DescriptionReferenceAbbr.
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.
IEC 61508-6T
1
See also section Maintenance.
Mission time: the period of time covering the intended use of the safety
function/device. After the mission time elapses, the safety device must
be replaced. Note that any T
M
values given cannot be regarded as a
guarantee or warranty.
EN ISO 13849-1T
M
￭ TÜV certificate
The TÜV certificate is available on the Internet at www.abb.com/drives/documents.
The Safe torque off function 225
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