Safety Analysis - Eaton XTOBP24BC1 Handbuch

1 ZB12-.../XTOB...BC1 and ZB32-.../XTOB...CC1 overload relays

1.4 Safety analysis

1.4 Safety analysis
34
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 (λ
Failure rate for detected safe failures (λ
Failure rate for undetected dangerous failures (λ
Failure rate for detected dangerous failures (λ
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
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:
Size
Category
1)
Performance Level (PL)
2)
MTTF after 3 years
d
1) The performance level is the result of the risk
assessment based on the percentage of risk mitigation
achieved with the control system's safety-related parts.
2) MTTF = Mean time to dangerous failure
d
ZB12-..., ZB32-... 11/16 MN03407004Z-DE/EN www.eaton.com
SIL1
92 %
-9
) 468 x 10
su
) 1.092 x 10
sd
-9
) 169 x 10
du
-9
) 394 x 10
dd
Value
1
c
54 years
/h
-9
/h
/h
/h
-3
: 2.2 x 10 h
avg