SonTek – a Xylem brand
FlowTracker2 User’s Manual (January 2019)
89
ii). The FlowTracker2 measures velocity in a sampling volume 10 cm (4 in) from
the probe tip.
iii). If the sampling volume is on top of or beyond an underwater object, velocity
data will be meaningless.
b) When working in very shallow water or near underwater obstacles (with the
sampling volume within 15 cm (6 in) of the obstacle), acoustic reflections can
potentially affect velocity data.
i). At each measurement location, the FlowTracker2 looks for these conditions,
and if necessary, adapts its operation to avoid interference.
ii). For most locations, any required changes do not affect system performance.
iii). In some environments, changes may result in a lower maximum velocity.
Boundary
Display
c) The FlowTracker2 records any changes required to avoid acoustic interference.
It reports this as Boundary QC. This value describes the effect (if any) of
boundary adjustments on performance. The Boundary QC variable (Bnd) can
have the following values (0 and 1 are the most common).
Figure 6:1 - Boundary QC Conditions
Boundary
Data
Evaluate
d) The Boundary Interference check looks for interference with underwater
objects that are in or close to the FlowTracker2 sampling volume. The
FlowTracker2 automatically adapts its pinging to minimize boundary interference,
but it can only adapt so much, and the resulting pings could still be influenced by
the boundary. The FlowTracker2 software receives two values from the firmware
to use in determining the amount of boundary interference: velocity ambiguity
and the best single ping precision, both available in m/s.
i). If the Boundary QC results are FAIR or POOR, this indicates possible
interference, and the FlowTracker2 will issue an alert before the measurement
is made.
0 (Best)
1 (Good)
2 (Fair)
3 (Poor)
•No boundary adjustments were necessary, or if necessary,
they have minimal impact on system performance.
Maximum velocity is at least 3.5 m/s (11 ft/s)
•Minor boundary adjustments were necessary, with
moderate impact on system performance. Maximum
velocity is at least 2.5 m/s (8 ft/s).
•Larger boundary adjustments were necessary, with notable
impact on system performance. Maximum velocity is at
least 1.2 m/s (4 ft/s).
•Major boundary adjustments were necessary, with significant
impact on system performance. Maximum velocity is less than
1.2 m/s (4 ft/s). The FlowTracker will still provide good
performance for lower flows
.
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