Pepperl+Fuchs KFD2-STC4-Ex Series - Safety Function and Safe State

2014-09
8
Safety Manual SIL KFD2-ST*4-(Ex)*, KFD2-CR4-(Ex)*
Planning
 Since the loop has a Hardware Fault Tolerance of 0 and it is a type A
component, the SFF must be > 90 % according to table 2 of IEC 61508-2 for a
SIL3 (sub)system.
SIL2 application
 The device shall claim less than 10 % of the total failure budget for a SIL2
safety loop.
 For a SIL2 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 SIL2 application operating in High Demand Mode of operation 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 loop has a Hardware Fault Tolerance of 0 and it is a type A
component, the SFF must be > 60 % according to table 2 of IEC 61508-2 for a
SIL2 (sub)system.
2.3 Safety Function and Safe State
Safety Function
The safety function of the devices is the transfer of the analog signals from the
input to the output with a tolerance of 2 %.
Safe State
The user must ensure that the ESD system reacts adequately when the outputs
are:
 < 4 mA or > 20 mA for the KFD2-CR4-(Ex)* and KFD2-STC4-(Ex)*
 < 1 V or > 5 V for the KFD2-STV4-(Ex)*-1
 < 2 V or > 10 V for the KFD2-STV4-(Ex)*-2
Reaction Time
The reaction time for all safety functions is < 20 ms.
Device type Input signals Output signals
KFD2-CR4-(Ex)* and
KFD2-STC4-(Ex)*
0/4 mA … 20 mA 0/4 mA ... 20 mA
KFD2-STV4-(Ex)*-1 0/4 mA … 20 mA 0/1 V … 5 V
KFD2-STV4-(Ex)*-2 0/4 mA … 20 mA 0/2 V … 10 V
Table 2.1
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