• 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 inverter 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 258).Use only ABB approved spare parts.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.Fault tracingThe indications given during the normal operation of the Safe torque off function are selectedby inverter control program parameter 31.22.The diagnostics of the Safe torque off function cross-compare the status of the two STOchannels. In case the channels are not in the same state, a fault reaction function isperformed and the inverter trips on an “STO hardware failure” fault. An attempt to use theSTO in a non-redundant manner, for example activating only one channel, will trigger thesame reaction.See the firmware manual of the inverter control program for the indications generated bythe inverter, and for details on directing fault and warning indications to an output on thecontrol unit for external diagnostics.Any failures of the Safe torque off function must be reported to ABB.Safety dataThe 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 channelsare not used.Life-time(a)CCFHFTCat.DC(%)MTTFD(a)PFDavg(T1 = 5a)PFDavg(T1 = 2a)PFH�(T1 =20 a)(1/h)SFF(%)PLSCSIL/SIL-CLFramesize208013≥90163301.3E-065.5E-076.2E-11>99e332×R8i208013≥90123901.6E-066.5E-077.3E-11>99e333×R8i208013≥9099801.9E-067.6E-078.4E-11>99e334×R8i208013≥9083602.1E-068.6E-079.5E-11>99e335×R8iThe Safe torque off function 261
