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Masoneilan 12400 Series Transmitter/Controller Instruction Manual | 45
8.3.
SAFETY REQUIREMENTS
8.3.1.
P
ROBABILITY OF FAILURE ON DEMAND
(PFD
AVG
)
This table reflects the achievable Safety Integrity Level (SIL) depending on the mean provability of failure on demand. The
specified failure tolerances in this case apply to a safety function operated in the Low Demand mode.
Safety Integrity Level (SIL)
PFD
avg
with Low Demand mode
4
≥
10
-5
to < 10
-4
3
≥
10
-4
to < 10
-3
2
≥
10
-3
to < 10
-2
1
≥
10
-2
to < 10
-1
8.3.2.
S
AFETY INTEGRITY OF THE HARDWARE
This table shows the achievable Safety Integrity Level (SIL) depending on the proportion of non-dangerous failures (SFF) and
the fault tolerance of the hardware (HFT) for safety-related type B subsystems.
Proportion of non-
dangerous failures (SFF)
Fault tolerance of the hardware (HFT)
0
1
2
< 60%
Not permitted
SIL 1
SIL 2
60% - < 90%
SIL 1
SIL 2
SIL 3
90% - < 99%
SIL 2
SIL 3
SIL 4
≥
99%
SIL 3
SIL 4
SIL 4
8.4.
SAFETY CHARACTERISTICS
8.4.1.
A
SSUMPTIONS
The specified characteristics are applicable under the following assumptions that have been made during the FMEDA.
•
The instrument is being
used as a transmitter
and the controller function is disabled (if applicable).
•
The instrument must be configured as a SIL 2 device with failsafe position defined as Fail Low (<3.6 mA).
•
In case of custom displacer, displacer weight must be lower the following rule:
Displacer Weight (gr) < 1600 x TT force x 4 / arm lengh
Torque tube force =1, 2 or 4
Arm length = 4", 8", 16" (side vessel) or other
i.e. 1600 x 1 x 4 / 4 = 1600 gr for a standard displacer and single force torque tube