General Information on Track Circuits - RGS Online

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Railway Group Approved Code of Practice GK/RC0752 Issue Two Date December 1998 Page F4 of 5 5 Track Circuit Fault Detector Withdrawn Document Uncontrolled When Printed <strong>General</strong> <strong>Information</strong> on Track Circuits The clip assembly should then be plainly marked for attention by the Permanent Way Engineer. The brush carriers can be raised/lowered to cater for flat or Pandrol type rail clips by moving the brush carrier handle to its vertical position to release the locking mechanism. Care must be taken to ensure that the rollers of the unit do not straddle any IRJs, causing “flicking” of adjacent track circuits. Short circuits between the rails can be difficult to locate, since, except for audio frequency types, the short circuit results in an identical drop in rail voltage along the length of the track circuit and gives no clue as to its physical location. Without the Track Circuit Fault Detector, it would often be necessary to sub– divide the trackwork to locate the faulty section. The detector is designed to be used on the trackwork of a track circuit where the feed and relay have been disconnected. It consists of two portable battery powered units: a transmitter and a receiver. Transmitter This is housed in a box incorporating an “on/off” switch and an LED indication. Yellow leads with clips are provided to connect the unit across the rails or lineside apparatus housing links. It is battery powered and outputs an intermittent high frequency voltage. Receiver This is housed in a box incorporating an “on/off” switch and an LED indication. It is battery powered and incorporates an internal aerial, amplifier and loudspeaker. When the receiver detects a signal from the transmitter it outputs an audible tone. Before commencing to test the bonding of a track circuit, the track circuit fault detector should be checked as follows: a) The transmitter leads should be connected together and the transmitter switched on. b) The receiver should then be switched on and held near the transmitter leads; an audible tone should be heard emitting from the receiver (this simple test will prove that the fault detector is working correctly). c) The feed and relay ends of the track circuit under test should be disconnected. With jointless track circuits, the track circuits either side of the track circuit under test should also be shorted out. d) The transmitter should then be connected across the rails at the feed end and switched on. The receiver is switched on and held near the rail; an audible tone should be heard emitting from the receiver. No tone may indicate a bad connection to the rails. If the rail connections are good, the fault is an open circuit, which may be found in the conventional manner. If an audible tone is heard, the receiver should then be carried along the track near to the rail and when the receiver passes the short circuit, a distinct drop in the volume of the tone will be noted. F4 R A I L T R A C K
<strong>General</strong> <strong>Information</strong> on Track Circuits 6 Mark 4 Direct Reading Phase Angle Meter Withdrawn Document Uncontrolled When Printed Railway Group Approved Code of Practice GK/RC0752 Issue Two Date December 1998 Page F5 of 5 e) With audio frequency track circuits it may not be necessary to disconnect the feed, as the receiver will detect the steady tone of the feed frequency until the short circuit is passed. If this method does not prove successful, the transmitter should be used in the conventional manner. f) The rail impedance limits the useful range of the device (as measured from the transmitter). Where this occurs, the transmitter is simply moved to another position within the track circuit and the test repeated. Details are contained in GK/RC0757 Part E. R A I L T R A C K F5
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