Xylem SonTek FlowTracker2 - Quality Control; Quality Control Parameters; Table 6:1 - Quality Control Parameters

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