Xylem SonTek FlowTracker2, User Manual

Page: 229 / 308

SonTek – a Xylem brand
FlowTracker2 User’s Manual (January 2019) 228
•
When working near boundaries or underwater obstacles, the system may need to
adapt its operation to avoid acoustic interference.
•
This is called boundary adjustment and is performed automatically by the system
at each measurement location.
•
The system reports a quality control parameter with each measurement location
that tells you if the environment has any effect on FlowTracker2 performance.
This quality control parameter is described in
Boundary Interference .
13.5. Beam Geometry and 3D Velocity Measurements
A single transmit/receive pair measures the projection of the 3D water velocity onto the
bistatic axis.
a) The bistatic axis is halfway between transmit
and receive beam axes (see Figure 13:3 ).
b) The velocity measured by each receiver is
called the bistatic velocity.
c) The FlowTracker2 uses one transmitter and
two or three receivers (for 2D or 3D probes).
d) See Probe Configurations for other
FlowTracker2 probe configurations.
e) Receivers intersect with the transmit beam
pattern at a common sampling volume.
f) Bistatic velocities are converted to Cartesian
(XYZ) velocities using the probe geometry (the
relative angles of transmit and receive beams).
Cartesian velocities give the 2D or 3D velocity
relative of the FlowTracker2 probe.
g) During the manufacturing process, probe
geometry is precisely determined by a
calibration procedure.
h) This calibration only needs to be performed
once.
i) No periodic re-calibration is required.
Figure 13:3 - Bistatic Axis
13.6. Sampling Volume Definition
The FlowTracker2 sampling volume is defined based on the following criteria,
a) The sampling volume is nominally 10 cm (4 in) from the tip of the probe.
b) The exact location varies
±
1.0 cm (
±
0.4 in) from probe to probe.
c) Precise sampling volume location is fixed for any given probe.