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4.1.3 DO Cal. Procedure for 0%
Saturation
When measuring a low concentration sample (less than
10% saturation), a second percent saturation calibration
point for a zero oxygen standard is often recommended.
Prepare a sodium sulfite solution:
a. Dissolving about 15 grams of Na2SO3 in about
250 mL of deionized water.
b. Transfer the solution to a BOD bottle or flask.
c. Add a stir bar to the BOD bottle or flask.
d. Insert the DO electrode into the bottle or flask
and use parafilm to seal the open area
between the bottle or flask and the sensor.
e. Place the bottle or flask on a magnetic stir plate
and gently stir the solution.
f. Wait at least five minutes for the DO electrode
to equilibrate.
Ensure the active measure mode is dissolved
oxygen as percent saturation.
Press the "Cal" key to start the calibration.
Ensure the DO electrode is in the prepared zero
oxygen solution and equilibrated.
Wait for the DO value to stabilize.
a. While the reading is stabilizing, the stopwatch
icon is shown and the reading flashes.
b. When the reading is stable, the checkmark icon
is shown, and the reading is solid.
Once the reading is stable, press the "Enter" key to
accept the DO value.
The meter will display the calculated offset value and
then proceed to the main measure mode.
Note: Press the "Measure" key at any time to abort the
calibration and return to the main measure mode.
26
Chapter 4 | Calibration
4.1.4 DO Cal. Procedure for
Concentration
For a dissolved oxygen as concentration calibration, a
minimum value of 2.0 mg/L (ppm) must be entered and the
entered concentration value must be within ±40% of the
factory default concentration value.
Ensure the active measure mode is dissolved
oxygen as concentration.
Press the "Cal" key to start the calibration.
Rinse the DO electrode and place into the prepared
DO standard.
Wait for the DO value to stabilize.
a. While the reading is stabilizing, the stopwatch
icon is shown and the reading flashes.
b. When the reading is stable, the checkmark icon
is shown, and the reading is solid.
Once the reading is stable, accept tor edit the
displayed DO standard value:
a. To accept the DO standard value, press the
"Enter" key.
or
b. To edit the DO standard value, press the or
key to change the value and then press the
"Enter" key to save the value.
i.
Press the key to increase by one
digit. Press and hold the key to
quickly increase.
ii.
Press the key to decrease by one
digit. Press and hold the key to
quickly decrease.
The meter will display the calculated slope value and
then proceed to the main measure mode.
Note: Press the "Measure" key at any time to abort the
calibration and return to the main measure mode.
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