Functional Safety KF**-CRG2-(Ex)1.D
Planning
2017-12
11
SIL 2 Application
• The device shall claim less than 10 % of the total failure budget for a SIL 2
safety loop.
• For a SIL 2 application operating in low demand mode the total PFD
avg
value
of the SIF (Safety Instrumented Function) should be smaller than 10
-2
, hence
the maximum allowable PFD
avg
value would then be 10
-3
.
• For a SIL 2 application operating in high demand mode the total PFH value of
the SIF should be smaller than 10
-6
per hour, hence the maximum allowable
PFH value would then be 10
-7
per hour.
• Since the control loop has a hardware fault tolerance of 0 and it is a type B
device, the SFF must be > 60 % according to table 2 of IEC/EN 61508-2 for a
SIL 2 (sub) system.
• The IEC/EN 61511-1 section 11.4.4 allows devices to be used in applications
one SIL higher than given by table 3 of IEC/EN 61508-2, if the device is
proven-in-use. The assessment and proven-in-use demonstration lead to the
result that the device may be used in applications up to SIL 2. However, it is
the responsibility of the end-user to decide on applying proven-in-use devices.
3.3 Safety Function and Safe State
3.3.1 Safe State
Relay contact output
The safe state is present when the output is de-energized.
Current output
The safe state is present when the output signal is < 4 mA or > 20 mA.
3.3.2 Safety Function
Relay contact output
The safe state is initiated when the input current falls below a certain value (fault
current Min) or exceeds a certain value (fault current Max).
Current output
The device transfers a current value with 5 % accuracy related to the full scale of
the output.
3.3.3 Reaction Time
The reaction time for all safety functions is < 1 s.
Note!
See corresponding datasheets for further information.
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