In-Situ TROLL 9500 Operators Manual - Manual (Page 94)

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TROLL 9500 Operator’s Manual 0095110 rev. 007 01/09
SENSOR CARE AND HANDLING
The D.O. sensor kit includes the following items for routine mainte-
nance of the D.O. sensor:
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SENSOR REMOVAL
Position the yoke of the sensor removal tool at the point
where the sensor meets the sensor block and pry the
sensor upward.
Always handle the sensor by the sides. Avoid touching
the membrane at the sensor tip.
MAINTENANCE/INSPECTION
Inspect the sensor and membrane if readings begin to drift.
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(AgCl) deposition.
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of algal growth or other contaminants, for crystallization that may
indicate a leak in the membrane, and to ensure no air bubbles are
trapped under the membrane.
CLEANING THE ELECTRODES
Remove the membrane module and clean the electrodes as follows:
Cathode. Use a polishing strip to buff
the platinum cathode until it is shiny. This
removes any deposits, increasing the
chemically active surface of the electrode
for a stronger D.O. signal.
Anode. If the sensor appears to be exces-
sively discolored from its original matte
grey color, clean the anode with ammonia
and a soft brush. Extreme discoloration
may be removed by soaking for a half-hour
in ammonia before cleaning with a brush.
The surface of the anode should appear
uniform, but not necessarily mirror-like.
SECTION 13: DISSOLVED OXYGEN—POLAROGRAPHIC
Regular cleaning will prevent pitting of the anode surface, caused
by accumulated silver chloride deposition. Severe pitting cannot be
removed; the sole remedy is to replace the sensor.
After cleaning, rinse thoroughly and shake to dry. Then fill and attach
a new membrane module as follows.
REPLACING THE MEMBRANE MODULE
The D.O. sensor performs best in clean water. In environments with
high organic content, the membrane can become fouled. Rips, tears
and other damage will also affect membrane performance. For best
results, replace the membrane when the slope and offset calculated
during calibration change dramatically.
The current applied is so small that the electrolyte solution can be
expected to last longer than the membrane in most applications
To replace a membrane module:
1. Make sure the area around port 2 is free of dirt and moisture, then
remove the sensor. Remove and discard the used membrane
module.
2. Inspect and clean the sensor as needed (see above).
3. Fill a new membrane cap with electrolyte and attach it to the sen-
sor. Refer to “Fill the Membrane Module” earlier in this section.
4. Install and condition the sensor. Refer to “Condition a Newly
Installed Sensor” earlier in this section.
Remember to condition the sensor for at least 2 hours,
preferably 10 hours, before recalibrating with a new
membrane. Even with all visible air bubbles removed, a
certain amount of gas will be trapped under the membrane. The
conditioning period will remove this excess oxygen.
SENSOR LIFE
The sensor body may be expected to last indefinitely so long as
the silver coating is not rubbed off the anode during cleaning. The
membrane module should be inspected regularly and replaced when
it shows wear or damage and when the slope and offset calculated
during calibration change dramatically.
STORAGE
Short-Term Storage (up to a two weeks)
Store assembled with membrane immersed in water. A suitable stor-
age bottle is included in the sensor box.
sensor
removal
tool
Cathode
Membrane
Membrane module
Anode
Polarographic
Dissolved
Oxygen
Sensor
o-rings