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Post by londonstuff on Jan 28, 2008 17:01:34 GMT
Again, probably an easy question to answer. When I stand at Turnham Green, on the eastbound platform, I can see the signals in the distance gradually changing back to a green aspect. However, the signal at the end of the platform (WK6), never goes green until there's a train about 200 metres away? The only thing I can think of it that it's an approach controlled signal, but I doubt this as there's no obvious reason for it. There's also a yellow 'Weak Field, Flag Down' sign - what's that for? Thanks  |
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Colin
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Post by Colin on Jan 28, 2008 17:14:15 GMT
The clue is the signal number  WK6 is a semi automatic signal - it's controlled and will therefore only go green when either the signaller or the program machine clears it. Because it'll almost always be operated by the program machine, it'll almost always clear on approach. The signals you can see approaching Stamford Brook are all autos (the signal numbers will start with an 'A') - so they will always clear straight back to green as the train clears the section. The 'WEAKFIELD DOWN' sign relates to the flag switch on the train. The weakfield, in simple terms, allows the motors to accelerate quicker by providing less resistance to the motors. Weakfield can only be used on certain sections of the District line - west of Putney Bridge/Turnham Green & east of Bow Road and it will lmit the train to 40mph. You can tell if the driver is using the weakfield as there'll be a black & yellow flag in the bottom left hand corner (as you look at an oncoming train) of the windscreen. If you see a green & white flag, that's the coasting control flag - no weakfield and no limit to the speed of the train. No flags up means the train is limited to 30mph, and of course no weakfield. |
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Post by londonstuff on Jan 28, 2008 17:26:10 GMT
Thanks for your quick answer:)
What's the reason for it being semi-controlled - or do you get a semi-controlled one after a certain number of automatic ones? I presume ones, such as westbound at Turnham Green are semis, as someone needs to choose the correct route for the train to follow (Richmond or Ealing Broadway), but can't think of an obvious reason (for a non-train driver!) for one eastbound.
While I think on, what's the reason that after some signals the insulated block joints are so far past a signal - sometimes when I'm sitting a carriage or two back, when passing a signal, it's still green - I would have thought it made sense to have it just behind the signal?
Questions, questions!
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Colin
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Post by Colin on Jan 28, 2008 18:14:22 GMT
Thanks for your quick answer:) No problem - it's just lucky I'm about What's the reason for it being semi-controlled - or do you get a semi-controlled one after a certain number of automatic ones? First off, LUL semi automatics are essentially the same as Network Rail controlled signals, the difference in name has a lot do do with the way in which it actually works and is more technical than is relevant for this thread - anyway, a 'controllable' signal, if you will, is needed where ever there are divergences, convergences, reversing moves, possibility of trains colliding, etc.........the list is endless.... They're not sited purely for the sake of it, there's always a reason - a need to have manual control of a particular signal. I presume ones, such as westbound at Turnham Green are semis, as someone needs to choose the correct route for the train to follow (Richmond or Ealing Broadway), Absolutely correct! but can't think of an obvious reason (for a non-train driver!) for one eastbound. There's no particular reason for it these days (other than perhaps to allow the signaller the opportunity to 'regulate' the service), but I believe at one time in the distant past there were sidings or an industrial link of some sort in the area. I vauguely seem to recall a thread on it in the early days of the forum..........rather than me trying to find it, perhaps someone with some knowledge could remind us? While I think on, what's the reason that after some signals the insulated block joints are so far past a signal - sometimes when I'm sitting a carriage or two back, when passing a signal, it's still green - I would have thought it made sense to have it just behind the signal? Not necessarily - these block joints don't just play a part in returning signals to danger, they can also dictate when signals behind clear. This is known as the overlap and factors such as line speed, gradient, etc come into play - it's all quite technical and I'd rather leave that to one of our signalling bods to explain!  ;D ;D ;D As one of my colleagues said to me in another thread, you keep asking and someone will keep answering ;D ;D |
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Post by c5 on Jan 28, 2008 18:17:09 GMT
I think it may also be there to send the Train Description forward, but am not certain on that!
