Dissolved Oxygen/Air Pressure Measurement - Consort C32 Serie Anleitung

Dissolved oxygen/Air pressure measurement

Dissolved oxygen measurement
Select the desired mode (ppm) or (%O 2 ) by pressing   . The display will immediately show the
1.
measured
value according to the previous calibration. Should you want to recalibrate, press CAL.
2. The display shows the salinity correction. Select the proper value and press OK. Leave salinity
correction to zero unless you are going to measure in heavily salted solutions such as e.g. sea-water (35
g/l). Select [CALIBRATE], press OK and follow the instructions on the screen until the calibration is
finished.
3. The electrode exposed to the air reaches an equilibrium corresponding to the partial pressure of oxygen
and thus to saturation in water at the given temperature. The instrument shows the measured saturation,
current, temperature, and will calibrate automatically when readings are stable.
4. After rinsing the electrodes with distilled water, immerse them in the samples and read the display.
Stirring the solution during the measurements promotes the homogeneity and is obligatory! The
advection rate must be at least 10 cm/s.
5. Rinse the electrode always after use and store it in distilled water.
•
A blinking decimal point warns you for unstable measurements. Wait to read the display!
•
Stirring the solution during the measurements promotes the homogeneity and is therefore always
recommended.
•
Hold MODE pressed and press
Air pressure measurement
Select the desired mode (hPa) by pressing   . Should you want to recalibrate, press CAL.
1.
2. Select [CALIBRATE], press CAL, adjust to the real air pressure and press OK.
•
Select [RESET] and press OK to reset the calibration.
Principle
The oxygen meter and its electrode function according to the Clark principle with silver as cathode and lead as
anode in an electrolyte cell. Oxygen gas present in the electrolyte is reduced to OH ions at the cathode. The
resulting current is diffusion limited and therefore proportional to the oxygen concentration in the sample solution.
This current is amplified, corrected, and displayed in mg/l, ppm or % dissolved oxygen.
Interferences
All substances which can diffuse through the membrane and for which 800 mV potential suffices for polarographic
reduction, will be reduced in the electrode. This will give a corresponding current contribution, if they are present.
Interference can be caused by ions entering the electrode through porous or mechanically damaged membranes
and by diffusion of other reactive gases apart from oxygen, e.g. CO 2 , Cl 2 , SO 2 , and H 2 S. These substances
react in undesired manner with the electrode. Acidic or basic gases change the pH value of the electrolyte
solution and thus disturb the reading, particularly when measuring small oxygen concentrations. High salt
concentrations in the sample solution can falsify readings too.

to change the resolution from 0.1 to 0.01 ppm or from 1 to 0.1 %.
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