Hach-Lange ORBISPHERE 31xxx Basic User Manual - Manual (Page 16)

In addition, the chemical reaction that takes place on the chloridized silver cathode leads to loss of
performance after a certain operation time.
As a result, a sensor service must be carried out to restore its original performance.
Method
The procedure for cleaning the H
2
electrochemical sensor requires the use of the ORBISPHERE
32301 Sensor Cleaning and Regeneration Center. This procedure is explained in detail in the
32301 Operator's Manual.
As an overview, H
2
electrochemical sensor cleaning consists of the following sequence of operations:
• Dechloridization of the cathode: This process removes the chloride film from the silver cathode
surface (carried out by the ORBISPHERE 32301).
• Rechloridization of the cathode: A layer of silver chloride is grown on the cathode's surface
(carried out by the ORBISPHERE 32301).
• Activation of the platinum anode: The center anode surface is polished, and treated with nitric acid.
Troubleshooting
Oxygen sensor
Problem Probable cause Possible solution
Sensor won't calibrate, even after
thorough servicing.
Repeated calibrations go beyond
"expected limits" of instrument.
MOCA 3600 only: Select membrane
from "Options/Membrane" menu.
Then, calibrate the sensor.
Instrument internal barometric
pressure sensor needs calibration.
Calibrate internal barometer against
a certified barometer. Do not correct
for sea level !
Wet membrane interface.
Wipe dry with a tissue and re-
calibrate.
"H
2
S insensitivity" option enabled.
Disable on the measuring
instrument.
"0000" O
2
levels displayed.
Wrong reading scale "XXXX"
selected for display unit. Change reading scale by selecting
"X.XXX, XX.XX or XXX.X".
Shorter than expected sensor
operation in relatively high dissolved
O
2
concentration.
High O
2
concentrations generate
deposits more quickly.
Install a less permeable membrane.
Turn off the analyzer when sensor is
not in a low O
2
concentration.
Unexpected or inaccurate dissolved
O
2
readings.
Air leak on product sample line.
Set flow rate to 100 mL/min. Wait
until stable, then slowly double this
flow rate.
The stable value of dissolved O
2
reading must be the same as
before. A variation related to flow
rate is a clear sign of an air leak in
the line.
High residual current.
Place sensor in de-aerated sample;
wait for low reading:
Check concentration against low
measurement limit (see tables in
Sensor membrane specifications
on page 3). If concentration is
significantly higher than low limit, try
a sensor service.
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