Chapter 17 Train Detection Track Circuits & Axle Counters PDF

17.3.13 Rusty Rails: Where there are rusty rails in the track circuited areas zig-zag welding using steel wire shall be done by P-Way staff on top of rail to ensure shunting of track circuit by the vehicle. Such identified locations to be provided with Axle Counters. Till suc...

17.3.13 Rusty Rails: Where there are rusty rails in the track circuited areas zig-zag welding using steel wire shall be done by P-Way staff on top of rail to ensure shunting of track circuit by the vehicle. Such identified locations to be provided with Axle Counters. Till such time axle counters are being provided, working instructions should be issued that points are operated only after physical verification of complete arrival of train by ASM, and facility of sectional route release be restricted to be provided only where it is essential. (Axle Counters shall not be provided in parallel to “Rusty Rail Track circuit”) Note: Refer to Annexure: 17-MS2 for maintenance schedule of DC Track Circuits. Section 4: Audio Frequency Track Circuits (AFTC) 17.4.1 Audio Frequency Track Circuits (AFTC) – General (a) The use of audio frequency permits the physical limits of an individual track circuit to be defined by tuned short circuits between the rail rather than the insulation in the rails themselves. These types of track circuit have distinct advantage of not requiring IRJs (except Point Zones) and offers considerable saving in IRJs and impedance bond, especially on tracks subjected to high speed, high axle load traffic or where there is an intensive service. (b) Main features of Audio Frequency Track Circuit are: (i) Built in time delay, therefore a slow to pick up QSPA1 Relay as TPR is not required. (ii) Can be used in most AC, DC electrified and non-electrified areas. (iii) Can be used in end or centre-fed configuration. (c) Only approved type Audio Frequency track circuit shall be used. (d) Track circuit shall not be configured in single rail mode operation. (e) Audio Frequency Track Circuit may be operated as local fed or in a remote fed mode. (f) Audio Frequency Track Circuit’s components are (i) Tuning unit (ii) Transmitter (iii) Receiver (iv) Power Supply (v) Track Connections (vi) Impedance Bond (as applicable) Chapter 17: Train Detection Track Circuits & Axle Counters Page 340 of 530 17.4.2 Installation and Maintenance of AFTC (a) Installation of track circuit shall strictly follow the instructions given for that type of track circuit. (b) Tuning area shall be devoid of check rails, level crossing, insulated bond and each fish plated joint shall be bonded with jumpers of adequate thickness. (c) Special precautions shall be taken to ensure the tightness of connection of rail and tuning unit. (d) A frequency assignment scheme for the track circuit shall be decided in advance and it shall be strictly followed. (e) Terminal junction on insulation joint to track circuits with the same frequency is prohibited; however, frequencies not belonging to same pair can be used. (f) Cable cores of same cable shall not be used for connecting transmitter & receiver of a track circuit. (g) When wiring and installing track circuit, circuit pairing should be observed in the line cables. Each transmission or reception shall use conductors from one same pair. Circuit pairing results in cable transmission parameters being changed and may induce significant cross talk levels in adjacent circuits. (h) The design and installation of field equipments should take in account the requirements for mechanised track maintenance and should not be hazard for men walking along the track. (i) Protection against atmospheric voltage surges shall be installed on each pair of conductors providing a link to the outside in order to limit the harmful effect of lightening on electronic equipment. This protective arrangement shall cover against both common mode and differential mode voltages on line. (j) Transmitter, receiver and power supply shall be mounted in standard relay rack in a manner to allow maintenance and testing staff to view the track relay while making adjustments. (k) TUs and ETUs shall be mounted at a minimum distance of two meters away from the near rail as it gives good safety margin to staff. (l) In case of failure of track circuit, attempt shall not be made to pick up the track circuit by adjusting the gain of receiver of TC without investigating the cause of drift in the receiver voltage. (m) Impedance bond within track circuit shall be tuned with the correct resonating capacitor across the auxiliary coil and this tuning shall match with the frequency of track circuit. Chapter 17: Train Detection Track Circuits & Axle Counters Page 341 of 530