DataSonde 4 only. Circulation brings a small undivided portion of a water body directly to the sensors which determine the true water quality measurements. Proper movement of water past the sensors prevents water stagnation at the surfaces of these sensors. Natural water flow or forced flow from mechanical stirring or agitation are the two most common forms of circulation for water quality monitoring devices. The operator can choose between several different common temperature compensation routines.
Depth is the vertical distance between the probe and the surface of the water.
A pressure transducer is used to measure the pressure at a particular point in the water column, and depth is calculated using the average density of water while compensating for any salt content. This allows the user to construct vertical profiles of other parameters in a water column. D.O. is measured in milligrams per liter as well as in percent saturation. Oxygen is less soluble in warm and salty waters, so the instrument compensates the apparent percent saturation for changes in temperature and conductivity. Sufficient sample flow is required to prevent falsely low readings due to depletion of oxygen in the solution in front of the probe.