2004 Point CT

[greensky52]

Thanks for your detailed explanation. I am glad to communicate with you all here. It is truely a useful forum~

But in Mod3 2004, Signal 121,123, 125, 127 must not be the same type... Is 123 a control signal?Emm... I am waiting for further information, maybe from another Peter~ Still thank you~

[PJW]

Thanks for your detailed explanation. I am glad to communicate with you all here. It is truely a useful forum~

But in Mod3 2004, Signal 121,123, 125, 127 must not be the same type... Is 123 a control signal?Emm... I am waiting for further information, maybe from another Peter~ Still thank you~

Beware that there are different signalling practices in use at different localities and indeed periods; that is why a candidate should always declare the practices to which they are working

203 Item 1
136 is a shunt signal- modern practice on NR is to give shunt signals overlaps, but that has not traditionally been the case and hence only a minority of the installations in the UK feature this. Therefore many are familiar with signalling they have worked upon and adopt these within IRSE exam. Indeed I would generally advise that the IRSE examiners are in fact more familiar with the practices of some years ago and that generally I'd advise working to a practice that doesn't give shunt routes overlaps (simpler and easier, also demonstrates more "difference" between the various classes of routes), but it is the candidate's choice. Sometimes the layout given suggests that shunts should be given overlaps, sometimes there is no hint, but in this one there are no overlap joints beyond 115, 129, 136 so certainly indicative that NOT expecting this practice. If they showed an overlap but it was your practice not to provide then state that as an assumption; conversely if they didn't show and you needed to have one then declare that as an assumption.
So if you are providing overlaps then you are right that 203 would be trailing points beyond 116/118 (or facing / conditional trailing points in swinging overlap beyond 114) and you would need to show relevant locking.
There are overlap symbols (certainly relevant for M/W moves up to 114) at the joints BF/BH and EB/EC and so I would assume that there are two possibilities for full overlap, though there is also a potential third possibility via 203R and 201R- there is I some little advantage in providing such (allows 142A(W) for example) but "bath-tub" swinging overlaps are complex for locking and in the limited time available in IRSE Exam it makes it desirable to ignore as on a "marks per minute" basis it is simply not worth it unless you are a genius and very quick and would otherwise finish the paper with time remaining!
Indeed unless a candidate is reasonably strong then I wouldn't advise attempting much for swinging overlaps at all- certainly where there are other weaknesses in people's attempts I concentrate on feedback re these rather than distract/ confuse / demoralise; hence don't assume that even a commented CT example is "perfect". The better the quality of the submitted work, the deeper the level of my comments.

203 Item 2
As above, yes it is.
To NR practice, facing points in the simplest swinging overlaps are not called, not are they locked.
However in almost all cases there are more track circuits to be included in the aspect of the signal if the points are in one lie rather than the other; hence in 142A(M) there will be an entries such as: (BH or 203N) and (EC or 203R). In the first case BH itself deadlocks 203 so there is no problem; if 203 started R then 203 would be locked if BH were occupied. However in the other case there would be problem: if 203 started R and EC were occupied then we would not want 203 to be able to go N or else 142 would be replaced to danger, yet EC would not normally lock 203. In these circumstances we need to ensure that it DOES lock 203 and therefore we have to provide a special

[greensky52]

Just back from weekend, it is so appreciate that you gave so detailed explanation for all of my questions. Forgiving me as a new man in signalling discipline... I need some time to comprehend all your explanations completely, and I think I also need to discuss these with my colleague, helping me understand all the meanings you mentioned. Thank you again... Later I will discuss with you if there is still something confused.

Furthermore, referring to your answer of point211, item 2: I do not think 212 is trailing point in overlap of 142, because 142's overlap is EK, but 212 is in EL. Do you think EK and EL both are overlaps of 142?...

As you mentioned above, I attach my attempt on Point 203 & 211, which were finished last week, before getting your explanation...so there were still some errors we juse discussed, please do not mind...


[quote='PJW' pid='1630' dateline='1276335367']

211 Item 2
The general issue re estimating distances on these sketches;
a) they are not to scale
b) there is certain definite info (inter signal distances),
c) there are

[PJW]

Just back from weekend, it is so appreciate that you gave so detailed explanation for all of my questions. Forgiving me as a new man in signalling discipline... I need some time to comprehend all your explanations completely, and I think I also need to discuss these with my colleague, helping me understand all the meanings you mentioned. Thank you again... Later I will discuss with you if there is still something confused.

OK take your time. Yes it is often a good idea to talk through wih someone else face-to-face.

Furthermore, referring to your answer of point211, item 2: I do not think 212 is trailing point in overlap of 142, because 142's overlap is EK, but 212 is in EL. Do you think EK and EL both are overlaps of 142?...

211 Item 2
The particular issue:
a) My assumption is that the switch tips of 212B would be some 5-10m to the left of the post of 142 and that 212A would be perhaps 50-60m from 212B since most single slips are quite tight.
b) 211 is not a facing point in a swinging overlap beyond 142 so there is no requirement for time of operation locking here; you are quite correct
c) 212 is a trailing point within the overlap beyond 142 and 211 is providing both flank (212B) and trapping (212A) to that overlap; therefore they must be locked whilst the overlap is required. Once however route 146 has been cancelled AND its approach locking released AND the route locking on track ES has been normalised AND the berth track ER has been occupied for long enough to have proved the train at a stand, then the locking can be released.
d) Distance from 146 to 142 is 650m and I assume ES to be 180m since it is an overlap track; therefore ES would be 470m long. Hence I'd put the time more like 47 sec than 30 sec which is too short and applicable to a much shorter berth TC (see timer values ) but since it isn't completely rediculous for the principle of such a control then I don't think you'd lose many marks for the wrong time

A route set from signal 142 to 146 reserves the railway

a) for the route itself (post to post) = ES, ER [because that is the distance over which the train is authorised to move]
and
b) the overlap beyond 146 to the marked overlap joint (or joints if there are alternative positions beyond facing points).
[because we wish to mitigate the risk in the event that the train fails to stop exactly where it ought to and therefore provide a safe overrun length]
In this case there is one extent of overlap; it is the joint at the left hand end of EK. There is one overlap which is the combined length = EL, EK which is a total of 200m beyond the signal. Hence 212 is within the overlap.

