Safe torque off function 143
Operation principle
1. The Safe torque off activates (the activation switch is opened, or safety relay contacts
open).
2. STO inputs on the drive control unit de-energize.
3. The control unit cuts off the control voltage from the drive IGBTs.
4. The control program generates an indication as defined by parameter 31.22 (refer to
the firmware manual of the drive).
5. Motor coasts to stop (if running). The drive cannot restart while the activation switch or
safety relay contacts are open. After the contacts close, a new start command is
required to start the drive.
Start-up including acceptance test
To ensure safe operation of the Safe torque off function, validation is required. The final
assembler of the machine must validate the function by performing an acceptance test.
The acceptance test must be performed:
• at initial start-up of the safety function
• after any changes related to the safety function (circuit boards, wiring, components,
settings, etc.)
• after any maintenance work related to the safety function.
Competence
The acceptance test of the safety function must be carried out by a competent person with
adequate expertise and knowledge of the safety function as well as functional safety, as
required by IEC 61508-1 clause 6. The test procedures and report must be documented
and signed by this person.
Acceptance test reports
Signed acceptance test reports must be stored in the logbook of the machine. The report
shall include documentation of start-up activities and test results, references to failure
reports and resolution of failures. Any new acceptance tests performed due to changes or
maintenance shall be logged into the logbook.
Acceptance test procedure
After wiring the Safe torque off function, validate its operation as follows. If the drive is
equipped with safety option +Q951, do the procedure shown in the documentation of the
option. If the drive is equipped with option +L537+Q971, do the procedure shown in the
CPTC-02 module documentation.
Action
WARNING! Follow the Safety instructions, page 13. Ignoring the instructions can cause
physical injury or death, or damage to the equipment.
Make sure that the drive can be run and stopped freely during start-up.
Stop the drive (if running), switch the input power off and isolate the drive from the power line by a
disconnector.
Check the Safe torque off (STO) circuit connections against the wiring diagram.
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