
Monitored Digital Input Modules
, Type F (T7411F, T7418F)
8
Industrial Control Services
Application
Simplex Configuration
Monitored digital input modules provide a suitable interface
to safety
-
critical input signals. The circuits in the monitored
digital input modules are automatically tested and
annunciated, providing a fail
-
safe interface to digital inputs.
This simplex input configuration is illustrated in Figure
3
.
Figure
3
. Single Monitored Digital Input Configuration.
Fault Tolerant Configurations
For fault tolerant applications, redundant monitored input
modules are used in a fault tolerant configuration. In one
configuration the redundant input modules are connected in
parallel to a single field input device as illustrated in Figure
4
. If redundant field sensors are installed in the field, the
modules are connected so that each sensor connects to one of
the modules as illustrated in Figure
5
. In these fault tolerant
configurations, each monitored digital input module is hot
replaceable. If a fault occurs on one module, it can be
removed and replaced while the system continues to correctly
sense the inputs from the remaining module(s).
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