+- IRSE Exam Forum (https://irse.signalpost.org)
+-- Forum: MODULES (https://irse.signalpost.org/forumdisplay.php?fid=3)
+--- Forum: Module 3 (https://irse.signalpost.org/forumdisplay.php?fid=6)
+---- Forum: Principles Queries etc (https://irse.signalpost.org/forumdisplay.php?fid=70)
+---- Thread: Bite-sized Revision Notes (/showthread.php?tid=49)
Pages:
1
2
RE: Bite-sized Revision Notes - PJW - 25-09-2008
YLP Wrote:I have several queries on the Notes:
3. Bite 18 Points (Point 3 bullet 5)
- For a point lying in a swinging overlap (but not the swinging O/L point), I think the route locking requires a condition on the position of the swing O/L point. Is there other ways to express this if we do not add a point condition?
Actually the mention of point conditions around a track in the route locking is much the same as the previous comment I think.
From your description I think that you may be meaning a trailing point that is in one of the possible overlaps but not the other as it is beyond the hinge. You are right that the calling of that point and also the locking of that point is conditional on the state of the hinge point and yes you do write that in as I have explained in my answer re 2006 to Alex.
RE: Bite-sized Revision Notes - PJW - 25-09-2008
YLP Wrote:I have several queries on the Notes:
4. Bite 18 Points (Point 6 bullet 3)
- Can you explain more why the route lock only needs to maintain after berth TC clear, but not require us to write all T.C from start signal till the berth TC?
I think you have misunderstood; Time of Operation Locking is subtly different from route locking.
T of Op is applies to certain facing points in a swinging overlap; these are therefore typically free to move from one lie to another whilst a train is routed up to the exit signal, provided that both of the overlaps are currently available (otherwise the swinging overlap locking would prevent). However we wouldn't want them to swing just at the moment when a train SPADed if there was then a signficant risk of the train reaching them in mid-stroke.
Hence if the points a are "close" (you may find some old books quote 20m, my experience nowadays when we have to calculate on the site specifics is that 40m is more like the limit) then T of Op is applied. This reflects the fact that until train reaches commencement of the dead track circuit they would otherwise be free and there would be insufficient time for them to complete any throw that had been started just prior to the SPAD being detected.
The entry therefore lists the "priming" condition- after route used but this itself does not lock. The lock is applied when the berth (and the issue is that it is ONLY the actual berth) track circuit is occupied; (i.e. locks the points early so as to be ready for a SPAD should it occur) and then once that same track has been occupied long enough (i.e. the risk of a SPAD has passed) then release the locking again.
Of course you often do get T of Op on the same points as swinging overlap locking; the T of Op ALWAYS locks N>R AND R>N whereas obviously any swinging O/L locking is only in one direction (although there may be the same routes but with different swinging overlap conditions for the converse swing). The points could potentially be trailers (or locked facers) in the overlap of some other routes yet obviously not those that apply T of Op.
RE: Bite-sized Revision Notes - PJW - 25-09-2008
YLP Wrote:Actually for the Point Control Table, I plan to use an old style C.T. (I think back to British Railway times...) that have blanks provided for Swinging O/L, and unlike NR practice it will not separate 2 rows for N->R & R->N cases (N->R and R->N will only be mentioned only when required). In the examples that I have it does incorporate point conditions when the points concern swinging overlap cases. Do you think it is acceptable for the examiner?
The examiners are very clear USE ANY PRACTICE WITH WHICH YOU ARE FAMILIAR. I vaguely remember the type of CT to which you refer (can you scan and post it here?).
Certainly I grew up with Western Region Control Tables and these assumed locking for example of dead tracks applied bothways unless stated in brackets (N>R) etc adjacent to each entry. Indeed there was a completly different CT for "counter-conditions" that was mainly what you'd call swinging O/L locking which I suspect used similar nomenclature.
So yes, it sounds like you are comfortable with something and you'd certainly not want to change horses at this stage! Be aware that my "bites" generally follow SSI practice and reasonably modern NR Principles, yet Alex has learnt rather older principles and generally follows an RRI approach.
"Mixing and matching" is a bit difficult and if you use a range of sources you won't be "pure"; the good news is that the examiners generally aren't either. They may be up to date with modern practices but I think most are far more comfortable with RRI than SSI. However there is no denying that it would be better to keep focussed on just one practice to avoid risk of mis-match or confusion; I don't know your background but Alex really has no choice than to just pick up what he can from where he can and thus there will be some inconsistencies.
To do really well in the exam perhaps the nuances are significant, but SPEED, COMPLETION, LACK OF SILLY OVERSIGHTS & MISTAKES are far more so. Don't worry too much about the frills; if you just want to do reasonably, concentrate on:
FOUL TRACKS / FLANK POINTS / ROUTE LOCKING / TIMING OFF OF OVERLAP LOCKING / APPROACH RELEASE / SHOWING THAT KNOW DIFFERNCE BETWEEN M/W/C/S CLASSES.
These are the things which I think generally separate the FAILS from the PASSES; any (well, most!) fool can get the tracks and points in the aspect level correct so these aren't worth many marks I think.
Hope these various responses have clarified, but if not please ask further,
PJW