The test must be carried out in a way that verifies the flawless
operation of the safety functions in conjunction with all system
components.
This is ensured by a controlled reaching of the response height
during filling. If filling up to the response height is not possible,
then a response of the measuring system must be triggered by
a suitable simulation of the level or the physical measuring
effect.
The methods and procedures used during the tests must be
stated and their suitability must be specified. The tests must be
documented.
If the function test proves negative, the entire measuring
system must be switched out of service and the process held
in a safe state by means of other measures.
In the double channel architecture 1oo2D this applies
separately to both channels.
1.7 Safety-related characteristics
The failure rates of the electronics, the mechanical parts of the
transmitter as well as the process fitting are determined by an
FMEDA according to IEC 61508. The calculations are based
on component failure rates according to SN 29500. All values
refer to an average ambient temperature during the operating
time of 40 °C (104 °F).
For a higher average temperature of 60 °C (140 °F), the failure
rates should be multiplied by a factor of 2.5. A similar factor
applies if frequent temperature fluctuations are expected.
The calculations are also based on the specifications stated in
chapter "Planning".
After 8 to 12 years, the failure rates of the electronic
components will increase, whereby the derived PFD and PFH
values will deteriorate (IEC 61508-2, 7.4.7.4, note 3).
Applies to overfill and dry run protection:
λ
sd
0 FIT
λ
su
461 FIT
λ
dd
1129 FIT
λ
du
358 FIT
DC
S
0 %
Basics
Service life
Failure rates
10 VEGAPULS series 60 - 4 … 20 mA/HART
Functional safety
31338-EN-070510
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