Fault Tree Analysis

Fault Tree Analysis


A Fault Tree Analysis (FTA) is essentially a logical representation of all the ways a particular fault, or failure, can occur. In this type of analysis, one identifies a particular failure or fault they are trying to analyze (i.e., a top-level undesired event) and then proceeds to evaluate that condition through a set of intermediary fault states that, if present, would result in that failure. Fault states are assumed to exist when certain events happen. This can be a single event, multiple events or even precursor fault states that can, themselves, be further expanded. The analysis continues until all potential causes of the particular top level failure event have been identified. For this reason, the FTA is referred to as a “top-down” approach.

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The series name has a double meaning:
(1) the spelling of the name r-e-l-e-a-s-e indicates that the series is intended to “release“ the non-expert down the path to reliable products and
(2) the complementary terms “REL” with “ease”, implying the series goal of “reliability made easy.”

Of course, reliability success is seldom easy, requiring expertise and tailoring with tradeoffs addressing life-cycle costs and other issues, but we hope that the series will help those not familiar with reliability practices understand the basics.

While it is unlikely that the reader will become an instant expert in reliability by reading the RELease guides, it is likely that he/she will gain a better appreciation of the basic tools that lead to designing and building reliability into products and systems. The number of pages in each guide is intentionally limited to address only the basics, with comprehensive authoritative references listed for those wanting to know more. The initial set of guides will be continuously expanded in the future. Please let us know how the series can be improved to meet your needs in introducing reliability to the non-expert, or suggest other topics you would like to see developed.

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Daniel Gonzalez





Publication Date:

December 2013

Table of Contents

1. What is a Fault Tree Analysis?       2
2. FTA Terminology       2
3. Before You Begin       4
  3.1 FTA Tools     5
4. Performing the FTA       6
  4.1 FTA Rules     6
  4.2 Basic Steps in Conducting the FTA     7
  4.3 Boolean Analysis     8
  4.4 Dependent Events     10
  4.5 Limitations     11
5. Example       11
  5.1 Define the Problem     11
    5.1.1 Smoke Detector Circuit   12
    5.1.2 Audio Alarm Circuit   12
  5.2 Define the Top-Level Event     13
  5.3 Construct the Fault Tree     13
    5.3.1 Battery Monitor Circuit   17
  5.4 Analyze the Fault Tree     21
  5.5 Determine the Reliability     23
  5.6 Analyze the Results     28
6. For More Information       28