Hardware Manual

Safe Torque off function 235
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. Setting of
the control program parameters is not needed. If an FSO-xx safety functions module
(option +Q973) is installed, do the procedure shown in the FSO module