VEGA VEGABAR 87 4 … 20 mA_HART - Operating Instructions - Manual (Page 55)

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9 Diagnosis, asset management and service
VEGABAR 87 • 4 … 20 mA/HART
45044-EN-131010
Error Cause Rectification
4 … 20 mA signal
missing
– Electrical con-
nection faulty
– Check connection according to
chapter "Connection steps" and
if necessary, correct according to
chapter "Wiring plan"
– Voltage supply
missing
– Check cables for breaks; repair if
necessary
– Operating volt-
age too low or
load resistance
too high
– Check, adapt if necessary
Current sig-
nal greater than
22 mA or less
than 3.6 mA
– Electronics
module in the
sensor defec-
tive
– Exchange the instrument or send it
in for repair
Depending on the reason for the fault and the measures taken, the
steps described in chapter "Setup" must be carried out again or must
be checked for plausibility and completeness.
Should these measures not be successful, please call in urgent cases
the VEGA service hotline under the phone no. +49 1805 858550.
The hotline is also available outside normal working hours, seven
days a week around the clock.
Since we offer this service worldwide, the support is provided in
English. The service itself is free of charge, the only costs involved are
the normal call charges.
9.5 Calculation of total deviation (according to
DIN 16086)
The total deviation of a pressure transmitter indicates the maximum
measurement error to be expected in practice. It is also called maxi-
mum practical deviation or operational error.
According to DIN 16086, the total deviation F
total
is the sum of the
basic accuracy F
perf
and the long-term stability F
stab
:
F
total
= F
perf
+ F
stab
The basic accuracy F
perf
is composed of the deviation F
Kl
and the
thermal change of zero signal and output span F
T
:
F
perf
= √((F
T
) 2 + (F
Kl
) 2 )
This applies to the digital signal output via HART, Profibus PA or
Foundation Fieldbus. With a 4 … 20 mA output, there is also the
thermal change of the current output F
a
:
F
perf
= √((F
T
) 2 + (F
Kl
) 2 + (F
a
) 2 )
To provide a better overview, the formula symbols are listed together
below:
•
F
total
: Total deviation
•
F
perf
: Basic accuracy
•
F
stab
: Long-term drift
Reaction after fault recti-
fication
24 hour service hotline
Meaning of the total
deviation