[SystemSafety] Which software for very basic FTA?

[Robin Cook]

Hi

I am currently (today) working on some fault trees and am using Visio
although I have FaultTree+ installed on the machine. Usually I use
FaultTree+ for the bigger and quantified trees. Today the aim is requirement
setting and specifically the decomposition of high level DAL requirements.
Hence A3 colour graphics to make the point. Visio does this better.

I have used MS Excel in the past. Before I had Visio, it was the best
graphics tool available to me. Drawing And gates and Or gates took a little
time but once I had written the macros to draw them, readily done (Or gates
have two 60° arcs meeting at a point not a rounded nose). It will maintain
graphical connections while dragging and dropping objects. One trick is to
set the cell width to 1.7 as that gives a close to square grid (yes, back in
the early '90s I spent a few minutes printing circles and squares). Also
learn the effects of shift, control and alt with the mouse button. And it
will do the arithmetic however you define it although I have written macros
to work the arithmetic with text input and output as it was then easier to
display on the graphics sheet. 

I would add that, having looked in detail at the arithmetic in FaultTree+, I
congratulate the design team for coping with users carrying out what I was
brought up to regard as poor analysis and still producing appropriate
results. I do however consider that it is too easy to put numbers into an
FTA application and believe the result at the top event. FT is a flexible
technique and, as such, needs careful application and review by
practitioners who understand what is being said/calculated.

So:
(i) MS Excel can do graphics even if only the windows primitives - a little
macro writing using polylines can help significantly;
(ii) In Visio or Excel event numbering is manual - in Excel you could have
an event table but I have always used FaultTree+ when reaching the size of
tree that would warrant this.
(iii) Printing needs to be set up in any application - they will all do it.
However I have come across some applications (20 years ago)where the printed
format is graphical in name only.

As for Open Source, I am aware at least one application but would always
check the arithmetic. I would also check the arithmetic of applications that
were not Open Source. Many older packages have a small numbers
approximation. Many packages have calculation options and you need to know
that your options selection is giving you an appropriate analysis. However
since you are talking simple qualitative trees - not a problem.

(Must see if I can reshape the Or gate on that Open Source FTA application!)

Best regards 
Robin Cook

Please send any reply to srcook at theiet.org


-----Original Message-----
From: systemsafety-bounces at lists.techfak.uni-bielefeld.de
[mailto:systemsafety-bounces at lists.techfak.uni-bielefeld.de] On Behalf Of
David MENTRE
Sent: 24 September 2013 10:38
To: systemsafety at techfak.uni-bielefeld.de
Subject: [SystemSafety] Which software for very basic FTA?

Hello,

I am planning to do some FTA (and possibly FMEA). Such FTA are going to be
very very basic (relatively small tree, no probabilities, no need for cut
set, etc.).

I could use MS Visio or similar drawing software. I am already using MS
Excel. However I would like to have (i) a graphical representation of the
tree, (ii) numbering of events (for traceability), (iii) printing
capabilities (print the tree on several A4 pages in readable form).

Which software, preferably Open Source or at least freely available, would
you recommend? I am working on Windows and Linux platforms.

Sincerely yours,
D. Mentré
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