The Safe torque off function 351
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
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 diagram 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.
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