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| Mechanical Interlocking 01/01/2013 at 18:34 #39932 | |
wain77
81 posts |
Any of you S&T types know anything about mechanical interlocking on lever frames? If so, how are OR conditions implemented? My setup has a 3-signal Home bracket signalling into 3 terminal platforms controlled in my box by levers 2,3, and 4, with a 1-signal Distant in advance controlled by lever 1. I want the Distant lever to be locked normal until 2 OR 3 OR 4 are reversed. Is it do-able with conditional interlocking, i.e.: 1 is free when 2 is reversed IF 3 and 4 are normal 1 is free when 3 is reversed IF 2 and 4 are normal 1 is free when 4 is reversed IF 2 and 3 are normal or is it done some other way? Thanks in advance! Sam Wainwright Log in to reply |
| Mechanical Interlocking 01/01/2013 at 18:39 #39933 | |
jc92
3687 posts |
the IF isnt neccesary assuming that for instance, to release 2 signal, the points have to be set in a way which would lock 3 and 4 at danger anyway. by adding the IF you're complicating the locking more than needed. the distant is more likely to have a 1 is free when 2,3 OR 4 are reversed. another alternative would be selection, ie one lever works all three signals, and the lay of the points releases the correct signal. in this case your locking for the distant would simply be 1 is free if 2 is reversed. is this for a model railway btw? "We don't stop camborne wednesdays" Last edited: 01/01/2013 at 18:40 by jc92 Log in to reply |
| Mechanical Interlocking 01/01/2013 at 19:03 #39935 | |
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wain77
81 posts |
Yes, the interlocking locks 3 and 4 if the route is set for 2, and I do want "1 is free if 2 OR 3 OR 4 is reversed", but I'm asking how that OR interlocking would be implemented in the interlocking itself; would you be using WHEN dogs on the lever tappets or some arrangements of notches and locks? My understanding of setting up an interlocking is based on this PDF. It's a theoretical exercise; I'm trying to get my head round the idea of setting up an interlocking. Why am I doing it? Cos I'm bored and it's interesting!  The layout is based on the Swanley New Barn Railway (with apologies to them!). Pic of the layout here.
Sam Wainwright Log in to reply |
| Mechanical Interlocking 01/01/2013 at 19:04 #39936 | |
Danny252
1461 posts |
As jc92 says, you can very, very often get rid of "If"s through inferring the positions of levers from what's already reverse - so you would never even need to check if 3 or 4 are reverse when pulling 2. A quick scribble on paper with my complete lack of knowledge of interlocking and a quick Google suggests it is possible to do it with conditional locking - my initial solution would probably make an S&T chap cry, though! Sounds like an interesting challenge for myself... (Although I believe all distants into terminal platforms must be fixed at caution, actually) Log in to reply The following user said thank you: wain77 |
| Mechanical Interlocking 01/01/2013 at 19:44 #39939 | |
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Danny252
1461 posts |
For further reading, this SRS article is (as always) brilliant: http://www.s-r-s.org.uk/SignallingPapers/02/3barV5.html Something I read also made me realise you could also do it electrically as well - in this case, you could have proving on 2/3/4 and electrically release 1 when one of them is proved to be off. Of course, that would be a complete waste of electrical gubbins - 2/3/4 are probably in view and don't require electrical proving, and you'd have to dig out a plunger to stick on 1! And you could do a ridiculous amount of conditional locking on one lever - check out Lever 84 at Exeter West: http://svrsig.co.uk/diags/S833-3.htm Log in to reply |
| Mechanical Interlocking 01/01/2013 at 20:40 #39940 | |
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clive
2789 posts |
My understanding is that the simplest approach for something like this is a swinging tappet - that is, the tappet can swing left or right (on the basis that it normally moves up and down). This is used to produce a OR facility - in this case 2 and 3 would have swinging tappets, with dogs between 1 and 2, 2 and 3, and 3 and 4.
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| Mechanical Interlocking 02/01/2013 at 00:36 #39957 | |
DriverCurran
688 posts |
If all routes are into a terminal platform then the distant really should be a fixed distant as you are unable to clear at least one of the signals applicable to that line (you cannot give a proceed aspect on the buffer stops, these count as a fixed danger aspect) unless you are looking at modelling very early railways where a distant indicated the occupancy of a platform or otherwise, any post grouping i.e after 1923 based model would be very unlikely to have rule book authorisation to clear a distant signal at a terminal platform. I will accept correction if required (this is my understanding of how terminal platforms dealt with distant signals. Paul You have to get a red before you can get any other colour Log in to reply |
| Mechanical Interlocking 02/01/2013 at 00:40 #39958 | |
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jc92
3687 posts |
" said:If all routes are into a terminal platform then the distant really should be a fixed distant as you are unable to clear at least one of the signals applicable to that line (you cannot give a proceed aspect on the buffer stops, these count as a fixed danger aspect) unless you are looking at modelling very early railways where a distant indicated the occupancy of a platform or otherwise, any post grouping i.e after 1923 based model would be very unlikely to have rule book authorisation to clear a distant signal at a terminal platform.certainly i recall reading that london bridge was signalled like this with distants indicating occupancy of platforms. the other consideration is wether the signal leading into the terminal line is semaphore or MAS. a colour light will give a yellow aspect anyway, whereas a semaphore cannot, hence the fixing of the distant. Buxtons distant signal is definetly fixed, and that has an acceptance home and an inner home. Morecambe also had fixed distants "We don't stop camborne wednesdays" Last edited: 02/01/2013 at 00:41 by jc92 Log in to reply |
| Mechanical Interlocking 02/01/2013 at 10:04 #39967 | |
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kbarber
1742 posts |
