LED 4 aspect signals

[theageofthetra]

In the signalling part of my rules training the general rule seems to be that the most restrictive aspect is displayed in the lowest lens (tunnels excepted) Now with the new LED ones my notes say that the lower lens can be all three aspects (red/yellow/green) & the upper one can be yellow. No unless my notes are wrong doesn't that contradict the most restrictive aspect being lower rule? If this is correct why are LED signals different? Am a bit confused!

 

[LowLevel]

It was the case generally with traditional 60s style multi aspect signals. Searchlight type signals, of which the modern Dorman LEDs resemble, have always been an exception though in that the main 3 aspects are in the same aperture, with just an extra yellow on top if the signal is capable of displaying a 2 yellow indication. Been that way for a very long time, though traditional searchlights are nearly if not totally extinct (dunno if any are left on the GE since Nottingham's were removed last summer - though there is one OOU at the exit to Redhill Tunnel on the up slow near East Mids Parkway that hasn't been recovered).

 

[30907]

Red remains the lowest aspect so no contradiction. Searchlight signals, used on ER, were the same.
IIRC the original idea was that the red we be easiest to sight. Same principle as road traffic lights but in reverse.

Beaten to It!

 

[Railsigns]

I don't see any contradiction either.

There are still some searchlight signals in use at Clacton.

 

[Wolf]

Red remains the lowest aspect so no contradiction. Searchlight signals, used on ER, were the same.
IIRC the original idea was that the red we be easiest to sight. Same principle as road traffic lights but in reverse.

Beaten to It!

yeah - signals are generally supposed to be positioned so the red is closest to the drivers eyeline because it is technically the most important aspect that can be shown (on a stop signal), hence why co-acting signals are other way round - red at top. Think that is Some LED signals now only have one light and can display up to 3 aspects.

 

[Railsigns]

hence why co-acting signals are other way round - red at top.

That depends on the position of the co-acting signal. For example, MP393/MP393CA at Manchester Piccadilly has the red aspect at the bottom of both heads.

 

[theageofthetra]

Thanks for clarification. I suppose what you are saying is that the lower lens is always CAPABLE of showing the most restrictive aspect but can show others. Not familiar with the Eastern searchlight signals referred to do you have any pics?

 

[snowball]

I think one of the reasons for having the most restrictive aspect at the bottom is supposed to be that any lens except the bottom one can be obscured by snow on the lens hood of the next lens down.

 

[LowLevel]

Thanks for clarification. I suppose what you are saying is that the lower lens is always CAPABLE of showing the most restrictive aspect but can show others. Not familiar with the Eastern searchlight signals referred to do you have any pics?

All you could ever want to know - http://signalist.co.uk/LNER.html

 

[Hornet]

Red remains the lowest aspect so no contradiction. Searchlight signals, used on ER, were the same.
IIRC the original idea was that the red we be easiest to sight. Same principle as road traffic lights but in reverse.

Beaten to It!

Also on the old stye 3/4 aspect signals the red was at the bottom so that it was not affected by any large build up of snow on any other aspects signal hood. A large build up of snow would obscure the other aspects to the point of becoming totally obscure. Not what you want for a Red on a busy commuter line!

 

[Rich_D3167]

I think one of the reasons for having the most restrictive aspect at the bottom is supposed to be that any lens except the bottom one can be obscured by snow on the lens hood of the next lens down.

That's one of the reasons. Another important reason is that the bottom aspect is closest to a driver's line of sight. If the signal is on the ground, then the aspects are the opposite way round (green on bottom, yellow in the middle & red at the top) for this same reason).

 

[W230]

Thanks for clarification. I suppose what you are saying is that the lower lens is always CAPABLE of showing the most restrictive aspect but can show others. Not familiar with the Eastern searchlight signals referred to do you have any pics?

Not always true either though. In 4 aspect signal areas where approaching a terminal (Brighton and Victoria to name a couple - I am sure there are many more) the penultimate signal has a yellow top and bottom, red in the middle.

But then again this post in termed 4 aspect signals so maybe this is irrelevant as its a 3 aspect signal in 4 aspect signalling area!

