GB1013568A - Improvements relating to track circuits for railway signalling - Google Patents

Abstract

1,013,568. Track circuits. BRITISH RAILWAYS BOARD. May 7, 1964 [Feb. 7, 1963], No. 5079/63. Heading B7N. In a continuous rail track circuit which is formed into a closed circuit by connections joining the rails at the ends A, B of the circuit, pulse generators are provided at each end of the circuit each of which delivers a current pulse to the track rails a predetermined time after receiving a pulse from the other generator and means are provided for indicating cessation of pulse generation. Each generator includes a coil 2 coupled to the rails which passes a pulse generated at the other end of the section to a delay device 6 which at termination of the delay energizes a pulse generator unit 4. The generated pulse is applied to a limiter 5 which supplies a signal to inhibit delay device 6 during pulse transmission and transmits the pulse to the rails via coil 3. A selective device 7 tuned 1 to the pulse recurrence frequency, i.e. T1+T2 T1+T2 where T1 and T2 are the delay times of the two delay services 6, respectively, provides an indication when pulse transmission ceases on entry of a train into the circuit. A further pulse generator 11, operating at a lower pulse recurrence frequency, triggers its associated pulse generator 4 to re-commence transmission when the section is free. The signals may be an audio frequency carrier signal modulated at the pulse recurrence frequency. The Specification also described how the apparatus may be time shared between adjacent sections and how aspect control may be achieved by alteration of the pulse recurrence frequencies.