Requirements for the operation of the STO safety subfunction

  • Operation is only permitted within the limits specified on the data sheets. This applies to an external safety controller, an external safety relay, as well as to the device and the approved safety options.
  • 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. The safety subfunction must therefore be requested for PL d as per EN ISO 13849-1 and SIL 2 in accordance with EN 61800-5-2 at least once every 12 months and for PL e as per EN ISO 13849-1 and SIL 3 in accordance with EN 61800-5-2 at least every 3 months with the mains voltage applied in order to achieve full test coverage. Adhere to the following test procedure for this purpose.

  • [1]

    Maximum 12 months for PL d/SIL 2

    Maximum 3 months for PL e/SIL 3

    [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.