How do AWS sunflowers work?

[D821]

I was playing Train Sim World 2 today and having a go at driving a Class 45 when I to look up what the AWS sunflower was.
I know what it's for, but how does it work? Does it just light up? Why does it have that pattern on the front?

Here's what I mean:

File:D5401 AWS 260108 d.adkins.jpg - Wikipedia

en.m.wikipedia.org

 

[_toommm_]

It’ll light up when an AWS magnet goes off and you have to cancel the alerter. Most of the time it will be because you’re running under cautionary aspects (double yellow, yellow), or a danger aspect (red); but it’ll also stay lit after an AWS for a speed restriction board (Morpeth board). Only once you pass a magnet for a green signal, will the sunflower turn off.

AWS though is quite primitive in that it can’t differentiate between the cautionary aspects and a danger aspect, so a driver would have to still keep their wits about them.

 

[Llama]

That older type will probably have a solenoid inside that slightly rotates a disc which will then show the yellow segments when a caution indication is acknowledged by the driver - the yellow segments will be hidden by black painted segments in front of the disc when a caution is received but not yet acknowledged, or when a clear indication is received at a clear (green) aspect or semaphore distant signal that is 'off'. When those older types began to fail (pretty rare) they could occasionally end up 'half cocked'. There is no electric illumination on them, but they do glow in the dark slightly.
Only recently I learned that the older types apparently had tritium in the yellow paint. Not seen one like that in recent years except on one of the ex-Scotrail 158s transferred to Neville Hill, maybe a couple of years ago.

Newer types of AWS sunflower use LEDs for the yellow, those have been the norm for ten years or so on the units round here.

 

[HSP 2]

It’ll light up when an AWS magnet goes off and you have to cancel the alerter. Most of the time it will be because you’re running under cautionary aspects (double yellow, yellow), or a danger aspect (red); but it’ll also stay lit after an AWS for a speed restriction board (Morpeth board). Only once you pass a magnet for a green signal, will the sunflower turn off.

AWS though is quite primitive in that it can’t differentiate between the cautionary aspects and a danger aspect, so a driver would have to still keep their wits about them.

IIRC the AWS display is not lit. A caution aspect will turn the display Black along with the sound of a horn (or bell I've forgotten which one is for caution).

 

[D821]

That's interesting, thanks to you both for taking the time to answer.

 

[swt_passenger]

I suspect the rotating (between two positions) was probably a design feature so that the eye detected the sudden movement as well as a change of colour.

Maybe they chose something that was already in use in another role away from the railway, but that was distinctly different to any other alarm or warning indicator. I expect across different control desk manufacturers there’d be loads of different lamp based indicators.

 

[Llama]

There was a distinctive click when the AWS changed on those old ones, both when going to all-black and to black/yellow.

The newer LED ones also make a slight click on receiving a caution (before acknowledging, and only when they are already in the 'caution' state) but as far as I know the yellow is given purely by illumination of an LED on those.

 

[uvarvu]

Quite an interesting video as the unit is disassembled to show its workings and then wired up to a circuit to demonstrate its use.

 

[Skie]

Newer types of AWS sunflower use LEDs for the yellow, those have been the norm for ten years or so on the units round here.

And even newer (cutting edge!? ) ones are just part of the dashboard that has gone fully digital on an lcd display. The 777's have their speedo and sunflower setup like this.

 

[Llama]

And even newer (cutting edge!? ) ones are just part of the dashboard that has gone fully digital on an lcd display. The 777's have their speedo and sunflower setup like this.

So glad CAF didn't go for those.

 

[D365]

So glad CAF didn't go for those.

Agreed. I'm not entirely sure why the sunflower is going digital now.

 

[Nym]

Agreed. I'm not entirely sure why the sunflower is going digital now.

AWS has always been digital.
North and South, on and off...

The new requirements of the GMRT for AWS Sounders and annunciations make it. Worse. The amount of complaints I've had from operators about audibility, I'm starting to loose count.

 

[sw1ller]

There was a distinctive click when the AWS changed on those old ones, both when going to all-black and to black/yellow.

The newer LED ones also make a slight click on receiving a caution (before acknowledging, and only when they are already in the 'caution' state) but as far as I know the yellow is given purely by illumination of an LED on those.

And that little click can save you from a rouge magnet in the dark too! Very handy. I wonder why the LED ones click? Maybe for the same reason and was requested to be put in place??

 

[swt_passenger]

Agreed. I'm not entirely sure why the sunflower is going digital now.

Presumably so they can hide it by software when eventually running on an ETCS only stretch of line?

 

[ComUtoR]

Agreed. I'm not entirely sure why the sunflower is going digital now.

Speaking to a Seimens Tech, he was saying that having the displays as digital brings huge advantages.

Being software based allows units to be upgraded and also allows backups. Having a complete backup when things go wrong is extremely advantageous.

 

[D365]

AWS has always been digital.
North and South, on and off...

