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Wolverhampton LED signals.

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Wolverhampton LED signals.

Unread postby scarpa » Wed Jun 14, 2017 7:03 pm

Although these unusual looking signals, there aspects look good from a distance I wonder on a bright sunny day replacement from an off aspect to an On aspect how distinct the change of aspect a train driver would see at what range he would lose the aspect as he approached it.
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Re: Wolverhampton LED signals.

Unread postby Mike Hodgson » Wed Jun 14, 2017 10:32 pm

I thought there were approved minimum technical specifications and sighting standards which covered issues such as visibility despite reflections, glare etc?
As for restoring signals to danger in the face of an approaching train, there is always going to be a point after which the driver won't see it, even if it were at the signal post itself. Surely AWS/TPWS give some degree of protection against a driver missing such an eventuality, again provided he hasn't already passed the device in question
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Re: Wolverhampton LED signals.

Unread postby Signal-sighter » Thu Jun 15, 2017 7:01 am

Mike Hodgson wrote:I thought there were approved minimum technical specifications and sighting standards which covered issues such as visibility despite reflections, glare etc?

There are, though sadly signal sighting is a much misunderstood and underestimated art even among many professional signalling engineers.
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Re: Wolverhampton LED signals.

Unread postby Fast Line Floyd » Thu Jun 15, 2017 11:01 am

Whilst AWS would be provided at all signals in the Wolves Scheme there would only be TPWS at signals that protect a conflict i.e. a junction.

There are minimum standard which all colourlight signal have to achieve to gain acceptance to be used on the national network, these requirements don't fully cover the effects of glare or visibility in fog and LED signals are really poor in fog (small bee in bonnet from my signal sighting days and my days at RSSB where I started the work on the current signal sighting document at the time expected to be a full railway group standard (RGS) but was watered down to a rail industry standard (RIS which is not mandate-able on the industry) after I retired).
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Re: Wolverhampton LED signals.

Unread postby scarpa » Thu Jun 15, 2017 12:35 pm

Even other types of LED signals are poor especially if installed on bends for sighting when close to the signal .Two examples the signal coming off the Kemble line protecting Swindon station . A co-actor signal would be useful . Colchester St.Boltoph East curve up towards Colchester also poor approaching the signal.
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Re: Wolverhampton LED signals.

Unread postby John Hinson » Thu Jun 15, 2017 1:39 pm

When I worked in the Safety Section at Watford in the 1990s, LED signals were a new idea (which we were all very suspicious of) and were undergoing considerable testing before implementation. I distinctly remember that two large areas of correspondence and testing involved the actual colour displayed and the spread of the aspect. Eventually both were configured to accurately match existing signals. It was considered critical that they should meet or exceeded all existing standards - which they eventually did.

So if these signals at Wolverhampton or elsewhere are actually inferior, something has gone wrong somewhere since then. If it is a sighting issue it shouldn't be significant whether the signal is of the conventional type or LED.

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Re: Wolverhampton LED signals.

Unread postby Fast Line Floyd » Thu Jun 15, 2017 4:33 pm

John Hinson wrote:When I worked in the Safety Section at Watford in the 1990s, LED signals were a new idea (which we were all very suspicious of) and were undergoing considerable testing before implementation. I distinctly remember that two large areas of correspondence and testing involved the actual colour displayed and the spread of the aspect. Eventually both were configured to accurately match existing signals. It was considered critical that they should meet or exceeded all existing standards - which they eventually did.

So if these signals at Wolverhampton or elsewhere are actually inferior, something has gone wrong somewhere since then. If it is a sighting issue it shouldn't be significant whether the signal is of the conventional type or LED.

John

A colour light long range signal should be visible from 800m distant in a straight line. The LED signals at Wolves probably do meet the laid down requirements, they certainly would for distance and colour.

But by default LED signals which have a number of LEDs positioned as a cluster behind a polycarbonate lens cannot be focused into a solid single beam like conventional signals can with a single light source and a pair of lenses to do the focusing.

Instead LED signals have a small individual lens as part of each LED which is not a precision lens so the end result is not a single light source like a conventional signal but instead a number of much smaller light sources. In clear weather in the direct line viewing an LED signal will exhibit a strong light but as you go off axis the light output drops off rapidly.

The conventional signal may be fitted with a lens with a hot spot for close up viewing, LED signals have a small group of brighter LED's which form a line in the upper quadrant of the signal furthest from the driver on a post mounted signal (and the lower quadrant for ground mounted signals) to provide this facility but it does not help long distance off centre viewing.

If you view the same signal in a thick mist or fog the water droplets in the atmosphere break up the light beam significantly and as a result LED signals having lots of small light sources end up giving little or no distance view at all, red being the worst colour with green being the second but as LED signals have more yellow LEDs than any other colour this colour will be visible from further away than the others. I have been told by a very senior signal engineer in Network Rail that Yellow is the most important colour but I'm not sure I agree with him.

LED signals are not required to be tested in mist or fog conditions and there are no laid down standards in this matter. This all said there are some direct LED replacements for SL35 signal bulbs which come as a kit to convert a conventional signal head to LED whilst retaining the decent solid beam of a conventional signal.
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Re: Wolverhampton LED signals.

Unread postby John Hinson » Thu Jun 15, 2017 5:09 pm

Fast Line Floyd wrote:I have been told by a very senior signal engineer in Network Rail that Yellow is the most important colour but I'm not sure I agree with him.

That has always been my understanding too.

Because you should only be approaching a red at low speed.

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Re: Wolverhampton LED signals.

