This is another question that I feeel is asking for a tabular approach.
However I don't really see it as a 3 way comparison; I think I might compare axle counter with Track circuits and then separately compare single rail and double rail TCs.
Your appoach wastes some time; you wrote that
1. A/C do not require insulated rail joints and then later on
2. TCs require either insulated joints or tuned zones
If you had presented as 3 columns, labelled: Consideration, A/C, TC
you could have written in the first box: Division into sections
in the 2nd: Drill rail and bolt head (traditional) or clamp head to rail (modern)
in the 3rd Install insulated rail joint or arrange tuned zone (if jointless)
and thus less time wasted writing effectively the same words to state an advantage for one and also repeat as a disdavantage for the other.
Certainly add more words in those boxes to explain what it is about each thing that makes it either good or bad- bit the thing I want to get across is that you don't have the time to waste by repeating.
Another minor presentational point; sometimes you leave a blank line within what is the continuation of the same idea, this then detracts from the advantage of doing so beween different items in a list. I can see perhaps why you did as lines are narrow; you could have still done so but made more visually separate by use of bullets, identing etc. The clearer it is to the examiner how many separate short ideas you have presented the better!
As far as content is concerned for
axle counters I think it was generally good, but perhaps some entries should have been more explicitly stated as advantage / disadvantage. Probably should have said more about the safety risk if pricedures are not followed and the delays in restoring normal service that are entailed by use of axle counters. Also the size of the affected area should an Axle Counter Evaluator fail and how sensible design can at least minimise the size of the effect on the operational railway.
Not convinced that the first cost is less (depends probably what train detection was there before etc) but whole life cost should be and indeed there are advantages to the PWay by the railw being able to be CWR without glued joints, but there is a flip side relating to the need to remove all the heads during tamping etc.
As far as content is concerned for
track circuits, again I don't disagree much. TC lengths will always be limited; I suppose what you mean is limited by physical application considerations to be less than the section could be thoretically for implementing Signalling Principles.
For
comparing TCs you were doing a form of comparision of differences but not really giving advantages and disadvantages. This really wasn't very convincig at all; I am not really sure that you understand the rationale for configuring sometimes as singleraila nd sometimes as double rail. To be fair to you, this does seem to be more appropriate thing to ask in a mod 5 Application paper than mod 3 Principles paper; after all this sort of detail is shown on a Location Area Plan but not a Signalling Plan. However I did not get a good feeling when you wrote "TCs completely isolated (both rails) may still operate correctly with IBJ failure"- I would regard it as a Principle that we arrange the track circuits such that an IBJ failure is detected and I am incredulous at the idea that any TC can be completely isolated from anything!
In essence we'd naturally always prefer to have both rails for our TCs and generally we can if
1. there were no traction supply etc to worry about and
2. if we could physically get into the pointwork the IBJs necessary to achieve this (generally we can't!)
However the railway is a system and we have to accept that
a) the prime purpose of the rails is actually to support and guide the train wheels and
b) in many areas the need for them to take the traction current back to the substation is rather more important than the signal engineer's desire to be able to tell where the trains are
Therefore we have to be realisic and compromise. Hence we say that we'll live with having one rail exclusively for our track circuit and we are prepared to share the other one. However when there is too much traction current to return in the one rail (650V dc railway except short track sections over points and some minor spurs), then we have to share both of them and delve into the "black art" of impedance bonds to try to keep our electrons separate from their electrons (not literally of course but you get my meaning). Hence I think I'd tackle this section by explaining what influences when we decide to use which configuration.
As you realised your answer thereafter became too much of a description of what NR does rather than concentrate on the issues that drive such a decision. Certainly started right but you should have continued in that vein by thinking of such things as:
1. power interruption
2. loose termination in cable to EAK (yellow mushroom)
3. telecomms drop out between EAK and ACE
4. miscellaneous metal objects near count head
5. count head loses alignment / drops off rail
6. count head needing to be removed from rail for engineering work such as tamping, ballast cleaning etc; where cables cross another track work on one line may affect many
7. reinstalled count heads could be re-installed incorrectly- either in a slightly wrong position such that no longer proves a train is beyond clearance point, or the positions of two heads could be transposed and thus the functionlity swapped
8. road railers entering a portion of line midsection from the adjacent track / leaving railway altogether at a level crossing
9. traversed by train with seized axle on a wheel skate causing miscount
You tended to talk more about the solution than the issue that gives rise to it, but you did normally give some explanation so not a complete disaster. However you didn't really address the issue of road-rail plant despite being explicitly told to do so- you will certainly lose significant marks for failing to do this.
A few points of detail in what you wrote- it is the count of a section which is reset, not the equpment. In the days of one ACE for each section perhaps this was one and the same thing; nowadays it is not.
Strictly speaking shouldn't restore the section until it is established to be clear; after all we have removed all route locking and dead track locking so points are free be swung; we really do have to be pretty sure! You are correct though that we wish to mitigate the risk associated with a human erro when establishing that the section can be restored which is why we impose Aspect Restriction Following Restoration- so that the train is verbally authoised to proceed through the section at caution , inspecting the line and what might be foul of it, prepared to stop short of any obstruction. Liklihood of collision should be extremely low, loss suffered if does occur should also be pretty minor so overall risk ranked as acceptable (if not entirely negligible).
You also seemed to talk a lot about conditional and unconditional rest but hadn't defined the meaning of these terms.
Hence although this answer was relatively long, it certainly wasn't your best. Don't despair though; I have seen far worse and to get a pass mark on a question you only need to get half marks and this one would have achieved that.
I think this flurry of activity should have convinced you not to be scared of such questions; I know you are doing it open book but that is fine at this stage as you are refreshing your knowledge and probably extending it in some areas and getting some practice at expressing your answer. Later on you will need to get some practice at working against the clock and closed book but you seem to be making "workmanlike" attempts and no doubt getting to understand which questions suit you best.
P. S.Haven't forgotten your aspect sequence attempt- it is on the list next
(09-07-2013, 08:20 AM)dorothy.pipet Wrote: An attempt at 2007 Question 8:
(untimed, open book)
"List the key advantages and disadvantages of axle counters, single and double rail track circuits for train detection.
A railway administration is going to provide axle counters and needs to define the rules and system requirements for managing miscounts and failures of the axle counter equipment. Describe the issues to be considered and appropriate control measures.
What issues need to be considered for the management of engineering work in axle counter areas, particularly where rail-road plant is being used?"
I expect I've somewhat mis-directed my answer towards "what Network Rail Standards mandate" rather than discussing the issues at a principle level.
