar and holds Lbr. The 10's digit is repeated to SM, which on moving off-normal makes a driving circuit for the selector SMS1 which hunts under control of Jtr for the group marked by F(SM). If the digit is greater than 5, SMS1 is cut off and SMS2 (not shown) begins to hunt. When the selector has been stopped on the wanted group, Tcr pulls up and the units digit is dialled direct into the selector. Dialling relay Lmr at the beginning of the digit energizes Hsr which energizes Rcr and at the end completes the test circuit over Ffr and releases Hsr which breaks the test circuit. If the line is idle, Ftr locks under control of Er and switches the test wire through and ringing proceeds as in the other circuit under control of Rcr, Csr. Toll working. The operator puts full earth on the c-wire shunting out Er. Metering, normal release and forced release. A local call is metered once, the meter operating on the relapse of Rcr and remaining energized throughout the conversation. 'formal release takes place when the calling party releases Asr, Llvr, Er, but if he holds the circuit for 30 seconds after the called party has released Csr, a thermostat Thr operates and causes a fault relay (not shown) associated with the line to operate.