Hanna Instruments HI 9142 - Manual (Page 9)

8 9
PROBE POLARIZATION
The probe is under polarization with a fixed voltage of
approximately 800 mV.
Probe polarization is essential for stable measurements with the
same recurring degree of accuracy.
With the probe properly polarized, 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 oxygen until it reaches an equilibrium with the
surrounding solution.
Whenever measurements are taken with a non-polarized probe, the
oxygen level revealed are both that of the tested solution as well
of the electrolyte solution. This reading is incorrect.
CALIBRATION PROCEDURE
Connect the probe to the instrument.
Turn the instrument ON by pressing
On/Off.
At start-up the display will show
all the used segments for a
few seconds followed by the
percentage indication of the
remaining battery life.
• After a few seconds “ Cnd
Prb” message appears, to
inform the user that the
probe is in auto-conditioning
mode (automatic polarization,
about 1 minute).
Note: Press any key (except On/Off) to skip conditioning
time.
• When the conditioning message disappears, the probe is
polarized and the instrument can be calibrated.
• The meter is now ready to operate.
If the probe is not connected, the display shows “ ---“ on both
LCD lines.
The auto-off feature turns the instrument off after about 8 min,
if no key is pressed.
The calibration is very simple and fast.
• Make sure the probe is ready for measurements (see initial
preparation at page 7), i.e. the membrane is filled with
electrolyte and the probe is connected to the meter.
• Switch the meter on by pressing the On/Off
key.
• For an accurate calibration, it is recommended
that you wait at least 15 minutes to ensure
precise conditioning of the probe.
• Remove the protective cap from the D.O.
probe.