Maintenance
D.O. Sensor Maintenance
To maintain the performance and accuracy of the dissolved oxygen sensor, the membrane should
also be replaced if it becomes damaged or contaminated with organic matter. Clean the membrane
with cotton wool saturated with alcohol
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 or paper towel to dry the area between the
sensors. Using a flat screw driver, lever the dissolved oxygen sensor out of the probe.
2.
With the sensor removed, 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 with distilled
water.
4.
To refill with electrolyte (1.0 M KOH), hold the probe vertical and place the nozzle of the
squeeze bottle above and beside the silver electrode. Squeeze the bottle to fill the probe
with electrolyte until it flows over the top of the sensor.
5.
Be sure that there are no bubbles inside the sensor. Tapping the side of the sensor (with a
ruler) can help dislodge any trapped bubbles.
6.
Again add more electrolyte to form a meniscus.
7.
Take a new membrane in hand and centralise it on top of the electrode and let it float on
the surface.
8.
Place the retaining nut over the membrane and screw down firmly so that the membrane is
well tensioned.
9.
Check that there are no bubbles in the electrolyte. If bubbles are found, repeat the above
procedure from step 5.
10.
Apply a smear of O‐ring grease to the o‐ring 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 cannot go
any further.
Figure 5: Exploded view of dissolved oxygen
sensor.