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Post by Deleted on Jan 29, 2008 0:58:47 GMT
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mrfs42
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Post by mrfs42 on Jan 29, 2008 1:59:58 GMT
Not necessarily - these block joints don't just play a part in returning signals to danger, they can also dictate when signals behind clear. This is known as the overlap and factors such as line speed, gradient, etc come into play - it's all quite technical and I'd rather leave that to one of our signalling bods to explain! ;D ;D ;D I'm not sure if any of what I'm about to type has been channelled by TOK, but there is a lot of difference between 'last wheel replace' or 'first wheel replace' [1] in design terms - I understand it in non-LU terms so I won't go into too much detail. A lot of factors need to be considered when you design a layout - where the block joints can be sited, what the following traffic is likely to be and how far the interlocking needs to 'hold' a route. If the following traffic is high density - close together then signals will generally replace to red as soon as the train has taken the signal (first wheel replace); if on the other hand and there are no outstanding SPAD [2] mitigation measures the signal can remain at green until the whole of the train has passed beyond it, sometimes quite a long way; remember that there will always be another red behind the green - so safety isn't compromised by keeping this signal at green and letting the last wheels of the train replace the stick. Why have the difference between first/last wheel replace? Well, sometimes you can't get the replacing block joint in the right place to 'drop' the signal, sometimes the signal at green [3] is used to simplify route holding circuitry. And for overlaps, well they're calculated: Overlap in metres = [0.51 x (V x V)] / [n plus or minus G] V x V = maximum permissible speed of line in km/hour G = percentage gradient plus/minus according to up/down n = ratio of train weight to braking force 10% on surface, 12% in tube. A third extra is added as a safety margin. You've also to factor in the headway time in signalling layout design - the time between two following trains passing a given point. With repeaters timetable headway can be maintained even if the stop signal cannot be seen - the Motorman Train Op will react to the Yellow changing to Green - in other places this is known as 'riding the yellows', however with train stops and a guaranteed brake application from them the T/Op is fully protected. For signalling design purposes LU has slow trains with good brakes and signal sighting can be optimised. [1] 'replace' = putting the stick back to red [2] Signal Passed At Danger [3] I might be able to compose something about GRs and WLs here, but my head is full of other things. |
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Post by mrfs42 on Jan 29, 2008 2:22:28 GMT
200m away from WK6 - that would make the train aroundabout half-way between FR571C/A571B and RWK6/A571C on track circuit DQ.
Is it because it's controlled by S2 (together with WK7)? Or am I barking up a completely inappropriate tree here?
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Post by railtechnician on Jan 29, 2008 10:44:54 GMT
Not necessarily - these block joints don't just play a part in returning signals to danger, they can also dictate when signals behind clear. This is known as the overlap and factors such as line speed, gradient, etc come into play - it's all quite technical and I'd rather leave that to one of our signalling bods to explain! ;D ;D ;D I'm not sure if any of what I'm about to type has been channelled by TOK, but there is a lot of difference between 'last wheel replace' or 'first wheel replace' [1] in design terms - I understand it in non-LU terms so I won't go into too much detail. A lot of factors need to be considered when you design a layout - where the block joints can be sited, what the following traffic is likely to be and how far the interlocking needs to 'hold' a route. If the following traffic is high density - close together then signals will generally replace to red as soon as the train has taken the signal (first wheel replace); if on the other hand and there are no outstanding SPAD [2] mitigation measures the signal can remain at green until the whole of the train has passed beyond it, sometimes quite a long way; remember that there will always be another red behind the green - so safety isn't compromised by keeping this signal at green and letting the last wheels of the train replace the stick. Why have the difference between first/last wheel replace? Well, sometimes you can't get the replacing block joint in the right place to 'drop' the signal, sometimes the signal at green [3] is used to simplify route holding circuitry. And for overlaps, well they're calculated: Overlap in metres = [0.51 x (V x V)] / [n plus or minus G] V x V = maximum permissible speed of line in km/hour G = percentage gradient plus/minus according to up/down n = ratio of train weight to braking force 10% on surface, 12% in tube. A third extra is added as a safety margin. You've also to factor in the headway time in signalling layout design - the time between two following trains passing a given point. With repeaters timetable headway can be maintained even if the stop signal cannot be seen - the Motorman Train Op will react to the Yellow changing to Green - in other