Xylem SonTek FlowTracker2, User Manual

Page: 89 / 308

SonTek – a Xylem brand
FlowTracker2 User’s Manual (January 2019)
88
in General mode and Discharge mode.
i). The standard error threshold for each measurement is the greater of the
following,
• σV Threshold
(default 0.01 m/s / 0.033 ft/s),
•
If the mean
σVx
for three or more completed stations measurements is
greater than
σV Threshold
, then increment the
σV Threshold
by the
mean value (
Mean σVx + σV Threshold
),
•
If the
σV Threshold
is larger than 0.250m/s, then set
σV Threshold
equal
to 0.250m/s.
•
If the mean spike filtered X-component velocity (high velocity has higher
σVx
) is larger than
σV Threshold
then set
σV Threshold
to 5% of X-
component velocity.
ii).
When σVx is greater than the standard error threshold for that measurement,
•
This may indicate interference from an underwater obstacle, a highly
turbulent environment, or highly aerated water,
•
At the first alert, repeat the measurement (perhaps after moving probe
location),
•
If the problem persists, evaluate the measurement environment. In some
cases, large variations may be unavoidable (e.g., in highly turbulent
waters).
iii).
σV Threshold
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 delete suspect stations and repeat the measurements.
f) If the point measurements X-component velocity standard error is 0 or if it
exceeds the updated
σV Threshold
then a Standard Error > QC warning is
given.
g) The velocity standard error checks are re-run (Discharge mode and General
mode measurement) to ensure the warnings are set with the most current data.
h) This criterion can be adjusted or disabled under Quality Control Settings .
Boundary Interference 6.1.3
The Boundary Interference quality control looks for interference from underwater
objects that are in or close to the FlowTracker2 sampling volume. The system tries to
avoid this interference, but you must be aware of system limitations.
a) The impact of underwater objects and or boundaries on the measurement is
related to the FlowTracker2 principle of operation.
i). Reflections can occur from the bottom, the water surface, or submerged
objects (e.g., rocks).