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Safe torque off (STO)
￭
The drive has a Safe torque off (STO) function in accordance with IEC/EN 61800-5-2.
It can be used, for example, as the final actuator device of safety circuits that stop
the drive in case of danger (such as an emergency stop circuit).
When activated, the STO function disables the control voltage of the power
semiconductors of the drive output stage, thus preventing the drive from generating
the torque required to rotate the motor. The control program generates an indication
as defined by parameter 31.22. If the motor is running when STO is activated, it coasts
to a stop. Closing the activation switch deactivates STO. Any faults generated must
be reset before restarting.
The STO function has a redundant architecture, that is, both channels must be used
in the safety function implementation. The safety data given is calculated for redundant
use, and does not apply if both channels are not used.
The Safe torque off function does not disconnect the voltage of the main and
auxiliary circuits from the drive. Therefore maintenance work on electrical parts
of the drive or the motor can only be carried out after isolating the drive from
the main supply.
Note:
•
If stopping by coasting is not acceptable, stop the drive and machinery using the
appropriate stop mode before activating STO.
•
The STO function overrides all other functions of the drive.
Wiring
The safety contacts must open/close within 200 ms of each other.
Double-shielded twisted-pair cable is recommended for the connection. The maximum
length of the cabling between the switch and the drive control unit is 300 m (1000 ft).
Ground the shield of the cable at the control unit only.
Validation
To ensure the safe operation of a safety function, a validation test is required. The
test must be carried out by a competent person with adequate expertise and
knowledge of the safety function. The test procedures and report must be documented
and signed by this person. Validation instructions of the STO function can be found
in the drive hardware manual.
Technical data
•
The voltage at the STO input terminals of the drive must be at least 13 V DC to be
interpreted as "1"
•
STO reaction time (shortest detectable break): 1 ms
•
STO response time: 2 ms (typical), 30 ms (maximum)
•
Fault detection time: Channels in different states for longer than 200 ms
•
Fault reaction time: Fault detection time + 10 ms.
•
STO fault indication (parameter 31.22) delay: < 500 ms
•
STO warning indication (parameter 31.22) delay: < 1000 ms.
EN – Quick installation and start-up instructions 19
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