Cheetsheet

Probability Logic Table

VotingFormulaComment
1oo1PASingle element system
1oo2PAPBBoth devices fail
2oo2PA + PB – PAPBEither device fails
1oo3PAPBPCAll devices must fail
2oo3PAPB + PAPC + PBPC – 2PAPBPCAny two devices must fail
3oo3PA + PB + PC – PAPB – PAPC – PBPC + PAPBPCAny device fails

PFD Equations

PFD equations (not simplified) assuming all devices in the voting scheme have the same lambda:

VotingPFDPFD Avg
1oo11−e−λt1 - e^{-\lambda t}1+e−λT−1λT1 + \frac{e^{-\lambda T}-1}{\lambda T}
1oo21−2e−λt+e−2λt1 - 2e^{-\lambda t} + e^{-2\lambda t}1+2e−λT−2λT+1−e−2λT2λT1 + \frac{2e^{-\lambda T}-2}{\lambda T} + \frac{1-e^{-2\lambda T}}{2\lambda T}
2oo21−e−2λt1 - e^{-2\lambda t}1+e−2λT−12λT1 + \frac{e^{-2\lambda T}-1}{2\lambda T}
1oo31−3e−λt+3e−2λt−e−3λt1 - 3 e^{- \lambda t} + 3 e^{- 2 \lambda t} - e^{- 3 \lambda t}1−116λT+3e−λTλT−3e−2λT2λT+e−3λT3λT1 - \frac{11}{6 \lambda T} + \frac{3 e^{- \lambda T}}{\lambda T} - \frac{3 e^{- 2 \lambda T}}{2 \lambda T} + \frac{e^{- 3 \lambda T}}{3 \lambda T}
2oo31−3e−2λt+2e−3λt1 - 3 e^{- 2 \lambda t} + 2 e^{- 3 \lambda t}1−56λT+3e−2λT2λT−2e−3λT3λT1 - \frac{5}{6 \lambda T} + \frac{3 e^{- 2 \lambda T}}{2 \lambda T} - \frac{2 e^{- 3 \lambda T}}{3 \lambda T}
3oo31−e−3λt1 - e^{- 3 \lambda t}1−13λT+e−3λT3λT1 - \frac{1}{3 \lambda T} + \frac{e^{- 3 \lambda T}}{3 \lambda T}

© 2022. All rights reserved.