Functional Safety K-LB-*.*, F*-LB-I, P-LB-*.*.*
Application Examples
20
21
-0
9
31
Example 2
–
Digital Output
–
Solenoid Drivers
The 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 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:
For the surge protection barrier P-LB-1.A the following characteristics are given:
The combination of both devices is done by simply adding the characteristics again as before.
The SFF and PFD
avg
values can be calculated by using the equations given above.
This means that for this specific combination the requirements for a SIL 2 safety loop
are still fulfilled.
Total failure rate
714 FIT
Dangerous undetected failure rate
10.3 FIT
PFD
avg
for T
1
= 1 year
4.51 x 10
-5
SFF
85 %
Table 7.6 Characteristics of isolator KFD2-SL2-Ex1.LK
Total failure rate
16.1 FIT
Dangerous undetected failures
0 FIT
Table 7.7 Failure rates of surge protection barrier P-LB-1.A
Total failure rate
730 FIT (rounded)
Dangerous undetected failure rate
10.3 FIT
PFD
avg
for T
1
= 1 year
4.51 x 10
-5
SFF
85 % (rounded)
Table 7.8 Sum of failure rates of isolator KFD2-SL2-Ex1.LK and surge protection barrier P-LB-1.A
