Metrohm 893 Professional Biodiesel Rancimat User Manual
Page 49
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6 Troubleshooting
893 Professional Biodiesel Rancimat
￭￭￭￭￭￭￭￭
41
Problem
Cause
Remedy
See also: The induction
time is longer/shorter than
expected.
The measurement
curves are extremely
noisy.
The air supply for the mea-
suring solution is directed
to the conductivity measur-
ing cell.
Loosen the tubing adapter on the measuring
vessel cover and turn the PTFE cannula such
that the air is no longer directed to the elec-
trode and fix it in this position.
Gas bubbles adhere to the
conductivity measuring cell
during measurement.
￭
Make sure that the measuring cell is clean
and free of fat. If necessary, clean thor-
oughly.
￭
In some cases, ultrapure water contains a
large proportion of dissolved air. In this
case, degas the ultrapure water before the
measurement for 5 to 10 min in a vacuum.
During the measurement,
sample evaporates in the
reaction vessel and con-
denses in the measuring
vessel. This results in con-
tamination of the conduc-
tivity measuring cell, which
in turn promotes adher-
ence of gas bubbles.
￭
Keep the measuring time as short as possi-
ble, by about 4 to 6 h. The induction time
can be reduced by about half by increasing
the temperature by 10 °C.
￭
Reduce the temperature to such an extent
that sample evaporation is minimized or
eliminated. However, this can substantially
extend the measuring time. The induction
time approximately doubles by reducing
the temperature by 10 °C.
￭
Use an oil separator (6.2753.200).
The curve shows a
step which means
that the induction
time is no longer
determined cor-
rectly.
Side reactions occur at the
start or during the mea-
surement. These reactions
cause the conductivity in
the measuring cell to rise.
￭
Use the Evaluation suppression in the
method.
￭
In addition to Endpoint(s) activate also
Conductivity (e.g. 200 µS/cm) as stop cri-
terion in the method and select the Stop
once all the criteria have been fulfilled
option. The evaluation parameters can be
optimized on the basis of this curve, or the
curve can be evaluated manually.
￭
Increase the Evaluation sensitivity
method parameter.