Aquaprobe
®
AP-7000 Instruction Manual
10401-00894 Rev M
All Aquaread® Optical Electrodes are incredibly sensitive. For example, the Turbidity
electrode is capable of measuring between 0 and 3000NTU with an internal resolution of
greater than 0.1NTU. This means that the electrode is able to detect changes in turbidity
that are less than 0.003% of the full range! The other optical electrodes have a similar level
of sensitivity.
It follows, therefore, that in order to provide stable, repeatable readings, the environment in
which the measurements are made must be completely stable and repeatable.
For this reason, the AP-7000 is
constructed with a matt black
aluminium sleeve and end cap that
enclose the sensing electrodes and
provide a closed, constant condition,
non reflective measurement chamber.
In order to obtain consistent
results, the measurement chamber
created within the Aquaprobe®
must remain physically constant
during both calibration and
measurement. It is therefore
essential that both the sleeve and
sleeve end cap are fitted during
calibration and operation of all
types of optical electrodes.
If an optical electrode is calibrated
under one set of conditions then used
to measure under another set of
conditions, the readings will naturally
be erroneous, especially at low
concentrations.
A perfect example of this is calibrating
with the end cap removed then
measuring with the end cap fitted (or
vice-versa). By changing the physical characteristics of the measurement chamber, you
also change the calibration and response of the electrode.
Another particular problem when trying to measure
very low concentrations is air in the form of both visible
and microscopic bubbles. These act like tiny prisms
and can refract and reflect both the excitation light and
the return signal being measured. The photograph to
the right was taken in a calibration tube after fresh
water was poured in. The bubbles are clearly visible in
the light beam.
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®
Ltd.
www.aquaread.com
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