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calibration sleeve and then immersed in the measured water for about 10 minutes, then re-calibrate the
meter. The electrode polarization and calibration must be performed every time when the instrument is
turned on.
5.3
DO Calibration
5.3.1
Steps for DO calibration
a)
Press to turn on the meter, press to choose the units: mg/L (ppm) and %.
b)
Insert the DO electrode into the calibration sleeve, screw tight the calibration cap, leave it for 3~5
minutes until the reading becomes stable.
c)
Long press and enter calibration mode. CAL will be flashing at the bottom right of LCD. Wait
until the reading becomes stable and the smiley icon displays on LCD, press to calibrate.
The calibration will be completed in a few seconds and then the meter goes back to measurement
mode. If the reading is not stable, wait a few more minutes until the reading becomes stable.
Remarks: The measurement principle of the polarographic dissolved oxygen is that the oxygen reacts
through the electrode membrane at the cathode and generates an electric current. Under the same
conditions, the measured value of the dissolved oxygen electrode in air is greater than it in water.
The calculation program of this instrument sets the display value of the instrument in the air to 110%
according to the characteristics of DO500 dissolved oxygen electrode. Therefore, when the electrode
is calibrated with the calibration kit of air, the dissolved oxygen saturation is 110%, and the dissolved
oxygen concentration is 9.07mg/L (77
°F
/25°C)
; when the electrode is immersed in water to test, the
dissolved oxygen saturation is 100%, and the concentration is 8.25mg/L
(77
°F
/25°C), which means
that the measured value in the air is 10% greater than it in water. Therefore, the meter is only
suitable to calibrate in air with calibration sleeve and then measure the dissolved oxygen in water.
5.4
Other calibration and adjustment
5.4.1
Zero-oxygen calibration
Zero-oxygen calibration is generally only needed when replacing a new electrode, replacing a diaphragm
cap, and when the electrode has not been used for a long time. Generally, it is not necessary to perform
zero oxygen calibration. The instrument has been calibrated for zero oxygen before it leaves the factory,
so it is not necessary to perform zero oxygen calibration for the first use. The zero-oxygen calibration is
carried out in the following steps.
a)
Prepare 100ml anaerobic water: Weigh 5g of anhydrous sulfurous acid (Na
2
SO
3
) in a 100ml beaker, add
100ml of pure water and stir to dissolve. The anaerobic water is valid within 1 hour.
b)
Connect the electrode with the meter, wait for 5 minutes and perform calibration according to Section
5.3.1.
c)
Immerse the electrode into anaerobic water, long press and the meter enters calibration mode,
wait for about 5 minutes until the reading is
≤ 0.15mg/L
. Press to calibrate, calibration will be
finished in a few seconds, the meter displays 0.00mg/L, and then rinse the electrode with pure water.
d)
If the reading is
≤0.02 mg/L
in 5 minutes, both the response time and zero oxygen error meet the
requirements, no need to perform zero oxygen calibration, press to return to measurement mode.
e)
If the reading is >0.15mg/L after 5 minutes, it indicates that the response of the meter is slow and the
zero oxygen error is large. User can replace the membrane cap or unscrew the membrane cap, take
