The Safe torque off function
Contents of this chapter
This chapter describes the Safe torque off (STO) function of the inverter and gives instructions
for its use.
Description
WARNING!
In case of parallel-connected drives or dual-winding motors, the STO must be
activated on each drive to remove the torque from the motor.
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.
When activated, the Safe torque off function disables the control voltage of the power
semiconductors of the inverter output stage (A, see the diagrams below), thus preventing
the inverter 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.
The Safe torque off function complies with these standards:
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The Safe torque off function 183
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