 

[b0b]

I'm sure the accountants have crunched the numbers :-but is it really cheaper to have a yellow upper, red-yellow-green lower , led, vs green-yellow upper, red-yellow lower?

I guess the former means the red-yellow-green part works in single 3 aspect signals as well...

I'm sad to see the end of signals with 4 distinct lights, something about one of those sitting on a long post with an HST rushing by just screams speed!

 

[Hyphen]

That's one of the reasons. Another important reason is that the bottom aspect is closest to a driver's line of sight. If the signal is on the ground, then the aspects are the opposite way round (green on bottom, yellow in the middle & red at the top) for this same reason).

You can see this in in practice around Birmingham New St. On some of the platforms they have signals mounted horizontally for space reasons, and the danger aspect is always closest to the platform edge (and hence the driver).

On the way out of New St eastbound (heading towards Proof House Jn) some lines have ground-mouted co-acting signals. The ground mounted signals have red towards the top, whereas those on the gantry have it towards the bottom.

 

[D6975]

I was travelling around the Midlands the week before last and noticed several places where signals were showing red as the upper of the two LED lights. I did wonder if the normal regs had been changed since the introduction of LED signals. (These were normal signals - not special in any way)
I can't remember specific places where I saw them, but they were in the Heart of England rover area.

 

[TDK]

The Ansaldo signals between Crewe and Manchester can show any aspect top or bottom I believe, this is if there is a failure apparently.

 

[edwin_m]

I'm sure the accountants have crunched the numbers :-but is it really cheaper to have a yellow upper, red-yellow-green lower , led, vs green-yellow upper, red-yellow lower?

I guess the former means the red-yellow-green part works in single 3 aspect signals as well...

I'm sad to see the end of signals with 4 distinct lights, something about one of those sitting on a long post with an HST rushing by just screams speed!

Having red/yellow/green in the lower lens is probably marginally better as it gets more of the aspects closer to the driver's line of sight. However this isn't enough for the standards to say that all signals must be like this, because other companies produce LED signals with single-colour lenses like the tradtional lamps. Yet others produce drop-in LED replacements for the lamps themselves, leaving the rest of the signal head as it is.

 

[Taunton]

The classic Searchlights were said to be unreliable because of the mechanism inside which moves the three coloured lenses in front of the lamp. This always puzzled me because the same mechanism has been pretty much universally used without issue nationwide in the USA since the first major colour light signals came along there, and still is. In fact, the LNER, who I believe were the pioneers of them in Britain, imported the first ones from the US.

As I understood it the traditional Searchlights were operated by a single pair of wires from the signalbox. The three coloured lenses inside were mounted horizontally in a strip, with the red in the centre, yellow one side and green the other side, and a spring to bias the assembly to show the red, central lens in front of the lamp. Positive polarity in the wires operated a motor connected to the slide which overcame the spring and moved the yellow into position, while negative polarity moved it the other way and showed the green in front. The current needed to be continuous to maintain this. No current, or a failure of the wiring, and the display reverted to red. The lamp itself, and the mechanism motor, were battery powered with a mains trickle charger.

 

[GB]

The old 4 aspect searchlight types on the GEML used to cause issues from time to time. If the signal was displaying a single yellow it would have to cycle through the red aspect to reach the the green. If the train was in the right place it was enough to set off the TPWS train stop.

 

[driver_m]

The Ansaldo signals between Crewe and Manchester can show any aspect top or bottom I believe, this is if there is a failure apparently.

They can and often do show the aspect the other way round. Tends to be the greens in the bottom filament that you'll see. Reds are quite rare in the top filament. (also on the Macclesfield line)

 

[ac6000cw]

The old 4 aspect searchlight types on the GEML used to cause issues from time to time. If the signal was displaying a single yellow it would have to cycle through the red aspect to reach the the green. If the train was in the right place it was enough to set off the TPWS train stop.

Driving TPWS off the actual signal mechanism (instead of from information about what the signal is meant to display i.e. it's control inputs) sounds like an engineering bodge/workaround to me....

