Re: Signalling queries

["Tony Gatt" <baulko@optushome.com.au>]

"Bradley Torr" <truenorth@one.net.au.SPAMTRAP> wrote in message
01c0f26a$c2b6f800$5c5e65cb@default">news:01c0f26a$c2b6f800$5c5e65cb@default...
>
>
> Tony Gatt <baulko@optushome.com.au> wrote in article
> <LW%U6.2386$S5.6165@news1.belrs1.nsw.optushome.com.au>...
>
> Tony, thanks for your reply (and the two others, from B. and Eddie Oliver
> which appeared on my news server at pretty much the same time :-) )
>
> > Correct, Staff working is by posession of a physical staff (metal peg /
> token)
> > of which only one is available at any time (under correct operating
> > proceedures). Train Order working is a monitored system in which a train
> > controller issues an authority to move between points that he decides
> would be
> > best for the movement of the train.
>
> So the difference between CTC and Train Order systems (both of which seem
> to be worked centrally) is that the movement of trains on CTC systems is
> governed by signal aspects monitored and controlled from a central
> location, while with Train Order working, train movements are governed by
> verbal/written confirmation direct from controllers in a central location?

Sounds pretty correct to me.

>
> > The wheels create an electrical circuit (in a track circuited area) that
> > releases a relay (in easy terms). Whilst the circuits are bridged, the
> relays
> > will remain released. When the train leaves the previous section, the
> connection
> > between the rails no longer exists, therefore enrgising the relay and
> releasing
> > th track circuit.
>
> OK, I had the wrong concept in mind. I thought it was as simple as a train
> coming along, and a wheel making contact with a switch of some kind
> attached to a rail, and that switch was connected to the signalling system.
> So, when a train enters a track circuit, the wheelsets and axles form part
> of a circuit? What voltages are we talking about for a typical track
> circuit? Does the current of a track circuit going from one rail to the
> other via the wheels and axles have any effect on the train or on-board
> equipment? When no train is occupying a track circuit, is there any
> connection or current between the circuit on one rail and the circuit on
> the other rail?

Yes, the connection between the two rails forms the circuit. I am unsure of the
voltages used in the field. They would have no effect on the onboard equipment
when you consider the voltages being passed from the overhead to the rail in the
electrified area.
When the train is out of the section, there is no connection between the two
rails. However, there are many types of track circuiting now, I only understand
the "isolated" section theory.

>
> How long is a typical track circuit anyway? I would guess that it would
> have to be at least as long as the maximum distance between any two
> wheelsets on any piece of rolling stock on Australian railways, so while a
> train is passing over a track circuit, there will always be at least one
> pair of wheels occupying the circuit.....

That would form a minimum, Maximum would be formed by the maximum allowance for
the electricals to traverse the area efficiently. Wheel counters are used on the
Unanderra / Moss Vale line between Unanderra and Robertson because of the length
of the sections.

>
> > No probs. There are a couple of signal engineers in here that will gladly
> give U
> > all the information U need.
> > I only can explain the basics :)
>
> That's okay, I only want the basics! :-) The last time I asked a signalling
> question - "What are catchpoints?" - I got deluged with a veritable tidal
> wave of incomprehensible jargon and technical nit-picking! (That's OK Ian,
> I forgive you now... :-) )...

Catchpoints are a set of points or a single point designed to "divert" trains
away from another line if they pass a signal at stop. Iff the line is not set
for the movement, the catch will be "open" to catch the train at a distance that
prohibits it coliding with another train. They are usually found on branch lines
or sidings.

>
> Regards
> BT
>