34
09/15 MN03407003Z-DE/EN
Average probability of a dangerous failure when the safety
function is on demand, using an interval of 36 months for
repeat test:
1st demand level
F
1/year (low demand mode):
PFD
avg
: 2.6 x 10
-3
h
The mean lifespan between two failures (MTBF) is 61 years.
For the safety-related parts of control systems as per
EN ISO 13849, the following data was determined at an
ambient temperature of 50 °C:
Size
Value
Category
1
Performance Level (PL)
1)
c
MTTF
d
after 3 years
2)
61 years
1) The performance level is the result of the risk assessment
based on the percentage of risk mitigation achieved with the
control system‘s safety-related parts.
2) MTTF
d
= Mean time to dangerous failure
