SonTek – a Xylem brand
FlowTracker2 User’s Manual (January 2019)
92
Figure 6:2 – FlowTracker2 Probe Orientation Relative to Stream Flow
ii). An angle of 0° means flow direction is perpendicular to the tag line (as desired
for an ideal measurement location).
iii). Only the X component of velocity (Vx) is used for discharge calculations. This
ensures proper discharge measurements regardless of the flow direction.
Velocity
Angle
Evaluate
e) The Velocity Angle measured is evaluated to ensure reliable data collection. The
velocity angle for a point measurement is computed from the de-spiked point
measurement mean velocity components as angle = atan2(Vy, Vx). The Max
Angle criterion (default 20º) is used as follows.
i). Velocity angle is checked only if velocity is greater than a fixed threshold (0.02
m/s; 0.07 ft/s).
ii). When measured angle is greater than Max Angle, a warning is given.
• Evaluate the measurement site to verify the measured angle is reasonable.
• Consider repeating the measurement if the angle does not appear
reasonable (perhaps after moving probe location).
• For large velocity angles, consider moving the measurement site.
iii). The Max Angle is checked with the completion of a point velocity
measurement and measurement section (see Timing of Warning Messages).
• User is notified of any stations that exceed the above criteria.
• If desired, user can go back and delete suspect stations and repeat the
measurements.
f) The Velocity Angle is checked at the end of each point velocity measurement and
if the measurement’s mean velocity X component is at least 0.02 m/s and if the
velocity angle is larger than Max Velocity Angle, then give the Velocity Angle >
QC warning.
g) The velocity angle check is re-run (Discharge mode and General mode
measurement) to ensure the warnings are set with the most current data.
h) Max Angle is active only in Discharge data collection mode.
i) This criterion can be adjusted or disabled under Quality Control Settings.
Sampling
Volume
Y
X
Probe
Coordinate System
Graduated Tag Line
Primary Flow
Direction
Mounting
Pin
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