29
7 Diagnosis, asset management and service
VEGAPULS WL 61 • Profibus PA
38062-EN-140801
Measurement error with constant level
Fault description
Error pattern
Cause
Rectification
1. Measured value
shows a too low or too
high level
Level
time
0
– Min./max. adjustment not
correct
– Adapt min./max. adjustment
– Wrong linearization curve
– Adapt linearization curve
– Installation in a bypass tube or
standpipe, hence running time
error (small measurement error
close to 100 %/large error close
to 0 %)
– Check parameter "Application"
with respect to vessel form,
adapt if necessary (bypass,
standpipe, diameter)
2. Measured value
jumps towards 0 %
Level
time
0
– Multiple echo (vessel top,
product surface) with amplitude
higher than the level echo
– Check parameter "Application",
especially vessel top, type
of medium, dished end, high
dielectric constant, adapt if
necessary
3. Measured value
jumps towards 100 %
Level
time
0
– Due to the process, the ampli-
tude of the level echo sinks
– A false signal suppression was
not carried out
– Carry out a false signal sup-
pression
– Amplitude or position of a
false echo has changed (e.g.
condensation, buildup); false
signal suppression no longer
matches
– Determine the reason for the
changed false signals, carry out
false signal suppression, e.g.
with condensation
Measurement error during filling
Fault description
Error pattern
Cause
Rectification
4. Measured value re-
mains unchanged
during filling
Level
time
0
– False echoes in the close range
too big or level echo too small
– Strong foam or spout genera-
tion
– Max. adjustment not correct
– Eliminate false echoes in the
close range
– Check measurement situation:
Antenna must protrude out of
the socket, installations
– Remove contamination on the
antenna
– In case of interferences due to
installations in the close range:
Change polarisation direction
– Create a new false signal sup-
pression
– Adapt max. adjustment
5. Measured value re-
mains in the bottom
section during filling
Level
time
0
– Echo from the tank bottom
larger than the level echo, for
example, with products with
ε
r
< 2.5 oil-based, solvents
– Check parameters Medium,
Vessel height and Floor form,
adapt if necessary
6. Measured value re-
mains momentarily
unchanged during fill-
ing and then jumps to
the correct level
Level
time
0
– Turbulence on the product
surface, quick filling
– Check parameters, change if
necessary, e.g. in dosing ves-
sel, reactor