As you mentioned above, I attach my attempt on Point 203 & 211, which were finished last week, before getting your explanation...so there were still some errors we juse discussed, please do not mind...

I'll look at in the next few days and then respond; I note that you did before recent comments.

[PJW]

As you mentioned above, I attach my attempt on Point 203 & 211, which were finished last week, before getting your explanation...so there were still some errors we juse discussed, please do not mind...

I'll look at in the next few days and then respond; I note that you did before recent comments.

A little later than advertised.......
please find attached some annotations on your Control Tables.

They are certainly quite good, but note:
1. Be careful that you don't "slip" yourself when looking at single or double slips- I think that you got confused between 211 and 212 for one route.

2. Where the points are in the overlap, once the train has been proved stopped at the protecting signal then the points must be released again. For some reason you got this right for 203 but wrong for 211.

3. Be consistent when doing route locking; if your standards are to include the dead locking tracks within the limits of the route locking (as NR current practice), then include any foul tracks within the route locking also. However it is usual that any overlap route locking extends only up to (i.e. not including) the dead track.

4. You had 135A(S) calling 211 the wrong way.

5. You did get a little confused re the swinging overlap locking for 203, but at least you had an attempt. I think that you muddled this a bit with the "time of operation locking"; this also applies to facing points in a swinging overlap but is subtly different regarding its imposition and role (although I accept it looks somewhat similar and will actually be released simultaneously- after all it is the same train coming to a stand at the same signal on the same track).
In essence TofOp is about locking points that are only a short distance beyond a signal just in case the train SPADs at the time they are moving- the imposition of the lock is only as a train gets close[/]; if the points are more than 50m beyond then no such locking is needed.
Conversely the entry for "swinging overlap" is what I still prefer to call "counter-conditional" as this explains better what it is for; this is needed when there is an [i]"OR" condition involving these points in the aspect level of the reelvant signals having these points within their swinging overlaps [see attachment]. This is needed therefore as soon as the route is set and indeed applies to any facing point within overlap, irrespective of distance from protecting signal.

Basically for this locking you put in far too many points; you only put in those points that are to be included within the overlap you wish to swing towards which are not within the overlap that you already have.
Similarly for tracks, except that you also don't need to include those tracks which deadlock your hinge points anyway.
Well done for recognising that 107 and 142B(M) oppose, but note that the locking on the points is only from N to R (i.e. Normal is OK as the overlaps are parallel, Reverse wouldn't be as the overlaps would conflict). Also the two entries are related; there are different ways of depicting, but a good way is basically as you have shown BUT not as two completely separate lines of entry but link them in an OR condition; the points can be swung Reverse if one overlap or the other overlap is in use, but not if both are.
I have added another sheet of my own that attempts to explain the sort of entries needed and what the locking is attempting to achieve- which I think you haven't grasped.

Overall though, pretty reasonable attempts!

[greensky52]

Recently put all concentration on Mod 2, forgot having put post here...But when I come back, surprised for me-- so detailed comments and extra information especially for my error!

Explanation about swinging overlap and TofOp are really useful for me. Indeed, I confused about these 2 definitions.

I know most of your explanation. But still a question:
for point 211 N>R: My question is about the standing time. I have read your paper particular in Time Value: LONGEST: TIME COMPLETELY TO STAND
for Release of Overlap: berth TC: 200m Time:30s ; berth TC: 400m, Time: 45s. Taking 136C(S) as example, berth TC is BK or BL, I think neither of their length can reach to 400m, seem only 200m. So I think maybe 30s here is much more reasonable. What about your view?

A little later than advertised.......
please find attached some annotations on your Control Tables.

[PJW]

still a question for point 211 N>R: My question is about the standing time. I have read your paper particular in Time Value: LONGEST: TIME COMPLETELY TO STAND for Release of Overlap: berth TC: 200m Time:30s ; berth TC: 400m, Time: 45s.
Taking 136C(S) as example, berth TC is BK or BL, I think neither of their length can reach to 400m, seem only 200m. So I think maybe 30s here is much more reasonable. What about your view?

The common timer is on "BK or BL"; i.e. the two inputs are used as a combined track circuit for these purposes. The timer will start when the first of them becomes occupied and will expire after the quoted time provided that at least one of them has remained occupied ever since it started. The combined length is something like 806-293m so say approx 500m and therefore a time of a little more than 45sec is appropriate.

[greensky52]

Oh, I see. many thanks~~
Have a nice weekend!

I have read your paper particular in Time Value: LONGEST: TIME COMPLETELY TO STAND for Release of Overlap: berth TC: 200m Time:30s ; berth TC: 400m, Time: 45s.
Taking 136C(S) as example, berth TC is BK or BL, I think neither of their length can reach to 400m, seem only 200m. So I think maybe 30s here is much more reasonable. What about your view?

The common timer is on "BK or BL"; the combined length is something like 806-293m so say approx 500m and therefore a time of a little more than 45sec is appropriate.