ABB ACS355 series, User Manual

Page: 417 / 436

Appendix: Safe torque off (STO) 417
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Appendix: Safe torque off
(STO)
What this appendix contains
The appendix describes the Safe torque off (STO) function of the drive and gives
instructions for its use.
Description
The Safe torque off function can be used, for example, to construct safety or
supervision circuits that stop the drive in case of danger. Another possible application
is a prevention of unexpected start-up switch that enables short-time maintenance
operations like cleaning or work on non-electrical parts of the machinery without
switching off the power supply to the drive.
Note: The Safe torque off function does not disconnect the voltage from the drive,
see the warning on page 424 .
When activated, the Safe torque off function disables the control voltage of the power
semiconductors of the drive output stage (A, see diagrams on page
419 ), thus
preventing the drive from generating the torque required to rotate the motor. If the
motor is running when Safe torque off is activated, it coasts to a stop.
The Safe torque off function has a redundant architecture, that is, both channels must
be used in the safety function implementation. The safety data given in this manual is
calculated for redundant use, and does not apply if both channels are not used.