LaMotte DO 4000 Dissolved Oxygen Meter - Manual (Page 6)

The dissolved oxygen test is also important to operators of waste water
facilities, both at the operation site and in the lab. Dissolved oxygen
levels are monitored at the wiers, and before the water leaves the plant
after being dechlorinated. In the laboratory the dissolved oxygen test is
used to analyze the BOD of the water.
DO METER BASICS
A voltage is applied across the electrodes of the Dissolved Oxygen
probe. Silver ions are oxidized at the anode producing silver chloride
and electrons. Oxygen is reduced at the cathode accepting electrons and
producing hydroxide ions. The current generated by the chemical
reactions is conducted through the filling solution. This current is
proportional to the oxygen concentration and is converted by the meter
to a dissolved oxygen reading.
The DO 4000 provides a digital readout of oxygen concentration in
mg/L or ppm, or percent (%) saturation. The meter compensates for
temperature and salinity which can effect the dissolved oxygen reading.
Built-in thermistors automatically provide a readout in degrees
centigrade (°C). Salinity levels from 0 to 30 parts per thousand (ppt) are
set with the “Salinity Comp” knob. An altitude correction can be
determined by consulting the Altitude Chart on page 13.
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