GB445515A - Improvements in track circuits for railways - Google Patents

Abstract

445,515. Railway signalling systems. GENERAL RAILWAY SIGNAL CO., Rochester, New York, U.S.A.-(Assignees of Rees, F. X. ; 37, Bancker Street, Albany, New York, U.S.A.) Sept. 11, 1935, No. 25291. Convention date, May 29. [Class 105] A direct-current relay R at one end of a track section is energized by time-spaced unidirectional voltage pulses applied at the other end of the section and having a peak value materially greater than the rated voltage of the relay. An automatic compensation for variation in the ballast resistance is thus obtained since with increased ballast resistance the inter-rail voltage rises (by reason of the smaller drop in the limiting resistance) to give a higher peak value to the relay current but on account of the higher decay rate of the current between the pulses, due to the higher ballast resistance, the mean current remains approximately constant. A resistance or reactance 3 is inserted in series with the track relay R and the higher voltage thus required serves to break down the film resistance of the wheel shunt. The voltage pulses may be obtained by inserting a copper-oxide type half-wave rectifier 5 in series with the secondary of a track-circuit feed transformer 4. Such rectifier has an effective resistance value which increases with decreasing current and thus further aids in the automatic compensation. The current decay rate, and therefore the average current can be adjusted by placing a resistance 7 across the rails at the feed end. The time-spaced voltage impulses may be given by a battery over a back contact of a vibrating relay.