Siemens SIMATIC ET 200AL - Page 96

Distributed I/O system
94 System Manual, 02/2018, A5E31861578-AF
Safety-related shutdown of ET200AL standard
modules
A
Introduction
The diagram below illustrates the fail-safe shutdown of ET 200AL standard modules.
In the configuration shown in the diagram below, all digital outputs that are operated with the
2L+ and 2M supply of the ET 200AL standard modules are switched to the safe OFF state.
This step achieves the safety class SIL2/category 3/PLd.
Principle of operation
The higher-level safety relay (for example: 3SK1) disconnects the 2L+ and 2M supply. This
switches all digital outputs operated with the 2L+ and 2M (switched) supply to the safe state.
The digital outputs connected to the 1L+ and 1M (non-switched) supply are not intended for
functional switching and therefore cannot be shut down safely.
There is no interaction between the outputs supplied by 1L+ and 2L+.
You can also integrate I/O modules that are operated solely at the supply 1L+ and 1M (non-
switched) in the structure of your distributed I/O system. These I/O modules are not affected
by a disconnection, they pass on the supply 2L+ and 2M (switched). The following figure
shows the modules DI and AI as an example.