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Functional Safety K*D0-RSH-1.1D.(F)*, HiC5861(Y1)
Planning
3.2
Assumptions
The following assumptions have been made during the FMEDA:
•
Failure rates are constant, wear is not considered.
•
Failure rate based on the Siemens standard SN 29500.
•
The safety-related device is considered to be of type A device with a hardware
fault tolerance of 0.
•
The device will be used under average industrial ambient conditions comparable
to the classification stationary mounted according to MIL-HDBK-217F.
Alternatively, operating stress conditions typical of an industrial field environment similar
to IEC/EN 60654-1 Class C with an average temperature over a long period of time
of 40 ºC may be assumed. For a higher average temperature of 60 ºC, the failure rates
must be multiplied by a factor of 2.5 based on experience. A similar factor must be used
if frequent temperature fluctuations are expected.
•
The nominal voltage at the digital input is 24 V. Ensure that the nominal voltage
do not exceed 30 V under all operating conditions.
•
Observe the useful lifetime limitations of the output relays.
•
The relay contacts must be protected against overcurrent with a suitable current
limitation. For this purpose, either the internal fuse or an external current limitation
with the same limit values must be used.
SIL 3 application
•
To build a SIL safety loop for the defined SIL, it is assumed as an example that this device
uses 10 % of the available budget for PFD
•
For a SIL 3 application operating in low demand mode the total PFD
of the SIF (Safety Instrumented Function) should be smaller than 10
hence the maximum allowable PFD
•
For a SIL 3 application operating in high demand mode the total PFH value
of the SIF should be smaller than 10
would then be 10
•
Since the safety loop has a hardware fault tolerance of 0 and it is a type A device,
the SFF must be > 90 % according to table 2 of IEC/EN 61508-2 for a SIL 3 (sub) system.
SILCL and PL application
•
The device was qualified for use in safety functions acc. to IEC/EN 62061
and EN/ISO 13849-1. The device fulfills the requirements for a SILCL of SIL 3
acc. to IEC/EN 62061 and due to the equivalency between these standards PL e
acc. to EN/ISO 13849-1.
avg
value would then be 10
avg
-7
per hour, hence the maximum allowable PFH value
-8
per hour.
/PFH.
avg
-3
,
-4
.
value
11
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