20 H-S81-HS Installation & Operation Manual — P/N LS10114-000HI-E:A 2/24/2015
General Description Safety-Related Modules in the H-S81-HS System
“Duplex” Configuration
This solution is characterized by a redundant configuration for both the central unit and the I/O
modules. Module redundancy increases system availability. In case of error or failure of a module
in “duplex” configuration, the broken module is automatically put in safety condition (OFF)
whereas the redundant one keeps operating. I/O module redundancy is possible only with safety
related modules.
1.5 Safety-Related Modules in the H-S81-HS System
This paragraph describes the measures undertaken by safety related modules in order to guarantee
the required reliability of the various applications.
1.5.1 Central Unit
The CPU features an external watchdog circuit that activates in case of failure. In standard operat-
ing conditions, the CPU cyclically tests the memory, internal voltage values and the status of RAM
lithium batteries. Should it detect any faults, the module would set in safety condition. If there is a
redundant CPU, the new CPU will carry out the monitoring functions without any interruptions.
The broken CPU can be replaced without the need of switching off the system.
Figure 1.4 “Duplex” Configuration
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