Dissolved Oxygen/Air Pressure Measurement - Consort C3 10-Serie Anleitung

Dissolved oxygen/Air pressure measurement

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Dissolved oxygen measurement
1. Select the desired mode (ppm) or (%O
immediately show the 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 ê to change the resolution from 0.1 to 0.01 ppm or
from 1 to 0.1 %.
Air pressure measurement
1. Select the desired mode (hPa) by pressing é ê . Should you want to
recalibrate, press CAL.
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 , Cl
2
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.
(C3x2x/C3x3x/C304x only)
) by pressing é ê . The display will
2
(C3x2x/C3x3x/C304x only)
, SO , and H S. These substances react in undesired
2 2 2
5