The SBE 16plus V2 probe is equipped with an dissolved oxygen sensor SBE 43. Presently the Winkler method is still the reference for calibrating oxygen sensors. Oxygen concentration should be expressed in mole per kilogram of solution but is still expressed as mg / l or ml /l (for oceanographers). These milliliters match the oxygen volume in gas state in normal conditions.
Principle
The dissolved oxygen sensor SBE 43 is an electrochemical sensor composed of one anode and one cathode dipped in an electrolyte solution separated of the ambient environment by a membrane permeable to oxygen. The dissolved oxygen molecules in the water diffuse trough the membrane to the sensor. They are then reduced on the cathode thus producing an electric signal. The amount of oxygen diffusing through the membrane is proportional to the partial pressure of oxygen in the ambient environment.
The dependency to agitation
As said previously, the electrochemical sensors consume the oxygen during the measurement and consequently need a flow of water or the readings might become artificially low. The measure of dissolved oxygen is hence dependant on the flow or the movement of the water over the membrane.