Rockwell Automation AADvance Controller Safety Manual - Manual (Page 12)

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1-2 Document: 553630
ICSTT-RM446K-EN-P Issue: 10 _C
Safety Manual (AADvance Controller)
 Previous experience and its relevance to the specific duties to be
performed and the technology being employed
In all of the above, the higher risk will require increased rigor with the
specification and assessment of the competence.
Terminology
Vocabulary and Conventions
The terms certification and certified are used widely within this
Manual, these terms refer principally to the functional safety certification
of the AADvance system to IEC 61508 SIL3 and other relevant standards.
This Manual contains rules and recommendations:
 Rules are mandatory and shall be followed if the resulting system
is to be a SIL3 compliant application. These are identified by the term
'shall'.
 Recommendations are not mandatory, but if they are not followed,
extra safety precautions shall be taken in order to certify the system.
Recommendations are identified by the term 'it is highly
recommended'.
Process Safety Time
The process safety time for the equipment under control relates to the
logic solver portion of PST
EUC
, it is the period a dangerous condition can
exist before a hazardous event occurs without a safety system as a
protection. It can be a fraction of a second or several hours, depending
on the process. A PST can be defined for a controller via the processor
module and independently for individual I/O modules, however, the
processor defined PST will always have priority over the I/O PST if the
I/O PST exceeds the processor value.
Fault Tolerance in Safety Applications
For safety applications you shall define how the control system will
respond in the presence of faults. As faults accumulate, this becomes the
system's defined state of degraded operation or fault tolerance level.
 Simplex systems are not fault tolerant and do not have the ability to
continue their operation in the presence of fault conditions, however
they are designed to fail safe where possible.
 Fault tolerant systems have redundant modules and processors that
allow the system to continue operation or to ensure that the system
fails safe in the presence of faults.