Problems with Calibrating Dissolved Oxygen

Problems with Calibration

Calibrating Dissolved Oxygen has been problematic, and has never worked correctly. Instead of displaying a consistent reading, when submerged in a liquid the probe will at first display a value of either 99% Dissolved Oxygen or -99% Dissolved Oxygen, and after a few seconds of sampling, will start jumping wildly, going from -99% to 50% to -37% to 77%, or following another, similar pattern.

The following techniques were used to calibrate Dissolved Oxygen:

Note that none of them have worked correctly.

The Chemistry department has a tank of water through which oxygen is constantly bubbled through, giving the solution a concentration of 100% Dissolved Oxygen or approximately 8 mg/l. The probe was submerged in the solution and calibrated both with Dissolved Oxygen % and Dissolved Oxygen mg/l with the appropriate atmospheric measurements taken.

Filling the calibration chamber slightly with water, then loosening the top of the chamber to allow for the water to evaporate, then allowing the water to sit for 10 minutes and evaporate, thus saturating the chamber. The probe was then calibrated with the Dissolved Oxygen % option, again, using the appropriate atmospheric measurements. This was attempted with both the computer modules we built and the YSI 650 unit.