This is the third of a series of articles describing the progress of the project.
The use of "now" and "the present" refer to 2004.
Despite the dismally wet winter and spring weather, work on the
signalling has continued apace and the last of the signal posts has
now been concreted into place. All of the cables have been laid in
the ground and the grass is now growing again, hiding the
trenches that were dug. The junction boxes for the connection of
various peripheral devices have all been fitted and the next major
item will be the control panel, which will be sited under the
footbridge.
We were fortunate to acquire a redundant roadside equipment box
for the control panel. This was spotted lying in a heap of junk in a
garden that was being cleared, and was obtained free of charge,
as the resident was just glad to see the back of it. After a clean-up
it proved to be in remarkably good condition, free from rust and
dents and only needing a coat of paint. We now have to cast a
suitable concrete base for it. The control panel itself is now under
construction by Tony Vereker.
We have overcome the brightness problem with the signal lamps,
by changing from 12 Volt DC to 24 Volt AC operation. The use of
24 Volts enables more powerful bulbs to be fitted, whilst giving a
smaller volt drop over the lengthy cable runs. The bulb life will
also be increased by the use of AC. The lamps we are now using
are 5 Watt SES mount, instead of the original 3 Watt MES, and
this in turn has required the replacement of the lamp holders in the
signal heads. We also found out by experiment, that the position
of the lamp filament relative to the reflector is critical if optimum
brightness is to be achieved.
Work is now concentrated on fitting the treadle switches. These
are industrial process switches made by Craig & Derricott, and
they have to be mounted on an adjustable baseplate fitted below
the track.
The design of this baseplate took some head scratching
because we didn’t want to have to drill into the track longitudinals,
but eventually a solution was arrived at which had the combined
virtues of being simple to fit, and easy to adjust.
The switches are
supplied with tempered spring steel blades, but we are having to
soften and bend these to a more suitable profile, after which they
have to be re-hardened and tempered before fitting back onto the
switch bodies. Each switch is having a stop arm added to the
switch body to limit the free travel of the blade in the up direction.
The blade has to be held level with the rail level, but must trip the
switch contacts when depressed by only two millimetres (i.e. half
the depth of a typical flange). To facilitate this, an adjuster screw
is fitted into the stop arm.
We are also looking at fitting an inductive sensing device to
replace the troublesome microswitch on the traverser. This never
stood a chance of working properly, being housed in a concrete
pocket that was always full of water and old leaves! The new
device is fully sealed and, having no moving parts, should be more
reliable.
It is now almost two years since the first drawings were made, and
over a year since physical construction started. Folk are now
beginning to ask "when will it all be ready?"
Actually, one signal is
already working, albeit powered from a temporary supply. We are
endeavouring to get one more powered up on a temporary basis
before the rally, to protect the blind area in the cutting. After that,
the remaining signals will not be fitted until the control panel is
ready, at which time the temporary feeds to the two working
signals will be removed. This dictates that the final switchover will
not be until the end of the season. This is no bad thing, as we will
then have the whole of the winter to fix any bugs in the system,
and it should be ready for full operation in 2005.
As some of you will know, I am also involved with the updating of
the CPMR Code of Practice, which was first published in 1995. I
have held off finalising this so that I can include a description of the
signalling, so it would be rather nice if 2005 could see the
completion of both projects. I might then be able to do some
model engineering!
On to Part four
Back to Signals menu
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