Operation principle
1. The Safe torque off activates (the activation switch is opened, or safety relay contacts
open).
2. The STO inputs of the inverter 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 (refer to
the firmware manual of the inverter).
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 inverter 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 inverter 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 inverter.
The Safe torque off function 321
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