Oxygen signal at air saturation

Problem

• The oxygen signal at air saturation, R1 [ raw signal ; V], is suddenly very different compared to previous calibrations.

Simple Solutions to Trivial Causes

Option 1: The stirrer speed (rpm) may have been changed, or the stirrer may have been left in the off mode.

Solution 1: Re-set the stirrer speed and re-calibrate.

Option 2: The gain setting may have been changed.

Solution 2: Compare calibration values at identical gain settings.

Option 3: The block temperature may have been changed.

Solution 3: Compare calibration values at identical temperatures.

Option 4: R1 is similar, but the oxygen calibration factor, Fc, may have changed, due to the use of a different oxygen saturation factor of the medium, F(M).

Solution 4: Compare calibration factors, Fc, at identical values of F(M).

Option 5: R1 has changed, but the oxygen calibration factor, Fc, remains similar, if the barometric pressure has changed (e.g. experiments carried out at different altitude). -

Solution 5: Compare calibration values, R1, at identical barometric pressure.

The problem occured after application of a new membrane

Lower R1

• The membrane thickness may have changed, possibly by inadvertently using two superimposed membranes.
• The membrane may have wrinkles in the area of the cathode.
• The black butyl rubber gasket may have not been applied properly in the centre, now partially blocking the cathode.

Higher R1

• The membrane may have been overstretched, or a thinner membrane is used.

The problem occurred after re-assembly of the O2k chamber

Lower R1

Option 1: The chamber may have been improperly positioned, with the blue POS holder (on the left or right side of the copper block) screwed too far into the chamber housing. This would allow only partial contact between the stirred medium and the cathode.

Solution 1: Follow the O2k start instructions MiPNet12.06 to insert the chamber properly.

Option 2:The electrolyte in the POS may have partially dried out.

Solution 2: Apply a new membrane, following sensor service instructions MiPNet08.04.

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