Requirements for operation of the STO safety subfunction

  • Operation is only permitted within the limits specified on the data sheets.
  • The built-in diagnostic function is limited in the case of a permanently enabled or permanently disabled STO safety subfunction. Advanced diagnostic functions are only performed when the status of the STO safety subfunction changes. This is why the safety subfunction must be triggered with connected line voltage at least once every 12 months for PL d according to EN ISO 13849-1 and SIL 2 according to EN 61800‑5‑2 to achieve complete test coverage. Adhere to the following test procedure for this purpose.

  • [1]

    Maximum 12 months for PL d/SIL 2

    [2]

    Internal diagnostics

    [3]

    High: No STO

    [4]

    Low: STO active

  • To achieve complete test coverage after a device reset (e.g. after switching on the supply voltage), the test transition (STO active → STO not active) may be started after > 700 ms at the earliest. The device signals the "ready for operation" or "STO – Safe Torque Off" state if it is not in fault state.
  • A detected hardware fault in the internal switch-off channels for STO will lead to a locking fault state in the device. If the fault is reset (e.g. by switching the supply voltage on/off or by activating the STO safety subfunction for at least 30 ms), a complete test with internal diagnostics in accordance with the above-mentioned test procedure must be performed subsequently. If the error occurs again, replace the device or contact SEW‑EURODRIVE Service.