14
Safe torque off (STO)
The drive has a Safe torque off function (STO) 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 Safe torque off is activated, it coasts to a stop. Closing the
activation switch deactivates the 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 in this manual is calculated for redundant use, and does not apply if both channels are not used.
WARNING!
The STO function does not disconnect the voltage from the main and auxiliary circuits of the drive.
Notes:
•
If stopping by coasting is not acceptable, stop the drive and machinery using the appropriate stop mode before
activating the 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
•
Minimum voltage at IN1 and IN2 to be interpreted as “1”: 13 V DC
•
STO reaction time (shortest detectable break): 1 ms
•
STO response time: Frames R3 and R6: 2
ms (typical), 10
ms (maximum) Frame R8: 2
ms (typical), 15
ms (maximum)
•
Fault detection time: Channels in different states for longer than 200ms
•
Fault reaction time: Fault detection time + 10ms
•
STO fault indication (parameter
31.22
) delay: < 500 ms
•
STO warning indication (parameter
31.22
) delay: < 1000 ms
•
Safety integrity level (EN 62061): SIL 3
•
Performance level (EN ISO 13849-1): PL e
The drive STO is a type A safety component as defined in IEC 61508-2.
For the full safety data, exact failure rates and failure modes of the STO function, refer to the drive hardware manual.
