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| Understanding repeater signals 27/01/2012 at 12:15 #28301 | |
maxand
1637 posts |
Here are two screen captures from Bristol with the Panel signals option turned off.  In each pic the repeater is showing caution while the following signal is showing danger. I always believed the purpose of a repeater was to indicate the same aspect as the following signal. Quote: Banner repeater signals repeat the indication of the following signal, where the driver's view of it may be restricted, for example because of track curvature or a bridge abutment.(Wikipedia, British railway signals) Apart from the fact that one cannot set routes to a repeater, there now seems no real difference between a repeater and a main signal, so why not replace them with main signals? There must be another reason. Thanks in advance for your help. Last edited: 27/01/2012 at 12:18 by maxand Log in to reply The following user said thank you: saxbophone |
| Re: Understanding repeater signals 27/01/2012 at 12:21 #28302 | |
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Laryk
56 posts |
Those aren't Banner repeaters. These are Banner repeaters - taken from Oxted sim (marked 1BR and 2BR) Post has attachments. Log in to view them. Last edited: 27/01/2012 at 12:22 by Laryk Log in to reply |
| Re: Understanding repeater signals 27/01/2012 at 12:28 #28303 | |
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Laryk
56 posts |
I can't remember what the signals in question are called - but if you read the "semaphore" section on the Wikipedia page you linked; the "distant" or "caution" type is the same in operation to the "R" marked signals. I hope that makes sense One of the reasons we have them is any train departing from Exmouth doesn't have a starter signal. If the "distant" (I'll be calling it this, but it may be wrong) signal wasn't there it would be like having 2-aspect signalling (ie only red/green.) so it provides the driver with an indication of the next aspect without any more Track circuits. Post has attachments. Log in to view them. Last edited: 27/01/2012 at 12:36 by Laryk Log in to reply |
| Re: Understanding repeater signals 27/01/2012 at 12:57 #28305 | |
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maxand
1637 posts |
Thanks Laurence for your quick reply and pointing me to the correct section of that article, from which I quote again: Quote: Not all lines use four-aspect signalling - three or two aspects are used where the headway and line speed allow. The three-aspect version uses three colour lights, omitting the top yellow. The two-aspect version has only the red and green aspects, with distant signals or repeaters (signals not equipped with a red aspect) giving advance warning of a red aspect.So what you're really saying then is that this type of repeater signal only behaves as a true repeater when the following signal is green (see pic below). It indicates yellow instead of red because that's the most restrictive it can get. It hasn't got red, but in this situation it doesn't need it. Thanks, that's clear now. :) Same location as my first pic, this time with route set: 
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| Re: Understanding repeater signals 27/01/2012 at 13:09 #28306 | |
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Laryk
56 posts |
" said:So what you're really saying then is that this type of repeater signal only behaves as a true repeater when the following signal is green (see pic below). It indicates yellow instead of red because that's the most restrictive it can get. It hasn't got red, but in this situation it doesn't need it. Thanks, that's clear now. :)That's how I understand it. By the way, there is a small section on Wikipedia dealing with Distant signals but it doesn't really add much more to what's been discussed Log in to reply |
| Re: Understanding repeater signals 27/01/2012 at 13:17 #28307 | |
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ralphjwchadkirk
275 posts |
Read the signals module of the rule book from RGS Online - that explains what distant and repeater signals do and mean.
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| Re: Understanding repeater signals 27/01/2012 at 13:43 #28310 | |
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maxand
1637 posts |
Thanks Ralph, but can you be any more specific than this? I've searched RSSB's site a few times, also looked through their PDF module files which I've downloaded, but there's hardly anything on repeaters. Do you remember which module it is? Post the name of the PDF file if you can, and I'll download it. They seem to be in the process of revising their site and nothing's where I remember seeing it. Thanks Last edited: 27/01/2012 at 13:44 by maxand Log in to reply |
| Re: Understanding repeater signals 27/01/2012 at 13:47 #28311 | |
headshot119
4869 posts |
" said:Read the signals module of the rule book from RGS Online - that explains what distant and repeater signals do and mean.It's not that much of a help as the current rule book makes no distinction between a distant and repeater signal. Only between a repeater and a banner repeater. Repeater : if the signal it repeats is at danger (red) it will show a caution (Yellow). If the signal ahead is at caution (yellow) or clear (green) the repeater will show green. Distant : If all signals in the section for which the distant applies are off the distant will be off. Otherwise it will be at caution. This does not mean that the next signal is always at danger. Banner Repeater : Shows a horizontal aspect if signal it applies to is at danger. Or shows a 45 degree angle if the signal it applies to is at caution or clear. There are also some banner repeaters which give an additional green clear aspect though I'm not sure of the meaning. "Passengers for New Lane, should be seated in the rear coach of the train " - Opinions are my own and not those of my employer Log in to reply |
| Re: Understanding repeater signals 27/01/2012 at 14:12 #28313 | |
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Late Turn
696 posts |
From previous discussions, I understand that repeaters and distants are all now termed distant signals (obviously excepting banner repeaters). From Module S1 - "A distant signal is a signal which cannot show a stop aspect or indication." There's further explanation of the 'off' indication on semaphore distant signals - "all associated stop signals worked from the same signal box are clear" - but this doesn't seem to include colour-light distant signals (which have the same meaning, of course, when the home signal is a semaphore). It's rather easier on multiple-aspect signalled lines though - the distant signals form a part of the aspect sequence shown in Module S1, obviously in varying combinations and always without a red aspect (so the signal in rear won't display yellow).
