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| k452 10/08/2011 at 19:26 #19320 | |
glyndavies
8 posts |
Why does K452 (London end if Alexandra Palace Plat 2) never show a double yellow?
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| Re: k452 10/08/2011 at 19:37 #19321 | |
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Stephen Fulcher
2078 posts |
It is probably a 3-aspect signal.
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| Re: k452 10/08/2011 at 20:45 #19324 | |
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glyndavies
8 posts |
No, It's a 4 aspect. It goes to double yellow on the sim but not in real life. It holds a single yellow then turns to double yellow for about half a second before clearing to green Log in to reply |
| Re: k452 11/08/2011 at 08:46 #19328 | |
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Stephen Fulcher
2078 posts |
In that case it is probably that the signal in advance is showing red, but when the signalman clears it, it goes straight to green and therefore K452 will only briefly show double yellow, probably for so little time that it is difficult to see, before going up to green as the HHR and DR relays will pick at roughly the same time.
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| Re: k452 11/08/2011 at 09:31 #19329 | |
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Firefly
521 posts |
Hi Glyn. Over what sort of time period have you noticed this? I can't think of any legitimate reason for it to behave that way. Is it a place that you visit regularly and if so can you see the next signal along the line K442? If you can see the next signal, have a look to see if K452 correctly follows K442 (Therefore I'm asking if K442 goes straight from Red to Double Yellow missing out the Yellow aspect) My best guess would be a TPWS or lamp proving fault on K418 signal. Kings Cross PSB does not have any indication of lamp failures or TPWS on either K442 or K418 signals as they are automatic signals. Automatic signals are just drawn on the panel to show the signaller where they are, they do not give the signaller any other information. (Kings Cross sees exactly the same as you see if you select the panel mode option on SimSig). I would guess that K418 either has a Red Lamp failure (unlikely as a train on an adjacent line would report it) or a high resistance relay contact in the lamp proving circuit (probably A1/A2 or D1/D2 of 418 ECR). K418 is unlikely to be fitted with TPWS, however a TPWS fault would cause the same symptoms. A fault like this could go unnoticed for a very long time because there's no way for the signaller to notice it and it doesn't stop any trains. The only way it would get discovered would be if a very switched on driver noticed it or if the technicians try to carry out routine maintenance on K452 and want to take a voltage reading on the top yellow. (which they'll never get). Even if the technicians go out on maintenance they may assume it's normal to skip the double yellow and just ignore it. (depends on the experience of the tech.) FF Log in to reply |
| Re: k452 11/08/2011 at 09:35 #19330 | |
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Firefly
521 posts |
Quote:In that case it is probably that the signal in advance is showing red, but when the signalman clears it, it goes straight to green and therefore K452 will only briefly show double yellow, probably for so little time that it is difficult to see, before going up to green as the HHR and DR relays will pick at roughly the same time.Stephen, if SimSig is correctly representing KX, the next 2 signals are both automatics. (Most of these simulations are spot on as they work from the signalling plans so I suspect it's correct) FF Log in to reply |
| Re: k452 11/08/2011 at 09:59 #19331 | |
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Stephen Fulcher
2078 posts |
I hadn't looked at the sim to see what the next signal was.
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| Re: k452 11/08/2011 at 11:23 #19334 | |
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broodje
184 posts |
Simsig is by no means 'the truth' it is however made to match the real thing as good as possible. The KX sim is based on the situation a few years ago. If I remember correctly the layout at Hithchin is a bit different now (some cross overs were moved) and there is a new connection made with the NNL and HS1. Oh, and the goods yard is gone. No doubt there were other changes done as well.
