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6 Safety-related applications
Failure limit value
The operating mode with low-demand mode is taken as the basis. The proportion of the device at PFH/
PFD of the entire safety circuit is less than 10 %.
Safety circuit according to IEC/EN 61508-1
Sensor
25 %
High-demand mode
PFH
Cycles/year
PFH
Cycles/year
The switching frequency must be taken into account when it comes to the useful life of the relay.
Due to the line inductance, weakly resistive inductive loads are permitted (cos ɸ > 0.95).
Exception: switching frequency 1000 cycles/year, admissible switching rate 6/min
6.9
Conditions
The specifications are valid under these 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 repair time (= replacement) is to be eight hours.
The failure rates of the external power supply are not taken into account.
The line fault detection is enabled.
The average temperature in which the device is to be used is 40 °C. Normal industrial conditions are
assumed here.
The specified fault rates refer to an average ambient temperature of 40 °C. For an average ambient
temperature of 60 °C, the specified fault rates have to be multiplied by a factor of 2.5. The factor of 2.5
is based on experience.
24
Device
< 10 %
C1
C2
-8
4.79 × 10
8.29 × 10
1000
100
C5
C6
-8
5.79 × 10
1.03 × 10
1000
100
Processing
15 %
C3
-8
-8
5.06 × 10
1000
C7
-7
-8
6.06 × 10
1000
Actuator
50 %
C4
-8
8.56 × 10
100
C8
-8
1.06 × 10
100
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