Re: Catchpoints - what are they?

[signal_spotter@my-deja.com]

Joseph,

It seems my previous attempt at drawing ascii representation of railway
lines didn't quite work. Hopefully this attempt will.

Loop lines are the adjacent line to the main line. I'll try to explain
it with a diagram.

  -0-0 S1  loop line         S2 -0-0  / catchpoint P10A (OL1 via P10N)
--+--------------0---------------+---/
        T1       OL6      T2          \
                 via P10R              \
                                        \
  -0-0 S4  main line    T4   S3 -0-0     \ points P10B  T6  OL1/4
--+--------------0---------------+--------------+-----------0--
        T3       OL6 via P10N        T5   S5 0-0-      S6 0-0-

So hopefully the diagram worked out. Anyway the legend is as follows:

-0-0   = signal, S1 denotes lever 1 etc
--+--  = track with blockjoint
--0--  = track with blockjoint that's an overlap point ie OL6 is the
overlap extremity for S6 and OL1/4 is the overlap point for S4 and for
S1 if P10 are reverse. OL1 is the overlap point for S1 if P10 are
normal.
T1     = track circuit name. A track circuit is an electrical circuit
that detects the presence of a train. The blockjoints are the
extremities of each track circuit.
P10A   = the catchpoints operated by lever 10 (A end ie closest end to
Sydney)
P10B   = points also operated by lever 10 (B end ie furthest from
Sydney)

So the operation is as follows. With P10 Normal ie catchpoints open,
points normal, you can signal a train from S1 (loop line) and S4
(mainline) simultaneously as both signals have valid overlaps. S1
detects T1, T2, T5 and (T6 when P10 reverse). So with P10 normal it
doesn't look at T6. S4 detects T3, T4, T5, T6 and P10 normal.

S6 detects T6, T5, (T4 when P10 normal), (T2 when P10 reverse).

P10 points are called 'facing' for moves from S1, S2, S5 and S6
and 'trailing' for moves from S3 and S4.

Anyway I hope this helps explain it a bit better.

regards Ian
Signal Design Engineer



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