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10.5 Maintenance of the Membrane
The membrane does not require replacement as long as it remains intact. If
punctured or suspected of leaking around the edges, it must be replaced.
To replace the membrane of the EDYSI sensor, see the separate leaflet with which
it is supplied.
To replace the ED1M membrane…
1. Unscrew the lower barrel and carefully remove it from the probe. Ensure that
the internal lexan barrel is not touched with the fingers, as the metallic surfaces
are easily contaminated.
2. Remove the plastic cap and membrane from the end of the barrel.
3. Cut a 30 mm square (approx.) piece of membrane material from your probe
maintenance kit. Hold this over the end of the barrel, and push the plastic
retaining cap back into place evenly. A little moisture on the outside of the
membrane will let the cap slip on easily. The excess membrane may be trimmed
off with a razor blade.
4. Pour enough 0.1 Molar KCl solution into the barrel to fill only 1/3.
5. Push the barrel carefully onto the lexan internal rod. As this is done, check for
leaks on the membrane. The internal rod can be used to gently "pump" the
membrane to check for leaks.
6. If no leaks can be seen, screw the outer barrel into place, so that the membrane
is evenly and smoothly stretched over the gold internal cathode (gold bead at
end). DO NOT OVER-TIGHTEN.
If the probe is washed off and put in fresh water, then, by viewing obliquely in a
strong light, it is possible to see electrolyte "streaming" from the tip if it is
leaking (even slowly). The effect is one of differential refractive index and is
quite sensitive.
If the response is low, or zero impossible, or reading over-ranged, fit a new
membrane.
10.6 Dissolved Oxygen Sensor Storage
The Oxygen probe should be kept moist when not in use to prevent the thin film of
electrolyte behind the membrane from drying out. To achieve this, the probe can be
stored with the tip in water.
For long term storage of several weeks or more, remove and empty the barrel.
Replace the barrel with the membrane intact. When the electrode is stored in this
way, the membrane should be replaced and the electrode refilled before use.