Last edited: 11/08/2011 at 11:24 by broodje Log in to reply |
| Re: k452 11/08/2011 at 11:52 #19335 | |
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Firefly
521 posts |
I did some panel tile replacement at KX about 3 years ago and Simsig was pretty near spot on for the sections of panel that I was working on. (Including the fact that the Auto Function on K712 at Hitchen has been disabled!) FF Log in to reply |
| Re: k452 11/08/2011 at 15:33 #19340 | |
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glyndavies
8 posts |
i've never seen it any different. and I often pop down on to the platform for a hour or so when I'm passing. When the next signal (442) is 1 yellow, 452 still stays as 1 yellow. Perhaps it's a speed restricting issue Log in to reply |
| Re: k452 11/08/2011 at 15:46 #19341 | |
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Stephen Fulcher
2078 posts |
Can you physically see the next signal at single yellow? If you can then there is in all probability a fault. Log in to reply |
| Re: k452 11/08/2011 at 17:15 #19344 | |
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glyndavies
8 posts |
Yes, clearly
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| Re: k452 11/08/2011 at 17:29 #19346 | |
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Firefly
521 posts |
Quote:If you can then there is in all probability a faultI agree, it's an interesting one tho. The HHR lines must be working because without them the signal will never show green. The yellow lamp must be working because Glyn sees it flash as the signal climbs up to Green A cross of the HHR and DR lines would cause it but I can't imagine that slipped through the net. I'll keep thinking. Log in to reply |
| Re: k452 12/08/2011 at 16:42 #19367 | |
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Firefly
521 posts |
Having given it further thought I believe it may be designed this way to overcome a braking problem. It's difficult to think of any fault that would cause a Yellow reading onto a Yellow yet allow a Green onto a Double Yellow. Other than incorrect wiring/cabling which is extremely unlikely it can't easily be explained. It is however permissible to have two single yellows in an aspect sequence if required to overcome braking distance issues. (details in GK/RT 0045, which is available for all to read on RGS online) FF Last edited: 12/08/2011 at 16:47 by Firefly Log in to reply |
| Re: k452 12/08/2011 at 17:27 #19368 | |
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kbarber
1742 posts |
That's interesting, I always thought it was repeated double yellows that were permitted; certainly that's what the GE had from 1949 (3 in succession in some cases) and I think I recall seeing it in the SSPs. Any idea when/why the change?
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| Re: k452 12/08/2011 at 20:30 #19376 | |
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Firefly
521 posts |
Quote:Any idea when/why the change?No idea I'm afraid. I wasn't even certain it was allowed until I looked it up. FF Log in to reply |
| Re: k452 13/08/2011 at 09:18 #19382 | |
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TomOF
452 posts |
The GE still has consecutive double yellows in places (particularly Stratford) and one of the sims i'm working on multiple signals are approach controlled unless the onward route is set or next signal clear due to insufficient overlaps on high speed lines, which could possibly apply at Kings Cross. So maybe not a fault but by design. The control tables or aspect sequencing charts would probably confirm for definate.
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| Re: k452 13/08/2011 at 15:49 #19393 | |
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Stephen Fulcher
2078 posts |
Rather strange one to be honest.
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| Re: k452 17/08/2011 at 12:54 #19512 | |
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clive
2789 posts |
" said:Quote:The change happened because of TPWS and ATC. Successive single yellows are permitted *if* a risk assessment has been done and appropriate mitigation is in place.Any idea when/why the change?No idea I'm afraid. A similar thing happened with the transition from 3 to 4 aspect signalling. If you work through the aspect sequences, you have an awkward situation when the second 4-aspect signal (let's call it S43) is red. The first one (S41) is yellow, which means that either the last 3-aspect signal (S39) is green and there isn't enough warning, or S39 shows double yellow and there's too much warning. In the latter case, you also have the issue that S39 can be the first warning signal for two different stopping points. Therefore you either had to make S41 approach controlled when S43 is red, or you had to make S37 be four-aspect but never show single yellow, and add a repeater S41R between S39 and S41; this shows Y when S41 is red and YY when S43 is red. It's now permitted to just have S39 show double yellow when S43 is red, with a 50% too long braking distance, *provided* that appropriate mitigation is in place to deal with the risk of the driver braking too late. In practice this means ATO or one of the enhanced versions of TPWS. Log in to reply |
| Re: k452 17/08/2011 at 18:05 #19533 | |
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LordSven
29 posts |
Maybe it's an issue of signal sighting or a short distance to the next signal? Or maybe you have found a defect!
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| Re: k452 18/08/2011 at 08:13 #19551 | |
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kbarber
1742 posts |
" said:
Interesting to see how the system continues to evolve. Are successive YYs still permitted as well? Log in to reply |
| Re: k452 18/08/2011 at 11:32 #19561 | |
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clive
2789 posts |
" said:Interesting to see how the system continues to evolve. Are successive YYs still permitted as well?Yes, they are. Log in to reply |