Hardware Manual

Safe Torque off function 241
 Abbreviations
Abbr. Reference Description
Cat. EN ISO 13849-1 Classification of the safety-related parts of a control system in
respect of their resistance to faults and their subsequent
behavior in the fault condition, and which is achieved by the
structural arrangement of the parts, fault detection and/or by
their reliability. The categories are: B, 1, 2, 3 and 4.
CCF EN ISO 13849-1 Common cause failure (%)
DC EN ISO 13849-1 Diagnostic coverage
FIT IEC 61508 Failure in time: 1E-9 hours
HFT IEC 61508 Hardware fault tolerance
MTTF
d
EN ISO 13849-1 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
PFD IEC 61508 Probability of failure on demand
PFH IEC 61508 Probability of dangerous failures per hour
PL EN ISO 13849-1 Performance level. Levels a…e correspond to SIL
SC IEC 61508 Systematic capability
SFF IEC 61508 Safe failure fraction (%)
SIL IEC 61508 Safety integrity level (1…3)
SILCL IEC/EN 62061 Maximum SIL (level 1…3) that can be claimed for a safety
function or subsystem
SS1 IEC/EN 61800-5-2 Safe stop 1
STO IEC/EN 61800-5-2 Safe torque off
T1 IEC 61508-6 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 on page 238.