Hach-Lange ORBISPHERE 31xxx Basic User Manual - Manual (Page 14)

Electrodes ammonia cleaning
1. Fill the sensor electrolyte reservoir with a solution
of 25% by weight ammonium hydroxide (NH
4
OH) in
water and leave for 10 minutes.
2. Rinse with tap water for at least one minute.
3. Inspect the sensor head. The counter electrode
should be a silver-white color.
4. If the counter electrode still shows deposits, repeat
the procedure.
C A U T I O N
Ammonia is dangerous! Please refer to the safety information from your chemical supplier.
Anode and cathode nitric acid cleaning
1. Check for the absence of silver deposit on the
central guard ring electrode walls, as such deposits
can make contact with the counter electrode.
2. To eliminate any silver residue inside the sensor
cell, it is sometimes required to repeat the chemical
cleaning using nitric acid (HNO
3
, not over 70% by
weight).
3. Also, the 32301 electrochemical cleaning does not
remove deposit on the cell’s plastic parts, so nitric
acid cleaning may be required.
Note: This procedure is not recommended for normal
maintenance, and should not be used more often than twice
a year, as the acid degrades the metal of the counter
electrode, thus reducing the sensor's life.
4. Place concentrated nitric acid into the sensor
electrolyte reservoir, and add 1 drop on the center
electrode.
5. Leave for no longer than 3 seconds.
6. Quickly empty the acid and rinse thoroughly under
tap water for one minute.
C A U T I O N
Nitric acid is dangerous! Please refer to the safety information from your chemical supplier.
Sensor face polishing
1.
2.
3.
1. Once the sensor has been cleaned, the face of the center electrode must be polished together
with the membrane support.
14 English