 

[edwin_m]

Driving TPWS off the actual signal mechanism (instead of from information about what the signal is meant to display i.e. it's control inputs) sounds like an engineering bodge/workaround to me....

I think this was part of the way TPWS was added to existing signalling without making too many changes to the circuits.

 

[W230]

I'm sad to see the end of signals with 4 distinct lights, something about one of those sitting on a long post with an HST rushing by just screams speed!

It's not all quite over yet. As part of the Gatwick resignalling scheme there are some new signals with 4 separate aspects and some new signals with the more common two aspects able to display all 4. All LED style though. I'd not seen 4 aspect LED in the 'old style' before but quite like them!

 

[CallySleeper]

IIRC i'm sure the signal on the down slow at East Midlands Parkway would be at almost ground level, yet the restrictive aspects are shown on the lower lens. Of course, I'll be damned if I can find a picture!

e: https://www.youtube.com/watch?v=O4e0NATqJXg at about 3:15 ish.

 

[John Webb]

.......As I understood it the traditional Searchlights were operated by a single pair of wires from the signalbox. The three coloured lenses inside were mounted horizontally in a strip, with the red in the centre, yellow one side and green the other side, and a spring to bias the assembly to show the red, central lens in front of the lamp. Positive polarity in the wires operated a motor connected to the slide which overcame the spring and moved the yellow into position, while negative polarity moved it the other way and showed the green in front. The current needed to be continuous to maintain this. No current, or a failure of the wiring, and the display reverted to red. The lamp itself, and the mechanism motor, were battery powered with a mains trickle charger.

The three colour filters were actually mounted in a holder moved by a relay fitted with a counterweight. This ensured that if the power to the operating relay failed, the colours moved under gravity to the red position rather than relying on a spring - which could break.

 

[Muzer]

Out of interest, were there ever any recorded instances of the mechanism seizing/jamming and showing the wrong aspect, despite the counterweight? I'd guess it would be designed very carefully to attempt to avoid that, but it's always a possibility with mechanical components (cf semaphores freezing and sticking at clear a long, long time ago). I assume that nowadays there would be some sort of proving - how does this work, just a microswitch type thing to ensure that the lenses are in the correct place?

 

[edwin_m]

I seem to recall the searchlight mechanism was detected so the previous signal would revert to danger. Some semaphore arms were/are detected so not new tech.

 

[John Webb]

Out of interest, were there ever any recorded instances of the mechanism seizing/jamming and showing the wrong aspect, despite the counterweight? I'd guess it would be designed very carefully to attempt to avoid that, but it's always a possibility with mechanical components (cf semaphores freezing and sticking at clear a long, long time ago). I assume that nowadays there would be some sort of proving - how does this work, just a microswitch type thing to ensure that the lenses are in the correct place?

With the mechanism enclosed in a weather-proof housing, there should be no problem of it sticking in any position due to adverse weather conditions.

None of my signalling books contain a diagram of the mechanism. I assume that as there was a direct mechanical linkage to the operating 'relay' as it is described, contacts operated by the relay would be used?

 

[carriageline]

I have had mechanical signals stick in the off position, mainly shunt signals though.

And from installations I have seen, proving (well, they are just repeaters in the box) are only used on signals you can't see. It's completly up to the signallers vigilance to realise if the signal hasn't gone back properly, and the same coming off.

I think the repeater works by having two contacts in the signal arm mechanism, one for on and off, and if neither are in contact then it shows as wrong. May be wrong
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[Taunton]

The LNER searchlights saved current by using a technique, which also came from the USA where it is still widespread, termed "Approach Lit", which meant they were normally dark until a train occupied the approach track circuit, when they would light up to the relevant aspect.

On straight lines this could mean when it first came into view there was no aspect shown for a short while. Gerry Fiennes, in "I Tried to Run a Railway", described one on the Spalding-March line which didn't light up until quite some time after it first became visible, and he said the crews used to make bets on what aspect it might eventually show!

I'm not sure how Approach Lit fits in with Detection of the aspect showing.

here's one with the back off

http://en.wikipedia.org/wiki/File:SearchlightSignalMechanism.JPG