ABB ACS380 Series, Hardware Manual

Page: 139 / 186

Safe torque off function 139
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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, as the final actuator device of
safety circuits that stop the inverter in case of danger (such as an emergency stop
circuit). 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 inverter.
Note : The Safe torque off function does not disconnect the voltage from the drive,
see the warning on page 146 .
When activated, the Safe torque off function disables the control voltage of the power
semiconductors of the drive output stage (A, see diagram on page
142 ), 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.