Attempted 2008 Q7 Filament lamp / LED

[adikarina]

Hi!
I have attempted Q7 from 2008 Module 5 paper.
Please review and provide feedback.

I have previously work on a project where I was involved in introducing LED lamp on filament lamp area, therefore, I have drawn from my knowledge from that project.

Thanks
Regards
Aditi

[PJW]

Hi!
I have attempted Q7 from 2008 Module 5 paper.
Please review and provide feedback.

I have previously worked on a project where I was involved in introducing LED lamp on filament lamp area; therefore I have drawn from my knowledge from that project.

Thanks
Regards
Aditi

Initial impression is that this would be a Credit; it is evident that "you know your stuff", the experience you mentioned shows through and you actually attempted to answer the question set:
Lineside signals and indicators can be illuminated with conventional filament lamps or with
LED technology. Describe the relative advantages and disadvantages of each of these technologies. As a minimum you should consider:
a) design considerations; and [5 marks]
b) installation and maintenance; and [5 marks]
c) reliability. [5 marks]
If the technologies were to be intermixed in a localised area, describe what technical and operational considerations might have to be made. [5 marks]

We set basically this question for GM Rail last year and my gut feeling is that your answer is as good as any we got there. I haven't yet marked it against the schedule which I used then, but if it didn't score in the credit band then I'd be surprised and would be wondering whether the marking basis had been "too Mainline" and thus would need amending to be fair for a "Metro" answer.

It's a sad fact that few provide what I believe to be "decent answers", so this one would be in the minority and thus generally deserving of "Credit". I would call it "workmanlike" in that it was sound (no dodgy "facts"), covered the necessary ground, kept to material relevant to the question, was of reasonable length and clearly presented.

I was pleased to see that you had learned from the module 7 question feedback and I thought your introduction valuable and nigh on perfect to "set the scene"- it may not earn marks itself but it gives a good impression and ensures that what else you write will be judged in the correct context as some of what you wrote would not be "correct"/"appropriate" for Network Rail for example.

The end paragraph did summarise your answer ok; however you could have got it to work harder for you in gaining some marks- see later.

You note that whereas my gut feeling is "Credit", it certainly isn't "Distinction"- so why do I say that? For me to subjectively feel "Distinction" requires something to be particularly special about the quality of the answer- being "perfectly sound" is not enough, it has to excite in some way- the examiner needs to feel that they want to read the answer for its own sake rather than because they are marking an exam paper. Hard to explain, but it is the same sort of thing that sells a "premium product" over a "commodity item"- the reason why many feel that it is worth paying the extra perhaps for an ipod over other manufacturer's products that are perfectly good but somehow lack the "must have" attractiveness.

On a mark scoring basis you probably ought to have presented your answer so it more clearly showed the examiner that you had given what would be needed to get your 5 marks for "design considerations", your 5 marks for "installation and maintenance" and your 5 marks for "reliability". Whereas you did include something of each in your answer it isn't obvious how many you were "claiming" from each category.

Your presentation was a bit wasteful in that filament disadvantage 1 and LED advantage 1 are really the same thing, similarly t filament disadvantage 2 and LED advantage 2. So when looked at carefully when awarding marks, there isn't as much to score as first appears; a tabular approach with three columns would be more economical of space and time. The first column could be the generic description, the second its applicability to filament lamps and the third its applicability to LEDs. You could consider i) sudden complete loss of light output, ii) sudden diminishing of lamp output, iii) gradual diminishing of light output, iv) gradual colour degradation, v) false light output and put some comment against each of these potential failure modes as experienced by each of the types of illumination. A tick in every box would certainly get you the maximum of 5 marks for reliability- you have gone that extra mile and demonstrated a range of possible failure modes that would detract from reliability and commented upon the likelihood and severity of faults with each solution which could cause that failure mode. When writing the paper you would know that it was not worth you writing more on this section of the question and you are also saying to the examiner: "I dare you not to give me full marks for this bit, even if I haven't included something you would otherwise be looking for".

