Hanna Instruments HI 9146 - Manual (Page 10)

10
With the probe properly polarized, oxygen is continually consumed
when it passes through the sensitive diaphragm and dissolves in the
electrolyte solution contained in the probe.
If polarization 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 is both that of the tested solution, as well as that
present in the electrolyte solution. This reading is incorrect.
Keep the protective cap on during polarization time and remove it for
calibration and measurements.
Note: If the probe is changed while the instrumen is ON, a conditioning
period is started.
SALINITY AND ALTITUDE COMPENSATION
If the sample contains significant concentration of salinity or if you are
performing measurements at an altitude different from sea level, the
read out values must be corrected, taking into account the lower degree
of oxygen solubility in these situations (see pages 18-19).
Remember to set the altitude and/or the salinity before taking any DO
measurements. The meter will automatically compensate for these factors.
DO MEASUREMENTS
Make sure that the instrument has been
calibrated and the protective cap has been
removed.
• Immerse the tip of the probe in the sample
to be tested. Allow approximately one
minute for the reading to stabilize.
• The Dissolved Oxygen value (in ppm) is
displayed on the primary LCD and the
temperature on the secondary LCD.
• Press RANGE to change the reading from
ppm to % and vice-versa.