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Section 6.
Quality Control
Quality Control (QC) is continuously performed on all variables collected during a
measurement in both Discharge and General Modes. The
are automatically reviewed at different stages of a measurement and if any values
exceed the expected criteria a warning is supplied.
6.1. Quality Control Parameters
Quality Control Parameters used to analyze the variables collected during a
measurement are discussed in the following section. The quality control parameters with
its expected values are supplied in
adjusted or disabled based on measurement site and or user requirements.
Parameter
SNR is the most important Quality Control parameter,
• It measures the strength of the acoustic reflection
from particles in the water,
SNR
• Without sufficient SNR, the FlowTracker2 cannot
measure velocity.
σV (velocity standard error) is a direct measure of the
accuracy of velocity data,
Velocity
• It includes the effects of turbulence in the river and
Standard
instrument uncertainty.
Error
Boundary QC evaluates the measurement
environment for interference from underwater
Boundary
obstacles,
Interference
• FAIR or POOR results may indicate significant
interference from an underwater obstacle.
Spikes in FlowTracker2 velocity data are removed
using a spike filter,
Velocity
• Some spikes are common and no cause for
Spike
concern,
• Too many spikes indicate a problem in the
Filtering
measurement environment (e.g., interference from
underwater obstacles or highly aerated water).
Angle is the direction of the measured velocity
relative to the FlowTracker2 X-axis,
Velocity
• Used for discharge measurements only,
Angle
• A good site should have small velocity angles,
FlowTracker2 User's Manual (January 2019)
Table
6:1. All quality control parameters can be
Table 6-1 - Quality Control Parameters
Description
83
SonTek – a Xylem brand
Quality Control Parameters
Expected
Ideally > 10 dB
Minimum ≥ 4 dB
Typically <
0.01m/s (0.03
ft/s).
Higher in
turbulent
environment.
• BEST,
• GOOD,
• FAIR,
• POOR.
Typically < 5% of
total samples.
Should be < 10%
of total samples.
Ideally < 20º
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