BECKHOFF TwinSAFE - Manual (Page 109)

Circuit examples
Application Guide TwinSAFE 107
2.18 Feeding in a potential group (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 contactors K1 and
K2 are connected in parallel to the safe output. Current measurement and testing of the output are active
for this circuit.
The diagnostic information from the KL/EL9110 (24 V is present on the power contacts) is negated,
afterwards combined with the feedback signals from contactors K1 and K2 through a Bool AND
composition and the result is applied to the EDM input.
Only the 24 V supply to the power contacts of the potential group is switched off with the NO contacts of
contactors K1 and K2. The 0 V connection of the power contacts is fed directly back to the 0 V of the
power supply.
The 0 V potentials of the load employed (in this case K3 and K4) is always fed back to the potential
group.
CAUTION
Supply voltage must never be applied to an output!
The 24 V supply voltage must never be applied to an output of a digital output terminal!
This wiring error is not reliably detected by the system.
CAUTION
Cross-circuits between the outputs!
Cross-circuits between the outputs of different digital output terminals must be avoided
at all costs. These are not detected by the system.
In accordance with DIN EN ISO 13849-2, the following measures are necessary for the
assumption of the error exclusion ‘external voltage’:
•
Use of separately laid cables
•
Protection against external damage (e. g. by use of a cable duct)
Notice
Safety consideration
The safety consideration ends at K1/K2. The EL/KL9110 and EL/KL2xxx terminals
used are not taken into account for the calculation.