04-10-2012, 12:29 PM
It's worth adding that almost universally today, a "DC" track circuit is powered by a transformer-rectifier set from a 110V AC supply. As there is a separate unit for each track circuit, this creates a "virtual battery" for each track circuit, electrically isolated from all others. The "DC" voltage will therefore actually be full-wave-rectified AC and so very lumpy compared to true DC, but the relay only cares about the mean DC level.
It would be perfectly possible to create a microprocessor-controlled track circuit with the ability to self-adjust for changing conditions or to report faults through a serial link, but this option isn't used in the UK.
I do seem to recall (i reserve the right to be wrong here!) that the new digital TI21 track circuit (EBI track 200) has some sort of self-diagnostic capability. I've also encountered the AF902 track circuit (former US&S product, now Ansaldo STS), which is microprocessor controlled and can interface to the interlocking through a serial link, so this also has that potential. It's not used in the UK.
reuben
It would be perfectly possible to create a microprocessor-controlled track circuit with the ability to self-adjust for changing conditions or to report faults through a serial link, but this option isn't used in the UK.
I do seem to recall (i reserve the right to be wrong here!) that the new digital TI21 track circuit (EBI track 200) has some sort of self-diagnostic capability. I've also encountered the AF902 track circuit (former US&S product, now Ansaldo STS), which is microprocessor controlled and can interface to the interlocking through a serial link, so this also has that potential. It's not used in the UK.
reuben