The new requirements of the GMRT for AWS Sounders and annunciations make it. Worse. The amount of complaints I've had from operators about audibility, I'm starting to loose count.

Good point, you caught me there

Can't comment on the GMRT requirements as my job only involves installing the equipment that we are told to install. But there is a HF element of course.

Presumably so they can hide it by software when eventually running on an ETCS only stretch of line?

The ETCS installations that I have seen so far all retain the physical sunflower. If you moved the sunflower onto an ETCS display, that would introduce a reliability risk - if the ETCS were to break down, you'd lose AWS functionality too.

Speaking to a Seimens Tech, he was saying that having the displays as digital brings huge advantages.

Being software based allows units to be upgraded and also allows backups. Having a complete backup when things go wrong is extremely advantageous.

Do those advantages outweigh the reliability risk described above? Not sure what you mean by a "backup when things go wrong".

 

[ComUtoR]

Do those advantages outweigh the reliability risk described above? Not sure what you mean by a "backup when things go wrong".

I would say yes.

I drive with an *HMI/DMI arrangement and there is a digital sunflower on the DMI display. The DMI is split into two screens so if one screen breaks you can switch the information to the other. Also if the entire DMI breaks there is a full backup DMI. Literally press a button on the back wall and it reboots to a backup computer. Having a built in redundancy is a bit of a gamechanger.

*Human/Driver Machine Interface

 

[D365]

I would say yes.

I drive with an *HMI/DMI arrangement and there is a digital sunflower on the DMI display. The DMI is split into two screens so if one screen breaks you can switch the information to the other. Also if the entire DMI breaks there is a full backup DMI. Literally press a button on the back wall and it reboots to a backup computer. Having a built in redundancy is a bit of a gamechanger.

Ah I see. Aside from dual-screen DMI, none of the ETCS retrofits I've worked on thus far have that kind of capability. No backup facility if the EVC (European Vital Computer) goes awry.

By the sound of it, it's a lot easier to build in that kind of redundancy on new-build rolling stock.

 

[ComUtoR]

Yeah, with new builds everything is much easier and there is the ability to push forward with everything.

The future of rolling stock is pretty decent. It's just a shame the galacial nature of the railway means most.of it is years away.

 

[Taunton]

It always seemed that when starting a journey it was random whether the yellow was displayed or not, dependent on the last aspect when driven from this cab. This could be on a non-AWS branch where the randomness would remain displayed, or not, all day, rather leading to it being ignored. It didn't seem to reset when the cab was switched in.

 

[ComUtoR]

On everything I drive it always switches to yellow when you open the cab. Without checking the current standards I wouldn't know if this was a mandatory requirement or not.

 

[Nym]

On everything I drive it always switches to yellow when you open the cab. Without checking the current standards I wouldn't know if this was a mandatory requirement or not.

It is.

As far back as BR Standard MT169 and all the way through to the latest GM/RT, activation of a cab will show the Yellow/Black indication on the sunflower.

 

[CAF397]

Standard AWS self test when opening the desk isn't it? AWS display shows black/clear, horn sounds. Acknowledge the horn, then display shows yellow/black and bell sounds.

 

[ComUtoR]

It is.

As far back as BR Standard MT169 and all the way through to the latest GM/RT, activation of a cab will show the Yellow/Black indication on the sunflower.

My thanks.

I suspected it would be but I've only driven under AWS so I don't know any different. Cheers.

Standard AWS self test when opening the desk isn't it? AWS display shows black/clear, horn sounds. Acknowledge the horn, then display shows yellow/black and bell sounds.

Yep.

There are also old school AWS test magnets at some locations that activated when coming out of a depot. They also pre date me but not doubt someone could give the reasons why they existed and some still do. We also have a weird AWS magnet going into a terminal platform. Some days it goes off and others it doesn't. I've never been able to lock down a specific reason why it sounds. No signal. It just sits there a few yards from the platform :/

 

[Nym]

AWS function is dependant on the type of receiver fitted to the vehicle, the modern electronic ones behave differently to the conventional switch detectors, most of them will be the retro-fit electronic units ever since the era of TPWS Mk.2 in the mid 2000s. However, the electronic receivers are forwards and backwards compatible with the conventional detectors, and they can be fitted interchangeably.

"Sometimes working" can also be a sign of a weak fixed AWS magnet or magnet pair, tolerances on AWS are, well, not that good to be honest, and since TPWS came in for "TETS" terminal station overspeed and fixed buffer protection, perhaps this AWS magnet has simply been forgotten about as it's not 'needed' since TPWS provides the protection now. All of this being conjecture, it could also be a speed dependant AWS magnet that's controlled by position detectors or track deltas that will sound if the signalling system detects what it deems to be 'overspeed'. There's a lot of weird things out there in the world of signalling that I don't think any of us will ever fully understand, other than the person who designed it to be put there.

Standard AWS self test when opening the desk isn't it? AWS display shows black/clear, horn sounds. Acknowledge the horn, then display shows yellow/black and bell sounds.

