Campbell Scientific CS511 Dissolved Oxygen Probe - Manual (Page 33)

Appendix C. PT4-L Agitator
C.1 Description
The PT4 agitator is a reliable, robust agitator for use in conjunction with probes
subjected to bio-fouling in ponds and stagnant water conditions (flow <5 cm/s).
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probes require a minimum water velocity across their membranes to function
properly. Therefore, to measure DO in stagnant water conditions, it is necessary
to move the water past the membrane to get accurate and reliable DO
measurements. In many instances, the water also has a high bio-loading and the
probes become fouled resulting in inaccurate DO measurements.
FIGURE C-1. Preventing Bio-fouling of a DO Sensor
The PT4 agitator overcomes these problems. The device is designed so that a
soft-bristle brush sweeps across the probe membrane or sensor tip. This sweeping
action of the brush provides the required water velocity as well as prevents the
membrane from becoming bio-fouled.
The optimum sweeping frequency depends on the design of the probe and type of
membrane used and water conditions. An ON-time of 0.25 s and OFF-time of 5 s
is suitable in most circumstances.
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