to show fouling point on the schem plan

[onestrangeday]

Dear Gentlemen:

I would like to know how the fouling point is shown on the scheme plan?
It's best to have an example of scheme plan if someone is willing to share around



Thanks

[PJW]

Firstly I should point out (have to be careful not to be sexist) that there are also some ladies who utilise this Forum as well (indeed I know you know that)!
Then I should say it is good to hear from you again.

On a current NR Signalling Plan then it is the CP "Clearance Point" which is shown; this is where the track circuit joint or axle counter head has to be to be sufficiently far from the convergence that a train on one route just beyond it will not hit a train routed over the other lie of the set of points. Hence it is a =matter of looking for the associated arrow and looking at the track section division to see if it is "foul" or "clear". I'll try to post a diagram later.


The fouling point is the place where the vehicles would actually just touch- the clearance point is what we need to consider because
a) we want a "passing clearance" a minimum space between vehicles
b) the train detection only knows where the axles are and a vehicle always overhangs that position and indeed is wider than the rails it runs upon.


HOWEVER, the IRSE often do not depict and expect students to use "their signalling common sense". Broadly this means judging if the tracks when parallel are at "6foot" apart or if they must be wider (e.g. the approach to an island platform etc). If at 6ft then it is a reasonable assumption to say that the clearance point of a crossover is bang opposite the switch tongues of the point on the adjacent line; similarly judge "by eye" where there is just a single lead.

Dear Gentlemen:

I would like to know how the fouling point is shown on the scheme plan?
It's best to have an example of scheme plan if someone is willing to share around



Thanks

[PJW]

Here is a diagram, showing that such are to scale longitudinally but not laterally! The colour code is standard for NR works
GREEN= old being removed by the project
BLACK= retained unaffected by the project
RED = new being provided by the project

Hatton Station Junction:
Looking at LJ272 points, there is a CP showing at what place the divergence has got wide enough. You will note that there was a track circuit joint just further away than the CP and the new axle counter head has been placed even further away. Therefore we know that the axle counter section LJZJ is not foul of moves over LJ272 Normal.

Indeed the axle counter head has been placed extremely "tight" to the CP for LJ271 points- had it been any further to the left then it would have been on the wrong side of that CP and would then have meant that LJKD would have been foul of moves being made over LJ271 reverse.
However it is just on the correct side of the CP so as soon as section LJZJ has become clear after a train has passed beyond signal LJ7453 when routed on the (B) route, it is safe to call LJ271 from Reverse to Normal (as we know the vehicle has gone far enough beyond those points once the count head has seen the last axle has passed from LJZJ to LJKD).
It is certainly not always possible to place track divisions on the "correct" side of the CP- it is OK for them to be placed between the CP and the point tips PROVIDED that the interlocking treats them as being foul.

For a normal crossover (note that the new LJ272/271 was in the past operated as 647A/B) tere will not be a CP in the middle- the tracks won't be 6ft apart. In this case though you can see there is actually a whole platform between those tracks (hence must be at least 3m apart and probably more), so that is why the CPs are contained within its length (and indeed it looks like LJ271 normal lie is itself the curved divergence). This is the sort of logic you need to employ on an IRSE layout if it does not show the CPs (it is probably only in the last 15 years or so that plans on NR have depicted, so IRSE just following the traditional approach)

The third CP on the diagram extract is associated with HS490 points and you can see that the old track joints were placed just further from the points than the CP. The new axle counters are actually just slightly further away(generally want to place before the old track circuits are decommissioned, can't go exactly on top of them, obviously no room to put the heads closer to the points without being the wrong side of the CP so therefore go further away.



Hatton North crossover:
This plan shows what I was saying in the earlier post regarding the usual positions of CPs at a crossover- effectively opposite the switch tongues on the adjacent track, with the count head / track joints being at least that far away. The head separating LJKF/LJRM is FOUL, but as both track sections lock the points identically, this is really of no consequence.

Note how far the CP is from the single lead LJ245; I guess these must be long slender points for relatively fast running and therefore they diverge much more gradually than the short stubby emergency crossover.

On a current NR Signalling Plan then it is the CP "Clearance Point" which is shown; this is where the track circuit joint or axle counter head has to be to be sufficiently far from the convergence that a train on one route just beyond it will not hit a train routed over the other lie of the set of points. Hence it is a =matter of looking for the associated arrow and looking at the track section division to see if it is "foul" or "clear". I'll try to post a diagram later.

Dear Gentlemen:

I would like to know how the fouling point is shown on the scheme plan?
It's best to have an example of scheme plan if someone is willing to share around



Thanks

[onestrangeday]

Hi Peter, it's my pleasure to hear from you again too!!
Thank you for your reply and detailed explanation plus examples of scheme plan used in UK. Perhaps things are different in countries, where in my country only the fouling point are shown on the scheme plan.

[PJW]

That is something to remeber to point out to the examiners then!

Hi Peter, it's my pleasure to hear from you again too!!
Thank you for your reply and detailed explanation plus examples of scheme plan used in UK. Perhaps things are different in countries, where in my country only the fouling point are shown on the scheme plan.