2008 CTs on 2012 IRSE tables

[dorothy.pipet]

Feedback and comments please?

[PJW]

Looking at your Notes sheet first-

Stating that shunt routes require all tracks clear is rather too dogmatic; it could well be a required operational move to get a train from the up siding into a platform which is already occupied by a train- they do have call on moves into them after all. You could say "shunt routes lock overlaps and prove tracks clear to the maximum extent consistent with the operational use envisaged"- but there again one could argue already implied by "current UK mainline signaling practice". One thing worth knowing is that whereas the layout is drawn by a retired signal engineer, the people who mark the papers are all fully aware of current NR practice.

Think your #1 note is useful means of depicting on CTs

Since layout itself states AWS and TPWS not shown, I wouldn't state that "not provided"; rather inconsistent with stated practice! I think you could just take the lead given by the layout, although perhaps better to cover yourself and state instead "AWS / TPWS not shown"

Somewhat confuses the note re point ends by bringing the route level into the sentence; the fact that they have one identity number means that are treated always as an entity for locking. Whereas "real" CTs would list the separate ends when considering their detection, would never do so when considering interlocking functions, so this isn't "exam shorthand". Indeed if there is an SSI boundary and by mistake the locking on all ends isn't checked before issuing a call on one end, then the result is a "Stockley" incident......


Route and Aspect

Another set of CTs where it is obvious that the candidate knows what they are doing; a bit of a rareity I fear.
Hence few comments and most of these are quite picky.

164B(M)-
Meaning of (TAC) not immediately obvious, but you were rather saved by writing it out in full later for 161A(M)

164B( C)-
I am assuming that wi= "with", though I am more used to w= "when", but the meaning is the same. However did actually need something extra here since the treadle is 100m prior to the signal, so a light loco approaching the signal would activate approach release but may then find the aspect reverts to danger when the treadle arm rises a few seconds after last being depressed by its last axle.
Similarly if the signal is not routed initially and a train (even a long one) comes to a stand at 164, the treadle arm may well have risen up since it is improbable that a wheel would be stopped immediately above it; result is the signal wouldn't ever clear.
Hence the condition actually needs to be stored- the treadle has been operated whilst the track was occupied and then remembered until the track subsequently becomes clear. A case for an explanatory # note.


161A(M)-
Sensible to put the note re considering but not calling 254 as flank; you could of course have used a "soft call" and set them if free to go but not lock or detect.
You should however have provided some overrun protection following a SPAD at 157 and maintaining it whilst BL occupied.


147B(M)-
In the availability expression for the overlap, all the points are equal, so should just read [253N, 254N, 255N or 253R]; the "wi" is incorrect here as it suggests only evaluating that 253 is free to go normal when 254 and 255 happen to be normal and does not imply the checking of 254's or 255's availability.

I think you are sensible to use the ROL for the shunt overlap; it is plain daft to give these routes a longer overlap than for the warner- I am not sure what the official NR standard now says but for a long time at least strict adherence would have resulted in that situation.

In the track controls for the swinging overlap, you have made a silly slip regarding the lie of 253 points; obviously the point ought to be detected in the opposite position for it to condition out the track.
However CH is actually also foul of the overlap over 253R unless 254R; you have missed that conditionally foul track.

The A/L timed release of 147 should be 30 secs and I'd also have expected the locking not to be imposed if CR clear; I know you have stated no comprehensive A/L release provided but provision of one track is simple and effective and certainly NR policy which you are claiming to follow.

124B(M)-
You seemed to decide not to show as opposing locking 152A(M) on the basis that there is no overlap via 236R beyond 131. However the train can stop at 131 and the overlap will time out, releaseing the locking on 236. Still don't want to be able to set 124B(M) so that opposing locking was in fact needed after all. Similarly from 156 etc.

Same comment re the approach release using BG Q; since this is even further from the signal than the previous case, the opportunity for signal clearance and thereafter signal reversion is even more likely as things are at present on your CT.

Another thing is that the aspect should be proving that there is no premature release stored for 149; hence FH Q should be proved "not operated" and indeed any stick circuit or timer implementing the aapproach release of 149 should be down proved- similar to Raynes Park control (that is usually shown on NR control tables by $16 against the relevant track).

So pssibly just a few things to learn and tighten up on, but overall another set of CTs to be proud to have shared; I am sure that many other users of this website will gain from looking at your attempts.

I'll try to look at the points tomorrow.

Feedback and comments please?

