Patent GB-577570-A (GB)
Title: Improvements relating to railway signalling systems
IPC: B61L3/22
Filed: 1943-10-27
Abstract: 577,570. Railway signalling systems. WESTINGHOUSE BRAKE & SIGNAL CO. LTD. Oct. 27, 1943, No. 17725. Convention date, Jan. 8. [Class 105] In a railway signalling system wherein cab signals are given by coded alternating current in the rails operating an inductive receiver on the locomotive there is applied to the rails of a section in rear of an occupied section an alternating current of lower voltage during the " off " periods between the impulses constituting the caution code whereby a more restrictive signal (stop) is given as a train approaches the exit end of a section in rear of an occupied section ; this arises from the increasing rail current during the " off " periods becoming capable of operating the locomotive receiver coils which action in conjunction with the current during the " on " periods of the code in effect gives an uncoded rail current. To guard against failure of the lower rail voltage a relay is included in series with this supply and a front contact of such relay is included in the line for the caution codedcurrent supply. This additional lower voltage supply is applied only in a section being supplied with a " caution " code. In the arrangement shown coded current is supplied to the rails of a section 5T under the control of a relay 5CTM operated at 180 or 75 times a minute according as the ahead section 6T is free or occupied as reflected by a relay 6H such code operating a code-following track relay 5TR to energize a relay 5H similarly determining the code applied to section 4T. With section 6T occupied the relay 6H closes its back contact 10 so that contact 12 of relay 5CTM is operated 75 times per minute. When contact 12 closes its back point an impulse of lower voltage alternating current is applied to the rails of section 5T from the secondary winding of an auxiliary transformer 5TTA through a slow release relay 5AR (energized by a full-wave rectifier 5R), the primary winding being energized over a back contact 11 of relay 6H. When contact 12 closes its front point an impulse of higher voltage alternating current is applied to the rails of section 5T from the secondary winding of a main transformer 5TT, the primary winding of which is energized over front contact 14 of the slow release relay 5AR. If now a train enters section 5T a caution signal will at first be given since the locomotive receiver will be operated by the 75 coded higher alternating current voltage immediately on entry but as the train proceeds along the section the rail current arising from the application of the lower alternating current voltage during the " off periods of the code will eventually increase sufficiently to operate the collecting coils of the locomotive receiver and the combined effect will be equivalent to that of an uncoded current and so give a stop signal a sufficient distance prior to the occupied section 6T. It will be seen that a battery 5TB is shown in series with the secondary winding of the main transformer 5TT to operate the track relay 5TR but alternating current may be employed, Fig 2 (not shown).