History of AWS

"terzal" <tdhew@> wrote in message
news:a56f51fb.0402111246.1d33a6e4@c om...
> Hi, Anyone know a link to a site giving a comprehensive history of the
> AWS system?? I'm trying to find out when it was first thought of,
> whether it was in a reaction to a particular accident etc. Thanks,

The GWR introduced 'Automatic Train Control' in 1906. This consisted of a
ramp in the 4ft, which was live if the signal was 'off'. A contact on the
loco rang a bell if the ramp was live, and blew a siren if it was dead, and
applied the brakes if the siren wasn't cancelled by the driver.
At nationalisation, an alternative system, AWS, was being tried on the
London Tilbury & Southend line which involved electro-magnetic induction to
transmit the signal to the train, without physical contact, and this system
was chosen for development as the BR standard, rather than the GWR system.
The GWR system however remained in use on the Western Region until the
1970s.
Peter

IIRC it was chiefly the Harrow and Wealdstone crash of 1952 which lead to
ATC (as was under GWR) being adopted nationally by BR as AWS.

"Peter Masson" <Peter.Masson1@> wrote in message
news:c0eb56$h15$1@titan....
>
> "terzal" <tdhew@> wrote in message
> news:a56f51fb.0402111246.1d33a6e4@c om...
> > Hi, Anyone know a link to a site giving a comprehensive history of the
> > AWS system?? I'm trying to find out when it was first thought of,
> > whether it was in a reaction to a particular accident etc. Thanks,
>
> The GWR introduced 'Automatic Train Control' in 1906. This consisted of a
> ramp in the 4ft, which was live if the signal was 'off'. A contact on the
> loco rang a bell if the ramp was live, and blew a siren if it was dead,
and
> applied the brakes if the siren wasn't cancelled by the driver.
> At nationalisation, an alternative system, AWS, was being tried on the
> London Tilbury & Southend line which involved electro-magnetic induction
to
> transmit the signal to the train, without physical contact, and this
system
> was chosen for development as the BR standard, rather than the GWR system.
> The GWR system however remained in use on the Western Region until the
> 1970s.
> Peter
>
>

"Clive D. W. Feather" <clive@on-the-train.> wrote in message news:<1M1K69LLxzKAFw9s@romana.davros.org>...

> pressing the button re-latches that circuit and moves the "sunflower" to
> yellow.

No it doesn't - pressing and releasing the button does. That isn't
mere pedantry. The need to press and release avoids the posibility of
a driver holding the button down continually, or the button being
(deliberately or accidentally) jammed with the contacts closed.

"Clive D. W. Feather" <clive@on-the-train.> wrote in message news:<1G8qo3OyjoNAFw1I@romana.davros.org>...

> I have circuit diagrams for AWS somewhere, but I was having to do that
> posting from memory.

If you do hapen to look at the diagrams, I'd be interested, as I'm
working from memory, too, and my recollection differs.

You suggested that:

> On the BR system, the fixed magnet closes a circuit which puts the
> "sunflower" back to all-black and starts a capacitor discharging. The
> electromagnet closes a second one which powers the bell and restores the
> charging current to the capacitor. If the capacitor discharges, that
> unlatches the circuit keeping the siren and brakes off; pressing the
> button re-latches that circuit and moves the "sunflower" to yellow

My recollection was that the permanent magnet tripped the receiver,
which opened an EP valve, allowing the timing reservoir to begin
emptying, sounding the horn, and, when pressure fell (after 3-5
seconds) causing a valve to trip and vent the brake pipe. This
sequece of events could be interrupted by either pressing and
releasing the button (at an aspect other than green or distant off, a
test magnet, severe permanent speed restriction warning or TSR), or by
the action of the opposite-poled electro magnet re-setting the circuit
(at a green aspect or distant off).

The visual indicator and bell operated in association with this.
There was a capacitor involved, that caused a two-second ring of the
bell, but whch was later removed from most loco's, giving a
half-second ring (some loco's acquired a sticker on the AWS control
boxes, stating that the modification had been done).

All this took place in the valve and relay units, an odd-shaped bit of
kit mounted on the cab bulkhead. There were seperate units for
vacuum-braked or dual/air braked locos.