Unread postby scarpa » Thu Jun 15, 2017 8:14 pm

The signals installed at Wolverhampton are of the VMS manufacture. They are equipped with a Cats eye as a train standing close to the signal the driver would be hard pushed to see the signalhead appearing as a square box with holes letting the aspect to be displayed .No hood provided . Not a patch on other LED signals available.All the improvement in signal design over decades has now been sadly lost
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Re: Wolverhampton LED signals.

Unread postby Signal-sighter » Thu Jun 15, 2017 8:59 pm

scarpa wrote:The signals installed at Wolverhampton are of the VMS manufacture. They are equipped with a Cats eye as a train standing close to the signal the driver would be hard pushed to see the signalhead appearing as a square box with holes letting the aspect to be displayed .No hood provided . Not a patch on other LED signals available.All the improvement in signal design over decades has now been sadly lost

Well, that's your opinion.
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Re: Wolverhampton LED signals.

Unread postby Fast Line Floyd » Thu Jun 15, 2017 9:20 pm

John Hinson wrote:
Fast Line Floyd wrote:I have been told by a very senior signal engineer in Network Rail that Yellow is the most important colour but I'm not sure I agree with him.

That has always been my understanding too.

Because you should only be approaching a red at low speed.

John

Quite so but you still need to actually see the red to stop at or on approach to it! I have some photos that I took a few years ago at Wellingborough which does prove that if it were not for the presence of the station there would have been no guide to a driver as to where a signal actually is until very close to it.
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Re: Wolverhampton LED signals.

Unread postby John Hinson » Fri Jun 16, 2017 3:24 am

Fast Line Floyd wrote:Quite so but you still need to actually see the red to stop at or on approach to it! I have some photos that I took a few years ago at Wellingborough which does prove that if it were not for the presence of the station there would have been no guide to a driver as to where a signal actually is until very close to it.

Identifying the position of a signal has always been a matter of route knowledge. In the past, I believe the standard was that a signal must be visible 200 yards away, otherwise a repeater must be provided. I doubt that standards have changed greatly. A driver seeing a yellow aspect of one sort or another at 100 mph+ will (or should) reduce the speed of his train suffciently to stop on seeing a red (or missing aspect of same).

But we are drifting away from Wolverhampton. If said signal is not visible at 200 yards (or the current standard) in all weather conditions then surely it needs a repeater provided? Has it been demonstrated that it cannot, or are we just forming opinions here?

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Re: Wolverhampton LED signals.

Unread postby Signal-sighter » Fri Jun 16, 2017 10:44 am

Signal sighting is a far, far more complex activity these days than it ever was in the past. I have no involvement with the Wolverhampton signals and don't know the area at all but I know some of the people who will have been included on the SSC and signed off its recommendations, and I know that they won't compromise on ensuring that any signal installed on the infrastructure today complies fully with the requirements of the current Standard (formerly GE/RT8037 now RIS-0737-CCS). If the signal needed a banner repeater to achieve a compliant minimum reading time then it would have one.

Like them or loathe them, VMS signals have full Network Rail product acceptance and meet all relevant requirements for conspicuity in all weather and lighting conditions. I feel much of the apparent dislike for VMS signalling products simply stems from the fact that they don't resemble what we think of as 'traditional' signal heads. There have been reliability issues in the past which seems to have been down to quality control problems during manufacture but they are here, they are relatively cheap, they don't require much maintenance, they work reliably and they aren't going to go away any time soon.
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Re: Wolverhampton LED signals.

Unread postby Fast Line Floyd » Fri Jun 16, 2017 2:48 pm

Signal-sighter wrote:

Like them or loathe them, VMS signals have full Network Rail product acceptance and meet all relevant requirements for conspicuity in all weather and lighting conditions.

Not weather tested as there are no standards that require weather testing although I would expect that the signal body should be water tight. Interestingly I prefer the VMS junction indicator to a conventional one and VMS was one company that took my photos from Wellingborough and were (or at least seemed) genuinely concerned about poor mist/fog performance of LED signals. VMS signals were first tested in the North of England (I forget where) and were well received by the drivers using them and they were photographed in heavy snow where their visibility is no worse than a conventional signal.

Interestingly the errant signals at Wellingborough have been fitted with banner repeaters since my photos were sent around a few senior people but this was done under the banner (excuse the pun) of line speed increases.

RIS-0737-CCS was the document that I started prior to my departure from RSSB but it was then under the title of GE/RT8101 Signal Sighting. Text wise they are identical in meaning but my lord and Master at RSSB wanted everything written his way rather than a way that can be understood......

It was partly my fighting to get the document into a readable and understandable format that caused my departure from RSSB as I wasn't going to put my name to a document that I would not want to use myself.

LED signals have led (again excuse the pun) to a number of SPADs, two of which occurred to two consecutive trains early one morning at Stirling Middle this was caused by the sun shining directly into the signal lens and washing out the red aspect making it appear yellow, the problem had never occurred there before the conventional head was replaced with the LED head. I was part of a committee to look into the visibility of LED signals following this and other incidents which with the help of a professional optical company it was decided that all LED signals are angled downwards by (if I recall correctly) something like 5 degrees below that required to centre the beam on the AWS magnet.
Last edited by Fast Line Floyd on Mon Jun 19, 2017 12:08 pm, edited 1 time in total.
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Re: Wolverhampton LED signals.

Unread postby StevieG » Sun Jun 18, 2017 11:48 pm

Fast Line Floyd wrote: " .... VMS signals were first tested in the North of England (I forget where). ...." .

Eden Valley Junction, Penrith (or the site of) ?
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