Reliability | Reliability Analysis | Methods | Failure Rate | Mean Time Between Failures | MTBF | Failure Mode Effective Analysis | FMEA

It is defined as the probability that a given system will perform it’s function adequately for it’s specified period of lifetime under specified operating conditions.

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Common measures are :

1. Failure rate.

2. Mean time between failures(MTBF)

3. Survival percentage.

Failure Rate:

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Rate which components of population fail.



Ns(t)- No. of components that survived during time ’t’

Nf(t) – No. of failures that occurred during the same time.

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Mean time between Failures(MTBF):

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The reciprocal of the failure rate(1/λ).


λ —-Failure rate.

Failure rate = (No.of failure )/(Time period during all components were exposed to failure)


Reliability Analysis:

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Failure Mode and Effect Analysis(FMEA)

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Purpose :

1. To recommend design changes.

2. To identify design weakness.

3. To help in choosing alternatives.

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Four Stages:

Ist Stage – System boundaries and the scope of the analysis is decided.

IInd Stage – Data Collection

Ex: Specification,Operating Procedure,Working Conditions.

IIIrd Stage– Preparing the component or parts list.

IVth Stage – Failure frequency and the functions of the part identified,causes of       failures,Failure detection.

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