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AC Track Circuit calculation questions
#1
Looking back at some past papers, I see that in 2000 there was a question on ac tracks rather than dc. What do we think the chances are of getting that again? I'm pretty much counting on doing well on the track calculation to get me a good way towards that magic 50% pass mark.

I say that if we get a question on ac tracks, we all walk out of the exam room. Who's with me, comrades?
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#2
BedfordBoy Wrote:Looking back at some past papers, I see that in 2000 there was a question on ac tracks rather than dc. What do we think the chances are of getting that again? I'm pretty much counting on doing well on the track calculation to get me a good way towards that magic 50% pass mark.

I say that if we get a question on ac tracks, we all walk out of the exam room. Who's with me, comrades?

There are ac tracks and ac tracks. If they are 50Hz then it is still reasonable to assume negligible volt drop along the rails and thus the treatment of all the various leakage currents as a single ballast current passing through a nominal "ballast resistance" is a valid approximation.

If you have to worry about the phase angle re ac vane track relays then you'd probably be right to avoid the question and choose another. Similarly once frequencies are in the main audio range 300-3000Hz then rail impedance cannot be ignored. Voltage does not even drop linearly along the length of the track so the simplification of "ballast resistance" breaks down and it all gets horribly complex so avoid like the plague.

No value in walking out of the exam room though as that'd be an almost definite fail. Yes do concentrate preparation on your favourite questions, but don't absolutely rely on them- they may not come up at all or may come up but tied in with something that you want to avoid. There are 10 questions of which you have to do 3; in reality you must expect that a couple of them may be completely impossible for you (e.g. a level crossing question is most unlikely to suit anyone from a Metro environment; similarly platform screen doors are likely to be unknown to Mainline candidates)- that should still leave a good choice for everyone to be able to choose the ones that they feel they can do best. So even if expecting to do the track circuit calculation do consider both it and the other options.

You have 10 minutes reading time to determine which to attempt; use it wisely. I suggest a skim read of the whole paper- there will be some questions that you might write-off after some 15 secs, but others may seem more hopeful and you may need the full minute to read and consider. With luck that leaves you 3 minutes to re-read each of those you identified as the most likely so that you can assure yourself that you really did understand what was asked, can tackle all of the question (bearing in mind the mark distribution within the question) and are interpreting it wide enough to really give a good answer to the actual quastion asked rather than just thinking that its topic is an area that you know a fair bit about.

There are certainly many that bank upon the track calcs- particularly those whose first language is not English. Conversely others just don't want to do the maths and thus would never attempt.
PJW
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#3
PJW Wrote:[quote=BedfordBoy]
Looking back at some past papers, I see that in 2000 there was a question on ac tracks rather than dc. What do we think the chances are of getting that again? I'm pretty much counting on doing well on the track calculation to get me a good way towards that magic 50% pass mark.

I say that if we get a question on ac tracks, we all walk out of the exam room. Who's with me, comrades?

I remember reading the exam review minutes and from the year with the ac TC question and it sounds as though there was a lynch mob at the ready. However the response from the examiner committee was to point students to the syllabus, an extract of which for module 5 says

"To understand and explain:
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#4
PJW Wrote:There are 10 questions of which you have to do 3; in reality you must expect that a couple of them may be completely impossible for you (e.g. a level crossing question is most unlikely to suit anyone from a Metro environment; similarly platform screen doors are likely to be unknown to Mainline candidates)- that should still leave a good choice for everyone to be able to choose the ones that they feel they can do best. So even if expecting to do the track circuit calculation do consider both it and the other options.

...

There are certainly many that bank upon the track calcs- particularly those whose first language is not English. Conversely others just don't want to do the maths and thus would never attempt.

I think the situation is actually a little worse than that, because there are also questions that would really only suit those from a maintenance background and others that would only suit those from a testing background. Although mainline designers like myself can learn the information for the purpose of passing the exam, it's no easier then learning about platform screen doors for example (which ironically I have actually had some experience of).

As for the number of candidates choosing the track circuit question, I think most people in this industry learn to express important information very concisely. So when they read in the exam reviews that one page per question is not good enough, if they're anything like me they feel a bit intimidated by the essay type questions.

I hope I'm not coming across as too negative - so far I've done well at the modules I've attempted, but I definitely have some frustrations so I thought I'd just get some thoughts out there. Back to the study now...

I was kind of joking about walking out of the exam, too.
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#5
BedfordBoy Wrote:
PJW Wrote:There are 10 questions of which you have to do 3; in reality you must expect that a couple of them may be completely impossible for you (e.g. a level crossing question is most unlikely to suit anyone from a Metro environment; similarly platform screen doors are likely to be unknown to Mainline candidates)- that should still leave a good choice for everyone to be able to choose the ones that they feel they can do best. So even if expecting to do the track circuit calculation do consider both it and the other options.

...

There are certainly many that bank upon the track calcs- particularly those whose first language is not English. Conversely others just don't want to do the maths and thus would never attempt.

I think the situation is actually a little worse than that, because there are also questions that would really only suit those from a maintenance background and others that would only suit those from a testing background. Although mainline designers like myself can learn the information for the purpose of passing the exam, it's no easier then learning about platform screen doors for example (which ironically I have actually had some experience of).

As for the number of candidates choosing the track circuit question, I think most people in this industry learn to express important information very concisely. So when they read in the exam reviews that one page per question is not good enough, if they're anything like me they feel a bit intimidated by the essay type questions.

I hope I'm not coming across as too negative - so far I've done well at the modules I've attempted, but I definitely have some frustrations so I thought I'd just get some thoughts out there. Back to the study now...

I was kind of joking about walking out of the exam, too.
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#6
BedfordBoy Wrote:I think the situation is actually a little worse than that,

See reply moved to REGULATIONS
PJW
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#7
Hi!
I am planning to sit the Module 5 exam this year and have by targetting the Track Circuit calculation questions. I have understood the DC track circuit part, however, i am a bit confused on the AC track circuit part.
Has anyone got a complete answer for any AC Track circuit calculations which i can use to understand the process.

Once I have done some further studying, I will be putting some attempted questions for review and feedback.

It would great others doing module 5 could also do some questions, so that the method and answers could be compared.

Thanks
Regards
Aditi
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#8
There is something in this thread. While looking at the calcualtions for an answer may give you some ideas, of course understanding the relevance of the calculation steps is difficult if you do not understand the principles of operation. That said, the one time the AC track question came up, it was effectively the same basic form as the DC question but you had to understand the impedance of frequency dependent components (albeit at the single operating frequency).

I have not got a good reference to AC track basics.

Have a go and see where you get stuck.

Peter
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