 1.
Station box and interlocked lever frame. The bells are
connected to the pushes in the fiddle yard
control shown below.
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Clutton comprises a passing
station on a single line - in model form it became a
station with a passing loop at the front and a fiddle
yard at the back - in the form of a dumbbell. I thought
long and hard about what irritated me most observing
other layouts and exhibiting and operating layouts.
Exhibiting puts enormous strains on the operators and I
wanted to reduce this load. The main problem I saw was
the operators being asked to do too much i.e. they had to
set routes, often through a multitude of points, set
section switches and maybe signals (dependant on the
layout). Once the train had passed, they were required to
reset the route, signals and section switches to the off
position The results of operators being asked to do to
much were seen with derailments at incorrectly set
points, engines moving that were supposed to be off and
fingerpoken troubles of sticking engines, found to be a
section switch or route incorrectly set. This is a subject I personally find of
great interest. Amazingly little has been written in the
model press on designing in reliability with notable
exceptions being an article by WE Ward-Platt (Railway
Modeller 'Oct 65) and Stewart Hine (Model Railways
Feb'76).
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 2. Fiddle yard control
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The criteria I set down were: -
A) Reliability B) Near the Prototype
C) Reduction in the
number of operations to achieve a desired result
D) High profile
E) Interaction between
different operators
I found inspiration in the
prototype - where you have interlocked lever frames with
block instruments relying on the interaction of two
people resulting in high reliability. This discussion
deals with the Block Instruments, which have eliminated
section switches on my layout.
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As this is a single line, I
made imitations of the Key Token Instruments (see photo
1) which comprise of 3 position wafer switches and a bell
key switch (a standard microswitch). Instruments are
duplicated in the fiddle yard and station box (lever
frame and station box are out on the front of the layout
for the visitor to see). The wafer switches control a
relay logic system that replaces ordinary section
switches. So instead of throwing a series of switches in
sequences, the wafer switch, dependant on what position
it is in, selects different combinations of sections. For
shunting purposes, providing both token instruments show
"token in", a strategically placed switch
overrides all sections in the station. Should either
token instrument be moved, the shunting switch is
isolated out. |
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Consulting the photographs, you
should see subtle differences between the instruments at
the station and in the fiddle yard. In operation, when a
train is accepted by the far signal box, the operator
turns the key token instrument to the appropriate
"key out". In reality a token is issued, I did
not see this as feasible, so a positive indication is
given via a meter, which represents the token. In the
station, the starting signals are interlocked with the token
instruments, a post 1948 amendment, not strictly correct for GWR practice
before this period. It was recommended in the inspector's report of
the Abermule disaster where the token was given back to the driver for
the section he had just traversed. It wasn't put into practice at all
locations. |
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How is this done? The diodes
ensure that should the switches be incorrectly set, the
relay will not energise and the meter will not release
the token and the train cannot therefore be driven into
the section. The relay logic is shown in simplified form
for a passing loop. A
split potential power supply is used, and the double pole
wafer switch selects between either side of the split
supply.
Does it work? It meets the
criteria that I set out at the beginning, while being
enormously satisfying to operate. At its first exhibition
outing (Railwells '93) the layout was very well received,
and the crowds around the station box vindicated my
attempts to put the operator out in the thick of it. It
is also great fun to operate, even for some BR staff that
had a go! Unlike any other layout that I have operated,
any green operator should be able to pick up how to
operate it very quickly, as its based on prototype
practice and anyone seriously interested in railways
should be able to work a signal box!
Recently the adoption of DCC means that
operation has moved nearer the prototype, I am no longer constrained
to run the track. I have left these pages as they show the
principles I adopted for conventional wiring.
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