Hanna Instruments HI 9141 - Manual (Page 6)

11 10
CALIBRATION
PROBE POLARIZATION
The probe is under polarization with a fixed
voltage of approximately 800 mV. Probe po-
larization is essential for stable measurements
with the same recurring degree of accuracy.
With the probe properly polarized, oxygen is
continually "consumed" when it passes
through the sensitive diaphragm and dissolves
in the electrolyte solution inside the probe.
If polarization 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 measured oxygen
level is both that of the tested solution as
well as that present in the electrolyte solu-
tion. This reading is not correct.
The calibration procedure is very simple and
should be performed every time the meter is
turned on.
•
Make sure the probe is ready for mea-
surements (see page 10), i.e. the mem-
brane cap is filled with electrolyte, the
probe is connected to the meter and prop-
erly polarized.
• Switch the meter on by pressing ON/OFF.
The "Cond" message appears on the dis-
play to inform that the probe is in auto-
conditioning (polarization) mode.
• Once the "Cond" disappears, the instru-
ment can be calibrated.
ON/OFF
THEN SCREW
BACK ON
THEN TAP
FILL FIRST
INITIAL PROBE PREPARATION
All HANNA DO probes are shipped dry.
To hydrate the probe and prepare it for use,
connect it to the meter and proceed as fol-
lows:
1. Remove the red & black plas-
tic cap. This cap is for ship-
ping purposes and can be
thrown away.
2. Wet the sensor by soaking
the bottom 2.5 cm (1") of the
probe in HI 7041S electrolyte
solution for 5 minutes.
3. Rinse the membrane (HI76407A supplied
with the meter) with electrolyte solution
while shaking it gently.
Refill with fresh
electrolyte.
4. Gently tap the
sides of the mem-
brane cap with
your finger to en-
sure that no air
bubbles remain
trapped. To avoid
damaging the
membrane, do not
tap the membrane
directly on the bot-
tom.
5. Make sure that the rubber O-ring sits prop-
erly inside the membrane cap.
6. With the sensor facing down, slowly screw
the cap clockwise. Some electrolyte will
overflow.
When not in use, protect the mem-
brane with the supplied cap.
Shipping
cap
black
red