Woodward Large Electric Sonic Valve II, Инструкция по установке и эксплуатации, Страница: 52 / 66

Manual 35076 LESV II
Woodward 50
Chapter 6.
Safety Management – Safe Position
Fuel Shutoff Function
Product Variations Certified
The SIL rated LESV for fuel shutoff is designed and certified to the functional safety standards according
to IEC61508, Parts 1 through 7. Reference the product FMEDA: WOO 17/07-039 R001, and
Certification: WOO 1707039 C001.
The functional safety requirement in this chapter applies to all LESVs. The SIL rated LESVs will have a
DU FIT of less than 826 FITS for Close to Trip Full Stroke.
According to IEC61508, the LESV is certified for use in applications up to SIL 3.
The LESV is designed and verified to withstand the worst-case (or greater) expected environmental
conditions as listed in other sections of this manual.
Covered LESV Versions
All LESVs are SIL certified for the shutoff function.
SFF for the LESV – Over Speed SIF (Safety Instrumented Function)
The LESV is only one part of a shutoff system that supports an over-speed shutdown SIF. This system
consists of a speed sensor, a processing unit, and a fuel shutoff actuation sub-system of which the LESV
is a component.
The SFF for each subsystem should be calculated. The SFF summarizes the fraction of failures, which
lead to a safe state, plus the fraction of failures which will be detected by diagnostic measures and lead to
a defined safety action. This is reflected in the following formulas for SFF:
SFF =
λ
SD
+
λ
SU
+
λ
DD
/
λ
TOTAL
Where
λ
TOTAL
=
λ
SD
+
λ
SU
+
λ
DD
+
λ
DU
The failure rates listed below, for only the LESV, do not include failures due to wear-out of any
components. They reflect random failures and include failures due to external events such as unexpected
use. Reference the FMEDA: WOO 17/07-039 R001for detailed information concerning the SFF and PDF.
Table 6-1. Failure Rates according to IEC61508 in FIT
Device λ
SD
λ
SU
λ
DD
λ
DU
Full Stroke 0 109 0 826
Full Stroke with PVST 108 1 370 456
According to IEC 61508-2, the architectural constraints of an element must be determined. This can be
done by following the 1H approach according to 7.4.4.2 of IEC 61508-2 or the 2H approach according to
7.4.4.3 of IEC 61508-2. The 1H approach should be used for the LESV.
Released