(01-10-2015, 04:07 PM)TheRailwaySignaller Wrote: (11-08-2015, 08:03 PM)PJW Wrote: (05-08-2015, 07:03 PM)BastowM Wrote: Hi All,
My attempt at this question attached. Any comments would be very much appreciated.
Routes: 105 A (M), 119 C ©
Points: 212
Practice: UK Mainline
$7 Temporary Approach Control
$10 At time of clearing
$46 timer value (seconds)
Many thanks,
Mike
Mike,
Please see attached.
Note that when I looked at I had not noticed that you had defined the $ refs here.
For IRSE Exam purposes, suggest don't worry re $7 and $46 etc.
Similarly suggest you need to use a blank that does not have the boxes which aren't worth your time filling in- I have indicated by placing your entries in square red brackets. Leaving those boxes blank would not be correct; therefore you need not to have them. Similarly remove superfluous design / check/ version boxes and of course the company identification from any design that you are going to take as your "blank format"
As far as entries are concerned, not much incorrect. The points and first route do seem pretty simple and it was only the 119C© which had any meat. I think the trap in 2013 that the usual expectation of opposing route locking was conspicuous by its absence, The things which escaped you were the "pseudo point-to-point" and the trapping, so always look to the flanks of the routes.
I've attempted this set of CTs and generally seemed to be on the right lines. What do you mean by "pseudo point-to-point"? Is it referring to that P219 and P220 should both be normal to protect trains starting from S138? thanks.
Point to point means interlocking the positions of two points to prevent the layout being put into a state that is not useful for any moves; typically where two point numbers are included into the same track section.
An example from the 2013 layout is to consider the 4 possible combinations of 218 and 219; the possibilities are:
- 218N, 219N for platform 2
- 218N, 219R for platform 1
- 218R, 219N for platform 3
- 218R, 219R isn't useful. Hence point-to-point prohibits to eliminate unnecessary degrees of freedom
It is fundamentally a historic throw back to mechanical locking- by locking points against each other, it can considerably reduce the amount of signal to point and signal to signal locking required; it is less useful for relay interlockings and fundamentally not sensible to provide in data interlockings.
There are some advantages in providing particularly in handsignalling, BUT overrall regarded now as a bad idea as exacerbates the effects of any failure and therefore increase the amount of any handsignalling (inherently risky) or even makes that impossible without winding points on the ground.
Pseudo point to point does not actually lock the points against each other; rather it seeks to get some of the advantage without the associated disadvantages by directly calling from the route those points that are
not in the route but are in the same track circuit as a point which is in the route, in order to drive them to the sensible lie-
- in some cases this gives flank protection,
- but in others it merely prevent them being left in a position that is not useful and could actually later get locked into that position so preventing the setting of another route that could have been a legitimate simultaneous movement.
Hence any route over 218 reverse ought to call 219 Normal even though it isn't going to pass over 219; if it doesn't the problem may later arise that 219 are locked Reverse and they are needed free to go Normal as flank in order to route a train along the transfer line into / out from platform 1.
- 219 does not actually give flank for the routes through 218 Reverse, but worth calling to prevent stitching up the layout unnecessarily.
- However calling 220 Normal is valuable for those routes over 218 Reverse since it affords an element of flank protection for those movements.
Hope that clarifies
