The points tables were also good.
For 233 however there is a typo as the locking in the overlap should of course be after 113A(M) not 133A(M).
The condition on that point call expression is stated as "w 231R$37" but I would not have expected detection to be relevant here, certainly not the way that SSI does swinging overlaps.
In general facing points are left where they happen to be lieing and any necessary facers beyond them set appropriately when the route is being set, it is only if not all the required overlap beyond them is available that the call is placed on the facers to move across to select a different overlap (since the route availability expression has already succeeded, one does know that at least one overlap must be possible).
Conversely the associated locking would need to be imposed unless the facing points can adopt their other position to swing to an alternative overlap. With RRI the circuits first check the other overlap is available, then call the facing points and then finally release the locking on those points no longer required in the former overlap only after the facers have achieved their new detection.
SSI actually just looks at the availability of the alternative overlap and simultaneously locks the new one, releases the old one and commands the facing points to move. It is actually non-compliant to standards in that respect; the locking of the overlap is still released even if the facing points never actually move.
So the actual $ ref used here does depend on the technology, but the locking should certainly be expressed as [113A(M) or 231N]; in spoken English it often is clearer to substitute the logical operator "or" by the word "except".
Also in that same expression should think about the possibility of the train coming to a stand in the platform but a fair way from the signal (perhaps it is a short train and the footbridge acces to the platforms is at the left hand end) so may need to time off the overlap with a train on BF but not BH; otherwise the junction area is locked up indefinitely.
Another thing is that the overlap locking on BJ, CJ isn't adding anything over and above the track occupancy that is stopping the points from moving by virtue of the dead locking anyway- the designer might perhaps decide to put in the data but it is logically superfluous and is certainly untestable (as opposed to route locking where there is "track bob protection" and the locking is held for 15s after a track section unexpectedly becomes clear). Just like route control tables only list as opposing route locking where actually needed and omits showing for those routes which are preventing by virtue of point availability whatever is actually there in the data, this is similarly superfluous and therefore should not be shown. If the designer does show then the tester must annotate, since cannot tick it and if left blank then looks as if not completed.
Hence I would have written for this entry:
[113A(M) or 231N (set & locked)]: BE [BF, BH ----or (BF or BH occ for 45s)]
235 (which you forgot to specify!)
This was good, but you sinned by utilising $39 without first defining its meaning.
Although you remembered the need for trapping on the vast majority of the relevant routes, you overlooked 129A,B.
You seem to have locked 235 after 109B(S) that I would not have done; there is a shunt ovbverlap shown beyond 127 but only including SE not SF. The locking is a bit restrictive re preventing what could otherwisehave been a simultaneous move and since the shunt overlap is actually shown then I don't feel that you should have locked; you'd have had a better excuse had the layout been silent on the subject. However given that you consider it necessary then in thi case it is correct that there is overlap locking on SE track (since does not deadlock points) but SF is superfluous (since it does).
A general item re saving valuable seconds in the exam relevant in several places but here in particular; where many routes have the same tracks for their maintained locking, then list the routes together and bracket so that you only hacve to write out the list the once for the several; pairing the routes from 146 & 148 would have been beneficial here for instance since they are so obviously the same.
All in all a very creditable set of Control Tables; the challenge is to do as many CTs so well within the time constraints of the exam; in 2007 candidates had 1 hour but within that time had also to draw a blank control table from memory and then arrange for these to be photocopied; if you could do both blanks within 12 minutes you were doing well.
You correctlly concentrated on the basic locking; it is important to do so in the exam. Don't worry about perfection; this is an exam not the day job.
If at work you only got 50 percent of the entries on a CT then you'd deserve to lose your license and your employment; in the exam you'd probably pass. Hence it is important to switch brain to "exam mode"; do attempt all CTs- whereas you might think that doing some well would be a better demonstration of your competence, in the exam it is necessary to accumulate marks. There is an allocation per route or per point; if you don't attempt all of them then you are throwing easy marks away whilst persuing others that are harder to get since the law of diminishing returns applies.