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| Re: Understanding repeater signals 27/01/2012 at 14:24 #28315 | |
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Aurora
183 posts |
Apologies if this is a stupid question, but what aspect does the distant signal show immediately after a train passes through it? Does it not change until the train passes the next signal with the signal prior to the distant remaining on red.
Nil. Log in to reply |
| Re: Understanding repeater signals 27/01/2012 at 14:27 #28316 | |
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clive
2738 posts |
" said:So what you're really saying then is that this type of repeater signal only behaves as a true repeater when the following signal is green (see pic below). It indicates yellow instead of red because that's the most restrictive it can get. It hasn't got redNo. In some countries, a repeater signal shows exactly the same aspect as the signal it repeats. It's up to the driver to know whether a red signal is the one that he stops at or the one that he passes because he's going to stop at another signal. The UK got rid of that idea back in the 19th century because of the risks of confusion, particularly in the dark. Instead, a repeater shows single yellow ("prepare to stop at next signal"  when the signal it repeats is red.A three aspect signal can be thought of as a stop signal (red/green) and a repeater (yellow/green) combined. With semaphores you have the two separate, one above the other, and indeed the Grub Water and Relief did it with coloured lights as well. London Underground also does that, but suppresses the repeater when the stop signal is red. But main-line practice is to show the more restrictive of the two aspects (so yellow for caution, green for clear). From this point of view a repeater is then just a signal that never shows red but provides the usual three-aspect or four-aspect sequences (you get outer repeaters that only show YY or G). There are signals that show the same aspect as the one they repeat. They're called "co-acting signals" and there are strict limits on how far apart the co-acting and main signal can be. Log in to reply The following user said thank you: maxand |
| Re: Understanding repeater signals 27/01/2012 at 14:34 #28317 | |
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Laryk
56 posts |
" said:Apologies if this is a stupid question, but what aspect does the distant signal show immediately after a train passes through it? Does it not change until the train passes the next signal with the signal prior to the distant remaining on red.You're understanding is correct. 
Last edited: 27/01/2012 at 16:25 by Laryk Log in to reply The following users said thank you: Aurora, saxbophone |
| Re: Understanding repeater signals 27/01/2012 at 14:40 #28318 | |
jc92
3629 posts 
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" said:" said:depends wether the distant is a) a colour light, not a semaphore (i think croes newyyd might have an exception here)Apologies if this is a stupid question, but what aspect does the distant signal show immediately after a train passes through it? Does it not change until the train passes the next signal with the signal prior to the distant remaining on red.You're understanding is correct. The distant signal has now way of knowing if a train has passed it as there is no detection. b) is provided with a suitable TC and locking but some will replaced behind a train (the one at chapeltown definetly does this) and some wont "We don't stop camborne wednesdays" Log in to reply The following user said thank you: Aurora |
| Re: Understanding repeater signals 27/01/2012 at 14:46 #28320 | |
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Laryk
56 posts |
" said:but some will replaced behind a train (the one at chapeltown definetly does this) and some wontInteresting. I assume for it to replace behind a train it has to have a TC - in that case why not use standard 3 aspect? Is it some sort of legacy issue, with a line being upgraded but retaining the original signals? Log in to reply |
| Re: Understanding repeater signals 27/01/2012 at 14:49 #28321 | |
Peter Bennet
5360 posts |
In real life most/all? distants are controlled by a lever in the box so go back when the signalman replaces the lever. In SimSig (mine anyway) they are automatic clear/restore due to Sim Platform limitations. Peter I identify as half man half biscuit - crumbs! Log in to reply |
| Re: Understanding repeater signals 27/01/2012 at 14:56 #28322 | |
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Late Turn
696 posts |
In some (most?) cases, a colour-light distant signal will replace itself to Caution even if the lever in the box is still reversed - not sure how widespread that is though. It might not happen immediately - often, at an absolute block box, the berth track circuit only extends 200yds or so in rear of the home signal. Quote: Interesting. I assume for it to replace behind a train it has to have a TC - in that case why not use standard 3 aspect? Is it some sort of legacy issue, with a line being upgraded but retaining the original signals? Because then you have to provide a distant signal in rear of that - which will inherit the same question! Quote: Does it not change until the train passes the next signal with the signal prior to the distant remaining on red. In either case, the stop signal in rear will remain at Danger until the train has passed clear of the overlap of the stop signal in advance (as the distant signal, replaced or otherwise, will not protect the train!). Last edited: 27/01/2012 at 14:56 by Late Turn Log in to reply |
