Vega VEGASWING 66 Safety Manual - page 8
8
4 Safety-related characteristics
VEGASWING 66 • Two-wire (8/16 mA)
45309-EN-130722
Allfiguresrefertoanaverageambienttemperatureof40°C(104°F)
during the operating time. For higher temperatures, the values should
be corrected:
•
Continuousapplicationtemperature>50°C(122°F)byfactor1.3
•
Continuousapplicationtemperature>60°C(140°F)byfactor2.5
Similarfactorsapplyiffrequenttemperaturefluctationsareexpected.
•
The failure rates are constant. Take note of the useful life of the
components according to IEC 61508-2.
•
Multiple errors are not taken into account
•
Wear on mechanical parts is not taken into account
•
Failure rates of external power supplies are not taken into account
•
The environmental conditions correspond to an average industrial
environment
The values for PFD
AVG
specifiedabovewerecalculatedasfollowsfora
1oo1 architecture:
PFD
AVG
=
+
λ
DD
x MTTR
+
PTC × λ
DU
× T1
2
(1 – PTC) ×
λ
DU
× LT
2
•
T1 (Proof Test Interval)
•
MTTR = 8 h
•
PTC = 90 %
•
LT = 10 years
A connected control and processing unit must have the following
properties:
•
The output circuit of the transmitter is judged according to the
quiescent current principle
•
"fail low" and "fail high" signals are interpreted as a failure, which
triggers a fault message
If this is not the case, the respective percentages of the failure rates
must be assigned to the dangerous failures and the values stated in
chapter Safety-related characteristics“ redetermined!
In multiple channel systems for SIL3 applications, this measuring sys-
temcanalsobeusedinahomogeneouslyredundantconfiguration.
The safety-related characteristics must be calculated especially for
the selected structure of the measuring chain using the stated failure
rates. In doing this, a suitable Common Cause Factor must be consid-
ered (see IEC 61508-6, appendix D).
Assumptions of the
FMEDA
Calculation of PFD
AVG
Boundary conditions re-
latingtotheconfiguration
of the processing unit
Multiple channel archi-
tecture