9
8
DISSOLVED OXYGEN CALIBRATION
The calibration should be verified:
• after approximately 20 hours of use
• whenever the electrolyte or membrane is
changed and after cleaning the electrode
• after use in aggressive solutions.
Accessories:
• 200 cc of HI 7040 solution
• 1 bottle of HI 7041 solution
Calibration at sea level:
•
Switch the meter ON, set
the knob to the "STB"
position and wait 30 min-
utes for a complete polar-
ization of the probe.
ZERO CALIBRATION
•
Switch from "STB" to "O
2
"
position.
•
Remove the membrane
protective cap, immerse
the probe in HI 7040 zero
oxygen solution and wait
for approx. 5 minutes.
•
The indications given by the instrument
must fall to stabilization levels. If the probe
has not been sufficiently polarized, the
readout will continue to fluctuate.
In this case, switch back
to "STB" position, place
the protective cap and
wait for a few hours for
complete polarization be-
fore proceeding.
OFF
O
2
STB
°C
OFF
O
2
STB
°C
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 degree
of accuracy.
With polarized probe, oxygen is continually
"consumed" by passing through the sensitive
diaphragm and dissolving 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.
If measurements are taken with a non-polar-
ized probe, the oxygen level detected by the
meter is the sum of the oxygen dissolved in
the tested sample and that of the electrolyte
solution itself.
By leaving the instrument in
the "STB" mode (i.e. keep-
ing the probe in a continual
state of polarization), the oxy-
gen of the electrolyte solu-
tion is progressively "con-
sumed", and the following measurements de-
tect only the quantity of oxygen dissolved 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 OFF.
OFF
O
2
STB
°C
OFF
O
2
STB
°C
OFF
O
2
STB
°C
