Re: Signalling queries - Jointless tracks

["B." <b.spammed@four12.net>]

"Paul Jones" <zifnab_spam_@goconnect.net> wrote in message
9g2bav$6elmj$1@ID-90616.news.dfncis.de">news:9g2bav$6elmj$1@ID-90616.news.dfncis.de...

> While we are on the topic of signaling systems, can someone please
> explain how jointless track systems work? Does it detect the time on
> the return path of the power on the tracks to determine where the train
> is, or does it have something to do with thoes biege boxes that are
> alyaws in triplets??

There are basically 2 different flavours of Jointless Track Circuit, the
audio frequency overlay type, and the type that uses 'electric joints'.

The audio frequency overlay jointless tracks simply transmit at about 10kHz
at the Tx end of the circuit, and a receiver at the Rx end looks for voltage
at this frequency.  At these sort of frequencies the attenuation in rail is
not insignificant, so unless the train is between the Tx leads and the Rx
leads, or within a short distance of this area, then the receiver will see
the AC and energise the output track relay.

These type of tracks are used in Victoria on the NE SG at the Level
crossings, and can be used to 'overlay' DC (plain & coded) Track Circuits
used for the signalling.  They are also to be found in every Crossing
Predictor acting as a short Island Track across the roadway.  The other
place they are used in numbers is across the TAR, to track lock the self
restoring turnouts at the remote loops.

The other type is that used for virtually all modern suburban track
circuits, 'jointless tracks'.  There are 3 types I know of in service,
Adtranz TI21's, CSEE, and the WSA FS2xxx (can't remember the proper model).
These are the ones that use the small trackside boxes.  These use much lower
frequencies, 1700Hz to 2600Hz IIRC.  In order to define the limits of the
track circuit, thru some sort of black magic the little boxes form a
resonant circuit at the required frequency that constrains the particular
frequency to it's block.  There is still a Tx and an Rx end, (you can get
centre fed tracks thou), and any train between the electric joint will drop
the output relay.  As you can probebly tell I've never had to deal with the
jointless tracks, only AFO's.

Well at least that's how I think it all works... E&OE

$ cat flame > /dev/null

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