" said:If all routes are into a terminal platform then the distant really should be a fixed distant as you are unable to clear at least one of the signals applicable to that line (you cannot give a proceed aspect on the buffer stops, these count as a fixed danger aspect) unless you are looking at modelling very early railways where a distant indicated the occupancy of a platform or otherwise, any post grouping i.e after 1923 based model would be very unlikely to have rule book authorisation to clear a distant signal at a terminal platform. Yet again this changed with (original) owning company and era. I believe it was the LBSCR that used distant arms to indicate whether a terminal platform was completely clear or partially occupied. (There may have been others but I'm not certain.) The indications were: both arms on - stop; stop arm off, "distant" on - platform partially occupied; both arms off - platform clear to buffer stops. Early layouts would typically have had working distants whatever the owning company. But if there was a 3-doll bracket governing entry to the platform there would most likely have been a 3-doll bracket distant too. Looks like two extra levers on the left hand end of the frame I'm afraid. It happened in real life too and it's most likely those levers would end up "numbered" A and B. A single distant arm worked for all arms on a bracket was fairly rare. That would definitely want conditional locking (what Modratec calls a "when" lock I'd refer to - informally - as an "or" lock and the means of achieving it as a sliding or swinging tappet, as Clive says). I would say it was such a rare beast that you'd need definite evidence of a location where it happened to be worth modelling it (the configuration was more likely at a junction where speeds were very close in either direction). But by the time a single distant arm was being provided for this application, the tendency would probably be to fix it at caution. Although it's a relatively recent thing to define a stop block as a stop signal within the signalling system, there was a move to do away with the logical nonsense of a clear distant reading onto stops quite some time ago. But don't ask me when. Again, it's likely to have varied considerably from one company to another. Early colour light (MAS) practice was to allow a green to read into a terminal platform. I have an idea the Southern Railway may have followed LBSCR practice by providing a yellow aspect to indicate a platform partially occupied (certainly Brighton had 3-aspect signals reading into the terminal platforms, as shown here http://www.wbsframe.mste.co.uk/public/pdf/Brighton_1932.40D.PDF). I believe greens reading onto the stops were originally provided at Euston (1965) and I have a suspicion the new standard requiring a yellow as the best aspect may have been (at least partly) a response to the Moorgate disaster of 1974 (certainly a passing remark by the instructor when I was at signalling school in 1978 suggested Euston had only recently been altered). Don't know if that helps at all? (Probably not, I fear.) K Log in to reply |
| Mechanical Interlocking 02/01/2013 at 12:15 #39982 | |
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clive
2789 posts |
" said:I believe greens reading onto the stops were originally provided at Euston (1965)That's certainly what all my sources say, and that's what I've done in the sim. But they were 2-aspect plus sub for calling-on; they did *not* use yellow to indicate an occupied platform. Quote: and I have a suspicion the new standard requiring a yellow as the best aspect may have been (at least partly) a response to the Moorgate disaster of 1974 (certainly a passing remark by the instructor when I was at signalling school in 1978 suggested Euston had only recently been altered).Paragraph 125 of the Moorgate report: "I have also been given to understand by Officers of the British Railways Board that consideration is being given to altering the signal aspect sequence leadig up to the buffer-stops lamp at Red. It has been proposed that, in future, the normal 3- or 4-aspect sequence will be followed with the final signal allowing entry to a platform showing Yellow when clear" Log in to reply |
| Mechanical Interlocking 02/01/2013 at 14:58 #39988 | |
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kbarber
1742 posts |
" said:" said:I believe greens reading onto the stops were originally provided at Euston (1965)That's certainly what all my sources say, and that's what I've done in the sim. But they were 2-aspect plus sub for calling-on; they did *not* use yellow to indicate an occupied platform. Sorry Clive, I should've been clearer, my understanding was as you say. Thanks for that quote from the Moorgate report too; confirms what I'd always understood from that instructor's comment. Log in to reply |
| Mechanical Interlocking 02/01/2013 at 16:39 #39999 | |
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wain77
81 posts |
Well, I've managed to work out a solution (I think). Lever 1 locks levers 2, 3, and 4 both ways. The tappets for 2 and 3 have conditional sliders and the tappet for 4 has a fixed slider (forgive me the oxymoron) all the sliders being lined up when the levers are normal. This arrangement means (I think) that 1 is locked while 2, 3, and 4 are normal. When any one of 2, 3, or 4 are pulled, lever 1 is released as the associated slider moves out of the way. Lever 1 is then pulled, which relocks at least one lever, ie if lever 2 is pulled, pulling lever 1 locks only lever 2 because the conditional slider is out of the locking paths, if lever 3 is pulled, levers 2 & 3 are locked by 1, if lever 4 is pulled, all three are locked by 1. This lack of return locking doesn't concern me, as the normal levers will be locked out anyway by the points being set against them. As for this not being proto, it is how the SNBR (a 7.25" gauge miniature railway) is worked, albeit with a Y/G 2-aspect colour light signal as the distant and a normal 3-aspect cls with route feather instead of 3 semaphores on a bracket. It's very interesting to see how much knowledge there is on this board! Sam Wainwright Log in to reply |
| Mechanical Interlocking 02/01/2013 at 16:52 #40001 | |
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wain77
81 posts |
I should also mention that the 'distant' stands at the end of the halt at the far end of the 'mainline' loop and is used to tell drivers if they have a platform road so they know how much welly they can give it up the hill back to the main terminus!
Sam Wainwright Log in to reply |