ROOTCASTLE / 工程實驗室
可靠性實驗室
MTBF、韋伯爾壽命與冗餘數學。
LOCAL CALCULATION · EDUCATIONAL MODEL
MTBF and availability
- Mission reliability R(t)
- 64.53 %
- Expected failures in mission
- 0.438
- Availability A
- 99.96 %
- Number of nines
- 3.4
- Expected downtime per year
- 3.5 h
- λ · FIT
- 5.00e-5 /h · 50,000
Model and assumptions
Constant failure rate (exponential distribution): R(t) = e^(−t/MTBF), λ = 1/MTBF. Inherent availability A = MTBF/(MTBF+MTTR); logistics and waiting time are not included. The probability of surviving to the MTBF is always 36.8 %: MTBF is not a guaranteed life.
R(t) = e^(−t/MTBF); A = MTBF / (MTBF + MTTR); downtime = (1 − A) · 8760 h
它是用於什麼
討論設備每年停機時間、冗餘單位的實際效益，或零件更換間隔起點時，可參考相同數據。此處展示 MTBF、韋伯分佈與冗餘計算及其公式；可更改假設，觀察結果的敏感度。
限制
製造商提供嘅 MTBF 數字通常係針對特定溫度同負載嘅預測；實際現場條件唔同會得出唔同結果。冗餘計算假設各部件獨立失效；共用電源、同一個軟件 Bug 或同一個維修失誤等共同原因會削弱實際效益。安全功能需要根據 IEC 61508 / ISO 13849 進行獨立評估。
參考文獻
IEC 61703:2016 (mathematical expressions for reliability, availability, maintainability) · IEC 61649:2008 (Weibull analysis) · P. D. T. O’Connor, A. Kleyner, 實用可靠性工程, 第5版 · NIST/SEMATECH e-Handbook, Assessing Product Reliability
教育模型。結果不足以診斷機器或確定安全運作極限。