5. System Integration
The safety-related device is broken down into two circuits that function independently from one another.
The first circuit is responsible for the primary function, the optical warning signal. The second circuit diagnoses
the optical warning signal, reporting back any faults it detects via a fault indicator relay.
The individual components are not sufficient to make qualify this safety-related device as a complete safety-
related system. A higher-level safety-related control and guidance system is needed for this, see Illustration 4 -
Example of a system integration of
the monitored warning light
. In the event of a fault, the higher level control
and guidance system is responsible for establishing safe conditions in the overall system.
The primary function of the safety-related device is creating an optical warning signal. This primary function can
serve as a primary safety function for a higher level, safety-related control and guidance system.
Beyond the primary function, the safety-related device also has a diagnostic function that can monitor the prima-
ry function channel. An online diagnosis in the sense of EN 61508 is only available if the monitoring function is
active for the primary function and the state of the fault relay output for the monitoring function is being actively
evaluated as a safety function by the higher level control and guidance system during request of the main func-
tion.
If the primary function is not being used as a safety function, then the monitoring function can nevertheless be
used as a secondary safety function for a higher-level, safety-related control and guidance system. In this case
the primary safety function must be part of the higher-level, safety-related control and guidance system.
Illustration 4 - Example of a system integration of the monitored warning light
Illustration 3 - simplified diagram
Control and
guidance system
Safety-related portion
identify critical statuses
Process
EUC
request
request
Report
Primary function:
produce flashing light
Monitoring function: Diagnose
production of flashing light
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