VEGA VEGAFLEX 86 Foundation Fieldbus - Manual (Page 70)

70
9 Diagnostics and service
VEGAFLEX 86 • Foundation Fieldbus
44233-EN-130910
Measurement error with constant level
Fault description Error pattern Cause Rectification
1. Measured value
shows a too low or too
high level
Leve
l
time 0
– Min./max. adjustment not
correct
– Adapt min./max. adjustment
– Wrong linearization curve – Adapt linearization curve
2. Measured value
jumps towards 100 % Level
time 0
– Due to the process, the ampli-
tude of the product 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 echoes, carry
out false signal suppression,
e.g. with condensation
Measurement error during filling
Fault description Error pattern Cause Rectification
3. Measured value
jumps towards 0 %
during filling
Level
time 0
– Amplitude of a multiple echo
(vessel top - product surface) is
larger than the level echo
– Check parameter "Application",
especially vessel top, type
of medium, dished end, high
dielectric constant, adapt if
necessary
– The level echo cannot be distin-
guished from the false echo at
a false echo position (jumps to
multiple echo)
– In case of interferences due to
installations in the close range:
Change polarisation direction
– Chose a more suitable installa-
tion position
– Transverse reflection from an
extraction funnel, amplitude of
the transverse reflection larger
than the level echo
– Direct sensor to the opposite
funnel wall, avoid crossing with
the filling stream
4. Measured val-
ue fluctuates around
10 … 20 %
Level
time 0
– Various echoes from an uneven
product surface, e.g. a material
cone
– Check parameter "Type of
medium" and adapt, if neces-
sary
– Optimize installation position
and sensor orientation
– Reflections from the product
surface via the vessel wall
(deflection)
– Select a more suitable installa-
tion position, optimize sensor
orientation, e.g. with a swivel-
ling holder
5. Measured value
jumps sporadically to
100 % during filling
Leve
l
time 0
– Varying condensation or con-
tamination on the antenna
– Carry out a false signal sup-
pression or increase false
signal suppression with con-
densation/contamination in the
close range by editing
– With bulk solids use radar sen-
sor with purging air connection
or flexible antenna cover