YSI ADV6600 - Manual (Page 113)

Section 9. Principles of Operation
ADV6600
Y S I
Environmental
Page 103
9-2.2. XYZ
Using the XYZ coordinate system, velocity measurements are
stored using a right-handed Cartesian coordinate system relative to
the Argonaut-ADV probe. The ADV6600 is a 3D Down-Looking
Probe – Down-Looking Operation with the following
characteristics:
• The positive Z-axis is defined as vertically up in the
direction of the probe’s mounting stem (which for this
probe is the same as the axis of the transmit transducer).
• The positive X-axis is defined perpendicular to the probe’s
mounting stem in the direction of receiver arm #1 (which
is marked with a red band and a small dimple (indicator)
near the socket of Beam 1).
• The positive Y-axis is defined based on the X and Z-axes
to make a right-handed coordinate system.
.
9-3. Effect of Salinity Variation on Velocity Accuracy
Salinity variations in the water being monitored can affect the accuracy of velocity measurements
because the speed of sound in water is dependent on its density. The accuracy effect is
approximately 2 % for each 12 ppt salinity difference between the true value and that present in the
software of the ADV6600. The default value in the software is 34.5 ppt, making the system ideal
for seawater applications. However, for freshwater studies, this salinity effect can cause an error of
up to 6 % in measured velocities unless it is corrected. If errors of this magnitude are important in
your studies, you can to correct your salinity default for use in velocity calculations by contacting
YSI Technical Support for instructions.
•
9-4. Pressure
The ADV6600 may include an optional strain gauge pressure sensor. The strain gage sensor outputs
data as an analog voltage. Sensor data are sampled by the ADV6600 electronics using a 12-bit A/D
converter. Data are converted to a 2-byte integer, scaling the A/D counts by 16 (giving a total count
range of 0-65520, with a step size of 16 counts).
The pressure data, stored in counts, must be converted to physical units (decibars) using the
following formula:
dBar = PressOffset + (PressScale x Counts) + (PressScale_2 x (Counts 2 ))