2007 Track circuit calculation, Q3

[Archie]

P.S.- one thing I forgot to ask is that I have applied to study the Mod 5 exam, but what is the content of the study pack, does it go over in detail of how to approach such calculations as track circuits etc?

I have had a look at others, just trying to jump into what is going on is a little tough, but given time I am sure I will be fine.

Have you looked at any of the attempts for some of the other questions to try to get an understanding of the way to approach things?

Peter

I think thisis one of the better Study Packs, but don't think of any of them as text books / "how to pass the examination" step-by-step instructions. They are not generally designed to teach the subject; rather than to give examples of previous questions and including activities designed to get you to think about things that you may not have otherwise thought about.

In this case there is one worked example as a model answer [1996 Question 6] and a selection of other past questions, a few of which are supplemented by some specific comments. However you'll find more on this website- the examples here aren't perfect but you can actually learn from other people's mistakes!

Right hello again, I am back as promised, with a revised attempt at the 'drop shunt' calculation. Please see what you think, and comments greatly received!!!

-PU current plus 10% for reliability=121mA
-DA current = PU current x 68% of PU current
121x0.68=82.28mA
-DA voltage = DA current x relay resistance
0.08228x20=1.645 volts
-Current supplied by feed = feed voltage-DA voltage/relay resistance
(10-1.645)/7=1.193A
-Ballast current = rail voltage/TC length
2.2/0.69=3.188A
-Current through 'drop shunt' = ballast current-current supplied by feed-DA current
3.188-1.193-0.08228=1.91272A
-Value of 'drop shunt'=DA voltage/current through shunt
1.645/1.912=0.86 Ohms

As quoted from the 'SMS, Signalling Maintenance Specifications,' minimum drop shunt value=0.5 Ohms, Preferred drop shunt value 0.8-1.0 Ohm

So this answer given falls into the 'preferred' drop shunt value.

Fingers crossed!!!