About Fault Tree Analysis

Fault tree analysis serves to quantify (predict) the reliability / availability of a system.

goal_br

Identify the real causes of a problem and narrow down the search space for rare errors.

result_br

Potential mechanisms of action that lead to errors. Focus on probable causes.

How to insert the Fault Tree Analysis component

The Fault Tree Analysis template can be used to start new projects or to extend existing projects. Please read chapter "The Templates" to learn more about how to start new projects.

In order to extend your project:

  1. 1
    Activate the Insert Ribbon Insert Ribbon
  2. 2
    Click the Add Tool button on the Insert ribbon
  3. 3
    Click the Fault Tree Analysis icon in the template catalog

The Fault Tree Analysis component is located in this cycle/phase combinations:

  • SIX SIGMA DMAIC: ANALYZE

Activate the right cycle by clicking its item at the blue left section of the template catalog. Then scroll the window to the right phase in order to find the module Fault Tree Analysis.

Basic Fault Tree Analysis. You can create fault trees using AND and OR gates. The module can calculate minimal cut sets as well as probabilities for main events.

Fault Tree Step By Step

Create and evaluate fault trees with Qualica Software

Learn how to create the logical structure of a fault tree, add gates and probabilities for leaf events, and evaluate the fault tree.

  • 1

    Sample System

    We want to create the fault tree for the following system.

    The pumping system as described here, fills a storage tank within 10 minutes. After that, the storage tank empties within 50 minutes. A full cycle therefore lasts exactly 1 hour.


    Once the switch is closed, the timer will open the contacts after 10 minutes.


    If this mechanism fails, an alarm signal sounds (triggered by the filling level of the storage tank). When the alarm sounds, the operator opens the switch to prevent the tank from failing due to overfilling.

  • 2

    Creating the Structure

    After you have started a new project using the fault tree component or added the component to your project, there is a new worksheet fault tree with some default items on the first level.

    • Click onto Failure Mode 1. This will become our top event for the fault tree.
    • Type the description for the top event: System Failure
    • Now change Failure Mode 2 to Filling
    • Use the mouse to drag Filling and drop it onto System Failure
    • Rename the third placeholder into Tank Failure and move it into the Filling event

    The fault tree should look like this:

    First 3 Items

    Now we have to add more events and gates:

    • Click Filling
    • Choose Insert Sub Item from the main ribbon and a new event will be added.
    • Rename the new event into Pump Failure

    Use Insert Item Before and Insert Item After to create new events on the same level. You may also try to use keyboard shortcuts:

    RETURN: adds a new element after the selected item

    SHIFT + RETURN: adds a new sub element

    Now add more elements until you get the following structure:

    Completed Fault Tree

  • 3

    Define logical operators

    In the next step logical operators have to be defined for all gates / groups of events. There are AND gates, OR gates, and "k out of n" for groups with more than 2 subordered events.

    All groups / gates have a small rectangular box at the right hand side. Clicking onto this box will show a menu to select the operator for this gate:

    • ≥ : OR operator
    • & : AND operator

    The two events under Control have to fail simultaneously to make the gate fail. Control is an AND gate. All other gates are OR gates, which is the default. Change the operator for Control into AND by clicking on the operator box.

    Gates

Need more information? Open questions? Please let us know.

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