Yes. AWS Self Test is part of the energisation characteristic of the system. All the way back to the "Electric" Brake and Horn Relay and "Baldwin" AWS EP Valve systems. (If anyone wants to know how the old EP valves worked, I can explain it, but it's very, very dry).

EP = Electropneumatic.

There are also old school AWS test magnets at some locations that activated when coming out of a depot. They also pre date me but not doubt someone could give the reasons why they existed and some still do. We also have a weird AWS magnet going into a terminal platform. Some days it goes off and others it doesn't. I've never been able to lock down a specific reason why it sounds. No signal. It just sits there a few yards from the platform :/

AWS Test Magnets now form part of an exam period, combined with TPWS Testing. As TPWS can't be tested by a fixed depot system, it is now integrated into a single test under the Unipart, Thales or Wabtec maintenance plans. So put simply, there isn't any need for it any more. They now use the "Magnet on a Stick" test.

 

[zuriblue]

I found an explanation of how the AWS works. This is the old school way, presumably everything is electronic noe.

AWS

The history of Diesel Multiple Units (DMUs / railcars) in Britain.

railcar.co.uk

 

[Nym]

If anyone wants a lot more reading...

RIS-0775-CCS Iss 3 - AWS and TPWS Application Requirements

This document sets out requirements and guidance for the application of the United Kingdom (UK) Class B train protection system ‘TPWS’, which comprises the Automatic Warning System (AWS) and the Train Protection and Warning System (TPWS).

www.rssb.co.uk

Link to RSSB Standard RIS 0775 CCS Issue 3, AWS and TPWS Application Requirements

PS: It's 211 pages long...

 

[DaveTM]

I'm sure someone with more S&T knowledge than me will come along soon to correct me, but I think I may be able to explain why this happens...

We also have a weird AWS magnet going into a terminal platform. Some days it goes off and others it doesn't.

In the AWS ramp on the track there is a permenent magnet facing "up" followed by a coil acting as an electromagnet that when energised faces "down". (I can't remember if north is "up" or south is "up" so I will say "up" and "down" for now). When a signal is at green the electromagnet is energised so the train sees "up,down" in quick succession and sounds the bell. With any other aspect (or if the power fails) the train just sees "up" and sounds the horn.

Now imagine you are on a bi-directional line and you go over an AWS ramp corresponding to a signal facing in the wrong direction. The train will either see "up", or "down,up". In either case the train will sound the horn because it has seen an "up" that wasn't immediately followed by a "down". There are two solutions to this. Either you live with it and provide the driver with a lineside sign to tell him there will be a spurious AWS activation (St Andrew's cross), or you find some way to inhibit the permenent magnet when trains are running wrong direction. As I understand it, in this case the permenent magnet is surrounded by a coil that when energised provides an equal and opposite magnetic field to that produced by the permenent magnet thus (in an ideal world) exactly cancelling it out. The train sees neither "up" nor "down" and does nothing. However if the current through the inhibiting coil isn't enough or is missing the train still sees a strong enough "up" that it sounds the horn.

We have a few of these in the Fratton area and occasionally they give spurious ASW horns. The signallers never seem particularly interested when you report these.

 

[_toommm_]

IIRC the AWS display is not lit. A caution aspect will turn the display Black along with the sound of a horn (or bell I've forgotten which one is for caution).

A caution aspect rotates it so it lights up, or if it’s digital, illuminates the yellow sections.

 

[alxndr]

In the AWS ramp on the track there is a permenent magnet facing "up" followed by a coil acting as an electromagnet that when energised faces "down". (I can't remember if north is "up" or south is "up" so I will say "up" and "down" for now). When a signal is at green the electromagnet is energised so the train sees "up,down" in quick succession and sounds the bell. With any other aspect (or if the power fails) the train just sees "up" and sounds the horn.

The mnemonic that I've been told to remember the direction of the magnets is Eskimos and Penguins. Eskimo for Electromagnet and North, Penguin for Permanent magnet and South. I'll be honest and say I don't know whether this is correct or not though, I've never taken a bar magnet out to check and the Strength and Polarity meter used to test them simply tells gives an E or P as appropriate and a colour indicating whether the strength is acceptable, beginning to fail, or unacceptable.

We have a few of these in the Fratton area and occasionally they give spurious AWS horns. The signallers never seem particularly interested when you report these

I can't speak for how things go in your neck of the woods, but reports of horn vice bell or horn vice nothing to make it to us on our part, and we do investigate them. Often it tends to be water ingress causing short circuits (in which case I get the turkey baster out for a quick way to dry things out temporarily), but this tends to end up blowing fuses and failing them completely. I have seen one or two horn vice nothings that have been harder to pin down, but generally speaking AWSs are one of the simpler things to fault find, even if the fix can be harder work as they're simply so bulky (and there's guaranteed to be one retaining nut that doesn't want to come off). The problem comes if it starts working properly before anyone gets there, as trying to find a fault that no longer exists is a bit trickier!