9 20050602 fault tree fmea - rwth aachen university fta is often used in praxis for risk and...
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Safety and Reliability EngineeringPart 9: Fault Tree and FMEA
Prof. Dr.-Ing. Stefan Kowalewski
Chair “Informatik XI”, Embedded Software LaboratoryRWTH Aachen University
Summer term 2006
Organizational Issues
Slide “Register for Seminars and laboratory course”Slide “Wahlen zum Studierendenparlament”No lecture on 28.06.2006 because Prof. Kowalewski is involved in the UMIC projectNext lecture on 05.06.2006 (last lecture)“EvaSys” survey.Please fill in the questionnaireNext exercise course is tomorrow the 29.06.2006Written examination on 12.06.2006 in AH III
Agenda
Reminder for the fault tree basics
Introducing new Fault tree elements
Introducing of FMEA
Examples for Fault tree and FMEA
Reminder: Fault Tree Analysis
Fault Tree Analysis (FTA) is a top-down approach to failure analysis Analysis proceeds by determining how a undesirable event can be caused by individual os combined lower level failures or eventsLogical connection between the events e. g. AND-gates and OR-gatesFTA is often used in praxis for risk and reliability studiesFTA is a method for analyzing causes of hazards(not identifying hazards)
Exercise Last Lecture 1/2
1
2
53
4
Minimal cut sets:•Failure of components 1 and 2
• Failure of components 3 and 4
• Failure of components 1, 5 and 4
• Failure of components 2, 5 and 3
RBD:
Exercise Last Lecture 2/2
Minimal cut sets:
•Failure of components 1 and 2
• Failure of components 3 and 4
• Failure of components 1, 5 and 4
• Failure of components 2, 5 and 3
Fault Tree:
More Elements
Up to now we saw AND-gates and OR-gates
There are a lot of other gates in Fault Tree Analysis which are use to express different things.
Can you imagine one?
New Elements
Voting OR:The output event occurs if k or more of the input events occur
Inhibit:The input events occurs if all input events occurs and an additional conditional event occurs
Priority AND:The output event occurs if all input events occur ib a specific sequence
XOR:The output event occurs if exactly one input event occurs
Basic Event Block in FTA
Basic Event:Basic initiating fault
External Event:(House Event) Event with probability 0 or 1
Undeveloped Event:Event that does not need further development
Conditioning Event:condition that con be applied to any gate
Introduction FMEA
Failure Modes and Effects Analysis (FMEA)
Uses Forward search
Initiating events: failures of individual components
Developed by reliability engineers
FMEA perform a Qualitative Analysis
FMEA Main Components
Initial:Individual componentsFunction:Analyze all functions of the componentFailure: Analyze the failure possibilitiesAnalyze the effect of the failureAnalyze the cause for the failureRisk evaluation:Estimation of the effect of the failureEstimation of the probability of the failureEstimation of the probability to detect the failure
FMEA Table 1/3
1. No.: Unique Number2. Component / Process: Name of analyzed component,
process or function3. Function: All list here all function of the component from
2. for the analyzed system (black-box-function)4. Failure Kind: For all functions form 3. list all possible
failure which can appear
No.Component /
Process Function Failure KindFailure Effect
Failure Cause
Failure Avoidance
Failur Detection B A E RPZ Measures
1 2 3 4 5 6 7 8 9 10 11 12 13
Quality AssuranceFMEA (Failure Modes and Effects Analysis) Page:
Department:FMEA-No.:Date:
FMEA Table 2/3
5. Failure Effect: List for all failures the consequences for other components and the over all system
6. Failure Cause: List the possible reasons for the failure7. Failure Avoidance: List all possibilities to avoid the
failure8. Failure Detection: List the possibilities to detect the
failure
No.Component /
Process Function Failur KindFailure Effect
Failure Cause
Failure Avoidance
Failur Detection B A E RPZ Measures
1 2 3 4 5 6 7 8 9 10 11 12 13
Quality AssuranceFMEA (Failure Modes and Effects Analysis) Page:
Department:FMEA-No.:Date:
FMEA Table 3/3
9. B: Number between 1 and 10 which denote the impact of the failure. (1 no impact; 10 great impact)
10. A: Number between 1 and 10 which denote the probability that the failure occurs (1 very unlikely; 10 very likely)
11. E: Number between 1 and 10 which denote the probability to detect the failure (1 very unlikely; 10 very likely)
12. RPZ: Risk Priority Number R=B*A*E13. Measure: Things that can be done to lower the RPZ.
No.Component /
Process Function Failur KindFailure Effect
Failure Cause
Failure Avoidance
Failur Detection B A E RPZ Measures
1 2 3 4 5 6 7 8 9 10 11 12 13
Quality AssuranceFMEA (Failure Modes and Effects Analysis) Page:
Department:FMEA-No.:Date:
Create a FMEA
First get all ComponentsDenote all function, failures, failure effects and failure reasonsAnalyze the possibilities to avoid the failure and to detectthe failure Decide the Numbers for A, B and ECompute the RPZ – Number.Analyze the Number with rules like:A, B and E should be lower 7RPZ should be lower than 125…If necessary do measures to lower A, B or E
Kinds of FMEA
There are often different kinds of FMEAs.Example : FMEA for System AnalysisFMEA for Construction AnalysisFMEA for Process AnalysisOften different tables and different meanings of the numbers
FMEA Example 1/2
FAILURE MODE AND EFFECTS ANALYSIS (FMEA) Page 3 of 3Subsystem/Name: DC motor P = Probabilities (chance) of OccurrencesFinal Design: 31/5/2000Model Year/Vehicle(s): 2000/DC motor S = Seriousness of Failure to the Vehicle Prepared by:
D = Likelihood that the Defect will Reach the customer
R = Risk Priority Measure (P x S x D) Reviewed by: Chris
FMEA Date (Org.): 27/4/2000 (Rev.) 31/5/2000)1 = very low or none 2 = low or minor 3 = moderate or significant4 = high5 = very high or catastrophic
Example FMEA 2/2
Durability test on leadsQC checkedIncreased staff in inspectionSet up customer complain department
60100
45
55
34
Unstable control loopEndanger operatorsSerious damage Customers complain Faulty products are identified
Faulty leadsIncorrect motion
Signal lossDefects in products
Provides voltage signalProduce final product
Motor3
RDSP
Action(s)Taken
RecommendedCorrective Action(s)
P.R.A.CurrentControl
Effect(s)Of Failure
Mechanism(s) & Causes(s) of Failure
FailureMode
FunctionPart Name
Part No.No.
Conclusion
Fault Tree Analysis is a top-down approach.There are a lot of elements to describe the reasons and connection which cause the failure
FMEA is an bottom-up approach.FMEA can be applied during the design processFMEA is structured process to analyze qualitatively failures and their effect on the system
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