19-01-2010, 10:11 PM
(This post was last modified: 10-12-2017, 06:51 PM by PJW.
Edit Reason: replacing missing WORD by pdf
)
(19-12-2009, 01:42 PM)merlin89 Wrote: May I submit my route control table (107AM and 107AS) it has mistakes which I'm very unsure on how to complete. How do you write tracks clear section for the full swinging overlap and also unsure about the comprehensive lookack how to add test for auto signals 105 and 103. Guess the more examples of filled in CT's I see and do the better I can become at filling them in.
Thanks in advance
I have had a go at 202BS as well. Many thanks for your comments too.
For signal 119 I'm unsure how to write CT table for a signal whose control is released by the Block at 'Line clear' I assuming as that to be what the 'B' on the schematic alonside 119 to mean. Is anyone able to give me a few pointers?
I have actually been struggling myself to get a paper copy of your CTs to look at- what version of Word is it? It looks fine on screen but I get nothing when I attempt to print it out (indeed print preview tells me such!)
Hence I will restrict my response to giving some hints re the specific questions asked:
1. Swinging overlap.
There are two options to prove at aspect level, either:
a) BJ, DB, 303R, 305R, 306N (because it gives you flank), [BK or 304R] (because the track is conditionally foul)
or
b) BJ, BK, 303N, 306N, 304N (because there is no rational reason for having 304R and traditionally we'd have put in point-to-point; there is a move to 204 so it also helps slightly by providing flank; whereas you could decide to omit detection proving, you'd then need to put in AE as a conditional foul track dependent on 304, so let's cut out all the complexity and frills and just put in neat detection of 304N) and 305N (flank again!).
The only other thing that needs to be shown is that 303 are not fixed but may be swung (subject to counter conditional locking and time of operation locking that would be shown on 303's own CT) but the important thing for the route table is that we'd need to depict that 107's aspect isn't dumped whilst that legitimate swinging of the overlap is taking place; therefore you need somehow to reference the "303N or 303R" to explain that whilst one or other detection is needed initially, the aspect is maintained off for a period of say 8 seconds following a call on the facing points, whether it be by point switch or by setting of a route forward from 111 or indeed a flank route such as 122(2)M into the Bay that needs as a precursor to knock the overlap from being directed over 303R to going instead over 303N.
The question how you depict this is of course up to you and your style of CT. NR's 11202 Control Tables had a specific "N or R" column in order to cover the "or swinging" functionality. Very good for a very simple swinging overlap, not so good for one like this and damned awful for more complicated ones with multiple facing swinging points. Actually in the latest 11202 for SSI this was abolished (OK I admit it, I MADE SURE that it was abolished and actually met almost no opposition!) and a new "$ note" was defined to cover that functionality. This allows the expression to be written more logically than attempting to tie together an expression split over separate columns for points N, points NorR and points R. Indeed we went so far as providing separate lines of entry for each of the separate overlaps- very much as I did above with a) and b). It is in my view sensible for the SSI data designer and SSI tester and straight forward for any reader- that's why i got the change made.
The traditional CT was however designed reasonably appropriately when implementing the logic by a mesh of relay contacts- it was relevant to how a designer would design the circuit and indeed useful to indicate to the tester potential pitfalls of such a design. In that sort of presentation then you'd aim only to mention the one signalling function once in the expression (saved contacts and wire!).
BJ would just go in neat, as per tracks in line of route.
303 would be put in the "NorR" column, but because there are other overlap controls dependent upon it then it'd actually have to go in twice-
once as 303N and be bracketed with entries such as 305N, 304N and
again lower down the same column as 303R and be bracketed this time with entries such as 305R and DB clear (but see below) relevant to that overlap position.
BK is a bit of a nuisance in as far as required clear due to being in the overlap when 303N, but is also required clear as a foul track when 303R unless 304 is also R wherre it would be a parallel move.
Hence either need to straddle the swinging overlap expression into the track column as well which makes the whole thing hard to read, or just put in an entry here that is (at least initially apparently unrelated to the swinging overlap) of [BK or (303R, 304R)] which is probably the most usual presentation.
Similarly the entry for DB would generally be [DB or 303N] written in the tracks clear column, not explicitly linked on the CT with the 303 entry in the "NorR" column though obviously logically associated.
SO TO GET BACK TO YOUR QUESTION- how to show on CT?
Goes back to the assumptions and railway standards / practices that you as a candidate declared you were following- you did, didn't you!!!
Is it RRI or SSI?
Is it NR Control tables of c 2000- 2009, or the very latest practice?
