Fault Tree Points

[PJW]

Hi

Am back with the attempt again and can anyone please look in to the attempt for any comments.

Feedback is most appreciated.

Thanks & Regards

A very definite improvement overall; you are now certainly getting the idea.  

A few more comments,that I hope will help:

1. I think it would have been a good idea to have included at least one AND relationship

2. It was a bit of a jump from "failed insulations" to "point failed to operate" that I think you realised and attempted to explain by a # note.  It would have been better had you depicted within the Fault Tree- indeed wit ould certainly have given you the opportunity to address item 1 simultaneously.

3. Should really have differentiated between a problem with the detection electrical contacts and the mechnical setting of the detection.

4. Whereas I think that the distinction between  "not set", "not locked" and "not detected" is a useful one to make, some causes will result in more than one of these.  I didn't really get the impression that you had enough understanding of points to assign the faults to the failures clearly- some items wer ok but other bits seemed confused.  
a) To me, the "point motor failing to drive" (because "no power available" or "bad connection to motor" or "motor failed" or "insulation causes track failure which locks points") is itelf an input to "points not set correctly" along with some of your other entries such as "lack of lubrication", "obstructed switch blade" etc.  
b) I'd take this as being the "coarse" rail positioning only,  then I'd consider the more precise positioning required in order for the machine's detection slides to be in the correct position.  
c) Then I'd consider the amount of misalignment (and indeed any other causes) that could prevent the engaging of the facing point lock.
d) Finally I'd consider any problems that there could be with the actual detection contacts and thereafter the line circuit to the location and interlocking.  Indeed I could also have onsidered failure of the point detection due to a supplementary detector or indeed the backdrive not positioning this portion of the switch rails correctly.

The top event would therefore be: signaller unable to achieve detection when calling points to opposite position".

Remember what the examiners are after from you:
a) demonstrate your knowledege of fault tree presentation,
b) demonstrate your knowledge of point machines, their component parts and how they operate,
c) demonstrate your knowledge of the signalling system as a whole and the railway environment,
d) demonstrate that you have read the question and your answer is targetted to precisely what was asked difficult for me in this case as you never actually defined what the question was!

Also check out this other thread


At an IRSE Exam Review a few years ago the following question was discussed

Question 10
Sketch a fault tree for either:
a) Loss of point detection;
or b) Loss of communication between a Signal Post Telephone and the signalling control room [10 marks]

Explain how such a fault tree could be used to estimate the likelihood of the failure occurring. [4 marks]

Based on your resulting fault tree, identify mitigating methods that could be implemented to reduce the risk of the fault occurring.


The attachment was presented as a possible answer to the first part of the question

[attachment=2041]