ABB ACS180-04S-03A7-1, Hardware Manual, Page: 161 / 192

The 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, as the final actuator device
of safety circuits (such as an emergency stop circuit) that stop the drive in case
of danger. Another typical application is a prevention of unexpected start-up
function 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 for the
power semiconductors of the drive output stage, 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.
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The Safe torque off function 161