User Guide

16
TAKING MEASUREMENTS
Make sure the meter has been
calibrated and the protective
cap has been removed.
Immerse the tip of the probe
in the sample to be tested.
For accurate dissolved oxygen
measurements a water move-
ment of 0.3 m/sec is required
at a minimum. This is to en-
sure that the oxygen-depleted
membrane surface is con-
stantly replenished. A moving
stream will provide adequate
circulation. To quickly check if the water
speed is sufficient, wait for the reading to be
stable and then move the D.O. probe. If the
reading is still stable, the measurement con-
ditions are right, while if the reading increases
the water movement is too low.
During field measurements, this condition may
be met by manually agitating the probe. Ac-
curate readings are not possible while the
liquid is at rest.
During laboratory measurements, the use of
a magnetic stirrer to ensure a certain velocity
in the fluid is recommended. In this way,
errors due to the diffusion of the oxygen
present in the air in the solution are reduced
to a minimum.
At all times, the time necessary for thermal
equilibrium to occur between the probe and
the sample must be allowed (a few minutes
for temperature difference of several degrees).