On Sun, 1 Apr 2007 10:08:13 +0100, Clive D. W. Feather wrote:
In article .com,
writes
And normally known as 'theatre type route indicators'. Except that in
the report into an accident at Euston in 1949, the inspecting officer
describes them as 'a route indicator of the music hall type'.
Was this a generally used term at one time, or is the inspecting
officer simply confused?
This kind of indicator was originally used in music halls or theatres to
indicate which act was being shown; the railway then appropriated them.
So both "music hall type" and "theatre" are reasonable names, though the
former probably went out of use as the music halls did.
Technically they are "alphanumeric indicators meeting sighting
requirement class 2", if I recall correctly. Stencil indicators meet
sighting requirement class 3.
That is the current terminology, which is intended to be technology-independent.
These indicators are now made in fibre-optic form with a single lamp
illuminating many dots via a bundle of fibres, but earlier versions had a
(usually 7 x 7) matrix of "Pygmy" lamps. Depending upon the particular
requirements of each one, each lamp could be used in several indications and the
wiring arrangements could be rather complex and difficult to set up if lamp
proving was required. As well as the semi-colloquial "Theatre", these were also
known officially as "Multi-lamp Route Indicators".
Stencils were different again, with a lamp showing through a mask, behind a
piece of frosted glass, so the indication is hidden until illuminated. Most
people will probably have seen something similar at pedestrian crossings, the
illuminated "WAIT" signs operate on the same principle.
As with MLRIs, Stencils are now (usually) newly provided in FO form, the only
difference between these two types is now their size (physical and indication),
and the number of indications which can be accomodated within a single box.
--
WZR