2014 Q1 Principles & Functional Testing

[PJW]

Hi,

I am part of a study group and we are currently working through the 2014 exam paper.

We would be grateful if you could review, critique and give feedback on our model answer (attached).

Regards,

Fran

Part a) for 4 marks, you had 6 bullets-

1. Broadly true, but not directly relevant to what you were asked, background only.

2,3 & 4. True and relevant, but better if more immediately juxtaposed with the contrasting description pertinent to Functional testing

5 & 6. Worded more to include all verification testing (so including things like inspection,, wirecount and continuity) rather than just the functional testing (i.e. power up, check that voltages are present / absent in accordance with conditions as dictated from looking at the circuit design or data design) which checks the behaviour implemented is what the design specified.

So not bad but it would have been more clearly (and economically in terms of time) presented as a table with a couple of columns for the different categories and a row in which you could have stated the ROLE / PURPOSE and another row in which you could have described the PERFORMANCE of the test.  Indeed you could perhaps have extended the table to more rows to tackle part b) of the question.

You wrote more than you needed to, yet your presentation didn't show the distinction obviously (although by the end it became evident that you understood the distinction, the difference had to be inferred than very in-your-face).

Part b.
You did give two sets of three bullets clearly which was great; however it looks very minimalist for 6 marks and therefore I deduce that the examiners must have wanted more detail.  The ii) was worse than i), because all you have really done is give a name and to give the example of "functional testing" as "function testing" really does not help!
For the 6 marks I think you ought to have written a sentence or two for each bullet to explain rather than just name the activity.
e.g. Proving that it is not possible to set the route-under-test whilst there is any opposite train movement still underway which requires the same infrastructure, but that route can set once the opposing movement has got behind the signal concerned (or if only an overlap opposed, been timed to a stand at its exit signal).

Whereas I might agree that correspondence testing sometimes contains an element of Principles testing whilst being largely a functional test, by including it in part ii) but with the enigmatic comment that it could be argued to be better in i) you rather weakened your argument initially about the distinction between the two categories.  However had you EXPLAINED WHY you said this, instead of detracting it could have enhanced your answer. 
I think you'd have been better to have chosen the example of Through Testing for this third bullet and then you could potentially have thrown in your example Correspondence of trackside functions to the control centre display as a bonus extra 7th built which was really a combination of end-to-end through test with a little Principles (check of signaller's view against Signalling Plan and site reality) thrown in to the activity- this could have been the "icing on the cake" as an addition to the basic answer requested since it displays more experience in that it is often pragmatic to undertake a combo-activity.

For the first bullet in b) ii) I think that I would have talked about the electrical testing of points, such as measuring the normal running current and the clutch slip current and checking the throw time of the switches.

Similarly I would have explain that a Strap &Function test ensures that a voltage is only fed to the end function when each of the circuit elements are in the state as required by the circuit design details and this is achieved by operating the relevant function until the contact breaks therefore losing the output, before then bridging that contact with a strap to regain the volts.