places this is known as 'riding the yellows', however with train stops and a guaranteed brake application from them the T/Op is fully protected. For signalling design purposes LU has slow trains with good brakes and signal sighting can be optimised. [1] 'replace' = putting the stick back to red [2] Signal Passed At Danger [3] I might be able to compose something about GRs and WLs here, but my head is full of other things. I understand where you are coming from with this explanation but I suspect that some may be confused by the concept of last wheel replacing of signals because it is always the leading wheels that drop the replacing track. Certainly on LU the replacing track blockjoints for the Met and the T4 loop are quite a way beyond the signals on the fast sections but in my experience (mostly Piccadilly line and Finchley Road to Preston Road on the Met) I wouldn't think far enough ahead to be considered as last wheel replacing though certainly two or three cars length but I am open to correction here. |
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Colin
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Post by Colin on Jan 29, 2008 13:35:40 GMT
200m away from WK6 - that would make the train aroundabout half-way between FR571 C/A571 B and RWK6/A571 C on track circuit DQ. Is it because it's controlled by S2 (together with WK7)? Or am I barking up a completely inappropriate tree here? WK 6 generally clears as we enter the platform (ie, the 200m in the original post is a tad optimistic) - and as for WK 7.........there's no such signal these days ;D ;D EDIT: thanks also to TOK for all those links - I think we may have to add the title of my assistant to your profile ;D ;D |
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mrfs42
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Post by mrfs42 on Jan 29, 2008 13:48:04 GMT
200m away from WK6 - that would make the train aroundabout half-way between FR571 C/A571 B and RWK6/A571 C on track circuit DQ. Is it because it's controlled by S2 (together with WK7)? Or am I barking up a completely inappropriate tree here? WK 6 generally clears as we enter the platform (ie, the 200m in the original post is a tad optimistic) - and as for WK 7.........there's no such signal these days ;D ;D I thought as much, but I was far too drunk to go searching in the outer reaches of the library - I'd managed to find the 1963 peril and I was happy with that! ;D ;D |
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Post by c5 on Jan 29, 2008 17:08:39 GMT
200m away from WK6 - that would make the train aroundabout half-way between FR571 C/A571 B and RWK6/A571 C on track circuit DQ. Is it because it's controlled by S2 (together with WK7)? Or am I barking up a completely inappropriate tree here? WK 6 generally clears as we enter the platform (ie, the 200m in the original post is a tad optimistic) - and as for WK 7.........there's no such signal these days ;D ;D EDIT: thanks also to TOK for all those links - I think we may have to add the title of my assistant to your profile ;D ;D The Programme Machine (S3) for WK6 is normally left in First Come. |
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Post by Deleted on Jan 29, 2008 18:56:59 GMT
first come first serve mode will clear the signal generally as the train clears the junction push button mode will allow the wk6 to clear straight away its not approched controlled programme machine mode will only allow it to clear if the time and train number and the t/d of the train is correct but as this is not always the case except usually the first few trains and the last couple then it wil stay in FCFS mode wk7 does not exsist and there used to be a siding between the to 2 eastbounds between turnham green and stamford brook
turnham green used to be alot complex till around the 70's at some point as in the bookwiring (site prints) there as been alot of amendments regarding sidings and the lever frame is a 36 lever v style frame but now only 12 levers are in use
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Post by railtechnician on Jan 29, 2008 19:23:09 GMT
first come first serve mode will clear the signal generally as the train clears the junction push button mode will allow the wk6 to clear straight away its not approched controlled programme machine mode will only allow it to clear if the time and train number and the t/d of the train is correct but as this is not always the case except usually the first few trains and the last couple then it wil stay in FCFS mode wk7 does not exsist and there used to be a siding between the to 2 eastbounds between turnham green and stamford brook turnham green used to be alot complex till around the 70's at some point as in the bookwiring (site prints) there as been alot of amendments regarding sidings and the lever frame is a 36 lever v style frame but now only 12 levers are in use Turnham Green signal cabin used to sit just west of the platforms, although it had been out of use for years it was only demolished in the early 1990s until which time it had been used by the telephone maintenance department as a local equipment store. |
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mrfs42
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Post by mrfs42 on Jan 30, 2008 0:53:41 GMT
The Programme Machine (S3) for WK6 is normally left in First Come. Ah, I forgot the the harmonisation with Cobourg St.  |
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;D ;D ;D
