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3.2.3 Span Calibration in Solution (Salinity-corrected ppM Mode only)
This span calibration provides an alternative to calibrating the Dissolved Oxygen sensor in air. It is
only available when the
90-FL
is in Salinity-corrected ppM mode. Please note that the normal AIR
calibration (section 3.2.2) is still available for Salinity-corrected ppM mode.
1.
Measure the Dissolved Oxygen content of the solution to be used for calibration. This is
generally done with a Winkler titration. The
90-FL
span calibration should be performed
immediately the Dissolved Oxygen content of the solution is known, as the value may not be
stable.
2.
Place the Dissolved Oxygen and Conductivity/TDS sensors into the calibration solution. Ensure
that the Conductivity/TDS sensor is calibrated and is correctly immersed (see sections 4.4 and
5.4).
The solution must be stirred at a moderate rate.
Allow the reading to stabilise. After a zero calibration, this may take up to 5 minutes.
3.
Select Oxygen Calibration. (
→
→
F1:Calibrate
→
→
F1:Oxygen
)
When the reading is above approximately 2 ppM, the
90-FL
will display the AIR/SPAN
calibration screen. Note the cursor underlining the “
A
” in “
Air
”.
9.10ppM 25.0
o
c
Oxygen AIR/SPAN Calibration, Press Enter
Use the numeric keypad to enter the Dissolved Oxygen value of the solution. The words
“AIR/SPAN” are deleted and the value being entered is displayed. The Conductivity or TDS
reading also appears as soon as the first numeric key is pressed.
Press the
to correct any errors.
Ensure that the Dissolved Oxygen, Conductivity/TDS and Temperature readings are fully
stable.
Press
to calibrate.
A “
∗
” in the display will be replaced by a decimal point after a successful air calibration.
4.
The
90-FL
is now calibrated and is ready for Dissolved Oxygen measurements. Rinse the
Dissolved Oxygen sensor in distilled water and blot dry before placing it into unknown
samples.