20
MW605 Dissolved Oxygen & Temperature Portable Meter
8. ALTITUDE & SALINITY COMPENSATION
Temperature, pressure (altitude) and salinity influence DO
concentration.
Cold water holds more oxygen and therefore DO concentration
increases with decreasing temperature. Compensation for
temperature-related solubility is done automatically using the
probe’s built in temperature sensor.
Altitude compensation
When measurements are done at an altitude below sea level,
oxygen solubility increases. Conversely for measurements made
above sea level, the oxygen solubility decreases.
Select the approximate altitude in the SETUP menu (see Altitude
Compensation for details).
Salinity compensation
The solubility of oxygen in water is also influenced by the amount
of salt in the water.
Freshwater holds more oxygen than saltwater does.
Seawater typically has a salinity of 35 g/L and the oxygen
solubility is 18 % less compared to fresh water at 25 °C. By entering
the approximate salinity value, the calibration and subsequent
concentration measurement will be compensated to display the
correct oxygen concentration. A 18 % error would result if the
salinity value is not entered.
The solubility of oxygen dissolved in water decreases in brackish
or seawater; or for measurements made at above sea level altitude.
