Thermo Fisher Scientific CyberScan DO 110 - Manual (Page 50)

Instruction Manual CyberScan DO 110
45
10 Dissolved Oxygen Probe
10.1 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.
10.2 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.
Since any deposits on the membrane surface act as a barrier to oxygen diffusing
through the membrane, the membrane must be cleaned at regular intervals to assure
maximum reliability.
After using the probe, rinse the probe in clean water and wipe it with a soft cloth or
paper to avoid any hardening of deposits. If growth develops on the probe, use a
disinfecting chemical to clean.
NOTE: Although the membrane is strong and not easily damaged, wipe it
gently while cleaning it. If the membrane is damaged or torn, the probe
will no longer function.
There are no special probe storage requirements.