•
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 particular 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. Per-
forming 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.
See also section Maintenance (page 198).
IEC 61508-6T
1
The Safe torque off function 201
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