(13-07-2010, 07:44 AM)greensky52 Wrote: I have a new attempt on Year 2003's. Please comment freely
Actually, I still have 2 things confused:
1 If the point is nominated only with letters, does it mean both ends of the point move separately? And if their names are XXA and XXB, they move simultaneously?
2 I still do not know which column to enter the swinging point...
It may be a few days before I get the time to comment in detail on the attempt, but regarding your doubts:
1. The point NUMBER is the interlocking entity and therefore is commanded to be set to a particular lie and then locked in that position. The LETTER suffix relate to the separate ends (almost always but not absolutely always) having a separate point machine to drive them. These are always commanded to move identically (although perhaps not always 100% simultaneously, but only staggered by a fraction of a second to avoid the simultaneous surge currents for the separate motors exactly coinciding for example). Obviously the separate ends may not achieve detection simultaneously (or indeed at all).
Hence at the route level of th Control Tables generally only concern ourselves with the number alone, but at the aspect level then need to consider all the separate ends and thus list the number with its letter suffixes
2. Depends what you mean.
Signal CT: Where there is a facing point as a hinge within a swinging overlap then the former standard NR Control Table had a specific "N or R" column- the meaning being "point detected either Normal or Reverse at the time of signal clearance, but signal aspect subsequently maintained off for a period of up to 8 seconds following the deliberate swinging of the overlap (by point key or forward route calling or flank route calling) in order to give the time needed for the new overlap to be established"
In practice I find the use of the separate "N", *N or R" and "R" columns quite cumbersome and confusing in anything other than the simplest swinging overlaps; hence I prefer (and the new standard reflects- not exactly a coincidence that!) just a list of points in a logical order, with each specified to be N or R respectively. Then an annotation such as a # note is needed to denote the "N or R or swinging...." functionality, but no specific column.
Point CT: The former standard NR Control Table had the swinging overlap controls listed to the right hand side of the sheet; it also listed at the bottom the "Time of Operation" locking applicable when facing points immediately beyond (say within 50m) signal; note that this one entry applies both for
a) N to R and also
b) R to N
which I feel is rather inconsistent with the other presentation of locking on that design of Control Table.
For the IRSE Exam I'd recommend NOT drawing all the specific columns on your blank, but just leave one wide column on the right hand side. Then for any point which actually needs the locking you can use the space as required to enter such locking. I would tend to divide horizontally into 3 portions, with the centre band being partially overlapping the N to R and partially the R to N portions of the rest of the table- hence the place to record the T of Op which applies both ways. The other area can be used for the "counter consitional" locking for swinging an existing overlap- you list the additional controls needed on the points in these circumstances and these fall into the three categories:
a) tracks that are in the new overlap but not in the exsting one and which do not dead lock the points anyway,
b) other points (generally beyond the facers being considered, but don't forget about flank as well) "set or available to move" into the lie needed for the new overlap, over and above those already needed in that same lie within the existing overlap,
c) opposing route locking normal for one of the pair of opposing sets of routes which would otherwise share an overlap when the points adopt their new lie but don't currently conflict with each other due to the existing point lie keeping these two overlaps parallel and separate.
A reminder not to worry about exactly HOW you show the locking- you do not need to use any specific format. Providing it s clear what you mean, then just record the locking in the manner most suitable to you. In exam conditions this may well not be 100% like anything that you have experienced in use on a particular railway.
PJW