BECKHOFF KL6904 - Manual (Page 13)

System description
KL6904 11
TwinSAFE digital input (KL1904) and output terminal (KL2904)
•
All current safety sensors can be connected
•
Operation with a TwinSAFE logic terminal
•
KL1904 with 4 fail-safe inputs for sensors (24 V
DC
) with floating contacts
•
KL2904 with four safe channels for actuators (24 V
DC
, 0.5 A per channel)
•
conforming to IEC 61508:2010 SIL 3
2.2.3 KL1904, KL2904 – Bus Terminals with 4 fail-safe inputs or outputs
The KL1904 and KL2904 Bus Terminals enable connection of common safety sensors and actuators.
They are operated with the KL6904 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 KL6904. The user configures the KL6904 terminal according to
the safety requirements of his application.
2.2.4 KL6904 TwinSAFE logic terminal with 4 fail-safe outputs
The KL6904 TwinSAFE logic terminal is a digital output terminal with four fail-safe outputs with 0.5 A,
24 V
DC
. The KL6904 meets the requirements of IEC 61508:2010 SIL 3 and
DIN EN ISO 13849-1:2006 (Cat 4, PL e).
2.2.5 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.