Hanna Instruments HI 9141 - Manual (Page 7)

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TAKING MEASUREMENTS
Make sure the meter has been
calibrated and the protective
cap has been removed. Im-
merse the tip of the probe in
the sample to be tested.
Make sure the temperature sensor is also
immersed.
Allow approximately one minute for the meter
to stabilize before reading on the display the
mg / L (ppm) value of dissolved oxygen.
For accurate measurements a minimum wa-
ter movement of 0.3 m/sec is required. This
is to ensure that the oxygen-depleted mem-
brane surface is constantly replenished. A
moving stream provides adequate circulation.
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 air oxygen into
the solution are minimized.
Always allow the time necessary for thermal
equilibrium to occur between probe and tested
sample (a few minutes if the temperature
difference is only several degrees).
ppm READINGS
The meters display the con-
centration of the dissolved oxy-
gen directly in ppm (mg/L).
If the sample contains significant salinity
concentration or measurements are per-
formed at an altitude different from sea
level, the readout values must be corrected,
• For an accurate calibra-
tion, it is recommended
to wait for 5-10 minutes to
ensure precise condition-
ing of the probe.
• Remove the protective
cap.
• Press the CAL key. The "CAL" message
is displayed to indicate that the calibra-
tion mode has been entered.
• The instrument will automatically standard-
ize itself to the actual saturation value and
after approximately 1 minute, will show
the ppm value corresponding to the maxi-
mum oxygen level soluble in water at that
particular temperature, altitude and salin-
ity (previously set).
Once the ppm value is dis-
played, the calibration is
completed.
• Press the FUNCTION key
and make sure F1 and F2
are set to the appropriate
altitude and salinity values
(see "Altitude Compensation" and "Salin-
ity Compensation" sections for details).
Notes: • The instrument must also be cali-
brated whenever the probe, the mem-
brane or the electrolyte solution are
changed.
• To exit the calibra-
tion mode at any
time, press the CAL
key.
CAL
CAL
FUNCTION