BECKHOFF TwinSAFE - Manual (Page 39)

Circuit examples
Application Guide TwinSAFE 37
2.6 ESTOP function variant 6 (Category 3, PL d)
The emergency stop button with two break contacts, the restart and the feedback loop are connected to
safe channels of an EL1904 input terminal. The testing of the signals is activated. The two emergency
stop signals are tested for discrepancy. Contactors K1 and K2 are wired to different output channels. The
A2 connections of the two contactors are fed together to ground. The current measurement of the output
channels is deactivated for this circuit. The testing of the outputs is not active.
Notice
Category
This structure is possible for a maximum of category 3, due to a possible latent error.
The EL2904 terminal is only SIL2 in this example- therefore, the entire structure is only
SIL2.
2.6.1 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 Single Logic
Logic channel 3 and 4 Single Logic