07-08-2010, 08:51 AM
(06-08-2010, 12:17 PM)Hort Wrote: 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.