PASCO PS-2108 Dissolved Oxygen Sensor - Manual (Page 9)

Model No. PS-2108 Dissolved Oxygen Sensor
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your software settings back to mg/L.
DataStudio: Click the Setup button on the DataStudio toolbar. Click the % button next to the Calibrate button and
select mg/L from the drop-down menu.
Note: Calibration is not required for measurements of relative DO content, such as before/during/after
experiment relative changes.
2. Click the Calibrate… button to open the Calibrate dialog.
3. Place the probe in 100% humidified air. When the readings stabilize around a value, click
the Set button. Then click OK. It may take a few minutes for the sensor to equilibrate for
calibration. The readings may not completely stabilize at one specific point.
Calibration in 100% humidified air is equivalent to calibrating in 100% air-saturated
water. This is because the oxygen must first pass through the electrolyte solution in the
Dissolved Oxygen Sensor to get to the cathode. The concentration of oxygen in both the
100% air-saturated water and the electrolyte solution will be equivalently proportional to
the partial pressure of oxygen in air, following Henry's law where
Cg = the solubility of the gas (oxygen)
Pg = the pressure of the gas over the solution
This relationship holds true whether the end of the sensor is immersed in the water or
suspended in air.
4. Before taking measurements of dissolved oxygen concentration, change your unit settings
back to mg/L.
Cg=k Pg
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