Beckhoff EL2904 - EL1904, EL2904 Terminal Description

System description
EL290418 Version: 3.2.2
3.2.3 EL1904, EL2904 - Bus Terminals with 4 fail-safe inputs or
outputs
The EL1904 and EL2904 Bus Terminals enable connection of common safety sensors and actuators. They
are operated with the EL6900 TwinSAFE logic terminal. The TwinSAFE logic terminal is the link unit between
the TwinSAFE input and output terminals. It enables the configuration of a simple, flexible and cost-effective
decentralized safety control system.
Therefore, there are no safety requirements for the higher-level controller! The typical safety functions
required for the automation of machines, such as emergency stop, protective door, two-hand etc., are
already permanently programmed in the EL6900. The user configures the EL6900 terminal according to the
safety requirements of his application.
3.2.4 EL6900 - TwinSAFE logic terminal
The TwinSAFE Logic Terminal is the link unit between the TwinSAFE input and output terminals. The
EL6900 meets the requirements of IEC61508:2010SIL3 and ENISO13849-1:2015(Cat4, PLe).
3.2.5 The fail-safe principle (Fail Stop)
The basic rule for a safety system such as TwinSAFE is that failure of a part, a system component or the
overall system must never lead to a dangerous condition. The safe state is always the switched off and
wattless state.