Vega VEGAMET 381 Ex Safety Manual - page 11
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Multiple errors are not taken into account
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Wear of mechanical not taken into account
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Failure rates of external power supplies are not taken into account
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The environmental conditions correspond to an average industrial
environment
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The repair time (exchange of the measuring system) after a non-
dangerous malfunction is 8 hours (MTTR = 8 h)
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To avoid fusing of the contacts, the outputs of the safety relays are
protected with a fuse, trigerring at 60 % of the max. contact current
load.
The powered transmitter must output an error current if it is powered
by a voltage outside the voltage range specified for the sensor input in
the operating instructions manual of VEGAMET 381.
A connected control and processing unit offers the following proper-
ties:
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The output circuit of the measuring system is judged according to
the quiescent current principle
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"
fail low"
and "fail high" signals are interpreted as failure and a
failure message is triggered
If this is not the case, the respective shares of the failure rates must be
assigned to the dangerous failures and the values stated in chapter
"S
afety-technical figure“ must be determined again!
In multiple channel systems for SIL3 applications, this measuring
system must only be used with diversitary redundancy.
The dafety-related characteristics must be calculated especially for the
selected structure of the measuring chain by means of the stated
failure rates. For this purpose, a suitable common cause factor must
be taken into account.
Boundary conditions re-
lating to transmitters
Boundary conditions re-
lating to the configura-
tion of the processing
unit
Multiple channel archi-
tecture
VEGAMET 381 Ex • 4 … 20 mA signal conditioning instruments
11
3 S
afety-related characteristics
39686
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EN
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