Thermo Fisher Scientific CyberScan DO 600 - Manual (Page 120)

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3.2 Dissolved Oxygen Probe
3.2.1 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.
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
DO probe comes with an in-built Temperature Compensation for the
membrane variation.
3.2.2 Probe Care
Under typical operating conditions, the probe should last for several
years. Proper care and maintenance will help you receive the maximum
probe life and ensure more accurate readings.
5 Units of measurement
6 Temperature reading & units
7 Temperature compensation mode
8 HI & LO Alarm limits
9 Alarm indicator
10 ppt indicator for input of salinity value
11 DO calibration point