Safe torque off function 143Operation principle1. The Safe torque off activates (the activation switch is opened, or safety relay contactsopen).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 tothe firmware manual of the drive).5. Motor coasts to stop (if running). The drive cannot restart while the activation switch orsafety relay contacts are open. After the contacts close, a new start command isrequired to start the drive.Start-up including acceptance testTo ensure safe operation of the Safe torque off function, validation is required. The finalassembler 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. CompetenceThe acceptance test of the safety function must be carried out by a competent person withadequate expertise and knowledge of the safety function as well as functional safety, asrequired by IEC 61508-1 clause 6. The test procedures and report must be documentedand signed by this person. Acceptance test reportsSigned acceptance test reports must be stored in the logbook of the machine. The reportshall include documentation of start-up activities and test results, references to failurereports and resolution of failures. Any new acceptance tests performed due to changes ormaintenance shall be logged into the logbook. Acceptance test procedureAfter wiring the Safe torque off function, validate its operation as follows. If the drive isequipped with safety option +Q951, do the procedure shown in the documentation of theoption. If the drive is equipped with option +L537+Q971, do the procedure shown in theCPTC-02 module documentation.ActionWARNING! Follow the Safety instructions, page 13. Ignoring the instructions can causephysical 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 adisconnector.Check the Safe torque off (STO) circuit connections against the wiring diagram.
