Safety Recommendation; Interfaces; Configuration; Useful Life Time - Pepperl+Fuchs SIL KFD0-SD2-*. Series Safety Manual

SAFETY MANUAL SIL K*D0-SD*-(EX)*.****(.SP), HIC2871

Safety Recommendation

3 Safety Recommendation
3.1

Interfaces

The device has the following interfaces. For corresponding terminals see data
sheet.
Safety relevant interfaces: input I, input II, output I, output II

Non-safety relevant interfaces: none

3.2

Configuration

A configuration of the device is not necessary and not possible.
3.3

Useful Life Time

Although a constant failure rate is assumed by the probabilistic estimation this
only applies provided that the useful life time of components is not exceeded.
Beyond this useful life time, the result of the probabilistic calculation is
meaningless as the probability of failure significantly increases with time. The
useful life time is highly dependent on the component itself and its operating
conditions – temperature in particular (for example, the electrolytic capacitors can
be very sensitive to the working temperature).
This assumption of a constant failure rate is based on the bathtub curve, which
shows the typical behavior for electronic components.
Therefore it is obvious that failure calculation is only valid for components that
have this constant domain and that the validity of the calculation is limited to the
useful life time of each component.
It is assumed that early failures are detected to a huge percentage during the
installation period and therefore the assumption of a constant failure rate during
the useful life time is valid.
However, according to IEC 61508-2, a useful life time, based on experience,
should be assumed. Experience has shown that the useful life time often lies
within a range period of about 8 ... 12 years.
Our experience has shown that the useful life time of a Pepperl+Fuchs product
can be higher
if there are no components with reduced life time in the safety path (like

electrolytic capacitors, relays, flash memory, opto coupler) which can produce
dangerous undetected failures and
if the ambient temperature is significantly below 60 °C.

Please note that the useful life time refers to the (constant) failure rate of the
device. The effective life time can be higher.
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