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 Safety data (page 235). It is assumed that all
dangerous failures of the STO circuit are detected by the proof test. To perform the
proof test, do the Validation test procedure (page 229).
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 Validation test procedure (page 229).
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.
The Safe torque off function 233
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