The other way to raise you game to get into the "Distinction" category is to read a bit more into the question, rather than just tackle what it seems to be at face value. Look for "hooks" within it on which you can attach markers to show that you are experienced and can interpret in a broad context; you need to stick to the question obviously but do just look at it from a range of different angles. Instead of just looking at "advantages / disadvantages", think a bit more about FOR WHOM (train operators, passengers, signallers / line controllers, maintainers, signalling designers, possession management), HOW (explain the consequences of a signal being out-how does the railway continue to operate, does it get fixed during the working day or only in possession hours etc) , IN WHAT CONTEXT (tube, sub-surface, open, stations, plain line auto section) and indeed THINK ABOUT THE WHOLE LIFECYCLE (specification, product approval, design, install, test, operate, maintain, decommission).

You could do this a little more throughout, but in particular the summary may have been the place to illustrate this.

[PJW]

Hi!
I have attempted Q7 from 2008 Module 5 paper.
Please review and provide feedback.

Thanks
Regards
Aditi

Further to my previous feedback, please find attached your answer with my comments inserted. Basically you will see this is in the form of questions that occur to me when reading your answer for an environment with which i am not familiar. Hence these aren't "mistakes" as such, but show you where I feel that you could have explained more / better. I think I'd have made similar comments had I known more re LU eenvironment- because it is YOUR job to explain, whether or not the examiner happens to know the answer. Of course had this been a subject area for which had deeper knowledge I may have felt that it as reasonable that you hadn't explained as I would have shared the same unwritten assumption / knowledge; on the other hand I may have been more critical if your answer fell short of perfection as less likely to "give benefit of the doubt".

An answer which didn't leave the "open ends" to which my comments allude would have been a better answer; you'd have explained the underlying assumptions and demonstrated your thought process to lead the unfamiliar reader to help them follow your argument.

What I have done in "track changes" is to give a demonstration of the sort of summary that I think would demonstrate wide experience and make the examiner think in terms of awarding a Distinction. Try to show how the answer given fits into the "bigger picture" of railway signal engineering- even though this is a module 5 paper, don't forget to make the connection to other knowledge perhaps more associated with mod1, mod3 or mod7.

When it comes to scoring, I think as an examiner I'd be struggling to award sufficient marks to substantiate my gut reaction of "Credit"; on average you'd need to be scoring at least 3 out of 5 for each of the sections. Where advantages of one equals disadvantages of the other I wouldn't give the same mark twice, so there would need to be more justification as to WHY you are claiming what you are- you did this sometimes but not consistently.

• Indeed I think that getting the 5 marks for "design" is actually very difficult- can't really see how to improve your answer to get much more (in the NR environment in which lamps are lamp proved but LEDs arguably don't need to be, it is a bit easier).
  
• The 5 marks for "maintenance / installation" seem much easier.
  
• It is the 5 marks for "reliability" where I feel that your answer wouldn't actually have got many but can see where those marks should have come from- see the comments in my previous response re the various potential failure modes.
  

Have a critical look at your answer and evaluate how many marks you would award yourself in each of the categories given on the question paper. Of course it does say consider those three angles "as a minimum", so the examiners would definitely need to reallocate some marks if you tackled from a wider perspective- hence you could compensate for not getting the 5 marks re "design" and I think that would be my approach.

Given that your other module this year is mod7, I suspect you ought to be studying more on reliability topics and systems engineering because I think you may be weak in these areas; I am guessing that you don't have much of an understanding of faults, failures, maintenance policy, maintenance interventions etc since you didn't display it in your answer.

[PJW]

For comparison, an answer to the same quesion from a mainline perspective.

Also attached is information found on the internet that I believe gives useful backround from an Indian perspective

[Hort]

I had a gone at this question. After finishing I felt that I did not have enough to write about. Is there a marking criteria for it?

H

[Peter]

I had a gone at this question. After finishing I felt that I did not have enough to write about. Is there a marking criteria for it?

H

Aside for a minute as to whether what you wrote was all relevant, bear in mind that in the exam you realistically have 30 mins to write, you have about 750 words here, which is quite a fast writing rate so you need to be able to say what you want within this sort of amount of text.

PJW alluded to a mark schedule that he put together for last year's mod 5 day, but I have not looked at this against one.

You have addressed each of the areas called for in the question and you have given roughly equal wight to each which is what the mark breakdown asked for.

One point that did stick out for me is that you have compared the signals which have SL35 lamps with one particular manufacture of LED signals. What I mean in that some of the "disadvantages" that you have quoted for SL35s is not a function of the fact that they are filament lamps, more that you have described features of the form of the traditional head. For instance, some new LED signals come with plug couplers, but if that were the only difference, why could SL35 heads not be made with plug couplers. So, make sure you focus on the unique elements of LED light sources vs filament lamps.

