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10.4 Cleaning the Dissolved Oxygen Sensor
If the silver anode of a Dissolved Oxygen sensor becomes contaminated with
materials such as sulphide, the electrode will become poisoned. This will cause
calibration to become more difficult and eventually impossible. The following
procedure can be used for less serious poisoning.
1. Ensure that the electrode is actually the faulty part of the system, by trying a
different electrode, cable or meter. If any of these items are not available, check
all cable connections, the meter's battery, the temperature readout and the
condition of the membrane. If the membrane is loose, has bubbles underneath it
or is dirty or greasy, replace it and try the probe again.
2. If you have determined that the probe is the faulty part…
(a) For the ED1M, completely unscrew and remove the barrel. The silver
anode is the wire wrapped around the sensor stem.
(b) For the EDYSI, remove the membrane and the pressure compensation
pump assembly (refer to the YSI instruction leaflet). The silver anode is
the triangular block inside the tip of the sensor.
The usual indication of poisoning of the silver anode is blackening.
3. Rinse the sensor to remove any loose particles.
4. Soak the electrode for 10 minutes in 5% Ammonia solution.
5. Rinse well under a tap.
6. If an ultra-sonic cleaning bath is available, add a few drops of detergent (eg:
dishwashing liquid) to the water so that it covers the silver anode. Turn on the
cleaner for approximately 5 minutes.
7. Rinse well under a tap.
8. Re-assemble the sensor, re-fill the electrode and fit a new membrane, as per the
instructions supplied with the sensor.
9. If the electrode still fails to calibrate or read correctly, TPS can attempt further
cleaning by electrolysis. This procedure removes the outmost layer of the anode
and actually reduces its size. Whilst the procedure is hard on the sensor, it does
often restore the probe's performance.
10. If poisoning is a problem for the EDYSI, then please refer to the YSI
instruction leaflet and TPS appendix to the leaflet regarding correct fitting of
the membrane.
