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Changing the Membrane
To change the membrane, perform the following steps, refer to figure 5.
1. Remove the dissolved oxygen sensor from the probe. To do this, lift the sensor
guard and rotate the bottom section of the probe to expose the sensors. Ensure
that the probe and sensors are completely dry. Use a cotton bud to dry the area
between the sensors. Using pliers, lever the dissolved oxygen sensor out of the
probe.
2. Unscrew the retaining ring and remove the old membrane.
3. Check the O-ring and discard if it is damaged then flush out the old electrolyte.
4. To refill with electrolyte (1.0 M KOH), hold the probe vertical and place the
nozzle of the squeeze bottle beside the silver electrode. Squeeze the bottle to
fill the probe with electrolyte until it flows over the top of the probe.
5. Be sure that there are no bubbles inside the sensor.
6. Take a new membrane and centralise it on top of the electrode and let it float
on the surface.
7. Place the retaining nut over the membrane and screw down firmly so that the
membrane is well tensioned.
8. Check that there are no bubbles in the electrolyte. If bubbles are found, repeat
the above procedure.
9. Apply a smear of O-ring grease to the body of the sensor and push it back into
the probe. Be sure not to damage the membrane and be sure to push the
sensor in until it clicks into place
10. Wait at least 2 hours for the sensor to stabilise then recalibrate the dissolved
oxygen readings.
Dissolved Oxygen Stirrer Maintenance
Figure 5: Exploded view of dissolved oxygen
sensor.