EUTECH INSTRUMENTS WATERPROOF CYBERSCAN PD 300 PHDISSOLVED OXYGEN METER, Инструкция по эксплуатации, Страница: 52 / 66

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8.2 Dissolved Oxygen Principle
The probe is a galvanic measuring element which produces
an output proportional to the oxygen present in the medium in
which it is placed. The galvanic probe design lets you take
measurements immediately – without the typical 15 minute
wait of other dissolved oxygen probes.
The probe consists of two parts:
•
An upper part consisting of an anode, a cathode, and
cable.
•
A lower part consisting of a membrane cap, membrane,
and electrolyte solution.
See Figures 40 & 41.
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 that a new sample must 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 2.5 cm/sec.
The permeability of the membrane to oxygen varies greatly
with temperature. Therefore compensation is needed for this
variation. The Eutech Instruments’ DO probe comes with an in-built Temperature
Compensation for the membrane variation.
Figure 40: Main parts of
Dissolved Oxygen electrode