interuptor on TI tracks

[Archie]

what are the workings of an interruptor on a TI track?

Many thanks

[PJW]

Functionally as per any other track circuit; if a vehicle goes where is shouldn't (off the road at trap points or displacing a sliding bufferstop) then the TCI is broken by the wheel flange and drops a repeat relay. Older installations would make this appear as a track circuit failure to the interlocking and signaller; more modern places treat it as a bespoke input.

Whereas the old practice would just to have connected the TCI in series with the track feed via the rails to the track relay, this would never be done for TI21 (now renamed Ebitrack 200 in the "digital version"), since these are frequency tracks and not suitable re the impedance.

what are the workings of an interruptor on a TI track?

Many thanks

[Archie]

so what it is you are saying that the interruptor has it's own circuit rather than being in series with the track circuit itself, but what do you mean by the impedance?

Many thanks

[PJW]

Indeed ;the TCI will have its own circuit.
This re[presents current standards for any form of track circuit.
Howver tt has to be the case for TI21, since these work at audio frequencies and therefore any track circuit jumpers are far more significant; whereas for a dc or 50Hz ac track their resistance is not too significant, at frequencies around 2kHz then the inductive impedance begins to make a difference.
In particular most TIs are used in jointless configuration and the length of the rail leads between the actual rail and the tuning unit is critical.

so what it is you are saying that the interruptor has it's own circuit rather than being in series with the track circuit itself, but what do you mean by the impedance?

Many thanks

[Jerry1237]

Just for reference, impedence is the AC's resistance to flow. More information can be had here at Wikipedia.

[Archie]

Thanks for the replies guys

[reuben]

The TI21 track circuit acts as a giant transmission line between the rail-mounted tuning units. Here, the distance between the two running rails has a significant inductance which effectively becomes a "hidden" component of the track circuit. furthermore, the rails are carrying a very high level of current.

the connections to a track circuit interrupter would not be the right distance apart to have the correct impedance, and also the cabling would not be able to carry the current.

therefore, any track circuit interrupter on a TI21 track must be implemented as a separate DC circuit, operating an independent "interrupter" track circuit relay in the location. This can then be combined with the true track circuit relay in the TPR circuit, or sometimes may be reported separately to the interlocking.

I should also point out that the traditional "analogue" TI21 track can only be used in "jointless" mode in plain line, with the above characteristics. However, the new "EBI track 200" replacement can be used in "jointed" mode, in which the tuning units are omitted, and instead the digital TX/ RX units in the loc act as simple unique frequency transmitters and receivers. In this case the product can be used, with significant length limits, through pointwork, and it should be able to support TCIs wired in series with the RX unit in a similar way to a DC track circuit.

[timpane]

Howver tt has to be the case for TI21, since these work at audio frequencies and therefore any track circuit jumpers are far more significant; whereas for a dc or 50Hz ac track their resistance is not too significant, at frequencies around 2kHz then the inductive impedance begins to make a difference.









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