Test Function; Safety Analysis - Eaton ZE serie Handbuch

1 ZE/XTOM overload relays
1.3 Description of device

1.3.6 Test function

1.3.7 Safety analysis

30
An additional Test button enables the operation of the auxiliary contact to be
checked. The Test button has a dual function here:
• Pressing the Test button opens the break contact 95-96. When the
button is released, the break contact closes again. This function can also
be used to switch off the motor manually.
• Pulling the Test button will trip the overload relay.
The N/C contact 95-96 opens and the N/O contact 97-98 closes. After
the Test button is released, the overload relay must be reset in the same
way as after normal tripping (￫ section 1.3.5, "Re-closing", page 29).
The following functional safety characteristics were determined for the
motor overload relay ZE/XTOM:
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 50 °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) is 61 years.
For the safety-related parts of control systems as per EN ISO 13849, the
following data was determined at an ambient temperature of 50 °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
ZE/XTOM 11/17 MN03407003Z-DE/EN www.eaton.com
SIL1
89 %
-9
) 372 x 10 /h
su
-9
) 868 x 10 /h
sd
-9
) 199 x 10 /h
du
-9
) 426 x 10 /h
dd
Value
1
c
61 years
-3
: 2.6 x 10 h
avg