DescriptionTerm
Mean time to dangerous failure: (Total number of life units)
/ (Number of dangerous, undetected failures) during a partic-
ular measurement interval under stated conditions (EN ISO
13849-1)
MTTF
D
Average probability of dangerous failure on demand (IEC
61508)
PFD
avg
Average frequency of dangerous failures per hour (IEC
61508)
PFH
Performance level. Levels a...e correspond to SIL (EN ISO
13849-1)
PL
Safe acceleration rangeSAR
Safe brake controlSBC
Systematic capability (IEC 61508)SC
Safe failure fraction (%) (IEC 61508)SFF
Safety integrity level (1...3) (IEC 61508)SIL
Maximum SIL (level 1...3) that can be claimed for a safety
function or subsystem (IEC/EN 62061)
SILCL
Safe motor temperature (EN/IEC 61800-5-2)SMT
Safe stop 1 (IEC/EN 61800-5-2)SS1
Safe stop emergencySSE
Safe torque off (IEC/EN 61800-5-2)STO
There are three categories of stop functions:
• stop category 0: an uncontrolled stop where power to
the machine actuators is removed immediately (STO)
• stop category 1: a controlled stop where the machine
actuators have power for stopping, after which the power
is removed (SS1)
• stop category 2: a controlled stop where the machine
actuators continue to have power SS2).
Stop category
Proof test interval. Defines the probabilistic failure rate (PFH
or PFD
avg
) for the safety function or subsystem. Performing
a proof test at a maximum interval of T
1
is required to keep
the SIL capability valid. The same interval must be followed
to keep the PL capability (EN ISO 13849) valid. Note that
any T
1
values given cannot be regarded as a guarantee or
warranty.
T
1
Introduction to the manual 19
To Next Page
Loading...