| Re: Understanding repeater signals 27/01/2012 at 15:19 #28324 | |
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headshot119
4869 posts |
" said:" said:Indeed the distant Down line replaces to caution once the train occupies the relevant track circuit." said:depends wether the distant is a) a colour light, not a semaphore (i think croes newyyd might have an exception here)Apologies if this is a stupid question, but what aspect does the distant signal show immediately after a train passes through it? Does it not change until the train passes the next signal with the signal prior to the distant remaining on red.You're understanding is correct. The distant signal has now way of knowing if a train has passed it as there is no detection. "Passengers for New Lane, should be seated in the rear coach of the train " - Opinions are my own and not those of my employer Log in to reply |
| Re: Understanding repeater signals 27/01/2012 at 16:16 #28332 | |
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Firefly
521 posts |
The practice for at least the last 20 years is that a distant/repeater signal must revert to it's most restrictive aspect as soon as the train passes the signal. The signallers panel will very rarely show the track circuit breaks performing this function. Here's an extract from Edinburgh showing how it works:-     The replacement function can be achieved using a treadle if there's not a suitable track circuit section to perform the task (Or on axle counter areas for example). FF Post has attachments. Log in to view them. Log in to reply The following users said thank you: Laryk, maxand |
| Re: Understanding repeater signals 29/01/2012 at 12:43 #28392 | |
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Firefly
521 posts |
Quote:Interesting. I assume for it to replace behind a train it has to have a TC - in that case why not use standard 3 aspect? Is it some sort of legacy issue, with a line being upgraded but retaining the original signals?The decision to use 2, 3 or 4 aspect is based upon headway requirements. (How many trains you need to fit on a particular length of line at any one time.) I've drawn some sketches:-  In the above 2 aspect area 2 trains, both running at 65mph would have to be 19kms apart to both get continuous green aspects. Therefore you could run 5 trains per hour assuming there are no station stops. If you put a station in you have to account for deceleration, acceleration and dwell time meaning you could only actually get 3 to 4 trains per hour. To increase your TPH you simply move the signals closer together.  or even  eventually your stop signals will become so close to the next distant (or repeater) signal that it becomes more economical to implement 3 aspect signalling.  Finally when you want to squeeze the last bit of headway out of the scheme you can install 4 aspect signalling. (note I've change the scale on this drawing 1km = 2 squares)  Of course the above is an over simplification because you have to consider trains running at different speeds, station stops, junction regulating, and delayed trains. I hope this all makes sense and helps you understand the process for deciding on 2, 3 or 4 aspect signalling. FF Post has attachments. Log in to view them. Log in to reply The following users said thank you: maxand, NCC1701, mfloyd, postal, Stephen Fulcher, Aurora, AndyG, saxbophone |
| Re: Understanding repeater signals 30/01/2012 at 12:36 #28433 | |
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kbarber
1712 posts |
" said:Apologies if this is a stupid question, but what aspect does the distant signal show immediately after a train passes through it? Does it not change until the train passes the next signal with the signal prior to the distant remaining on red. Yet again this seems to depend on era - and perhaps on individual engineers' preferences too. With thanks to Firefly for his sketches, the decision to implement 2-, 3- or 4-aspect signalling is down to cost - each signal equals <a lot of> £££ (<even more> $$$) and - certainly on British Rail from the 1960s onwards - there was pressure to minimise the numbers. In a number of places, signalling was installed that (sometimes many years later) was insufficient for services that were wanted or needed. Each additional track circuit adds cost as well. On the other hand, signal engineers are conservative animals and tend in the direction of overprovision, at least until they can be certain what they're installing is safe. Hence, historically, on 3- and 4-aspect sections, auto signals were provided with separate overlap track circuits and reverted to danger soon after the front of the train had passed. (This was certainly the case as late as the beginning of the 1960s, I saw it in Barking box which was commissioned about 1961). By the mid-60s it had been realised that, as the signal next in rear protected the signal whose overlap was occupied, this was unncessary and separate overlap tracks disapeared on auto signals (they remain universal on controlled signals). The pendulum then swung the other way and I believe the 2-aspect auto sections between Southampton and Brockenhurst had repeaters that remained green until their associated stop signals reverted to danger. Of course there were probably exceptions here & there in any case, where circumstances were thought to warrant a different installation. So yet again, research into actual locations is the only way to find out what actually happens. Log in to reply The following users said thank you: Aurora, saxbophone |