[PJW]

Looking at your points CTs

233
This one seems pretty straight forward- makes me worry we have both missed something!
You queried providing flank by switch diamonds; you are correct that calling the points nomal doesn't really protect. However conversely if 231 is being used in normal lie, there really is no value in not getting 233 normal. One could certainly argue that if they fail to achieve detection then there would beno reason to hold 109A(M) etc at danger, but as far as the points CT is concerned then yes 233 should be set and locked. Note that if 233 were initially reverse and were locked so by occupancy of CS, then 231 wiuld itself be locked reverse; therefore by including in 109A(M) 233 "normal or free to go" haven't made more restrictive. It may not give you much but if it costs you nothing then might as well do it; after all traditionally the 3 point ends 231 and 233A/B would have been operated as 231A/B/c an keeping the setting and locking cnsistent will probably lead to fewer mistakes when railway being operated in degraded mode.

The only other comment is really a repeat of one I have recently made on your 2007 point CTs. I would not list the overlap track sections where these tracks are already shown as dead locking the points. I note that you listed CT (but not CS) in the route holdng after 154A(M) and CS, CT after 152B(M) and 156B(M); I consider these superfluous entries as it adds no more locking than is there anyway by virtue of the neat tracks.


254
Not sure why you deleted (FB or 253N) in the R>N locking; I would have included.

Again I would not have shewn the overlap tracks in the maintained locking on the points.
I would however have included CH in the locking after 159A(S); I think this is just a random careless error on your part; I am making the assumption of SSI with 15sec track bob protection of course- if this did not exist (the attempts to implement on RRI were generally given up as a bad idea) then I would only show route locking to the track PRIOR to the dead track locking.

I don't understand why you deleted the 149A(S) entry; I am gussing that since this is a shunt class route you are saying that 254 could be reverse with the shunt O/L at the CH/CG joint. However there is no forward route from 157 that way and don't see why this route would be treated differently- I am sure that this shunt overlap is intended to define the length beyond 159 shunt signal rather than being associated with shunt class routes to main aspects.

Another example of something I recently pointed out on the 2007 CTs; I would write the locking on the trailing points within the swinging overlap as [147B(S) or 253R$28] (where $28 means "correct or freee to go)

The other thing that perhaps you either didn't notice or perhaps realise the significance; points 255 and 254 are both in the same track circuit CH. Traditionally there would have been point-to-point locking between these sets; getting both points reverse simultaneously would have been prevented by direct interlocking between them, going back to mechanical locking practice.

This is not currrent NR practice (tended to die out in late 1970s / early 1980s), but pseudo point-to-point is definitey sensible; i.e. making sure all the routes that call one of them reverse, call the other set normal.

Obviously it is definitely necessary that routes over 254R call 255N as that is the only path for the train; it is sensible that routes over 255R call 254N even though the train does not traverse. This is for two reasons; it tends to give an elemnt of flank protection (albeit often not perfect) and also to avoid adversely affecting operability. Consider a train using 166A(S) and which has just cleared CG, still occupying CH; points 257 have therefore become free to call normal, yet if 254 just happened to be lieing reverse then 157 route could not be set and trains would be delayed for no good reason.

Lookout for two differently numbered point ends within the same track circuit as your trigger to consider pseudo-point-to-point; for example also on this layout notice that points 244B and 245A are both in CN.

Therefore you should have listed all routes over 255 reverse as applying normal calls to 254; if doing their CTs then these routes would be shown as setting and locking but not detecting (to avoid any detection failure unnessarily preventing aspect clearance).



SUMMARY

So some comments but not a lot much wrong. Practice helps you speed up and time is of the essence in the exam, but remember that in the 2013 exam that Control Tables are only one of the three questions that you have to do. In your case these look well under control; don't forget your preparation for the other 2/3rds of the examination! Students don't pass anymore on CTs alone.

Feedback and comments please?

[dorothy.pipet]

you say that "real" CTs would list the separate ends when considering their detection.
Actually this seems to me to be dying out, presumably since a Points Summation sheet is now common.

Is it a reasonable short-cut in the exam, or would I be expected to write all the point ends in?

[PJW]

I am very pleased that you say the practice is dying out; I have had a "bee in my bonnet" for years and when we were re-writing 11202 to better match SSI (or similar) data, then I did press for my summation sheets.
It gets absolutely ridiculous to list all the supplementary detectors every time- it just clutters everything, you can't "see wood for trees" and basically forces the tester to put meaningless ticks on the CT (as typically is summated in IPT and then the common identity used throughout); this means that on the rare occasion where there IS a true need to test that separately included in a function it often then gets overlooked. I'll celebrate this as one little victory in the war of PJW against the world then!

