Eaton ZB12/XTOB BC1 Series, Manual

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Safety analysis
45
03/15 MN03407004Z-DE/EN
Safety analysis The following functional safety characteristics were
determined for overload relays ZB12 and ZB32:
For low demand operating mode with a 1oo1 architecture,
consisting of type A subsystems and a hardware fault
tolerance (HFT) of 0 (see Table 3 in EN 61508 Part 1 and
Table 2 in EN 61508 Part 2) for the overload relays at an
ambient temperature of 55 °C:
• Motor protection (overload)
– Safety integrity level
– Safe Failure Fraction (SFF)
– Failure rate for undetected safe failures
(
l
su
)
– Failure rate for detected safe failures
(
l
sd
)
– Failure rate for undetected dangerous failures
(
l
du
)
– Failure rate for detected dangerous failures
(
l
dd
)
Average probability of a dangerous failure when the safety
function is on demand, using an interval of 36 months for
repeat test:
1st demand level
F
1/year (low demand mode):
PFD
avg
: 2.2 x 10
-3
h
The mean lifespan between two failures (MTBF): 54 years
For the safety-related parts of control systems as per
EN ISO 13849, the following data was determined at an
ambient temperature of 55 °C:
SIL 1
92 %
468 x 10
-9
/h
1,092 x 10
-9
/h
169 x 10
-9
/h
394 x 10
-9
/h