Systems Engineering –
Risk Analysis with FMEA
Special Topics
Fishbone Chart
FMEA
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Risk/Failure Models
 At the ‘project’ level.
 At the system or device level.
 Common methods include Fishbone
analysis or FMEA
 FMEA – Failure Modes and Effects Analysis
2
Fishbone Chart




‘Cause and Effect’ Analysis
Create an Ishikawa or Fishbone Chart
Head is ‘Problem’ – Skeleton are the ‘Causes’
Typical categories, 5M’s + E






Man
Machine
Material
Method
Measurement
Environment
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Industrial Monitoring Sensor
Create a
Fishbone Chart
for ‘Sensor Not
Working’
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Analysis Tool – FMEA
 Failure Mode and Effects Analysis
 FMEA is an ‘enhanced’ Cause and Effect
Analysis. (the 5M’s plus E)

Do Fishbone Chart for Industrial Sensor.
 Apply FMEA to a Design or Processes at
many levels.
 Systems often have many SPFs – single
points of failure.
5
Design Tool – FMEA
The Concept of FMEA:
 People Make Mistakes
 Products and Processes Fail
Anticipate these errors and eliminate them with
design or process changes !!
6
FMEA Example
How many
ways can a
floppy disk be
inserted ??
What design
features make
this possible??
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FMEA Steps
-The traditional approach
1.
2.
3.
4.
5.
6.
Team activity
Select component, system, process step, etc.
Identify possible failure modes.
Identify causes of failure modes.
Identify effects of failures.
Estimate (1-10 ranking):
1. Occurrence – how often (1=not, 10=often)
2. Severity – how bad (1=not, 10=severe)
3. Detection – how easy (1=easy, 10=difficult)
7. Calculate RPN – ‘risk priority number’
8
FMEA RPN example
Occ
1
1
1
1
10
10
10
10
Sev
1
10
1
10
1
10
1
10
Det
1
1
10
10
1
1
10
10
RPN
1
10
10
100
10
100
100
1000
Comments
No Problem
No action, easy to detect.
No action, not often or severe.
Action
Chronic problem, fix ?
Chronic and severe, fix
Chronic and customer issues, fix
Bad, Bad, Bad – top priority
Rules for OSD Values
Threshold for Action – Varies
Thresholds 55-100 (?)
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From National Instruments
10
From National Instruments
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Detection in Design or Manufacturing
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POTENTIAL FAILURE MODE AND EFFECTS ANALYSIS
Design FMEA
System
Subsystem
Process FMEA
Component
Part Number
Internal Use Only
Page
Design or Process Responsibility
FMEA Number
Prepared by
Telephone #
Original FMEA Date
FMEA Revision Date
Core Team
Design Item or Process
Function Requirements
Potential Failure Mode Potential Effect(s) of Failure
S
e
v
C
l
a
s
s
Potential Cause(s) /
Mechanism(s) of Failure
O
c
c
Current Design or
ProcessControls
D
e
t
R
P
N
Recommended Actions
Responsibility & Target
Completion Date
Actions Taken
S
e
v
O
c
c
D
e
t
.
Many versions of this chart…
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R
P
N
Occurrence and Severity
 O and S are
often the two
critical factors
and some
analysis just
looks at these
two.
14
From Dieter
Industrial Monitoring Sensor
15
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FMEA Summary
 Combines ideas of ‘Cause and Effect’ chart,
mistake proofing, and risk.
 Useful to identify and prioritize possible
failure modes and fixes.
 Possible Fixes :




High reliability components,
De-rate components,
Redundancy,
Change the design.
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FMEA
- A Requirements Approach
 FMEA often starts with:
 Identify possible failure modes.
 How? – guess, experience, brainstorm, etc.
 Consider –



Requirements are what the system is supposed to do.
Counter-requirements (not being met) are failure modes.
Use counter-requirements to populate the FMEA table.
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Design FMEA Example
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Design
FMEA
Coyote
Hoist
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Class Discussion – Process FMEA
 You are responsible for developing a process to stuff
several hundred envelopes for a charity group.
 Each envelope is to contain three separate flyers and a
cover sheet with the recipients name on it. After
folding, the name must show in the cutout in the
envelope. The final step is to seal and place stamps on
the envelope for mailing.
 Develop a PFMEA* for this process.
*Process FMEA
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