Logan Fault and
Event Tree Analysis
LOGAN is a powerful yet easy
to use program for the construction and evaluation of Fault
and Event trees.
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Full Fault/Event Tree integration
Integrated reliability database (data not supplied)
Printout in conventional top-down format or LOGAN horizontal
fault tree format
Compatible with Microsoft Windows? 95/98/Me/XP/NT/2000
Minimal cutset analysis
Various forms of sensitivity analysis
Optimisation of proof test intervals to meet minimise
testing while achieving safety / reliability targets
Interfaces with the
ASENT the most powerful R&M Toolkit |
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Various forms of sensitivity analysis
Optimisation of proof test intervals to minimise testing
while achieving safety/reliability targets |
General Operation
LOGAN Fault & Event Tree for Windows is a program for the construction, evaluation
and printing of Fault and Event Trees in the Windows environment.
Fault trees can be linked to event trees by specifying a fault
tree which calculates a branch probability. If the fault trees
contain common events, the effects of the resulting non-independence
are fully accounted for. The system uses the Windows Graphical
User Interface for the construction of Fault (or Success)
Trees and Event Trees. The system lays out the diagrams automatically
for optimum presentational clarity.
Editor
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The graphical editor allows the Fault Tree or Event Tree
structure to be built up on the screen and the associated
event or branch descriptions and numerical data to be
entered. Some of the main features are:
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Create transfer events or rejoin transfer events to
allow the trees to be split onto several pages
Move up and down between the transfer events
Option to automatically number the pages to your specified
format
Copy and paste data between events |
Evaluation
LOGAN performs a full cutset analysis for Fault Trees and
for Event Trees which are linked to fault trees. The cutset
generator generates the minimal cutsets in terms of basic
events. Cutsets containing more than the specified number
of basic events are discarded. The system average failure
probability or failure rate and unavailability is calculated
from the probability of failure or failure rate and repair
time or proof test interval of the basic events. The program
identifies the use of inconsistent data (e.g. attempting to
AND two events entered only as failure rates) helping to prevent
errors in Fault Tree construction.
Sensitivity
Analysis
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A number of different Sensitivity Analyses can be performed
to determine the dependency of the system results on the
failure rate or probability of each event and on repair
times and proof test intervals. The calculations that
can be performed are as follows:
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Fussel-Vesely importance
The effect on the top event of setting all probabilities
to 1 (Fault Tree only)
The effect on the top event of increasing failure rates
by a factor of 10 (Fault Tree only)
The effect on the top event of increasing all events by
a factor entered by the user (Fault Tree only) |
Graphical
Output
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LOGAN for Windows generates high quality Fault and Event
Tree diagrams. Two formats of Fault Tree are available:
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A horizontal format which presents all the data for
the Fault Tree in a convenient data table.
A traditional top-down format. |
Proof Test Interval Optimisation
An additional feature is available which calculates the optimum
interval between maintenance of protective systems. This function
finds an optimum set of proof test intervals which minimises
the test requirements whilst maintaining the required system
failure frequency or probability of failure. For every event
in the Fault Tree which represents unrevealed failure of a
protective component, the system requires entry of the maintenance
man-hours required to carry out the proof test. Alternatively,
some other measure such as the cost of the proof test could
be used.
The program takes as its input the target top event frequency
(which may be, for example, equal to the originally calculated
top event or the required top event frequency). Using the
results of the sensitivity analysis, the program carries out
an iterative Gaussian minimisation process and calculates
a set of proof test intervals which minimises the total proof
test effort (or cost) whilst still achieving the target failure
rate. This often results in very long proof test intervals
for the least sensitive items. It is possible, therefore,
to enter a 'cap' or limit value on the proof test intervals,
which is the maximum time period which is considered acceptable
between the tests.
Link to Reliability Database
This feature allows the fault tree data to be imported from
and exported to an Microsoft Access? database according to
the data reference field entered. This facility can be used
to create a central databank.
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