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CHAPTER 6 Maintenance
The Oxygen Optode requires very little maintenance.
When the membranes on traditional oxygen consuming sensors (based on electrochemical principles),
often called Clark sensors, are fouled the water mixing in front of the sensor membrane becomes poorer,
which influences the measurement directly.
Since the Optode consumes no oxygen, the ability to diffuse gas has no influence on the measurement
accuracy. However, if the fouling is in the form of algae that produce or consume oxygen, the
measurement might not reflect the oxygen concentration in the surrounding water correctly.
Also the response time of the measurements might increase if the sensing foil is fouled. Therefore, the
sensor should be cleaned at regular intervals depending on the fouling condition at the site.
Field experiences have demonstrated that AADI Optodes typically are a factor of 2-4 more fouling
resistant than electrochemical oxygen sensors from other manufacturers and then the AADI conductivity
sensors.
The Optode housing can be cleaned using a brush and clean water. Carefully, use a wet cloth to clean
the sensing foil.
Figure 6-1: Example of fouling on an RCM 9 with an Oxygen Optode 3830 (Optode version with
SR-10 output) mounted to it: The Optode was still giving correct readings.
Fouling consisting of calcareous organisms (e.g. barnacles),
can be dissolved by dipping the sensor/instrument in a weak
acid solution (e.g. 7% Vinegar).
If the sensing foil is scratched or if the protective black layer
on the foil is removed the sensor will still work as long as
there is enough Fluorophore on the foil.
If severely damaged (so that the sensor gives unrealistic
readings) the sensing foil must be replaced (Sensing Foil Kit)
and the sensor recalibrated.
NOTE! Enter new calibration coefficients and perform a new
two point calibration when changing the sensor foil.
The fluorescence life time measurement technology provides
for very good long term stability. There is however a minor
bleaching (break down) of the luminophore for every
excitation of the foil. For the AADI Optodes this change is
minimized by use of exceptional stable foil chemistry and
careful excitation. Experience show that the foils have very
good durability and generally become more stable over time.
In figure 5-2 typical drift versus the number of excitations
(samples) is depicted.
page 35 of 93
TD 269 OPERATING MANUAL
OXYGEN OPTODE 4330, 4831, 4835
June 2017
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