YSI ADV6600 - Manual (Page 129)

Section 9. Principles of Operation
ADV6600
Y S I
Environmental
Page 119
The unique YSI chlorophyll system available as an option for use with the ADV6600 consists of a
probe which is similar in concept to the sonde-type fluorometers, but is much smaller, making it
compatible with the probe ports of the YSI 6820, 6920, 600 OMS, and 6600 sondes. The output of
the sensor is automatically processed via the sonde software to provide readings in either generic
fluorescence units (percent full scale; % FS) or µg/L of chlorophyll. No pump is required for the
YSI system allowing the sensor to operate off of the internal batteries in the ADV6600. Like the
YSI 6026 and 6136 turbidity probes, the YSI 6025 chlorophyll probe is equipped with a mechanical
wiper to periodically clean the optical face either by manual or automatic activation. With these
features, the YSI chlorophyll sensor provides the same level of performance as the sonde
fluorometers, but is much easier to use and can be deployed in environmental water for several
weeks without the need for service. In addition, the probe will be a component in sondes that can
acquire up to ten other parameters simultaneously with chlorophyll, rather just providing the single
parameter.
9-16.2. Effect of Fouling
Field optical measurements are particularly susceptible to fouling, not only from long term build up
of biological and chemical debris, but also to shorter term formation of bubbles from outgassing of
the environmental water. These bubbles can sometimes be removed in short term sampling
applications by simply agitating the sonde manually. For studies longer than a few hours where the
user is not present at the site, the quality of the chlorophyll data obtained with a fluorescence sensor
that has no capability of mechanical cleaning is likely to be compromised. The YSI 6025 probe is
equipped with a mechanical wiper that makes it ideal for unattended applications. The wiper can be
activated in real-time during discrete sampling operations or will function automatically just before
each sample is taken during long term unattended monitoring studies. The number of wiper
movements and the frequency of the cleaning cycle for the unattended mode can be set in the sonde
software. Generally, one wiper movement is sufficient for most environmental applications, but in
media with particularly heavy fouling, additional cleaning cycles may be necessary.
9-16.3. Effect of Temperature
While the effect of temperature on the chlorophyll sensor itself is very small, YSI experiments have
indicated that the fluorescence of phytoplankton suspensions can show significant temperature
dependence. For example, the apparent chlorophyll content of our laboratory test samples of algae
increased from 185 to 226 µg/L when the temperature was dropped from 21 °C to 1 °C even though
no change in phytoplankton content took place. In the absence of compensation, this effect would
obviously result in errors in field chlorophyll readings if the site temperature were significantly
different from the calibration temperature. This temperature error can be reduced by employing a
chlorophyll temperature compensation routine (“Chl tempco”) resident in the sonde software.