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The supply voltage must be monitored externally for undervoltage (< 19.2 V), the ambient temperature
monitored externally at the installation site (max. <+ 60 °C, mean + 40 °C), and the detection of short
circuits and interruptions in the output line with interlock must also be used.
Safety characteristics according to IEC 61508 Edition 2
SU
5.03
The entire failure rate is 558 FIT.
The MTBF is therefore 205 years.
The fault rates are used to calculate the average probability of failure of the designed function in the
event of a request for the operating type "low demand" and the probability of a hazardous failure per hour
for the operating type "continuous demand".
Low-demand mode
The following PFD
T [PROOF]
PFD
avg
T [PROOF]
PFD
avg
High-demand mode
The following PFH value (high demand rate) results from the fault rates:
PFH = 1.27 × 10
The requirements when it comes to the PFH value for a SIL3 system are therefore met.
The values for 1, 2, 3, 4, 5, 6, 7, 8, and 10 years mean that the calculated PFD
permissible range for SIL3 according to table 2 from IEC/EN 61508-1. They meet the requirement of not
covering more than 10 % of the safety circuit or are better than or equal to 1.00 × 10
5.4
Conditions
•
The failure rates of the components used are constant over the period of use.
•
The spread of faults through the device in the system is not considered.
•
The failure rates of the external power supply are not taken into account.
•
The specified fault rates relate to an ambient temperature of 40 °C. For an ambient temperature of
60 °C, you have to multiply the fault rates by a factor of 2.5. The factor of 2.5 is based on empirical
values.
SD
DU
0
1.27
values (low demand rate) result from the fault rates.
avg
1 year
2 years
-6
5.54 × 10
1.13 × 10
6 years
7 years
-5
3.61 × 10
4.27 × 10
-9
/h
5 Safety-related applications
DD
0
3 years
-5
-5
1.72 × 10
8 years
-5
-5
4.96 × 10
SFF
DC
D
79.76 %
0 %
4 years
5 years
-5
2.33 × 10
2.96 × 10
10 years
-5
6.93 × 10
values are within the
avg
-4
.
-5
21
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