LaMotte DO 4000 Dissolved Oxygen Meter - Manual (Page 9)

POLARIZATION
Polarization is the term used to describe when the probe has reached
equilibrium, and is able to produce stable, reliable measurements. For
the probe to be polarized, voltage must continually be applied to the
probe, allowing the oxygen reaction to proceed. When voltage stops, the
reaction no longer continues and the probe is no longer considered
polarized. When either ppm or %SAT is selected on the meter, a voltage
is automatically applied across the electrodes, but the reading is not
accurate until the 15 minute “warm up” time has elapsed. The DO4000
has a constant polarization feature, which allows a small voltage to be
continuously applied to the probe, even when the meter is turned off,
eliminating the 15 minute warm up time. To select the constant
polarization option, set the small button between the connectors to the
OUT position. Since it does use power to keep the probe constantly
polarized, it is recommended this feature not be used if there will be a
span of several hours between measurements.
Do not leave probe polarized for prolonged periods of time
(overnight). Prolonged use will cause membrane fouling and require
more frequent anode cleaning.
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