Assumptions; Safety Function And Safe State - Pepperl+Fuchs KFD2-SCD2-Ex LK Series Manual

Functional Safety KFD2-SCD2-Ex*.LK, HiD2038
Planning
3.2

Assumptions

The following assumptions have been made during the FMEDA:
• Failure rate based on the Siemens standard SN 29500.
• Failure rates are constant, wear is not considered.
• External power supply failure rates are not included.
• 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 application program in the programmable logic controller (PLC) is configured to
detect line faults (lead breakage or lead short circuit).
3.3

Safety Function and Safe State

Safety Function
The safety function of the device is fulfilled, as long as the output repeats the input current
(4 mA to 20 mA) with a tolerance of 2 %.
A dangerous detected failure is present if the output current is less than 4 mA or greater
than 20 mA due to the line fault detection.
A dangerous undetected failure is present if the tolerance limits for the signal transfer
are exceeded and the output current is between 4 mA and 20 mA.
Reaction Time
The safety reaction time is the maximum time required from the occurrence of the fault
to the reaction of the outputs in normal operation without faults.
The combined fault detection and fault reaction time is the time in which the device outputs
react to an occurred fault. See chapter 3.4.
Note
See corresponding datasheets for further information.
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