Looking at your points CTs
233
This one seems pretty straight forward- makes me worry we have both missed something!
You queried providing flank by switch diamonds; you are correct that calling the points nomal doesn't really protect. However conversely if 231 is being used in normal lie, there really is no value in not getting 233 normal. One could certainly argue that if they fail to achieve detection then there would beno reason to hold 109A(M) etc at danger, but as far as the points CT is concerned then yes 233 should be set and locked. Note that if 233 were initially reverse and were locked so by occupancy of CS, then 231 wiuld itself be locked reverse; therefore by including in 109A(M) 233 "normal or free to go" haven't made more restrictive. It may not give you much but if it costs you nothing then might as well do it; after all traditionally the 3 point ends 231 and 233A/B would have been operated as 231A/B/c an keeping the setting and locking cnsistent will probably lead to fewer mistakes when railway being operated in degraded mode.
The only other comment is really a repeat of one I have recently made on your 2007 point CTs. I would not list the overlap track sections where these tracks are already shown as dead locking the points. I note that you listed CT (but not CS) in the route holdng after 154A(M) and CS, CT after 152B(M) and 156B(M); I consider these superfluous entries as it adds no more locking than is there anyway by virtue of the neat tracks.
254
Not sure why you deleted (FB or 253N) in the R>N locking; I would have included.
Again I would not have shewn the overlap tracks in the maintained locking on the points.
I would however have included CH in the locking after 159A(S); I think this is just a random careless error on your part; I am making the assumption of SSI with 15sec track bob protection of course- if this did not exist (the attempts to implement on RRI were generally given up as a bad idea) then I would only show route locking to the track PRIOR to the dead track locking.
I don't understand why you deleted the 149A(S) entry; I am gussing that since this is a shunt class route you are saying that 254 could be reverse with the shunt O/L at the CH/CG joint. However there is no forward route from 157 that way and don't see why this route would be treated differently- I am sure that this shunt overlap is intended to define the length beyond 159 shunt signal rather than being associated with shunt class routes to main aspects.
Another example of something I recently pointed out on the 2007 CTs; I would write the locking on the trailing points within the swinging overlap as [147B(S) or 253R$28] (where $28 means "correct or freee to go)
The other thing that perhaps you either didn't notice or perhaps realise the significance; points 255 and 254 are both in the same track circuit CH. Traditionally there would have been point-to-point locking between these sets; getting both points reverse simultaneously would have been prevented by direct interlocking between them, going back to mechanical locking practice.
This is not currrent NR practice (tended to die out in late 1970s / early 1980s), but pseudo point-to-point is definitey sensible; i.e. making sure all the routes that call one of them reverse, call the other set normal.
Obviously it is definitely necessary that routes over 254R call 255N as that is the only path for the train; it is sensible that routes over 255R call 254N even though the train does not traverse. This is for two reasons; it tends to give an elemnt of flank protection (albeit often not perfect) and also to avoid adversely affecting operability. Consider a train using 166A(S) and which has just cleared CG, still occupying CH; points 257 have therefore become free to call normal, yet if 254 just happened to be lieing reverse then 157 route could not be set and trains would be delayed for no good reason.
Lookout for two differently numbered point ends within the same track circuit as your trigger to consider pseudo-point-to-point; for example also on this layout notice that points 244B and 245A are both in CN.
Therefore you should have listed all routes over 255 reverse as applying normal calls to 254; if doing their CTs then these routes would be shown as setting and locking but not detecting (to avoid any detection failure unnessarily preventing aspect clearance).
SUMMARY
So some comments but not a lot much wrong. Practice helps you speed up and time is of the essence in the exam, but remember that in the 2013 exam that Control Tables are only one of the three questions that you have to do. In your case these look well under control; don't forget your preparation for the other 2/3rds of the examination! Students don't pass anymore on CTs alone.
233
This one seems pretty straight forward- makes me worry we have both missed something!
You queried providing flank by switch diamonds; you are correct that calling the points nomal doesn't really protect. However conversely if 231 is being used in normal lie, there really is no value in not getting 233 normal. One could certainly argue that if they fail to achieve detection then there would beno reason to hold 109A(M) etc at danger, but as far as the points CT is concerned then yes 233 should be set and locked. Note that if 233 were initially reverse and were locked so by occupancy of CS, then 231 wiuld itself be locked reverse; therefore by including in 109A(M) 233 "normal or free to go" haven't made more restrictive. It may not give you much but if it costs you nothing then might as well do it; after all traditionally the 3 point ends 231 and 233A/B would have been operated as 231A/B/c an keeping the setting and locking cnsistent will probably lead to fewer mistakes when railway being operated in degraded mode.
The only other comment is really a repeat of one I have recently made on your 2007 point CTs. I would not list the overlap track sections where these tracks are already shown as dead locking the points. I note that you listed CT (but not CS) in the route holdng after 154A(M) and CS, CT after 152B(M) and 156B(M); I consider these superfluous entries as it adds no more locking than is there anyway by virtue of the neat tracks.
254
Not sure why you deleted (FB or 253N) in the R>N locking; I would have included.
Again I would not have shewn the overlap tracks in the maintained locking on the points.
I would however have included CH in the locking after 159A(S); I think this is just a random careless error on your part; I am making the assumption of SSI with 15sec track bob protection of course- if this did not exist (the attempts to implement on RRI were generally given up as a bad idea) then I would only show route locking to the track PRIOR to the dead track locking.
I don't understand why you deleted the 149A(S) entry; I am gussing that since this is a shunt class route you are saying that 254 could be reverse with the shunt O/L at the CH/CG joint. However there is no forward route from 157 that way and don't see why this route would be treated differently- I am sure that this shunt overlap is intended to define the length beyond 159 shunt signal rather than being associated with shunt class routes to main aspects.
Another example of something I recently pointed out on the 2007 CTs; I would write the locking on the trailing points within the swinging overlap as [147B(S) or 253R$28] (where $28 means "correct or freee to go)
The other thing that perhaps you either didn't notice or perhaps realise the significance; points 255 and 254 are both in the same track circuit CH. Traditionally there would have been point-to-point locking between these sets; getting both points reverse simultaneously would have been prevented by direct interlocking between them, going back to mechanical locking practice.
This is not currrent NR practice (tended to die out in late 1970s / early 1980s), but pseudo point-to-point is definitey sensible; i.e. making sure all the routes that call one of them reverse, call the other set normal.
Obviously it is definitely necessary that routes over 254R call 255N as that is the only path for the train; it is sensible that routes over 255R call 254N even though the train does not traverse. This is for two reasons; it tends to give an elemnt of flank protection (albeit often not perfect) and also to avoid adversely affecting operability. Consider a train using 166A(S) and which has just cleared CG, still occupying CH; points 257 have therefore become free to call normal, yet if 254 just happened to be lieing reverse then 157 route could not be set and trains would be delayed for no good reason.
Lookout for two differently numbered point ends within the same track circuit as your trigger to consider pseudo-point-to-point; for example also on this layout notice that points 244B and 245A are both in CN.
Therefore you should have listed all routes over 255 reverse as applying normal calls to 254; if doing their CTs then these routes would be shown as setting and locking but not detecting (to avoid any detection failure unnessarily preventing aspect clearance).
SUMMARY
So some comments but not a lot much wrong. Practice helps you speed up and time is of the essence in the exam, but remember that in the 2013 exam that Control Tables are only one of the three questions that you have to do. In your case these look well under control; don't forget your preparation for the other 2/3rds of the examination! Students don't pass anymore on CTs alone.
(28-06-2013, 09:07 AM)dorothy.pipet Wrote: Feedback and comments please?
PJW