7
and desirable since it will minimize air pockets in the solution. Air pockets
can compromise dissolved oxygen measurements. If the electrode solution
does not overflow, an insufficient amount was added. Repeat the process
with a new membrance cap assembly if air bubbles or air pockets are visible
when the meter is inverted. Membrane cap assemblies can not be reused.
NOTE: Air bubbles outside the cathode (6 mm in diameter in the center of
the probe) will not interfere.
9. Rinse excess electrolyte from the outside of the membrane cap assembly
and the electrode. The pH of the electrode filling solution in polargraphic
dissolved oxygen meters changes with time resulting in less accurate
results. It is recommended that the membrane and electrode filling
solution be changed every 2 - 4 weeks depending on usage. Because of the
configuration of the membrane and electrode, the membrane is stretched
by the cathode and cannot be reused. It must be replaced.
Polarization
If the meter has not been used for seven days or longer the electrode will not
be fully polarized. A fully polarized electrode is indicated by a small, flashing,
asterisk in the lower right corner of the display when the meter is OFF. If the
asterisk is absent, turn the meter ON and allow the electrode to fully polarize.
This may take 2-3 minutes. The asterisk will appear to indicate full polarization.
Calibration
Calibration should be performed daily. (Be sure the electrode is filled and fully
polarized before calibrating)
1. Turn the meter ON.
2. Press and hold
MODE
until ‘%’ is displayed.
3. Remove the electrode cap. The electrode membrane must be clean and dry
or the calibration will be incorrect. Do not touch the membrane. Skin oil will
affect the electrode response.
4. Moisten the sponge in the electrode cap with distilled water or tap water. Do
not soak the sponge.
5. Replace the electrode cap on the electrode. There must be an air gap
between the membrane and the sponge.
6. Wait until the reading stabilizes. Press and hold
CAL
until ‘CAL’ is shown on
the display. The readings will blink ‘101.7’ and ‘SA’ will appear. ‘SA’ will not
appear if the calibration fails.
7. When the calibration is complete ‘End’ will appear and the meter will return
to the measurement mode.
Optional Zero Oxygen Calibration
The zero oxygen calibration will improve the measurement accuracy for very
low or very high dissolved oxygen samples.
1. Place the electrode in a zero dissolved oxygen calibration solution, such as
5% sodium sulfite.
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