Operation Principle - ABB ACS560 Hardware Manual

Operation principle

1. The Safe torque off activates (the activation switch is opened, or safety relay
contacts open).
2. The STO inputs of the drive control unit de-energize.
3. The control unit cuts off the control voltage from the output IGBTs.
4. The control program generates an indication as defined by parameter 31.22
(see the firmware manual of the drive).
The parameter selects which indications are given when one or both STO
signals are switched off or lost. The indications also depend on whether the
drive is running or stopped when this occurs.
Note: This parameter does not affect the operation of the STO function itself.
The STO function will operate regardless of the setting of this parameter: a
running drive will stop upon removal of one or both STO signals, and will not
start until both STO signals are restored and all faults reset.
Note: The loss of only one STO signal always generates a fault as it is
interpreted as a malfunction of STO hardware or wiring.
5. The motor coasts to a stop (if running). The drive cannot restart while the
activation switch or safety relay contacts are open. After the contacts close,
a reset may be needed (depending on the setting of parameter 31.22). A new
start command is required to start the drive.
The Safe torque off function 199