YSI ADV6600 - Manual (Page 85)

Section 5. Mounting and Installation
ADV6600
Y S I
Environmental
Page 75
5-2.2. Flow Interference
As noted above, the ADV6600 measures velocity in a small sampling volume, ~25 cc, located about
7 cm (2.8 inches) from the tip of the probe. The placement of the sampling volume relative to other
structures in the water must be considered so that the ADV6600 measures velocity free from flow
interference.
The ADV6600 probe should be installed well clear of any
underwater structures, particularly those upstream.
Consider the size and location of nearby structures, and
the probable magnitude and direction of flow when
choosing an installation site.
Although the system’s internal compass will compensate
the head orientation as it relates to the Earths magnetic
field, it sometimes makes data analysis easier to check
when the ADV6600 is oriented such that the marked
receiver arm (there is a permanent dimple and a semi-
permanent red-band indicating Beam 1) is roughly
perpendicular to the expected direction of flow, as shown
to the right. The arm is marked with an indentation on
the bubble above the receiver arms as shown at the right.
5-2.3. Interference from Magnetic Material
The ADV6600 uses a compass sensor to report velocity data in Earth coordinates and to compensate
automatically for rotation of the sonde during deployment. Ferrous metal in the mounting structure
near the instrument can affect the accuracy of compass measurements and hence the accuracy of
velocity data. Ideally, all mounting fixtures should be designed using non-ferrous metals or plastics.
However, if a magnetic (ferrous) material such as iron or steel pipe must be used, the ADV should
be offset from the pole as much as possible to minimize magnetic interference from the support.
Additionally, a compass calibration should be performed by rotating the entire ADV6600 and its
mount so that the best possible compensation for the ferrous material can be accomplished.
Preferred Flow Direction to
Avoid Flow Interference
Major Flow Direction
Transducer
Marker