From: brennan@cunixf.cc.columbia.edu (Joseph Brennan)
Subject: Re: Question: ATC <=> steam engines?
Keywords: ATC INDUSI SJ steam
Reply-To: brennan@cunixf.cc.columbia.edu (Joseph Brennan)
Organization: Columbia University
Date: Tue, 7 Apr 1992 17:54:17 GMT

The following is from wares@rhoda.fordham.edu, where they do not
receive Usenet, so I am posting for him:

	This is from _The Horizon Book of Railways_, with contributions by Lt.
Col. T. M. Simmons, A.M.I. Mech.E. [et al]. London: P. Hamlyn, c1961.
 	Among the illustrations in this chapter is one of Gresley class A4
Pacific, no. 60007 [British Railways renumbering], "Sir Nigel Gresley."
_________________________________________________________________________

	"The Great Western Railway, which is now the Western Region of
the nationalised British Railways, has been conducting intensive
experiments with Automatic Train Control since 1905; the had installed
it on all of the company's main lines before the last war. The system
consists of a timber ramp 40 ft long, on which is mounted an inverted
T-bar, the highest point being 3 1/2 ins. above the running rail
level. The ramp is fixed between the rails and is liked with the
ordinary signal. It is charged with electricity when the signa is at
'clear', and locomotives working routes equipped with the system have
a box containing a relay gear fitted on the front axle. Below this and
directly attached to it is a shoe or plunger which projects to within
2 1/2 ins. of the rail level and consequently is lifted each time the
engine passes over a ramp.
	"The method of operation is simple. As long as the ramp is
energised, that is, as long as current is flowing through it, the 'All
Clear' bell rings in the cab of the engine, and the train proceeds on
its journey uninterrupted.  However, should the train come up to a
signal at 'Caution' and begin to pass the ramp controlled by this
signal, then the ramp is immediately de-energised and the gear in the
locomotive operates at once. The brakes are applied, and as a warning
hooter sounds in the cab, the train is brought to a stop. ....
                                                                        
	"The standard [British Railways] system has discarded the ramp
entirely, and there is no actual contact between the tack installation
and that fitted on the locomotive.  In place of the ramp ... about two
hundred yards before each distant signal, two magnets are positioned.
The first of these ...  is a permanent magnet, and the second an
electro-magnet which is only energised when the signal concerned shows
'Clear'. Fixed on the underside of each engine is a magnetic receiver
connected to electric circuits in the engine, and these come into
action according to the signal indication through the track magnets.
	"As a train approaches a signal at 'Caution', and when the
receiver on the engine passes over the permanent magnet in the track,
the armature of the receiver is moved cutting off the current to an
electro-pneumatic valve ...  However, cutting off the current to the
valve does not cause it to act immediately because a condenser
maintains the current through it for one second.  When the signal
indicates 'Caution', the electro-magnet in the track is not energised,
and the electro-pneumatic valve releases after one second and causes a
horn to sound in the cab. Whereupon the driver pulls a resetting
handle and prepares to reduce speed by means of the ordinary brake
handle. Unless he does this within three seconds of the sounding of
the horn, the train barkes will begin to be applied automatically. ...
	"If the train approaches a signal showing 'Clear', the
electro-magnet in the track in energised, but the receiver on the
train still passes first over the permanent magnet and the sequence of
events just described proceeds in the same way. However, the
electro-magnet, being energised, causes the armature of the receive to
return to its normal position which operates a relay box and a bell
rings loudly in the cab. .... This operation follows the first in less
than a second, and current is restored to the electro-pneumatic valve
before the condenser has emptied. In this way the valve is prevented
from acting to sound the horn and start an application of brakes. ...
	.... "The principle has been adopted that should a fault
arise, whatever its cause, or kind, the result would be a 'Caution'
indication.
	"It will be noted that a 'Caution' indication to the driver is
dependent on the permanent magnet only, and a 'Clear' indication
requires a positive cancellation ...
	....
	"The American railroads have for many years incorporated
Automatic Train Control on a number of their routes. As far back as
1922, 49 of the major roads were ordered to install either of the two
completely electrical systems that at that time had been developed.
Both schemes used electrical induction to set up an electrical current
in devices mounted on the locomotive.
	"One of the systems, known as the 'intermittent type',
incorporates an electro-magnet attached to the track circuit operating
the block signals. The magnet is positioned on the sleepers, or 'ties'
as they are called in the United States, alongside the rails at each
signal. With the signal at 'Stop' the magnet is actuated so that it
would affect a receiving unit on a locomotive passing over it, thus
putting the electrical device controlling the brakes in action. ....
	"The second American type is known as the
'continuous-inductive system', and in this the track circuit itself
was used to actuate induction coils mounted on the locomotive. This
system responds at all times--not just to signals, that is, to track
conditions ahead, but to anything which interrupted the circuit. An
open set of points or a broken rail would set the control in
operation."