Use Of The Sto Function; Fig. 14 Twinsafe Outputs Connected To Sto Inputs - Beckhoff AX8-1 Series Documentation

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Use of the STO function

Restart lock
The restart lock is to be implemented in the higher-level safety controller.
Alternatively, this can be adapted by the user or the machine manufacturer by modifying
CAUTION
the fail-safe program on the AX8911.
OSSD signals on X15 and X25
The test pulses must not exceed a length of 3.5 ms. Longer test pulses can lead to trigger-
ing of the STO.
CAUTION
Alternatively, this can be adapted by the user or the machine manufacturer by modifying
the fail-safe program on the AX8911.
Cross-circuits / external power supply
The higher-level safety controller is responsible for checking the wiring between the safety
controller and the TwinSAFE inputs of the AX8911 (X15, X25). The necessary tests and
CAUTION
checks arise from the risk and hazard analysis carried out by the machine manufacturer.
Testing the X15 and X25 inputs
The functions of the STO inputs 1 and 2 of the connections X15 or X25 are tested internally
by the AX8911 TwinSAFE drive option card. The external test pulses for detecting cross-
Note
circuits or an external power supply serve only to check the correct wiring between the
safety controller and the TwinSAFE drive option card.
Using the STO inputs with TwinSAFE outputs
In this application case the STO inputs 1 and 2 of the digital inputs X15 and, if applicable, X25 are wired
directly to safe outputs, for example of an EL2904. When using the EL2904, the safe outputs are
parameterized in such a way that the test pulses are active, but the parameter Current Measurement active
is disabled. If other TwinSAFE outputs are used they must also be parameterized in the same way so that
test pulses are active at the output.
A filter is implemented within the logic of the AX8911 (default 3.5 ms) so that the test pulses of, for example,
the EL2904 cannot lead to a switch-off of the STO channels.
Fig. 14: TwinSAFE outputs connected to STO inputs
AX8911 - TwinSAFE Drive Option Version: 1.0.0
Use of the STO function
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