YSI 6500 Environmental Process Monitor - Manual (Page 51)

Proper Use and Care of the 6500
Section 5
The following sections are designed to help you in these important areas by providing maintenance
tips for the overall sonde deployment, help in implementing a quality assurance protocol, and
suggested service methods and intervals for the sonde sensors.
5.2.1 SONDE MAINTENANCE AT THE DEPLOYMENT SITE
ALGAE AND DEBRIS AS THE MAJOR PROBLEM
The problem most likely to be encountered with regard to the overall sonde deployment in
municipal wastewater effluent is fouling from algae (and occasionally other debris) passed
through from the clarifier of your treatment system. These algae will inevitably collect on any
object immersed in the outfall stream, and, unless periodically removed, can seal off the probe
compartment of the sonde. Once algal build-up occurs, it isolates the sensor environment from
the bulk effluent. Thus, even though the sensors themselves may be relatively free of fouling and
may be performing correctly within the isolated probe compartment, the readings may be non-
representative with regard to the water that is exiting your treatment plant.
To avoid, or at least minimize, this problem, it will be necessary to periodically remove the algae
from the sonde. This may require the complete removal of the unit from the effluent stream and
“hands on” removal of the fouling. Removal of the sonde is easier if it has been installed using
an optional sonde mounting kit. See Appendix D, Accessories, for more information.
MINIMIZING THE EFFECT OF ALGAE AND DEBRIS
The collection of algae on your sonde and the frequency of cleaning can be minimized by the
overall deployment configuration and the way in which the sonde is attached to the strut. As
outlined in Section 2, Installation, it is preferable to angle the sonde with (rather than against) the
current of the stream. This configuration will maximize the chances that much of the algae will
be swept free of the sonde rather than collecting.
Remember that no matter what precautions you take, debris will still collect on the sonde and the
fouling will have to be removed by periodic cleaning. Cleaning will be easier if the method of
mounting allows for easy removal and replacement of the sonde. A little extra time spent on
implementing a good mounting arrangement using the optional sonde mounting kits will save a
lot of time in subsequent cleaning operations. See Appendix D, Accessories for more information.
The frequency with which you will have to remove fouling from your sonde varies with the water
being monitored and with the physical arrangement of the sonde, but the need for cleaning can
usually be ascertained by visual inspection. You can do no harm by excess cleaning, so it is best
to err on the side of caution, removing and cleaning the sonde if any significant fouling is even
suspected.
5.2.2 CALIBRATION CHECKS
YSI Incorporated 6500 Environmental Process Monitor 48