2008 Q9 - Signallers indications

[dorothy.pipet]

An untimed, open book attempt for comments please.

[Peter]

An untimed, open book attempt for comments please.

What you have put is a lot of detail which, on first reading is a good description of the conditions for each of the indication elements to show. One important thing that the question asks for that is missing is the extent of the overlap. The question specifically asks for the indications associated with the swinging (or alternative) overlaps and hence I would expect there to be some mention of how the end of the overlap is shown.

You mention that the track occupied indications are red, but I cannot see that you have described what the route set indications look like.

You would need to specify what practice you are following because some systems light route indications in the overlap and some do not. If you do not give any clue, the examiner may try to work out what practice you are following, or use the UK as a default. This may work in your favour or may not! You have alluded to SSI, but how this is shown on a panel would vary form place to place in the UK.

I think you have covered this by your note in blue immediately below your diagram, (but it is not clear and I think I have read it right) and that is the matter of making indications big enough on the VDU to avoid single block failure meaning that the indication is not shown correctly, or on a panel having more than just one lamp indication for each function. Arguably, this is something not directly related to the question, but might get you more marks in a borderline scenario).

[PJW]

My initial thought when seeing the number of annotated indications shown on the diagram of the answer, was "surely this quantity and level of detail would not be required by an IRSE question". I then read the question and it most distinctly asks to "describe all the indications .... for swinging or alternative overlaps from signal 129" as well as "identify components of the indications by suitable names" and that is certainly what you have done.
However I think you have taken it too far in the context of the exam; I do not think you can afford the time to write out each full identity.
Think about the PRINCIPLES because that is what they are really after and then concentrate your efforts on one example of each; draw the whole diagram yes, but identify only the specific subset of those indications that you want to discuss in your text. Do enough to show you know the naming convention; naming another in a similar manner adds little and you must focus on "marks per minute" when faced with a question that will take too long to completely answer.

As far as the overlaps are concerned, then I think they want you to explain:
1. The ROL
2. The full o/L over points Normal
3. The full o/L over points Reverse
including
a) timing out by train proved to a stand
b) the ROL stepping up to a full overlap by forward route setting (and then made obvious by subsequent cancellation).

I think you could have made a little table with the various UKEs listed in vertical columns and the various scenarios of ROL, N O/L and R O/L being considered by each of the horizontal rows, applying a tick for those whch would be illuminated. Hence for the ROL the IBKU would not be lit whereas for the N O/L then it would be lit. Similarly the I221NU would be shown lit for both the ROL and the N O/L, but not for the R O/L.


As far as the normal UKE and TKE functionality is concerned I think the important things to include in description are-

1. Shows red if track occupied; if white route lights were previously lit these are extinguished but will illuminate again if track becomes clear whilst locking still in force;

2. If a section containing points is occupied without any route having been set, all apertures will illuminate red as a "flood", whereas if a route is locked over the section then it is only those lights in the line of the locked route which will show red and those off-route remain dark. In my experience, sites vary whether the same applies where there is only overlap locking without route locking; I would actually expect a flood since the move is unauthorised but am accustomed to seeing it differently sometimes;

3. Loss of point detection will extinguish the one route light showing the point lie; hence could use the example of I233ANU being different from I2333ANKU (but actually it looks to me as if you have labelled these the wrong way around! whereas the RKU / RU do seem correct). This assumes the standard BR850 RRI circuits; as Peter alluded to the Western Region was different in that although it never showed route lights into the overlap (the locking of the overlap actually accomplished by a relay associated with the signal berth track) instead of just extinguishing ay the NUKE it flashed the NUKE and RUKE alternately- a practice that has become standard for IECC indications (not sure about SSI operated panel indications).
In fact you covered this element reasonably ok, but I think that putting the UKEs in one column and (where applicable) the related TKE in the next may have been clearer and quicker. Note though that you stated that the NT "lit when route set N and track occupied" is wrong; the NT should instead be "lit whenever the track is occupied unless there is a route set over the points reverse". You seem to know this from what you go on to write in the last para on page 2.

The question asked for normal and failure conditions; the failures that I would include would be-
1. Rightside track failure SOWC
2. Wrongside track failure SCWO
3. Rightside points failure- loss of detection
4. Rightside points failure- failure to move at all when called
4. Rightside points failure- failure to achieve opposite detection having been called.
[There is not a huge amount to say, some very similar to each other but at least showing you have considered all the most likely failure scenarios and thus addressing the question.]

I think in this I would refer to the N / Out Of Correspondence / R indications associated with the Individual Point Switch. I don't see the signal indications as being requested by the question; however could be worth noting that if swing the overlap and the points do not achieve their new detection within the critical 8 seconds then the signaller would observe from the signal indication that the driver had suffered an aspect reversion.

Overall you answer had a lot of useful content but to maximise your marks potential you would have been wise to-
1. Consider the question in the context of the module syllabus
2. Think about what the examiner is really interested in finding out about your experience and knowledge; not going to tell much from getting you to label multiple similar instances
3. Determine the fastest and clearest way of giving information- a truth table is the way I would have tackled showing the outputs for all the UKEs for the various scenarios of overlaps and failures. I consider the TKEs simpler so would have simply explained about the track overrides the route, the track floods unless there is a route in which case it is only displayed where the route is locked.

I think that your answer would have passed, despite being a bit too much "regurgitation of detail as technician" and not enough "truly answering what was asked, displaying an engineer's understanding". Despite not covering the whole scope, it didn't wander off its own way and did show some knowledge and understanding.

An untimed, open book attempt for comments please.

What you have put is a lot of detail