GB1020039A - Improvements in or relating to railway signalling systems - Google Patents

Abstract

1,020,039. Track circuits. MULLARD Ltd. Jan. 8, 1964 [Jan. 11, 1963], No. 893/64. Heading B7N. A system for detecting the presence of a train on a section of continuous track comprises a signal generator A connected across one end of the track section for producing a plurality of signals of different frequencies, a second generator B connected across the outer end of the section and producing the same plurality of signals at the same frequencies and detectors D1-D3 connected across the track intermediate the generators, each responsive to one generated frequency. The zones over which the generators influence the detectors overlap so that a shunt, i.e. a train axle, across the rails anywhere in section αA prevents detector D1 responding to a signal from generator A and a shunt in section #B prevents it from responding to a signal from generator B. Similarly a shunt in sections #A or #B prevents detector D2 responding to signals from generators A and B respectively and a shunt in sections γA or #B prevents detector D3 responding to the signals from A and B respectively. The arrangement thus provides five subsections, i.e. L-R, R-Q, Q-U, V-T and T-Y which are signalled as occupied when detectors D1, D1 and D2, D2, D2 and D3, D3 are de-energized respectively.