reliability calculaions

8/9/2019 Reliability Calculaions

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Reliability Calculations

What, Why, When&

How do we benefit from them?

Electronic Components Consulting Services Inc.


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Who am I?

Harvey Altstadter 34 years experience in Component Engineering and Reliability

Military

Commercial Commercial Space

HR Electronic Components Consulting Services nc

Consultant to ndustry

!3" #$%&$%4'

Electronic Components Consulting Services Inc.


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What are Reliability Calculations? Methodology for analyzing the e!ected or actual

reliability of a !roduct, !rocess or ser"ice, and

identifying actions to reduce failures or mitigate theireffect#

$ %tress nalysis

$ Reliability 'redictions

$ (M) *(ailure Mode and )ffects nalysis+ or$ (M)C *(ailure Mode )ffects and Criticality nalysis+

ardstic- for com!arison of design a!!roaches

$ Cost./enefit 0rade


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()y *o Reliability Calculations+ Ma-e the !roduct more reliable$ %elling feature

$ Reduce returns

$ 1ower costs

$ )nhance or maintain com!any re!utation

$ Com!arisons with com!etition

Customer re2uest$ 3esign goal$ Hard Re2uirement


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%tress nalysis

Establis)es t)e presence o, a sa,ety margin$ 4ood engineering !ractice

$ )nhances system life$ 'ro"ides in!ut data for Reliability 'rediction

3escribes o!erating condition as a !ercentage of rating

$ Customer re2uirement

$ 5alidates com!liance with 3erating Criteria


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Reliability 'redictions *M0/(+

If you don6t li-e the numbers###

###gi"e me fi"e minutes, I will ma-e u! a better one


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Reliability 'redictions *M0/(+ -orm t)e basis o, Reliability Analyses

Compute predicted system ,ailure rate or

Mean .ime /et0een -ailures -ailure Rate is usually expressed in -ailures per "1!or "1#)ours

M./- is usually expressed in terms o, )ours

Example2 ,or a system 0it) a predicted M./- o, "111 )ours on average t)esystem experiences one ,ailure in "111 )ours o, operation or a -ailure Rate o,

"111 per "1!)ours

Met)odology se accepted standards

Model ,ailure rates o, components Analy5e system

Calculate t)e system predicted ,ailure rate or M./-

Evaluate prediction vs target or re6uired M./-

Evaluate stress or temperature reduction design c)anges

Evaluate practicality o, design c)ange especially 0)en M./- is sel, imposed


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Reliability 7redictions 8Continued9 Common Standards

M:&H*/;&$"'


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4eneral a!!roach to 'rediction Model ,or a single part consists o, a number o, ,actors multiplied toget)er

ss 7 4 8 98 % 8 0

ss 7 %teady %tate (ailure rate

4 7 4eneric or /ase (ailure Rate

9 7 9uality (actor

% 7 %tress (actor

0 7 0em!erature (actor

$ :ther factors; (irst ear Multi!lier or )!erience (actor

Model ,or a unit

Consists o, t)e sum o, all o, t)e individual part ,ailure rates multiplied by an

Environmental -actor )

Source o, -actor n,ormation& varies 0it) met)od used

:oo?up table

Calculation based upon complexity

Reliability 7redictions 8Continued9


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Reliability 7redictions

0he first cut is made with little analysis to get a

rough idea where the design is relati"e to the

desired outcome

/etter numbers come from better insight into

the design

(actors to be considered include 3uty Cycle

and refined 0hermal and %tress nalyses


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(M) or (M)C Design FMEA

-MEA is a bottoms up met)od o, analy5ing and improving a design

Heavily used by S automotive industry

C)rysler -ord


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-MEA or -MECA 8Continued9

Process FMEA

Similar to a *esign -MEA but is applied to a manu,acturing process

or serviceB .)e obDect is to use t)is met)odology to optimi5e

processesB

FMECA

A -MECA is similar to a -MEA

Criticality is computed in place o, R7= B

-MECAs are used extensively in military aerospace and medical

e6uipment ,ields ,or bot) design and process reliability analysisB

M:&H*/;&"!$# is a 0idely accepted standard ,or -MECAsB


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Ho0 do 0e bene,it ,rom t)em+


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(amous(lubs /R0 */ay rea Ra!id 0ransit+

$ (M) not !erformed or inade2uate

:scillator Crystal (ailure. :!en# :scillator (re2uency went u!

$ 0rain s!eed increased ra!idly

$ 0rain o"ershot last sto!

$ 0rain rammed barrier at high s!eed

$ 5ery serious accident

/rowns (erry


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Reliability Calculations

%ummary

$ What; nalysis 0ool-it

$ Why; 'roduct Im!ro"ement Reduced Cost$ When; )arly for 3esign (eedbac-

'rior to Com!letion to 5alidate 4oals

$ /enefit;Reduced (ield (ailures

Reduced Warranty Costs /etter CustomerRelations

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