Safe torque off function 145
number of pole pairs.
Notes:
• If a running drive is stopped by using the Safe torque off function, the drive will cut off
the motor supply voltage and the motor will coast to a stop. If this causes danger or is
not otherwise acceptable, stop the drive and machinery using the appropriate stop
mode before activating the Safe torque off function.
• The Safe torque off function overrides all other functions of the drive.
• The Safe torque off function is ineffective against deliberate sabotage or misuse.
• The Safe torque off function has been designed to reduce the recognized hazardous
conditions. In spite of this, it is not always possible to eliminate all potential hazards.
The assembler of the machine must inform the final user about the residual risks.
Maintenance
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 2 years. The test procedure is given in section
Acceptance test procedure (page 143).
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 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 143.
Use only ABB approved spare parts.
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.
Fault tracing
The indications given during the normal operation of the Safe torque off function are
selected by drive parameter 31.22.
The diagnostics of the Safe torque off function cross-compare the status of the two STO
channels. In case the channels are not in the same state, a fault reaction function is
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