ABB ACS880-04F, Hardware Manual, Page: 153 / 172

Safe torque off function 153
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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.
The Safe torque off function of the drive complies with these standards:
Standard Name
EN 60204-1:2006 + AC:2010 Safety of machinery – Electrical equipment of machines – Part 1: General
requirements
IEC 61326-3-1:2008 Electrical equipment for measurement, control and laboratory use – EMC
requirements – Part 3-1: Immunity requirements for safety-related
systems and for equipment intended to perform safety-related functions
(functional safety) – General industrial applications