Patent GB-916635-A (GB)
Title: Improvements relating to automatic telecommunication switching systems
Inventor: WARMAN BLOOMFIELD JAMES
IPC: H04Q3/42
Filed: 1959-01-01
Abstract: 916,635. Automatic exchange systems. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. Dec. 31, 1959 [Jan. 1, 1959], No. 102/59. Class 40 (4). In a system in which a start circuit seizes a control circuit which sets a finder to a calling line, the line circuit comprises a bi-stable circuit which is set by the action of the start circuit and thereby returns a signal to the start circuit permitting the line-finder action to proceed. The bi-stable circuit is reset when the linefinder finds the calling line. This arrangement prevents the start circuit from seizing a further control circuit in the event of a protracted hunt by the line-finder originally allocated to the call. As shown, closing of the line loop +, -, causes the application of marking potential to lead ml and starting potential to lead stl, the latter operating start relay ST which starts a line hunter F looking for the marking ml; when this is found test relay T operates, stops the switch and brings up TS which releases ST. Meanwhile, ST has also caused selector H to hunt for a free register having access to a free transmission bridge XB which has access to the calling group. The requisite tests are made by TFB and TF respectively, the selector stopping when both operate and TFS then comes up. Saturable core C is normally in the reset state and when TS operates it is changed to its set state over winding Ws and the consequent output pulse from winding Wo operates PS. Relay TT now operates and signals the identity of the calling line to the register in coded form over banks F2, F3 and group indicating strappings to wires h. Double voltage is obtained for this purpose by connecting a charged condenser C in series with the exchange battery. Relay TT releases PS and TS, whereupon TT releases. The register then seizes a free transmission bridge XB and sets its line-finder LF by revertive impulsing. Relay BB then comes up to earth the P-wire and bring up cut-off relay K which locks. Relay K energizes the reset winding Wr of the core C. The call is then set up in known manner. If another call is waiting then when TT releases, with ST up F and H hunt as before differential relay DF co-operating with arc F4 to ensure that the switch F takes another step before the test relay T again becomes effective as described in Specification 916,632. If the start circuit completes its operation for the second call before K has operated in respect of the first call, then when the line hunter again tests the first line, with core C now in the set condition, the output winding Wo will not give an output pulse and PS will not operate. Relay TT therefore fails to operate and no identity is signalled to the register. With TS and TFS up, a timer AT is started. If K operates during this period T releases to clear down the start circuit, otherwise AB comes up at the end of the period and operates TT to signal the identity to the newly seized register which thereupon tries to effect the connection. Relay AB also changes over the condition of CO which substitutes the standby start circuit ST2 by releasing PG therein and operating PG in the present start circuit. CO may also bring up an alarm. The standby circuit may operate as a restoring circuit for locked-out lines in a manner similar to that described in Specification 916,632 with the exception that LT tests the line loop directly instead of via a potentiometer and a transistor. Specification 886,279 also is referred to.