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Functional Safety 2016
November, 2016 - London
Page 8 of 17
What can be expected in IEC 61511:2016 Edition 2 in relation to
Proof test Coverage
Within the IEC 61511-1:2016 ed 2 redlined edition Clause 11.9 there are a number of sub-
clauses addressing the requirement to evaluate the proof test coverage factor:
CL 11.9.2 d) “
the estimated failure related to each mode, due to random hardware
failure, which would contribute to a dangerous failure of the SIS which are
undetected by the diagnostic tests and undetected by proof test
”. Therefore both
the diagnostic coverage and the proof test coverage is required under edition 2.
CL 11.9.2 h) “
the coverage of any periodic proof tests, the associated proof test
procedure and the reliability for the proof test facilities and procedure;
” further
requirement for proof test coverage in edition 2.
CL 11.9.5 b) “
evaluate the effect of possible improvement measures on the
identified devices or parameters (e.g., more reliable devices, additional defences
against common mode failures, increased diagnostic or proof test coverage,
increased redundancy, reduced proof test interval, staggering tests, etc.);
”
From this increased emphasis identified within edition 2 it can be assumed that appropriate
evaluation and assessment will be required in addressing C
PT
.
Practical Example of Proof Test based on a basic SIF
Figure 1: Simplified diagram for High Integirty Pressure Protection System (HIPPS)
PT1
PT3
PT2
Final
Element
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