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Functional Safety K-LB-*.*, F*-LB-I, P-LB-*.*.*
Application Examples
Example 2 – Digital Output – Solenoid Drivers
The Pepperl+Fuchs digital output modules can be categorized into two groups – loop powered
devices and bus powered devices.
Bus powered Solenoid Drivers
If a bus powered Solenoid Driver from Pepperl+Fuchs is considered it is possible to use
virtually the same calculation method as used for NAMUR NE 22 inputs described above.
The basic requirements are:
1. Signal type of the safety loop = digital
2. Signal direction of the safety loop as seen from the perspective of the safety DCS = output
3. Safe state of the field device allocated to the surge protection barrier = de-energized
4. Desired SIL level of the safety loop = SIL 2
A standard KFD2-SL2-Ex1.LK device has the following characteristics:
Total failure rate
Dangerous undetected failure rate
PFD
avg
SFF
Table 7.6
For the surge protection barrier P-LB-1.A the following characteristics are given:
Total failure rate
Dangerous undetected failures
Table 7.7
The combination of both devices is done by simply adding the characteristics again as before.
The SFF and PFD
Total failure rate
Dangerous undetected failure rate
PFD
avg
SFF
Table 7.8
This means that for this specific combination the requirements for a SIL 2 safety loop
are still fulfilled.
for T
= 1 year
1
Characteristics of isolator KFD2-SL2-Ex1.LK
Failure rates of surge protection barrier P-LB-1.A
values can be calculated by using the equations given above.
avg
for T
= 1 year
1
Sum of failure rates of isolator KFD2-SL2-Ex1.LK and surge protection barrier P-LB-1.A
714 FIT
10.3 FIT
-5
4.51 x 10
85 %
16.1 FIT
0 FIT
730 FIT (rounded)
10.3 FIT
-5
4.51 x 10
85 % (rounded)
31
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