BECKHOFF TwinSAFE - Manual (Page 63)

Circuit examples
Application Guide TwinSAFE 61
2.10 Protective door function with area monitoring
(Category 4, PL e)
The protective door uses a combination of break and make contacts on the safe inputs of an EL1904. The
testing of the inputs is active and the signals are tested for discrepancy (200 ms). The feedback loop is
read in via a safe input. The proximity switches S3 and S4 are wired to safe inputs and detect, for
example, when a dangerous machine part is in a safe position so that the protective door may be opened
when the machine is running. The testing of these inputs is deactivated so that the static 24 V voltage of
the sensors can be used.
The contactors K1 and K2 are connected in parallel to the safe output. Current measurement and testing
of the output are active for this circuit.