IMPROVEMENTS IN OR RELATING TO RAILWAY SIGNALLING APPARATUS AND SYSTEMS

摘要

1451431 Continuous rail track circuit GEC-GENERAL SIGNAL Ltd 16 Oct 1973 [18 Oct 1972] 47938/72 Heading B7N In a continuous rail track circuit with ends defined by shorting links 14, 16, in which a low frequency transmitter 22 supplies a signal, e.g. of 375 hertz, to the centre of the circuit which in the absence of a train is picked up by receive coils 26, 46 disposed near the ends of the circuit and connected to receivers 24, 44 and in which higher frequency overlay track circuits having transmitters 30, 48 supplying a carrier signal modulated by a track circuit tone are used to define clearly the ends of the circuit, the overlay track circuit transmitter 30 at the leaving end of the track circuit is also modulated with cab signalling tones 40, indicating the condition of an adjacent track side signal 28 and possibly speed and other restrictions. In each overlay transmitter, e.g. 30 a carrier source 34 feeds a modulator 36 in which the carrier, e.g. of 25 K hertz is modulated by the track circuit tone which can be the frequency of the transmitter 22, the modulator associated with the leaving end circuit is also fed from the cab signalling source 40. Each of the track circuit receivers 24, 32, 44, 56 controls a relay 58, 60, 62, 64 having a contact in the signal control circuit of the preceding track section. The connection of the overlay transmitters to the track is adjacent the receive pick up coils, e.g. 26 of the main track circuit. The cab signals are picked up by pick up coil 82 on the train in the approach to the connection point and on the train the signals are demodulated 84, decoded 86 and applied to a drivers display 88 which is self latching to retain the display until the next signalling location is reached.