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150 Safe torque off function
Competence
The maintenance and proof test activities of the safety function must be carried out by a
competent person with adequate expertise and knowledge of the safety function as well as
functional safety, as required by IEC 61508-1 clause 6.
Fault tracing
The indications given during the normal operation of the Safe torque off function are
selected by drive parameter 31.22.
The diagnostics of the Safe torque off function cross-compare the status of the two STO
channels. In case the channels are not in the same state, a fault reaction function is
performed and the inverter trips on an "STO hardware failure" fault. An attempt to use the
STO in a non-redundant manner, for example activating only one channel, will trigger the
same reaction.
See the drive firmware manual for the indications generated by the drive, and for details on
directing fault and warning indications to an output on the control unit for external
diagnostics.
Any failures of the Safe torque off function must be reported to ABB.
Safety data
Preliminary safety data for the Safe torque off function is given below.
Note: The safety data is calculated for redundant use, and does not apply if both STO
channels are not used.
Frame
SIL/
SC
size
SILCL
U
= 380...480 V
1
R10, R11
3
3
* According to Table E1 EN/ISO 13849-1
•
The following temperature profile is used in safety value calculations:
•
670 on/off cycles per year with T = 71.66 °C
•
1340 on/off cycles per year with T = 61.66 °C
•
30 on/off cycles per year with T = 10.0 °C
•
32 °C board temperature at 2.0% of time
•
60 °C board temperature at 1.5% of time
•
85 °C board temperature at 2.3% of time
•
The safety data is calculated for redundant use, and does not apply if both channels
are not used.
•
The STO is a type A safety component as defined in IEC 61508-2.
•
Relevant failure modes:
•
The STO trips spuriously (safe failure)
•
The STO does not activate when requested
A fault exclusion on the failure mode "short circuit on printed circuit board" has been
made (EN 13849-2, table D.5). The analysis is based on an assumption that one
failure occurs at one time. No accumulated failures have been analyzed.
PFH
SFF
PFD
(T
= 20 a)
PL
1
(T
(%)
(1/h)
e
99.55
4.18E-09
3.66E-05 9.14E-05 15080
MTTF
PFD
D
avg
avg
= 2 a)
(T
= 5 a)
1
1
(a)
DC
Cat.
HFT
CCF
(%)
>90
3
1
80
3AXD00000586715
Lifetime
(a)
20
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