Re: Signalling queries

["Bradley Torr" <truenorth@one.net.au.SPAMTRAP>]

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?

> 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?

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.....

> 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... :-) )...

Regards
BT