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2012 CT- "SSI data" format
#1
For about the last decade now, NR has adopted a form of Control Table which is much more closely aligned to SSI data structure.  Most new interlockings in the UK are currently SMARTLOCK or WESTLOCK which both utilise variants of the SSI data language and so this form of CTs are the style that many are most familiar.  From that perspective it makes sense that they use in IRSE Exam.

Indeed one of the main reason they were introduced was to avoid the waste of time and effort that previously existed for Designers and Checkers to have to produce CTs that were not directly useful in writing data (indeed as a tester one sometimes felt that you were the first person actually to look at the data and the CTs together!) and that some of the entries were not useful for the tester either.  This was particularly the case with:
  • route locking (the PRR file action entry tested at time of setting route and fundamentally pretty obvious if wrong, the FOP file tested one as "pre-functional" yet the whole list of track were written down for each opposing route and needed to be ticked even though no testing to be done);
  • approach locking lookback (typically the MAP file tested in portions, but having tested an area of the file listing track/ points / signals then if testing another signal which looked back into same area thenonly had to check the entrance and exit points for that route as the "bi in the middle" was thsame as had been tested previously.
Hence the presentation in the CTs of "just the sub-route  and / or sub-overlap that does the locking and is the one listed in the availability test"; similarly in A/L just "entry and exit point(s)".

From an exam perspective, this presentation saves time which is great for the candidate.  Problem is that it also doesn't show the totality of the locking the examiner will expect- if you are judged to have given only "half an answer" then the chances are that the score you are given will only be a percentage of half the available marks.

Hence you DEFINITELY need to do something to show the examiner enough. 
  • Obviously you can't do the sub-route CT and the MAP search diagram for the whole interlocking when only got 30mins to do a couple of routes and a point.
  • Conversely you can't just say your style of CT does not show on the Points CT and the Route/Aspect CT; although this is true, it is disingenuous as these are supposed to be read in conjunction with something else that you haven't provided.
Some people in the past have asked for advice what to do about the situation.  This year for the first time I think I have been given some actual attempts at IRSE exam papers using a blank based on the NR SSI style.  I have given some feedback on how best to apply for exam purposes, in a mixture of comments appended and separate emails.
I am now putting these on this Forum so that others can see and consider; there are attempts also for 2013 and 2014.   These should be considered as a set, as I have not made generic comments on each example.

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CONTROL TABLES
 
Mainly put my comments on the sheets.
Those that relate to what is worth including / omitting for IRSE Exam purposes I have not always repeated each time these are relevant.
I think that use of the SSI type CTs are fine and generally I have been very impressed with your notes; you will be having time by the form of presentation and I am sure that the examiners will “need something extra” from you to compensate and these really are good for that, stating assumptions and explaining.
HOWEVER DON’T QUOTE STANDARDS- instead EXPLAIN THE SIGNALLING RATIONALE as the reason.
 
In a couple of cases you have actually demonstrated that perhaps have not fully understood things (e.g. swinging overlap CT- for the simple case, you did the complicated one well, the aspect sequence to 127 and indeed up to 125 but that is probably just an oversight).  There is a bit of a risk that you may reveal such weakness to examiner that otherwise they may not have noticed, but overall you clearly show your knowledge and experience in interlocking.
 
Regarding the use of sub-routes; seems to me that best to do little extracts of just the ones you use on a sheet within the Special Control Notes area.  Not very onerous and “shows willing”.

However I would recommend that you have a general notes sheet (I suggest the first sheet should be on A4 answer paper) and use this for:
  • Stating the standards to which you are working (presumably 2017 Network Rail for SSI derivative interlockings)
  • Stating that not showing AWS, TPWS controls, SGRC, ESOC, route bars etc.
  • Putting any assumptions you are making for the layout regarding speeds, distances, foul tracks etc
  • Defining any $ or # notes
  • Then explaining that route locking is on separate CTs that you are not including but take the form 
    [list the headings and
    show for a pair of relevant Track sections,
    one being the first track in a route showing that it relies on the Route Normal and its own track, plus the track bob 15 secs or next track occupied;
    then similar for a second track that shows holds to the previous subroute-
    ideally you might have an example on the layout when a sub-route actually cascades from two routes that converge. 
    If you do that and include the sketches of the relevant sub-route diagrams A/B/C/D.. nomenclature on the sheets on which you use, I am sure that this will be enough to overcome any “cheating” that the examiners may feel you have done by avoiding presentation requiring all the tracks to be listed for each opposing route, that is clearly a large time saving.

 
As far as the Comprehensive A/L lookback is concerned, I definitely think you need to show something-
I have squeezed in an idea on the 125A(M) CT.

It is definitely not just a question of listing the first and all the last tracks as exit points;
you also need to hint at the conditioning that is done within the file
regarding point positions
also the logic within the overall master programme that if an intermediate track is found to be occupied then the MAP file returns an unconditional FAIL and on the other hand if it encounters an intermediate signal which is Free of A/L then it will return an unconditional PASS; other than that it continues until it finds one of the nominated exit labels on the route CT.
  In my view you should draw the whole diagram relevant for the route with the CAL and also explain this logic as above.


Attached Files
.pdf   2012 Q1 Control Tables- SSI format.pdf (Size: 498.05 KB / Downloads: 39)
PJW
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