For 233 however there is a typo as the locking in the overlap should of course be after 113A(M) not 133A(M).
The condition on that point call expression is stated as "w 231R$37" but I would not have expected detection to be relevant here, certainly not the way that SSI does swinging overlaps.
In general facing points are left where they happen to be lieing and any necessary facers beyond them set appropriately when the route is being set, it is only if not all the required overlap beyond them is available that the call is placed on the facers to move across to select a different overlap (since the route availability expression has already succeeded, one does know that at least one overlap must be possible).
Conversely the associated locking would need to be imposed unless the facing points can adopt their other position to swing to an alternative overlap. With RRI the circuits first check the other overlap is available, then call the facing points and then finally release the locking on those points no longer required in the former overlap only after the facers have achieved their new detection.
SSI actually just looks at the availability of the alternative overlap and simultaneously locks the new one, releases the old one and commands the facing points to move. It is actually non-compliant to standards in that respect; the locking of the overlap is still released even if the facing points never actually move.
So the actual $ ref used here does depend on the technology, but the locking should certainly be expressed as [113A(M) or 231N]; in spoken English it often is clearer to substitute the logical operator "or" by the word "except".
Also in that same expression should think about the possibility of the train coming to a stand in the platform but a fair way from the signal (perhaps it is a short train and the footbridge acces to the platforms is at the left hand end) so may need to time off the overlap with a train on BF but not BH; otherwise the junction area is locked up indefinitely.
Another thing is that the overlap locking on BJ, CJ isn't adding anything over and above the track occupancy that is stopping the points from moving by virtue of the dead locking anyway- the designer might perhaps decide to put in the data but it is logically superfluous and is certainly untestable (as opposed to route locking where there is "track bob protection" and the locking is held for 15s after a track section unexpectedly becomes clear). Just like route control tables only list as opposing route locking where actually needed and omits showing for those routes which are preventing by virtue of point availability whatever is actually there in the data, this is similarly superfluous and therefore should not be shown. If the designer does show then the tester must annotate, since cannot tick it and if left blank then looks as if not completed.
Hence I would have written for this entry:
[113A(M) or 231N (set & locked)]: BE [BF, BH ----or (BF or BH occ for 45s)]
235 (which you forgot to specify!)
This was good, but you sinned by utilising $39 without first defining its meaning.
Although you remembered the need for trapping on the vast majority of the relevant routes, you overlooked 129A,B.
You seem to have locked 235 after 109B(S) that I would not have done; there is a shunt ovbverlap shown beyond 127 but only including SE not SF. The locking is a bit restrictive re preventing what could otherwisehave been a simultaneous move and since the shunt overlap is actually shown then I don't feel that you should have locked; you'd have had a better excuse had the layout been silent on the subject. However given that you consider it necessary then in thi case it is correct that there is overlap locking on SE track (since does not deadlock points) but SF is superfluous (since it does).
A general item re saving valuable seconds in the exam relevant in several places but here in particular; where many routes have the same tracks for their maintained locking, then list the routes together and bracket so that you only hacve to write out the list the once for the several; pairing the routes from 146 & 148 would have been beneficial here for instance since they are so obviously the same.
All in all a very creditable set of Control Tables; the challenge is to do as many CTs so well within the time constraints of the exam; in 2007 candidates had 1 hour but within that time had also to draw a blank control table from memory and then arrange for these to be photocopied; if you could do both blanks within 12 minutes you were doing well.
You correctlly concentrated on the basic locking; it is important to do so in the exam. Don't worry about perfection; this is an exam not the day job.
If at work you only got 50 percent of the entries on a CT then you'd deserve to lose your license and your employment; in the exam you'd probably pass. Hence it is important to switch brain to "exam mode"; do attempt all CTs- whereas you might think that doing some well would be a better demonstration of your competence, in the exam it is necessary to accumulate marks. There is an allocation per route or per point; if you don't attempt all of them then you are throwing easy marks away whilst persuing others that are harder to get since the law of diminishing returns applies.
(28-06-2013, 09:09 AM)dorothy.pipet Wrote: Comments and feedback please?
PJW