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Hybrid applications of IEC61511 – Laurie Blackmore
Disadvantages include:
§
SIS is as big or even bigger than the non-61511 (API) design leading to increased
complexity of operation, maintenance. This increases the risk of systematic faults - the
primary cause of major incidents
§
Testing frequency is still based on API RP14C (3 months transmitters, 1 year SDV‘s)
rather than (longer) IEC61511 intervals. This reduces ability to focus on the high-risk
functions
§
The engineering cost and potential schedule increase associated with the elements of
IEC61511 is incurred without the benefit of equipment rationalisation or reduced testing
costs.
These increases are considerably less than in the previous case.
Lifecycle/contract issues:
§
Make sure it is clear in the contract if IEC61511 applies to only safety or includes asset
etc. This affects engineering hours.
This is the most common form of hybrid
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API design but with SIL assessment and validation