CPL signals and how they operate (NW Mailing List)

[NW Mailing List]

Thanks to everyone that has been contributing to the discussions.  I for
one, have learned a great deal.  I was completely unaware of intermediate
steps between all amber position lights to the colorized version that was
in place when I started looking.  Please allow me to restate what has been
presented to check my understanding.



First, in 1958, the lenses for lamp positions zero and one were changed
from amber to red, and the logic was changed such that when those lamps
were lit (and only then), the N (neutral or center) lamp would be unlit.

Was the lower arm N position lens in home signals changed to red at this
time as well or did this come later?



Rick stated in his post:  “It was several years later that Top and Bottom
were changed to green.”

So now we would have the familiar 0 and 1 red, 45 and 46 amber and 90 and
91 green.  What about N at this time?  Was it off all the time or was it
lit with 45 and 46?



I don’t have a complete set of ETTs, but is it possible to track these
changes by the aspect diagrams printed during this evolutionary period?
Did they show two horizontal reds for “stop and proceed” along with three
vertical ambers for “clear”?



More to follow shortly,
Jim Cochran

On Fri, Jan 24, 2020 at 6:33 AM NW Mailing List <nw-mailing-list at nwhs.org>
wrote:

> Jim
>
> Position lights weren't supplanted by CPLs.  And we have to be careful
> with semantics here.  What the N&W ended up with were "Colorized Position
> Light" signals.  Most purists agree that Color Position Lights"those
> favored by the B&O are an entirely different genus.  The N&W CedPL signals
> were an evolution. The first mutation in 58 only changed the Left and Right
> bulbs to red and extinguished the center bulb at the same time.  The other
> two positions were still three fog penetrating yellow.  It was several
> years later that Top and Bottom were changed to green.  In both cases the
> signal heads weren't changed just the light bulbs.  It was still later that
> the center bulb (only on top heads) was removed.  There was logic work to
> turn the center bulb on and off before it was just removed.
>
> The coded track system was used on the Shenandoah Div first as part of the
> cab signal and Automatic Train Control system.  The tradeoff was that it
> could use the rails to convey occupancy information between blocks and
> reduce the number of pole line wires but with more relays and logic.
>
>
> Stoney
>
> Rick C Stone
>
> NWHS #0001
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