ABB ACS880-07 Hardware Manual page 250

250 Safe torque off function
Abbr. Reference
FIT IEC 61508
HFT IEC 61508
MTTF EN ISO 13849-1
d
PFD IEC 61508
avg
PFH IEC 61508
PL EN ISO 13849-1
SC IEC 61508
SFF IEC 61508
SIL IEC 61508
SILCL IEC/EN 62061
SS1 IEC/EN 61800-5-2
STO IEC/EN 61800-5-2
T1 IEC 61508-6
Description
Failure in time: 1E-9 hours
Hardware fault tolerance
Mean time to dangerous failure: (The total number of life units) / (the
number of dangerous, undetected failures) during a particular
measurement interval under stated conditions
Average probability of dangerous failure on demand
Average frequency of dangerous failures per hour
Performance level. Levels a...e correspond to SIL
Systematic capability
Safe failure fraction (%)
Safety integrity level (1...3)
Maximum SIL (level 1...3) that can be claimed for a safety function or
subsystem
Safe stop 1
Safe torque off
Proof test interval. T1 is a parameter used to define the probabilistic
failure rate (PFH or PFD) for the safety function or subsystem.
Performing a proof test at a maximum interval of T1 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 T1 values given
cannot be regarded as a guarantee or warranty.
See also section Maintenance (page 161).