Answer to 2003 Part A Q2

[alexgoei]

Hello Peter,

Appended please find my answer for the Part A Q2 Point Control Table question. Appreciate it if you can go through it and let me have your comments.

I have been quite busy recently so have to catch up and regain momentum now that the exams are now less than 2 months away. Not going to be helped either as end-September is expected to be quite busy workwise.

I have also appended the 2003 layout as I think the track circuit boundary impacting Points 211 and 212 have been omitted (deliberately or not by the examiner) from the layout and therefore I have included to show where the boundary should be for the purposes of putting together an answer.

Thank you once again for your time and look forward to you comments

Regards


Alex

[PJW]

Alex,

Yes it certainly is ramp up time now.

This week I am busy in the eveings with getting ready for the module 2/3 event at Signet at the weekend. Realistically it'll have to wait until about next Wednesday / Thursday I am afraid as I also have appointments on Mon & Tues evenings next week (unless of course anyone else is prepared to comment in my absence.

Actually by chance I think I have been given the same CTs by someone else so it might make an interesting comparison; however for now I have to prioritise written questions!


What I can say though is that there should be a joint between 211A and 212B. The version of the plan that I am looking at does and there are two hand points in rear of 308 signal leading to a locomotive shed as well as siding. I didn't know of the IRJ but I was aware that there were two versions of the plan on the loose; I don't know the history but preumably the one you have (I have somewhere as well) must have been the draft version that shouldn't have become public- I assume that after the exam there was some version control problem and the wrong copy became archived; the copy I have says Version 2 clw 15/05/2003.

To be honest I think that I have found what I regard as at least one mistake on most of the layouts for the various years (in truth this is not completely unknown in the real world, but certainly IRSE layouts do seem to have proportionately more); don't forget that they are produced by volunters in own time and do not warrant the same level of independent check. Generally they are reasonably trivial and shouldn't throw anyone who has confidence that they know what they are about; if you spot something in the exam then DO NOTE IT as an assumption (but on your answer paper not the layout since although that may be collected in at end of exam it is not put as part of your answer papers). In this case you realised that it must be wrong; that is a good sign that you are learning!

PJW

[alexgoei]

Hello Peter,

Thank you for your reply. How very interesting! At least I got my track circuit boundary correct!

My layout was purchased directly from the IRSE Office on one of my trips to the UK possibly in 2005.

Interestingly my copy says "Version 3.clw.02/09/03" which is very odd since this would be very close to the exams. Or does it mean February 9?

Look forward to your comments.

Thank you & Regards

[PJW]

Hello Peter,

Thank you for your reply. How very interesting! At least I got my track circuit boundary correct!

My layout was purchased directly from the IRSE Office on one of my trips to the UK possibly in 2005.

Interestingly my copy says "Version 3.clw.02/09/03" which is very odd since this would be very close to the exams. Or does it mean February 9?

Look forward to your comments.

Thank you & Regards

VERY INTERESTING- so yours is the LATER copy (definitely means September). Beware the last minute mod done in a hurry; a wise tester always asks themselves "OK the designers have put the known fault right, but have have they @%7

[PJW]

Had a bit of a chance to look at your CTs for the 114 routes only so far; please see attached.
It is the opposing route locking that you need to concentrate on at present I think (very common misunderstanding juding by last weekend!)

PJW

[PJW]

Here belatedly are my comments on the points CTs; I know I still have some more routes to feedback on from this batch but alt least some food for thought for now.

Also I think that you may have got one past me on 114(M); I hadn't realised that 212 provide trapping from the Middle siding; just goes to show why I always like to do the points before the routes to learn the layout properly!

I can't find a copy of the actual mod 3 question paper for 2003 (I have a pdf of what claims to be all papers but it goes direct from mod 2 to mod 4!).  
If I understand you correctly, you are saying that in 2003 a candidate just did part A CTs with no answer from part B.  I was unaware of this and it strikes me as very odd, although I know this was about the time that the aspect sequence question moved from mod 2 to mod 3 and thus things may have een in a state of flux. I'd be interested in what more detail you can give me.

PJW

[alexgoei]

Hello Peter,

I have the following points for clarification after going through your comments about answer for Point 212. The gist of them are:

How should a point-to-point arrangement like this be reflected on a Points CT? Do we separate the ends of the points so 212A, 212B and 212C have separate tables? (just guessing but under exam conditions very hard to do given time constraint). Also note your comments made about this on page 63 para 5 of your

[PJW]

[quote=alexgoei]
Hello Peter,

I have the following points for clarification after going through your comments about answer for Point 212.  The gist of them are:

How should a point-to-point arrangement like this be reflected on a Points CT?  Do we separate the ends of the points so 212A, 212B and 212C have separate tables? (just guessing but under exam conditions very hard to do given time constraint).  Also note your comments made about this on page 63 para 5 of your

[PJW]

Perhaps you can show us how you would enter Point 212 on the Points CT.

It would also appear that the point-to-point arrangement appears to be very popular with the examiner and is found in the 1999 and 2000 papers. In fact the 1999 paper on the two points to be completed was a slip with a crossover on one side.

I have made comments on yours to facilitate the clarification process and these are found in the appended file.

Look forward to your comments

See attached which I hope clarifies my explanation which I think confused you as you seem to understand the locking itself.

Re 1999

A double slip is almost always associated with single ends on the adjacent lines. Be clear why we occasionally use them is to save space (length). Assuming need to cross from signal 119 to either of the lines to its left and from 117 to the Branch, this could have been achieved by the simple crossover 304A/B and thereafter another simple crossover 305B/C- however the successive ladder would have reduced the length available for siding 1.

A double slip allows the two crossovers to be overlapped to an extent- the cost is lower speed, more complexity, higher maintenance burden etc. but the gain is the ability "to fit a quart into a pint pot".

For similar reasons note the 301 / 302 arrangement. This has the same functionality as a facing and then a separate trailing crossover; but there would not have been space to fit both of these in within the length available between tunnel and station platforms. Providing a scissors (with its mini diamond crossing at its centre) has many disbenefits but the overriding advantage of getting the required layout flexibility in the confined space.
This is another classic case of point-point- you could never want both points reverse simultaneously.

If wanted to show on CTs then I'd put in Remarks column for 301 called N to R: "Requires 302N" and conversely on 302's CT for call N to R: "Requires 301N".

However I'd advise NOTactually to implement point-point, but JUST USE AS TOOL to help you recognise the point calling by routes that you might otherwise miss.
In this case ensure: ALL ROUTES OVER 301R CALL 301N and vice versa.

If you miss this out then you'd be allowing (unless very cleverly realise the situation and thus add in some clever route locking entries- which is not actually as good when you consider degraded mode operations) both 108A(M) and 107B(M) to be simultaneously set (would not otherwise have incompatible point calling requirements and unlikely to "see" as an opposing route); this would set things up for a collision at the scissors crossover!

So look for the tell-tale signs associated with two point ends within the same track circuit- not 100% definite that there needs to be some FLANK / TRAPPING / PARALLEL MOVES / SCISSORS point calls but probably 9/10 there should be so certainly ought to initiate a warning alarm to focus on the area with such in mind.

PJW