ABB ACS880-34, Hardware Manual

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Safe torque off function 217
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Safe torque off function
Contents of this chapter
This chapter 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 (such as an emergency stop circuit). 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.
When activated, the Safe torque off function disables the control voltage of the power
semiconductors of the drive output stage (A, see diagram below), 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.