Fundamentally I wouldn't (for IRSE Exam purposes) worry too much about it. Have a reasonable atttempt to get the fundamental controls of a swinging overlap recorded and I am sure you will do well- nuances of presentation aren't important- demonstrating that you know about FOUL and FLANK etc is much more so.
Note what I haven't discussed here is the point availability for the route to set in the first place- you need to write a logical expression involving 303, 305, 304 and 306 which evaluates to TRUE if one or other (or both) of the two overlaps is available. You don't (in the more traditional CTs at least) need to define which is set if both are available; this is inherent in the other entries to be made on the various point CTs. Remember that in the IRSE Exam; if you decide to do a route CT recognising a swinging overlap, you are duty bound to ensure that if the examiners have also asked you to do one of the relevant point CTs that you do this in a self-consistent manner. You can get away without doing swinging overlaps, but to do on certain sheets and not on related sheets is indefensible!
2. Comprehensive A/L lookback
Remember that you need to go back to at least the sighting distance of the signal that is the furthest away (on the approach) which suffers a change of aspect when the signal whose CT you ar writing changes aspect from least restrictive to Red.
In this case actually, 105 and 103 are auto signals. Hence it is nic and simple- just ist the tracks backwards from 107:
BD, BC, BB, BA. To get extra "Brownie points" may be worth stating the assumption that BA does indeed extend back to the overlap of the signal in rear and thus of adequate length tthat 103 not visible once it is occupied (cunningly the IRSE plan doesn't actually show this!).
However let us assume that 105 had instead been a controlled signal with say facing crossover 300 in BC track for a wrong direction move along Up Main with 204 as a main aspect signal. BB would ourely be the overlap track and thus the berth track of 105 would be an extra track ZZ.
In that case the approach locking entry for 107 would have been
BD, [(BC, BB) or 300R] -------------
ZZ, BA --------- or 105 ARAFOAL or 300R
where ARAFOAL = At Red And Free Of Approach Locking
(but you may have a column heading worded as such or saying "or Route Normal".
The issues are
a) in the first section in rear you nee to worry about points that would deflect a train from reaching the signal whose CT you are writing
b) the second section in rear is "conditioned out" by 105 being ON since any aspect sequence reversion from 107's replacemnt won't have perculated further back as 105 was always at Red.
If your heading entry refers to Routes Normal (as per standard free wire BR RRI circuits with latched NLR relays) then you'd write 105A(M) or whatever and not put in the point condition. If you are using a system where there is one ALSR per signal then you instead write the signal number, but need to add the relavnt point conditioning that says despie the signal being OFF, for the route up to 107 it is, in effect, ON.
c) in general the third section back is conditioned out by EITHER the first or the second signal being ARAFOAL. However since 103 is an auto then BA can simply be lumped in with ZZ; if it too had been a controlled signal then the entry would have been
APPROACH TRACKS CLEAR or SIGNAL ARAFOAL
ZY ----------------------------------[105A(M) or
103A(M)]
assuming that BA is 103's O/L track and ZY is its berth track extending at least the sighting distance on approach.
3. 119 signal.
The B symbol is probably intended to mean what you say though frankly to me it should be "on the post" and refer to really released by Block- i.e. a Line Clear from the signalbox in advance under Absolute Block working (double line). This signal protects a single line operated under Tokenless Block and I am not overly sure how those signals are generally presented.
Again don't worry too much about detail- the essence is that you recognise that there effectively needs to be a "release" from the adjacent signalbox before the route from 119 can be set. Indeed when the signaller attempts to set 119 then there has to be a period of that signalbox "offering" to the adjacent sgnalbox which will automatically reply (provided signaller has left their switch in "Accept" and various conditions are met) and if a response is received back in the defined time window and conditions at the local box (i.e. 307 free to go R, opposing locking from 126(2)M is free) then the route will set, otherwise it will time out and give up. Also you need to know that the other signaller can in emergency withdraw their Acceptance at any time and thus cause aspect reversion at 119. Effectively all this takes the place of proving opposing locking from the signal not shown off the end of the plan and indeed the lack of continuous train detection.
To get all the marks you'd need to know details of Tokenless Block [how is this fair for example to a candidate from India which probably doesn't have any such method of working single lines????- discuss!!], but the key thing is that the candidate recognises that there MUST be something else other than the track circuits and opposing signals that are depicted on the plan, assumes some method of working that MAKES IT SAFE.
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For comparison with tour attempts I attach some Point Control Tables on which I have previously commented.
PJW
