BECKHOFF TwinSAFE - Manual (Page 8)

Foreword
6 Application Guide TwinSAFE
1.2.3 Description of safety symbols
The following safety symbols are used in these operating instructions. They are intended to alert the
reader to the associated safety instructions.
DANGER
Serious risk of injury!
Failure to follow the safety instructions associated with this symbol directly endangers
the life and health of persons.
WARNING
Caution – Risk of injury!
Failure to follow the safety instructions associated with this symbol endangers the life
and health of persons.
CAUTION
Personal injuries!
Failure to follow the safety instructions associated with this symbol can lead to injuries
to persons.
Attention
Damage to the environment or devices
Failure to follow the instructions associated with this symbol can lead to damage to the
environment or equipment.
Notice
Tip or pointer
This symbol indicates information that contributes to better understanding.
1.2.4 Explanation of terms
Designation Explanation
B10
d
Mean number of cycles after 10% of the components have dangerously
failed
CCF Common Cause Failure
d
op
Mean operating time in days per year
DC
avg
Average diagnostic coverage
h
op
Mean operating time in hours per day
MTTF
d
Mean Time To dangerous Failure
n
op
Mean number of annual actuations
PFH Probability of a dangerous failure per hour
PL Performance Level
PL
r
Required Performance Level
T
cycle
Mean time between two successive cycles of the system (given in
minutes in the following examples, but can also be given in seconds)