The Safe torque off function 151
STO function maintenance
After the operation of the circuit is validated at start-up, the STO function shall be
maintained by periodic proof testing as per the following maintenance intervals:
See also STO acceptance test procedure on page 148.
Note: See also the Recommendation of CNB/M/11.050 (published by the European
co-ordination of Notified Bodies) concerning dual-channel safety-related systems with
electromechanical outputs. The proof test for the function must be performed at the
following intervals, based on the safety integrity requirement:
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, follow the STO acceptance test procedure on page 148. Record all
maintenance and proof test activities in the machine logbook.
Note: Use only ABB approved spare parts.
Competency for STO operations
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.
Mode of operation Defined maintenance intervals
High demand maximum 20 years
Low demand maximum 2 years
Safety integrity Defined maintenance intervals
SIL 3 or PL e (cat. 3 or 4) at least every month
SIL 2 (HFT = 1) or PL d (cat. 3) at least every 12 months
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