1oo1 PFD
avg
Calculator
Formula:
PFD
avg
= ½ λ
DU
× TI
Dangerous undetected failure rate λ
DU
per hour
per year
per 1000 h (FIT×10
6
)
Test interval TI
years
months
weeks
days
hours
Include proof test coverage (C
PT
)
Proof test coverage C
PT
(0–1)
Lifetime LT
years
months
weeks
days
hours
PFD
avg
:
—
Also calculate STR (spurious trip rate)
Formula:
STR = λ
S
+ λ
DD
Safe failure rate λ
S
per hour
per year
per 1000 h (FIT×10
6
)
Dangerous detected failure rate λ
DD
per hour
per year
per 1000 h (FIT×10
6
)
STR:
—