User Guide

8
PROBE POLARIZATION
When the probe is under polarization it is
continuously fed with a voltage of approxi-
mately 800 mV.
Probe polarization is essential for stable mea-
surements to be taken with the same recur-
ring degree of accuracy.
In the presence of the polarized probe, oxy-
gen is continually "consumed" by passing
through the sensitive diaphragm and dissolv-
ing in the electrolyte solution contained in the
probe.
If this operation is interrupted, the electrolyte
solution continues to be enriched with oxy-
gen until it reaches an equilibrium with the
surrounding solution.
Whenever measurements are taken with a
non-polarized probe, the oxygen level detected
by the meter is both that of the tested sample
as well as the oxygen present in the electro-
lyte solution itself.
By leaving the instrument in
the "STB" mode, which sig-
nifies keeping the probe in a
continual state of polariza-
tion, the oxygen which is
present in the electrolyte solution is progres-
sively "consumed", and the following mea-
surements detect only the quantity of oxygen
present in the sample to be tested.
Therefore, in order to keep the probe continu-
ously polarized it is necessary to switch the
meter to the "STB" mode and wait for at least
30 minutes. This should be done with the
probe covered with the protective cap and
filled with some electrolyte solution.
Polarization is not maintained
when the instrument is
switched to the "OFF" posi-
tion.
OFF
O
2
STB °C
OFF
O
2
STB °C