Re: [NSW] Granville question re signals

[signal_spotter@my-deja.com]

In article <itbw5.16813$cr3.444008@ozemail.com.au>,
  "Chris Downs" <cvdowns@ozemail.com.au> wrote:
> I stood at the Sydney end of Granville's platforms 1 & 2 for  half an
hour
> last night.
>
> Watching OP yo-yos on the up main they were leaving Granville and
running
> express to Lidcombe.  Four up main signals are visible, Granville up
main
> starter (1), up main intermediate before Clyde (2), Clyde up main
starter
> (3) and the following up main signal (4) on the way to Auburn.
>
> When a train leaves Granville on no occassion did sig 1 clear before
sig 2.
> I assumed sig 1 was being hald at danger by the signaller but
continued
> observation suggested this wasn't necessarily the case.  Once the
train is
> well on its way to Auburn the aspects shown at 1=G/Y, 2=G/Y, 3=G/R &
4=R/R.
> 1 & 2 show the same aspect due to the short distance between 3 & 4.
The
> part I don't understand however is that 2 when from G/Y to G/G several
> seconds before 1 went from G/Y to G/G every time.  The result was a
sequence
> of four signals showing G/Y, G/G, G/Y & G/R.
>
> Does anyone know why this is so?
>
> Ta
>
> Chris
>
>
Possibly due to the delay in processing. (1) signal would look at (2)
at G/G before stepping up to G/G in the logic.

ie The SSI data for S1 aspect sequence would look as follows:-

G s 73                 (R/R)
if S2 set <y           (test for S2 memory at 'better than G/R')
then G s 5             (drive top green lamp ie output 5)
     G c 7             (turn off top red lamp)
     if S2 set fyy     (test for S2 memory at G/Y)
     then G c 3        (turn off bottom red lamp)
          if S2 set g       (test for S2 memory at green)
          then S1 set g     (set S1 signal memory to green)
               G s 1        (drive bottom green lamp)
          else S1 set fyy   (set S1 memory to G/Y)
               G s 2        (turn on bottom yellow lamp)
          \
     else S1 set y          (set S1 memory to G/R)
     \
\


Hope this helps.

regards Ian
Signal Design Engineer


Sent via Deja.com http://www.deja.com/
Before you buy.