BECKHOFF TwinSAFE - Manual (Page 92)

Circuit examples
90 Application Guide TwinSAFE
2.15 Safety switching mat / safety bumper (Category 4, PL e)
Safety switching mats or safety bumpers work according to the cross-circuit principle. The contact
surfaces of the device are wired to safe inputs of an EL1904. The testing of the inputs is active and the
signals are tested for discrepancy (200 ms). As soon as a cross-circuit between the signals is detected
(switching mat is stepped on), a logical 0 is signalled by the EL1904 input terminal. If the cross-circuit is
no longer present, a logical 1 is signalled. The feedback loop is read in via a safe input. The testing of the
input is active here also. 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.
2.15.1 Parameters of the safe input and output terminals
EL1904 (applies to all EL1904 used)
Parameter Value
Sensor test channel 1 active Yes
Sensor test channel 2 active Yes
Sensor test channel 3 active Yes
Sensor test channel 4 active Yes
Logic channel 1 and 2 Short cut is no module fault
Logic channel 3 and 4 Single Logic
EL2904
Parameter Value
Current measurement active Yes
Output test pulses active Yes