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182 The Safe torque off function
Maintenance
After the operation of the circuit is validated at start-up, the STO function shall be
maintained by periodic proof testing. In high demand mode of operation, the maximum
proof test interval is 20 years. In low demand mode of operation, the maximum proof
test interval is 10 years; see section
There are two alternative procedures for proof testing:
1.
Perfect proof testing. It is assumed that all dangerous failures of the STO circuit
are detected during the test. PFD
procedure are given in the safety data section.
2.
Simplified proof testing. This procedure is faster and simpler than perfect proof
testing. Not all dangerous failures of the STO circuit are detected during the test.
The PFD
value for STO with the simplified proof testing procedure is given in
avg
the safety data section.
Note: The proof testing procedures are only valid for proof testing (periodic test, item
5 under section
Start-up including validation
changes made in the circuit. Re-validation (items 1...4 under
validation
test) must be done according to the initial validation procedure.
Note: See also the Recommendation of Use CNB/M/11.050 (published by the European
co-ordination of Notified Bodies) concerning dual-channel safety-related systems
with electromechanical outputs:
•
When the safety integrity requirement for the safety function is SIL 3 or PL e (cat.
3 or 4), the proof test for the function must be performed at least every month.
•
When the safety integrity requirement for the safety function is SIL 2 (HFT = 1) or
PL d (cat. 3), the proof test for the function must be performed at least every 12
months.
The STO function of the drive does not contain any electromechanical components.
In addition to proof testing, it is a good practice to check the operation of the function
when other maintenance procedures are carried out on the machinery.
Include the Safe torque off operation test described above in the routine maintenance
program of the machinery that the drive runs.
If any wiring or component change is needed after start-up, or the parameters are
restored, do the test given in section
Use only spare parts approved by ABB.
Record all maintenance and proof test activities in the machine logbook.
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.
Safety data (page
185).
values for STO with the perfect proof testing
avg
test) but not for re-validation after
Validation test procedure (page
Start-up including
179).
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