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necessary, calibrate it according to standard value measured by aneroid barometer. Refer to parameter
setting P4.3 for the procedure of aneroid barometer calibration.
5.2.5
Salinity compensation
The instrument has manual salinity compensation. It is set in the parameter P4.2 (0 to 45 ppt). To obtain
accurate readings in mg/L and ppm, it is necessary to know the salinity of the test sample and input
salinity value into the instrument. As the salinity of the solution increases, the level of DO decreases.
Generally, salinity of freshwater is 0 to 0.5ppt, salinity of seawater is 35ppt.
5.3
DO Calibration
5.3.1
Saturated oxygen calibration
a)
This procedure requires the use of a calibration sleeve to allow the probe to be calibrated in a
humidity-saturated atmosphere.
b)
Check if the sponge in the calibration sleeve is damp. Attach the calibration sleeve to the probe.
Tighten the locking cap. Be careful not to have water droplets on the head of the sensor cap. Wait for
5 to 10 minutes after turning on the instrument in order to saturate the air in the calibration sleeve
with water vapor. In addition, wait for the temperature to completely stablize.
c)
Long press to enter the calibration mode, and
CAL
is flashing in the upper right corner. Wait for
the stable icon to appear and stay on LCD, press to calibrate. Once
100%
becomes stable,
the saturated oxygen calibration is completed.
5.3.2
Zero-oxygen calibration
Zero-Oxygen calibration is only performed when a probe or sensor cap is replaced, the probe 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)
Preparation of 100ml of oxygen-free water: in the 100ml beaker, weigh 2g of anhydrous sodium
sulfite (Na
2
SO
3
) and add 100ml of distilled or deionized water to dissolve. Oxygen-free water is only
effective within 1 hour.
b)
Put the electrode into the oxygen-free water, wait for 3 to 5 minutes after the instrument is turned
on, and wait for the temperature and DO reading to completely stabilize. The DO reading should be
very close to 0.1mg/L.
c)
Long press to enter the calibration mode.
CAL
will be flashing at the bottom right corner. Wait
for a stable . Press to calibrate and the zero-oxygen calibration is completed.
5.4
Special notes for calibration
a)
Optical dissolved oxygen probes have better stability and smaller calibration drift compared to
conventional electrochemical dissolved oxygen electrodes, which means that the meter can maintain
