ABB ACS255 User Manual page 26

5.10.8. Enabling the "STO" Function
The "STO" function is always enabled in the drive regardless of operating mode or parameter changes made by the user
5.10.9. Testing the "STO" Function
Before commissioning the system the "STO" function should always be tested for correct operation, this should include the following tests:

With the motor at standstill, and a stop command given to the drive (as per the start source method selected in parameter 9902
DIGITAL INPUTS FUNCTION SELECT):
o
De-energise the "STO" inputs (Drive will display ""InHibit").
o
Give a start command (as per the start source method selected in parameter 9902 DIGITAL INPUTS FUNCTION SELECT) and
check that the drive still displays "Inhibit" and that the operation is in line with the section 5.10.4 "STO" Operation and
section 5.10.5 "STO" Status and Monitoring

With the motor running normally (from the drive):
o
De-energise the "STO" inputs
o
Check that the drive displays "InHibit" and that the motor stops and that the operation is in line with the section 5.10.4
"STO" Operation and section 5.10.5 "STO" Status and Monitoring
5.10.10. "STO" Function Maintenance.
The "STO" function should be included within the control systems scheduled maintenance program so that the function is regularly tested for
integrity (Minimum once per Year), furthermore the function should be integrity tested following any safety system modifications or
maintenance work.
If drive fault messages are observed refer to section 13.1 for further guidance.
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