Hach-Lange ORBISPHERE 31xxx Installation and Maintenance - Manual (Page 34)

32
Maintenance
5.3.5 O
3
Sensor only: final center electrode cleaning
Once the O
3
sensor has been successfully cleaned and polished, a final nitric acid treatment
should be applied, as follows:
Place the dish with the polishing cloth on a flat surface.
Spread a little polishing powder onto the cloth.
Mix with a few drops of water to get a grey, milky liquid.
Make sure to use the correct polishing powder for your
application. See the spare parts tables in
Sensor parts on
page 37 .
Note: Use one polishing cloth per sensor model, to prevent a
possible contamination through metal particle transfer.
Holding the sensor vertically, and using a circular motion,
polish the sensor face for at least 30 seconds, until the
electrodes are clean and shiny.
This step may need to be repeated several times.
Make sure to avoid skin contact with the polishing cloth; it
should be kept free of dust and grease.
Remove the membrane support with installation tool.
Rinse the support and sensor cavity with a strong jet of clean
water.
Use distilled water if the water quality is doubtful.
Carefully inspect that the tiny groove between the center
electrode and the guard ring electrode is totally clean and free
of polishing residue.
Clean only with a strong water spray. The edge of a paper
sheet can be used to remove sticking residue.
Place the sensor in a vertical position on its base.
Fill the electrolyte reservoir with a few drops of water, just
enough to cover the outer electrode. The center electrode
must be kept dry.
Place a drop of nitric acid on the center electrode, covering
only the electrode and guard ring. Avoid spilling acid into the
water. Wait less than a minute, then rinse thoroughly under
tap water.
CAUTION
Nitric acid is dangerous! Please refer to the safety
information from your chemical supplier