430 Appendix: Safe torque off (STO)
Abbreviations
Declaration of conformity
Declaration of conformity (3AXD10000414701) is available on the Internet. See
section Document library on the Internet on the inside of the back cover.
Certificate
TÜV certificate (3AXD00000600767) is available on the Internet. See section
Document library on the Internet on the inside of the back cover.
Abbreviation Reference Description
CCF EN ISO 13849-1 Common cause failure (%)
DC EN ISO 13849-1 Diagnostic coverage
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 EN 62061 Maximum SIL (level 1…3) that can be claimed for a safety
function or subsystem
STO IEC/EN 61800-5-2 Safe torque off
T1 IEC 61508 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 425).
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