MaintenanceAfter the operation of the circuit is validated at start-up, the STO function shall be maintainedby periodic proof testing. In high demand mode of operation, the maximum proof test intervalis 20 years. In low demand mode of operation, the maximum proof test interval is 5 or 2years; see section Safety data (page 196). It is assumed that all dangerous failures of theSTO circuit are detected by the proof test. To perform the proof test, do the Acceptance testprocedure (page 191).Note:See also the Recommendation of Use CNB/M/11.050 (published by the Europeanco-ordination of Notified Bodies) concerning dual-channel safety-related systems withelectromechanical outputs:• When the safety integrity requirement for the safety function is SIL 3 or PL e (cat. 3 or4), 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 whenother maintenance procedures are carried out on the machinery.Include the Safe torque off operation test described above in the routine maintenanceprogram 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 test given in section Acceptance test procedure (page 191).Use only spare parts approved by ABB.Record all maintenance and proof test activities in the machine logbook.￭ CompetenceThe maintenance and proof test activities of the safety function must be carried out by acompetent person with adequate expertise and knowledge of the safety function as well asfunctional safety, as required by IEC 61508-1 clause 6.194 The Safe torque off function