Chippy wrote:
> "Clive D. W. Feather" <clive@on-the-train.> wrote in message news:<1G8qo3OyjoNAFw1I@romana.davros.org>...
>
>
>>I have circuit diagrams for AWS somewhere, but I was having to do that
>>posting from memory.
>
>
> If you do hapen to look at the diagrams, I'd be interested, as I'm
> working from memory, too, and my recollection differs.
>
> You suggested that:
>
>
>>On the BR system, the fixed magnet closes a circuit which puts the
>>"sunflower" back to all-black and starts a capacitor discharging. The
>>electromagnet closes a second one which powers the bell and restores the
>>charging current to the capacitor. If the capacitor discharges, that
>>unlatches the circuit keeping the siren and brakes off; pressing the
>>button re-latches that circuit and moves the "sunflower" to yellow
>
>
> My recollection was that the permanent magnet tripped the receiver,
> which opened an EP valve, allowing the timing reservoir to begin
> emptying, sounding the horn, and, when pressure fell (after 3-5
> seconds) causing a valve to trip and vent the brake pipe. This
> sequece of events could be interrupted by either pressing and
> releasing the button (at an aspect other than green or distant off, a
> test magnet, severe permanent speed restriction warning or TSR), or by
> the action of the opposite-poled electro magnet re-setting the circuit
> (at a green aspect or distant off).

If the permanent magnet causes the EP valve to open immediately, would
that not cause the horn to sound immediately also (ie, before the
equipment has decided what aspect is showing). It hasn't gone over
the electro yet, and a Caution warning should only be given when time
has elapsed such that it is assumed the electro has been passed, and
is dead.

IIRC there is a timing capacitor in relay units which provides the
timeout for sounding a warning. I have a circuit diagram at work, I
came across it the other day in some old training course notes, just
by chance. I can scan and mail it if this would be useful (would it
be out of place in a.b.p.r do you think - strictly speaking it's not a
picture ?).



Wobbly Bob

"Wobbly Bob" <never.read@> wrote in message
news:4037C8C0.7020600@...
> IIRC there is a timing capacitor in relay units which provides the
> timeout for sounding a warning.

According to my 1960s book that's correct. The capacitor maintains the
current through the relay for one second, so if the electro magnet is passed
within that time the relay is held and the warning/braking sequence is not
started.

Roger

Wobbly Bob <never.read@> wrote in message news:<4037C8C0.7020600@>...

> If the permanent magnet causes the EP valve to open immediately, would
> that not cause the horn to sound immediately also (ie, before the
> equipment has decided what aspect is showing). It hasn't gone over
> the electro yet, and a Caution warning should only be given when time
> has elapsed such that it is assumed the electro has been passed, and
> is dead.

Yes, there will be a capacitor for that purpose, hence the fact that a
warning is given at a green aspect if the inductor is passed too
slowly.

My point was that the timing to the brake application was by timing
reservoir, rather than capacitor.

Chippy wrote:
> Wobbly Bob <never.read@> wrote in message news:<4037C8C0.7020600@>...
>
>
>>If the permanent magnet causes the EP valve to open immediately, would
>>that not cause the horn to sound immediately also (ie, before the
>>equipment has decided what aspect is showing). It hasn't gone over
>>the electro yet, and a Caution warning should only be given when time
>>has elapsed such that it is assumed the electro has been passed, and
>>is dead.
>
>
> Yes, there will be a capacitor for that purpose, hence the fact that a
> warning is given at a green aspect if the inductor is passed too
> slowly.

<1 3/4 MPH IIRC

#
> My point was that the timing to the brake application was by timing
> reservoir, rather than capacitor.

Then the two time delays operate consecutively, ie the EP valve
doesn't open immediately the Permanent magnet is encountered, but
after the capacitor has discharged, *then* the timing chamber controls
the brake application, which is not what your original post implied
(or at least what I inferred), as it did not mention any delay to the
EP valve opening.

Again, quite by chance, today I found a small diagram at work with
schematic diagrams for steam loco's, both the electrical and pneumatic
sides. There is indeed a timing chamber in this arrangement.


Wobbly Bob