Operation principle
1. The Safe torque off activates (the activation switch is opened, or safety relay contacts
open).
2. The STO inputs on the inverter control unit de-energize.
3. The control unit cuts off the control voltage from the inverter IGBTs.
4.
The control program generates an indication as defined by parameter 31.22 (refer to
the firmware manual of the inverter).
5. 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 new start command is
required to start the drive.
Start-up including acceptance test
To ensure the safe operation of a safety 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.
Note:
If the drive is equipped with safety option +Q951, do the procedure shown in the
documentation of the option.
Note:
All inverter modules of the inverter unit must be powered and connected to the STO circuit
during the acceptance test.
Action
WARNING!
Follow the safety instructions given in Safety instructions. Ignoring the instructions can cause
physical injury or death, or damage to the equipment.
196 The Safe torque off function
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