Zero Calibration:
• Dip the probe into HI 7040 zero
oxygen solution and stir gen-
tly for 2-3 minutes.
• Allow 2 minutes for the LCD readout to
stabilize.
• Adjust the zero D.O. calibration
trimmer until the display reads
"0.0".
Note The zero calibration screw is
located close to the probe
connector.
Slope Calibration:
It is suggested to perform the slope calibration
in satured air.
• Rinse the probe in a large amount of clean
water to remove any residual zero oxygen
solution.
• Dry the probe tip and allow a few minutes for
the LCD readout to stabilize.
• Press and hold the CAL key.
• Adjust the slope trimmer on
the top of the meter to read
"100%" on the LCD (while still
holding the CAL button).
Note The slope calibration screw
is located farthest from the probe
connection.
• Release the CAL key and the
LCD will display the value in
ppm of oxygen.
The zero calibration of the HI 9142 is very
stable, therefore this procedure needs only to
be performed whenever the probe is re-
placed.
However, because the slope calibration is
more critical, it is recommended to perform
this procedure every week.
%
CAL
7
CALIBRATION PROCEDURE
PROBE POLARIZATION
The probe is under polarization with a fixed
voltage of approximately 800 mV.
Probe polarization is essential for stable mea-
surements 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 elec-
trolyte 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 surround-
ing solution.
Whenever measurements are taken with a non-
polarized probe, the oxygen level revealed is
both that of the tested solution as well as that
present in the electrolyte solution. This reading
is incorrect
The calibration is very simple and fast.
• Make sure the probe is ready for measure-
ments (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 press-
ing 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.
ON/OFF
6
