User Manual

<14. CALIBRATION OF DO (Dissolved Oxygen)>
14-3
IM 12A01A02-01E 5th Edition : Oct. 31, 2013-00
14.3 Manual slope calibration
Calibratethesensitivityofthesensorwithasolutionofknownoxygenconcentration.
First,analyzetheoxygenconcentrationofasamplesolutionandthencalibratethesensor
sensitivity to adjust to this value. From the actual measurement of salinity and temperature,
obtainthedissolvedoxygenconcentrationbyreferringtoTable1inAppendix4andenterit.
When salinity must be considered, perform the calibration manually.
Notethefollowing:
• Quicklyanalyzethesamplewatertopreventthedissolvedoxygenconcentrationor
temperature from changing.
• Beforeanalyzingthesamplewater,analyzethereferencewithacalibratedlaboratory
instrument.
• Toeliminateanydiscrepancies,thelaboratoryinstrumentmusthavebeencalibratedwith
thesamecalibrationdataasspeciedinISO5814.
Conrmthatthereadingoftheinstrumentisstableandthesensorisclean.Ifthereading
remains unstable, set the sensor in the maintenance mode and wash off any stain on the sensor
membrane. Return the sensor to the sample water and leave it until the reading becomes stable.
l Salinity compensation
To compensate salinity, select “Enabled” in “Measurement setup” – “Salinity compensation” –
“Compensation” (see Section 13.2.4).
PerformcalibrationbyreferringtoTable1inAppendix4.
Example:
When the atmospheric pressure is 101.325 kPa, the solution temperature is 22.5°C, and the
salinityis30g/kg(3wt%seawaterequivalent):
(1) Calculate the saturated concentration of desalinated water.
 AccordingtoTable1inAppendix4,thesaturatedconcentrationis8.74mg/lat22°Cand
8.58 mg/l at 23°C.
The value at 22.5ºC is calculated as follows:
  8.74+(8.58–8.74)×(22.5–22)=8.66mg/l
(2) Compensate the value for salinity.
The compensation value for 30 g/kg salinity at 22.5°C is calculated as follows:
  0.0453+(0.0443–0.0453)×(22.5–22)=0.0448mg/l
0.0448×30=1.34mg/l
(3) Calculate the saturated concentration of the solution (for calibration).
The saturated concentration for 30 g/kg salinity at 22.5ºC is calculated as follows:
  8.66–1.34=7.32mg/l
14.4 Temperature calibration
For the most accurate measurements, it is important to have a precise temperature
measurement. Measure the temperature with a high-precision thermometer and adjust the
sensor reading accordingly. For best accuracy, this should be done as near to the normal
operating temperature as possible.
DO
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