3.6.29 · D1FMEA — failure mode, effect, severity, detection, RPN
FMEA us dhundli chinta ko — "kuch toot sakta hai" — har part ke liye ek single number mein badal deta hai, taaki engineers hazaron possible failures ko rank kar sakein aur pehle sabse bure ko fix kar sakein. Woh number teen seedhe sawaalon se banta hai — kitna bura? kitna likely? hum kitne andhre mein hain? — inhe aapas mein multiply karo.
Parent note FMEA — failure mode, effect, severity, detection, RPN padhne se pehle, tumhe usmein aane wala har word aur symbol khud se clear hona chahiye. Yeh page unhe ek-ek karke banata hai, kuch nahi se, har ek usse pehle wale par tikaa hua.
Rocket ki picture bhool jao. Risk work ke liye ek spacecraft sirf boxes ka ek stack hai jisme har box ek kaam karta hai , aur woh boxes ek doosre se wired hain. Agar ek box garbad kare, toh uske padosi usse feel karte hain. Yeh idea ki "feeling wiring se phailti hai" — yahi poora reason hai ki FMEA exist karta hai.
Definition System, Subsystem, Component
Component — sabse chhota part jo tum name karte ho aur jiske baare mein chinta karte ho (ek battery cell, ek bearing, ek line of code ka allocator). Picture: ek chhota akela box.Subsystem — components ka ek group jo ek function karta hai (puri battery, poora attitude-control unit). Picture: ek bada box jo chhote boxes ko rakhta hai.System — poora spacecraft. Picture: sabse bada box.
Yeh layers kyun? Kyunki ek tiny box ka fail hona ek bade box ko push kar sakta hai, jo sabse bade box ko push karta hai. FMEA ko yeh ladder chahiye taaki woh consequences ko upar trace kar sake .
Ek component sirf "fail" nahi hota; woh ek specific tarike se fail hota hai. Ek battery cell short ho sakta hai, leak ho sakta hai, ya open-circuit ho sakta hai — usi part ke teen alag failure modes hain.
Failure Mode = ek specific tarika jisme ek component apna kaam karna band kar deta hai.
Picture: ek akele box mein kai labelled "exit doors" hain, ek door har tootne ke tarike ke liye.
Intuition Sirf "yeh toot gaya" kyun nahi bolte?Kyunki fix is baat par depend karta hai ki woh kaun se door se gaya. Ek cell jo short karta hai use fuse chahiye; ek cell jo leak karta hai use seal chahiye. "Yeh toot gaya" tumhe design ke liye kuch nahi batata. Failure mode woh actionable unit hai.
Jab ek component kisi exit door se guzarta hai, toh takleef Section 0 ki ladder par upar jaati hai.
Effect = ek failure mode ka consequence, ladder ke har level par describe kiya gaya:
Local — component par khud kya hota hai.Subsystem — usse rakhne wala box kya notice karta hai.System — poora spacecraft kya karta hai.Mission — ground par baithe insaan kya kho dete hain.
Picture: ek arrow nested boxes par chadhta hua, upar jaate jaate aur dar lagaata hua.
Dekho ki wahi event neeche "minor" hai aur upar "fatal" hai. Yahi exact reason hai ki hum upar trace karte hain aur local level par kabhi nahi rukते.
Failures ko rank karne ke liye hum unhe measure karein. "Bura" jaisi words sort nahi ho sakti; numbers ho sakti hain. FMEA teen alag qualities ke liye 1-se-10 integer scale use karta hai.
Intuition 1 se 10 kyun, aur integers kyun?Ek chhota, jaana-pehchaana range jo ek insaan judgement se assign kar sake. Yeh jaanbujh kar coarse aur roughly logarithmic hai — 9 se 10 ka jump ek poori category change lagta hai (mission-lost → crew-lost), na ki chhota sa +1. Hum chahte hain ki scale aise match kare jaise insaan badhte khatre ko perceive karta hai.
S S 1 ≤ S ≤ 10 effect kitna damaging hai yeh batata hai.
S = 1 S = 10 Picture: consequence ka thermometer — cool = harmless, laal-garam = catastrophic.
O O 1 ≤ O ≤ 10 likely hai.
O = 1 O = 10 Picture: dicon ka ek stack — thode dice = rare, bahut dice = tum ise zaroor roll karoge.
Yeh wala sneaky hai. D kitna detect karne mein fail karte ho.
D D 1 ≤ D ≤ 10 failure ko time par pakadna kitna mushkil hai .
D = 1 D = 10 Picture: ek fog dial — clear = hum ise aate dekh rahe hain, ghana fog = yeh bina warning ke lagta hai.
Common mistake Detection scale "ulta" chalta haiLow D accha hai (hum pakad lete hain), high D bura hai (andhre mein hain).
Yeh beginners ko trip karta hai kyunki S O D matlab "detection" word se ulta hai. D andherapan " (blindness) padhein.
Ab har failure ke liye teen seedhe numbers hain. Hum inhe ek mein fold karte hain taaki sort kar sakein.
Intuition Multiply kyun karo, add kyun nahi?Multiplication factors ko saath mein kaam karne deta hai. Agar koi ek factor tiny ho (maano O = 1 poore product ko neeche kheench leta hai — ek rare failure low priority rehti hai chahe woh severe ho. Addition yeh nahi kar sakti: 10 + 10 + 1 = 21 10 × 10 × 1 = 100 "ek chain utni hi dangerous hai jitna uske factors hone dein — ek safe factor product ko bachaa leta hai."
S everity, O ccurrence, D etection — zor se bolo: "Kitna S ad, kitni baar O ccur, kitna D ark."
108 karna hai. FMEA RPN bands ko actions se map karta hai.
RPN band
Matlab
Action
< 50 trivial
sirf monitor karo
50 – 150 notable
design review, test, decide
150 – 500 serious
redesign karo ya redundancy add karo
> 500 unacceptable
flight se pehle fix karna zaroori
Intuition Fix karne ke baad re-score kyun?Ek fix (ek fuse, ek spare wheel, ek naya sensor) S , O , D living document hai: fix karo → recompute karo → naya band check karo. Tum literally danger number ko girte hue dekh rahe ho.
Thresholds and mitigation
Har foundation exactly agla feed karta hai: tum Severity (S
Yeh foundations wider vault mein plug hote hain:
Risk Management in Spacecraft Design — FMEA iske andar ek tool hai.Reliability Engineering — Occurrence ke peeche failure-rate data supply karta hai.Redundancy and Fault Tolerance — Severity kam karne ka classic tarika.Quality Assurance and Testing — Detection scores feed karta hai.Systems Engineering V-Model — lifecycle mein FMEA kahan hota hai.Mission Assurance — woh umbrella jo FMEA demand karta hai.Mars Climate Orbiter — woh failure mode jise kisine likha hi nahi.
Answer cover karo aur parent note kholne se pehle khud test karo.
A component is... sabse chhota named part jiske baare mein tum chinta karte ho (ek cell, ek bearing, ek allocator).
A failure mode is... ek specific tarika jisme woh component toot sakta hai — uska "exit door".
An effect is... ek failure mode ka consequence, local, subsystem, system, aur mission levels par padhaa gaya.
Severity S effect kitna bura hai, 1 10
Occurrence O mission mein failure kitna likely hai, 1 10
Detection D failure pakadna kitna mushkil hai (blindness), 1 10
The RPN formula is... RPN = S × O × D 1 1000
Why multiply instead of add? taaki ek safe factor (jaise O = 1
What does D = 10 bura — disaster aane tak bilkul detect nahi hota.
After a mitigation you must... S , O , D