(02-09-2010, 06:21 PM)alexgoei Wrote: Hello PJW,
With respect to your comments of 22nd August, my responses are:
8 Characters on MARI. In Appendix D of Colourlight Junction Signalling NR/SP/SIG/19609 dated Sept 2006 (in the IRSE Support Materials), it states that S must not be used in a MI except as part of a combination of characters (please see appended).
You are right, so it does. The great thing about standards is that there are so many to choose from! Seriously though, I hadn't realised that this had crept in; presumably in certain scenarios where numbers are also displayed there could be a confusion between "5" and "S". However there are definitely many places that do display "S"- the standard is not retrospective. Hence I agree that perhaps we should choose another indication instead, but don't get too hung up over this level of detail and prescription in this standard- this is not really what the exam is all about.
Quote:9 Yes. Please see my explanation as to how I intend to route and reattach the locomotive. Freight train stops short of signal 119. Engine uncouples from rest of the train. Signal 119A(S) clears (not included in layout) and the engine proceeds to Station D, uses points 228 A and B to traverse to the Up Main where it changes end. Proceed after signal 128 clears before proceeding towards Junction C where it stops in front of shunt signal 114. Engine then recouples rest of train. Proceeds when signal 116 clears.
This is the sort of explanation that you should have put on the plan for the examiner.
Note though wouldn't need a shunt route or PL aspect on 119; the engine would be signalled on a normal running aspect since the track would be clear- it is not actually yet "shunting". Similarly would't need to provide 114 GPL.
Quote:11 The basis I chose MAY-FA for Junction C was after reading Colourlight Junction Signalling NR/SP/SIG/19609 dated Sept 2006, Section 10.1 (extract appended) suggesting that MAY-FA is possible or have I got it wrong?
As I intended to say last time, a flashing aspect sequence certainly possible depending on what speed the divergeing points are considered to be; I feel the examiners have created uncertainty in this. If one assumes 40km/h then that equates approximately to 25mph and flashing aspects not appropriate, but I do agree that could read the information on the plan differently and then flashing aspects very sensible.
Quote:With respect to my comments of 28 August, my comments are as follows:
2 Noted. With respect to signal 110, it is a signal transiting to 3 aspect signal with Green, Yellow, Red. It is at 0.5 SBD (Service Braking Distance) like the 4 aspect signals. Erroneously YY is there but blanked off.
Indeed; I think what you did was right but you hadn't given enough information to make that clear. If 110 is the last 4 aspect signal then the distance to the next signal and from the previous signal should be 0.5 SBD. Since there will ot be a signal ahead for which 110 would show double yellow then the top yellow is CORRECTLY blanked out; iyt needs to appear to be a 3 aspect head yet YY is an impossible aspect. The reason why I queried it is that you had not given a clue as to the signal it was reading up to, nor dimensioned it and thus I could not be sure what your intentions were.
Quote:3 Noted. Beyond F the plan was to have 3 aspect signaling. For signal 113, the distance to signal 119 should be 1000 metres, and not 1975 metres (wrongly notated).
As above- if there is to be 3 aspect signalling ahead, wouldn't that make 135 signal like 110 in that it would be the last of the 4 aspects and thus wouln't show YY?
Quote:7 Thanks for the clarification about Red buffer stop light for the Bay but no need for the Siding. Correct? Now I know Trap Points must be incorporated even though the layout does not show it. Seem odd at first.
Sidings would generally have buffer stop lights as well; the issue is more whether they are shown on the Signalling Plan. In a case like this they almost certainly would be, but where there is a significant length / width of "unsignalled railway" then the Signalling plan wouldn't even show the tracks other than a representation of the layout immediately on the approach to any signal protecting the running line or as otherwise needed to "give context"- hence the buffer stops unlikely to show- it is really a question of whether they are relevant to the area of interest which is depicted.
Trap points; yes the idea is that where they are needed the candidate must add. I understand it seems odd but think of it like this; the track engineer draws the plan to provide the track to give the required train movements, but it is the signal engineer's job to make it operable and safe. Trap points are not required to make the moves but are a dsafety measure; therefore up to the signal engineer to decide how many and where to place.
Quote:8 I thought it would have been acceptable to have left the freight wagons at Junction C on the Down Main since there would only be 2 freight trains per night doing this during the hours from 0100 to 0600 hrs and therefore managed. All passenger train movements would have stopped.
I am not disagreeing; however I believe that you should have put that explanation on your paper so that the examiner could follow your logic.
Quote:9 standage was only for those trains like ECS to be stabled at Down Bay or Up Siding.
Fine; best to make that clear to examiner though by depicting on plan.
Quote:The location of signal 126 was more driven by the need for the train to have adequate service braking distance....agree could be further forward and therefore in line with signal 128.
Yes clearly the braking distance required is reduced by virtue of the attainable speed, so take advantage of that; best to have parallel signals whenever you can.
Quote:10 For the single line branch, I followed that of Sudbury Branch which is in the Study Pack.
So you have!
Note however that the Sudbury branch OTW section starts at 868 signal whereas you have the boards in mid-section.
Interesting- looks like the Eastern Region did things a little different to the Western Region!
I am more used to the boards being placed in conjuction with the exit signal. I am interested now to find out what is "off the plan" as it seems that there must be a signal in rear of 825 to which presumably the track circuiting extends at least ...
Presumably the circuits (or in this case SSI must look for a sequence BBV occ, treadle operated, BBW occ, treadle normal but I really would have expected a directional treadle. However the Eastern were very keen to eliminate mechanical treadles and invented an electronic treadle known as a FREDDY= Flange Reading Electronic Detector Designed at York and I think this was only ever the equivalent of a single arm treadle (non directional) so that may have been the motivation. Thanks for teaching me something from my own Study Pack!
Quote:Can I just replace the treadle with an axle counter at the same location just beyond the Stop Board?
Do I need to indicate one or two counters?
Similarly should I replace the treadle at EA with two axle counters, one counting in and the other counting out?
I did have a track circuit at least up to EB to detect the presence of the train. I did this in consideration that I did not want the train on the Branch to hold up trains on the Down Main.
Utilising axle counters could be done in one of several ways:
a) use a single head to implement what would otherwise be the OTW-NS section. It would count axles just before they left EB track circuit and thus represent the state of the line the whole way to the bufferstops at G. As far as signaller and driver concerned, they would operate the line under OTW-NS regulations but we'd actually achieve higher safety integrity. No infrastructure other than possibly the Stop board for the return direction at G (but even this could be dispenced with- the movement authority could be "to travel to G and return from G"). Wouldn't need the OTW treadle.
b) implement the whole of the branch train detection using axle counters. Thus a head just within CY track, a head in lieu of the EA/EB joint at 130 signal, a head at whatever extent of EB was selected which would then be the limit of the final section up to and including G as a) above.
c) As b) but an additional head at the left hand end of the platform and thus spluit the section to be "the long single line portion" and separately "plafform track at G"= EC
d) If bothering to arrange some form of secure transmission to the far end though then I think would actually provide a signal and the line would be worked under TCB regulations with axle counter train detection for the entire length
This is assuming a single Axle Counter Evaluator which determines the occupancy status of all the various sections. Early axle counters only did one section and therefore there was a need for two heads at each boundary, one for each section (making sure of course that axle was counted IN to the adjacent section before being counted OUT of the section it was originally within).
You are right that you need EB to be at least the berth track of 130 and therefore say 200m minimum. To give signaller enough time to respond and clear signal before train has stopped than much longer section required and postioning at 132 sensible. If however want 132 ever to utilise its Green aspect, then needs to be a decent length on the approach to this signal.
PJW
