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Scale distances on layouts
#1
Im getting a little confused on how to read the scales as applied to the signals on the IRSE layouts; are they incremental per each signal or are they the distances between signals? Either way how do you work out lenghts of berth TC's etc especially when there are two in a station. Could somebody enlighten me please?
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#2
Splitting tracks in stations is normally there to allow seperate detection of a specific length train (also read about Lime Street control). Hence, in modern day parlance, you would need to have the signal, standage in rear of 10-20m, length of the longest train and some additional distance behind the train in case the driver doesn't position the train according to the designer's thinking. Assuming a platform of 450m, a train length of either 200 or 400m, you could assume,
10m standage,
200m train,
15m standage,
block joints,
15m standage,
200m train,
10m standage.
Therefore, your block joint would be at 225m. However, you also need to consider track circuit type as two end fed TI21s require ~20m either side of the "joint". It is possible to mitigate that by having a centre fed TI21 but that is another thread.

If you just need detection, then a single track as berth to the exit signals at either end of the platform is fine. You then need to consider AWS ramp location and/or suppression for wrong direction movements.

I hope you understand my poor basic explination of tracks lengths and justification to NR practice!

As for the distances shown by the arrows for distances between signals, the are signal centreline to signal centreline. Usually, the distance and signal ID are shown.

Have you a scale rule? If not buy one. Sometimes they give one out in the exam but don't presume they will. Get used to using one and be careful of scale changes (not usual in the exam!).

Jerry
Le coureur
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#3
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(13-09-2010, 08:29 AM)Jerry1237 Wrote: Splitting tracks in stations is normally there to allow seperate detection of a specific length train (also read about Lime Street control).

As for the distances shown by the arrows for distances between signals, the are signal centreline to signal centreline. Usually, the distance and signal ID are shown.

Have you a scale rule? If not buy one. Sometimes they give one out in the exam but don't presume they will. Get used to using one and be careful of scale changes (not usual in the exam!).

Jerry

Module 3 layputs are not to scale but are generally (within any given area) proportionate and hence dimensions for one direction can be assumed applicable to the other or a distance estimated as a proportion of a defined one.

Generally the distance from one running signal to the next is given, but occasionally the standage between two opposite direction signals, as at platforms.

Don't forget that when using platfrorm tracks t time out overlaps / opposing locking that it is the combined length of time that one or other of the platform tracks is occupied that is important; you probably don't even need to consider their individual lengths
PJW
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