Nova-Tech DO 700 - Manual (Page 22)

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7. ELECTRODE MAINTENANCE
The DO 700 electrode produces an output proportional to the oxygen
present in the medium in which it is placed. The galvanic probe design
allows for immediate use—unlike the typical 15 minute warm-up period
required for polargraphic electrodes.
The probe consists of two parts. The upper part consists of the anode,
cathode, and dual cable. The lower part consists of a pre-assembled
cap, and electrolyte solution.
Oxygen diffuses through the membrane onto the cathode, where it is
consumed. This process produces an electrical current which flows
through the cable to the meter. The electric current produced is
proportional to the oxygen that passes through the membrane and the
layer of electrolyte. This makes it possible to measure the partial
pressure of oxygen in the sample at a given temperature.
Since the DO in the sample is consumed by the cathode it is essential
to have flow past the membrane of the probe to prevent the occurrence
of false readings. The probe uses very little oxygen for its
measurement. This enables it to function correctly with liquid
movement as low as 2 inch/sec across membrane.
The permeability of the membrane to oxygen varies greatly with
temperature. Therefore compensation is needed for this variation. The
DO 700 probe comes with built-in temperature compensation for the
membrane variation.
Proper maintenance will help you maximize probe life and achieve
most accurate readings.
Deposits on the membrane surface act as a barrier to oxygen diffusing
through the membrane, so clean the membrane to assure maximum
reliability. After each use, rinse the probe with clean water to avoid any
hardening of deposits or bacterial growth.
NOTE: Although the membrane is strong and not easily damaged,
wipe it gently while cleaning it. If the membrane is punctured,
damaged, or torn, the probe will not function properly.