H74.0.05.6C-06
Operating Manual GMH 3651
page 9 of 18
6 The Oxygen Sensor
6.1 Design of Sensor GWO 3600
6.2 Electrode Maintenance
If electrode can no longer be calibrated, it needs maintenance.
Attention! The electrolyte is a corrosive.
To maintain electrode please proceed as follows:
1. Unscrew diaphragm head and wipe clean of electrolyte solution using a paper cloth. Do not touch
electrolyte. If your skin had contact with electrolyte, immediately rinse thoroughly with clear water.
2. Clean silver cathode with sand paper (grain size 240). Do not polish silver cathode, surface should stay
rough. Remove all dust.
3. Remove filling screw and top up lost electrolyte (e.g. using disposable syringe))
4. Put back and tighten filling screw.
5. Top up diaphragm head with electrolyte avoiding air bubbles and place on table (cover table with
absorbent paper first).
6. Keep electrode in a vertical position and screw diaphragm head to the electrode from the bottom.
Electrolyte will be forced out of the diaphragm head and spill over (put on disposable gloves or use
paper towel to touch diaphragm head).
7. Wipe up excess electrolyte with paper cloth.
The oxygen electrode is an active electrode consisting of a silver cathode
and a lead anode with the electrolyte being potassium hydroxide (KOH). In
case of oxygen being present it will be reduced at the silver cathode, i.e.
the electrode supplies a current. No oxygen means no current either. The
oxygen measurements use up both the silver cathode as well as the lead
anode. The electrode is subject to ageing. Therefore, we recommend to
maintain the electrode at monthly intervals (p.r.t. 'Electrode maintenance')
Please note: Make it a rule to always store the electrode in a
humid environment.
- in the storage flask filled with water
- in another container filled with water
If electrode has not been used for some time, clean diaphragm
with soft cloth and remove deposits, if any (algae, bacteria
etc.).
Electrode design
The electrode housing is made of PVC. With the exception of the electrode
shaft all parts need to be maintained regularly and be replaced if
necessary.
o Protective flask
: The protective flask is used to moisten the
diaphragm. This The prolongs service life of the electrode. The
protective flask contains water. Attention! Use water only; never use
potassium chloride (KCI); this is only required for storage of pH-
electrode.
o Diaphragm head
: the diaphragm head is covered with a teflon
diaphragm. It will be filled with KOH electrolyte and screwed onto the
electrode shaft (no air bubbles). Damages in the diaphragm, large air
bubbles or air bubble rings in the diaphragm head will result in
erroneous measurements. This may also be the reason for errors in
the calibration. The diaphragm head is a spare part and can be
ordered individually.
o Filling hole
: If the electrode is used at high temperatures or if it has
been stored without its protective flask for a longer period of time,
some electrolyte will be lost due to evaporation. During maintenance
make it a rule to unscrew diaphragm head, remove locking screws
and top up electrolyte using a syringe. Replace and tighten locking
screws.
Attention when working with electrolyte! The electrolyte is
corrosive! (strong base, KOH)
Filling hole
Electrode shank
O-ring
Diaphragm cap