As far as IRSE exam is concerned then certainly reasonable approach; just make sure that n your initial notes sheet for the set of CTs that you state something along the lines of:

"Point detection is assumed to include all ends (functional and supplementary detectors) and the down proving of motor contactors"

you say that "real" CTs would list the separate ends when considering their detection.
Actually this seems to me to be dying out, presumably since a Points Summation sheet is now common.

Is it a reasonable short-cut in the exam, or would I be expected to write all the point ends in?

[DLMC]

I have a question of 124B(M). As it is already mentioned that present of 126B is required before set 124B(M). Then why shall we consider the 152A(M), 156A(M), pt 242 status etc in 124 CT? I think those consider shall list in 126 CT weather in 124 CT.

Please comment. Thank you.

Looking at your Notes sheet first-



124B(M)-
You seemed to decide not to show as opposing locking 152A(M) on the basis that there is no overlap via 236R beyond 131. However the train can stop at 131 and the overlap will time out, releaseing the locking on 236. Still don't want to be able to set 124B(M) so that opposing locking was in fact needed after all. Similarly from 156 etc.

Same comment re the approach release using BG Q; since this is even further from the signal than the previous case, the opportunity for signal clearance and thereafter signal reversion is even more likely as things are at present on your CT.

Another thing is that the aspect should be proving that there is no premature release stored for 149; hence FH Q should be proved "not operated" and indeed any stick circuit or timer implementing the aapproach release of 149 should be down proved- similar to Raynes Park control (that is usually shown on NR control tables by $16 against the relevant track).

So pssibly just a few things to learn and tighten up on, but overall another set of CTs to be proud to have shared; I am sure that many other users of this website will gain from looking at your attempts.

I'll try to look at the points tomorrow.

Feedback and comments please?

[PJW]

Thanks for your question; it illustrates why it is important to declare your railway's practices.

The attempt we were discussing here reflected:
UK mainline practice using Multiple Aspect Signalling,
implemented via Route Relay Interlocking / Solid State Interlocking.
In such a context, a "pres-set shunt" means that there is a GPL signal positioned partway along a main route and when the signaller sets the main route, the GPL is automatically cleared as a precursor to the entrance signal. The aspect of the GPL proves ALL the controls applicable the main entrance signal are satisfied and once it has cleared (and only then) does the main signal clear. This is done so that the driver on the main route does not pass the GPL displaying ON; note though that the route associated with the GPL as a shunt signal isn't set.

I think that the situation familiar to you is what we would call a preceding shunt and is how the locking would be arranged on a mechanical lever frame. In such a scenario the signaller first clears the shunt signal and then clears the main signal which reads over it and indeed there would be mechanical locking preventing that route from being set unless the GPL had already been set. Some relay based systems could implement the same type of logic and in such a scenario then you'd be right that the locking would be carried by the GPL and this used to summate and then get reflected in the main route. This is not UK mainline practice for colour light signalling; hence it would be WRONG IN THAT CONTEXT.

However it would equally correct to have answered an IRSE Exam question in your way IF YOU DECLARE THE RELEVANT RAILWAY WHOSE PRACTICE IT REPRESENTS.

So beware taking bits of information from one place and combining with bits from somewhere else as you can end up confusing different practices.
Learn one practice, stick to it and make sure to tell the examiner which railway it relates to.

I have a question of 124B(M). As it is already mentioned that preset of 126B is required before set 124B(M). Then why shall we consider the 152A(M), 156A(M), pt 242 status etc in 124 CT? I think those consider shall list in 126 CT weather in 124 CT.

Please comment. Thank you.

Looking at your Notes sheet first-



124B(M)-
You seemed to decide not to show as opposing locking 152A(M) on the basis that there is no overlap via 236R beyond 131. However the train can stop at 131 and the overlap will time out, releaseing the locking on 236. Still don't want to be able to set 124B(M) so that opposing locking was in fact needed after all. Similarly from 156 etc.

Same comment re the approach release using BG Q; since this is even further from the signal than the previous case, the opportunity for signal clearance and thereafter signal reversion is even more likely as things are at present on your CT.

Another thing is that the aspect should be proving that there is no premature release stored for 149; hence FH Q should be proved "not operated" and indeed any stick circuit or timer implementing the aapproach release of 149 should be down proved- similar to Raynes Park control (that is usually shown on NR control tables by $16 against the relevant track).

So pssibly just a few things to learn and tighten up on, but overall another set of CTs to be proud to have shared; I am sure that many other users of this website will gain from looking at your attempts.

I'll try to look at the points tomorrow.

Feedback and comments please?

[DLMC]

Thanks a lot. It is clear for me now.

Thanks for your question; it illustrates why it is important to declare your railway's practices.

[asrisaku]

Hi

I have practiced and compared the model answer below.

Any comment is welcome!

Thanks
Arnut