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2012 - Oct - Walsh - Audio Frequency Track Circuit Reliability Investigation 2012 - Oct - Walsh - Audio Frequency Track Circuit Reliability Investigation

Alexander Walsh BEng(Computer)


Audio frequency track circuits are used extensively in railway signalling to detect the presence or absence of rail traffic. When track circuits fail they will indicate a section being occupied as part of their fail-safe design. This typically results in rail traffic being stopped and/or delayed.

The scope of this investigation is to gain a more thorough understanding of the design, specifications, operation and behaviour of these track circuits. An experimental approach has been used to relate theory with field measurements.

Frequency sweeps provide a new perspective to examine tuning and may prove to be an invaluable tool in diagnostics. A thermal testing program is identifying frequency drift in analogue transmitter and receiver units, The rail current meter is enhanced to allow simpler fault finding and an intermittent transmitter detector is developed.

The data and results of this investigation have identified reliability improvements that are expected to reduce the number of repeat failures and to better aid in the diagnosis of intermittent faults.


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