•
STO fault indication (parameter 31.22) delay: < 500 ms
•
STO warning indication (parameter 31.22) delay: < 1000 ms
￭ Abbreviations
DescriptionReferenceAbbr.
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.
EN ISO 13849-1Cat.
Common cause failure (%)EN ISO 13849-1CCF
Diagnostic coverageEN ISO 13849-1DC
Hardware fault toleranceIEC 61508HFT
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 13849-1MTTF
D
Average probability of dangerous failure on demand, that is,
mean unavailability of a safety-related system to perform the
specified safety function when a demand occurs
IEC 61508PFD
avg
Average frequency of dangerous failures per hour, that is,
average frequency of a dangerous failure of a safety related
system to perform the specified safety function over a given
period of time
IEC 61508PFH
Performance level. Levels a…e correspond to SILEN ISO 13849-1PL
Systematic capabilityIEC 61508SC
Safe failure fraction (%)IEC 61508SFF
Safety integrity level (1…3)IEC 61508SIL
Maximum SIL (level 1…3) that can be claimed for a safety
function or subsystem
IEC/EN 62061SILCL
Safe torque offIEC/EN 61800-5-2STO
Proof test interval. T
1
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 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.
IEC 61508-6T
1
See also section Maintenance.
196 The Safe torque off function
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