ABB ACS560 Hardware Manual page 209

Term or Reference
abbreviation
MTTF D EN ISO 13849-1
PFD avg IEC 61508
PFH IEC 61508
PFH diag IEC/EN 62061
PL EN ISO 13849-1
Proof test IEC 61508, IEC
62061
SC IEC 61508
SFF IEC 61508
SIL IEC 61508
STO IEC/EN 61800-5-2
T 1 IEC 61508-6
T M EN ISO 13849-1
λ Diag_d IEC 61508-6
λ Diag_s IEC 61508-6
The Safe torque off function 209
Description
Mean time to dangerous failure: (Total number of life
units) / (Number of dangerous, undetected failures)
during a particular measurement interval under stated
conditions
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
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
Average frequency of dangerous failures per hour for the
diagnostic function of STO
Performance level. Levels a...e correspond to SIL
Periodic test performed to detect failures in a
safety-related system so that, if necessary, a repair can
restore the system to an "as new" condition or as close
as practical to this condition
Systematic capability (1...3)
Safe failure fraction (%)
Safety integrity level (1...3)
Safe torque off
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.
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.
Dangerous failure rate (per hour) of the diagnostics
function of STO
Safe failure rate (per hour) of the diagnostics function
of STO