Another area that you could (should) have explored was the other types of signals and indicators (I think the question aid line side signals and indicators, not just signals), so GPLs, Banners, JIs etc.

A few points on the details that you wrote:

Be careful about what you mean with "proving"on LED. You are right about the graceful degradation so proving and reliability are sort of interlinked. It is unlikely that what drives the lamp proving is actual feedback on the light output (although this is possible with some manufacturers, there are issues around what this means). Perhaps look into what is actually being monitored.

Check out what the "whole life" maintenance regime for LED signals. True, SL35 needs changing when it goes (perhaps 8000 hours) but LEDs do not, you'll find that most LED signals are only specified to be compliant for 8-10 years so the whole unit needs to be routinely replaced. Comparison issue here would involve discussion between "lamp fault" reaction vs planned replacement long term.

Installation and maintenance - you mention about frequency of visits for mtce. Bear in mind that currently, whatever the technology of light output, the requirement to clean the lens is the thing that is becoming the critical issue. remove that (whatever the light source) and things get easier.

Are LED complete heads that much lighter, or have you fiddled the numbers? Yes components may be lighter, but the complete assembly is not much different. However, LED technology does allow for alternatives which will make lighter signals possible.

Not sure about some of the comments about maintenance needing to be done by type of signal. If that were true of other equipment, we would not intermix track types or different point mechanisms. Maintenance and Faulting teams are a bit more versatile than you give them credit for here.

Overall, a good length answer - some good points, some important bits omitted (but I do't think that you could write everything on this subject in the time) and some bits that are not entirely relevant / true.

[PJW]

I had a gone at this question. After finishing I felt that I did not have enough to write about. Is there a marking criteria for it?

H

PJW alluded to a mark schedule that he put together for last year's mod 5 day, but I have not looked at this against one.

I attach a mark schedule that I put together for myself, so that I had something against which to assess any submitted answers last year. I don't know if the examiners do something similar, but I guess they might. However I am sure that it wouldn't be a "tick list" and indeed, depending on the candidate's background, could be inappropriate to particular answers. However it would form some type of benchmark to make sure the question was "do-able" and to fix the mark allocation in the first place when setting it.

This was primarily based on comparison in NR environment between SL35 conventional lamp head and the Dorman "3 aspects in one housing" product (which initially was the only approved product and also GM Rail had an example).
As I commented to Aditi, the schedule therefore not 100% appropriate to the scenario she described, but probably is rather more so to yours.

Do note that I couldn't actually get myself enough marks in one of the sections and even though I asked around I really didn't get much more content that I considered pertinent. So whereas it is A marking schedule it certainly is not the marking schedule . However may be worth applying it yourself to rate your own effort to see what you come up with- it should certainly be beneficial to start "thinking as an examiner" as you make the final approach to the exam. Don't understimate importance of exam technique.

[PJW]

In order to have enough material for answering IRSE questions, certainly expanding your reading is a sensible approach. To be honest I suspect that very few students look up anything but a tiny fraction of the IRSE reading list. I can understand why; however do try to be a bit more widely read; the internet can make this much more easy than it was. For example you can rapidly find good summary articles such as this one on various manufacturers LED signals. These are not likely to answer any one question directly but can help build up that base level of underpinning knowledge which can come in extremely useful when answering questions

[Jerry1237]

There are some interesting differences wrt filament to LED lamps. Personally, I struggle with LED due to the intensity of light especially at close quarters. However, with incandescent lamps being forced out of production, LED is technically mandatory. It has obvious advantages such as decreased maintenances, a more predicatable and gradual degredation of its light output, reliability etc.

One of the early concerns levels at LED on mainline was the colour differences plus the hot spot wasn't in its traditional place. Colour can be altered and I was actually involved in a trial where mixing of colours on a new signal head produced odd colours or undesired aspects! Remember, signal indicitions are there SOLELY to supply information to the driver that will allow them to control the train appropriately.

That said, for me the biggest issue is still the brilliance at close up distances which are required due to the light levels mandated in standards written for incandescents. There is also a large environmental cost due to the constuction of the LEDs, partially in their creation and mostly in their distruction but that, in this case in an aside.

Jerry