Comprehensive Manual58
© 2018 Nortek AS
An appropriate Velocity Range for a flow will typically produce a Horizontal Range (m/s) and Vertical
Range (m/s) which is larger, but not significantly so, than expected velocities. Horizontal refers to
the X and Y instrument velocity components, Vertical to the instrument Z component. Most users
will want to match the Horizontal Range to flow conditions. If you expect large velocities aligned with
the Vectrino Profiler's Z velocity component, make sure the reported Vertical Range is large enough.
Highly turbulent flows (e.g. a turbulent jet) will typically need a larger Velocity Range than mean
velocities suggest.
When adjusting the Velocity Range to improve correlation, try moving to a slightly higher value first.
In most circumstances a too large Velocity Range is better than a too small Velocity Range.
The Velocity Range is set appropriately, but there are low correlation regions in the profile.
These are due to pulse interference, also called weak spots, where a past acoustic pulse's boundary
echo is interfering with the current pulse's processing. Weak spots have fairly distinct symptoms.
There will be a region of increased amplitude (and SNR) accompanied by low correlations, while
velocities will be very spikey and noisy.
For the Vectrino Profiler: The simplest method to deal with weak spots is to use the Adaptive ping
interval algorithm mentioned above. Adjusting the velocity range manually will move the weak spot
around. If the Adaptive ping algorithm cannot eliminate the weak spot, manually adjusting its position
to the least important part of the profile is a good option. Set the Adaptive check: interval to an
appropriate value based on measurement conditions. Over a hard boundary where the Vectrino
Profiler position is fixed Once will work well. In moving probe or boundary measurements, select an
interval reflecting expected time scales for changes in the probe or boundary position.
The Bottom Distance is reporting incorrect values or is noisy (Vectrino Profiler).
In the Bottom Check tab of the configuration dialog:
If available, a physical measurement with a ruler can confirm the bottom distance measurement.
If measuring over a rough boundary, be aware the return echo will be fairly complex and the bottom
distance will be subject to increased uncertainty. Alternative methods of determing bottom
distance will be needed.
Check the Minimum depth (mm): and Maximum depth (mm): values and make sure they span the
expected distance to the bottom.
Check the Cell size (mm): and make sure it is also set to the desired resolution. Larger cells will
create coarser estimates in the bottom position.
If the bottom distance flips between two different values, a second echo is being identified as the
bottom. Check the Center Beam tab in the main window display to see the amplitude profile from
the bottom check ping and look for additional echos at roughly integer multiples of the expected
bottom distance.
Hard bottoms, in particular metal surfaces, can generate strong echos which overwhelm the
receivers and create a very broad bottom peak. This will increase uncertainty in the bottom
location. Set the Gain reduction (dB) to a value which results in the bottom peak having an
amplitude of approximately -10 dB in the Center Beam tab of the main window display.
Probe Check data does not look right. One or more of the beams has a higher amplitude.
All four beams should show roughly the same amplitude and profile shape.
Check for an obstruction in the beam path. These may be fairly obvious such as a piece of
vegetation or debris. If measuring near objects, such as in the wake of a cylinder, echos from
vertical boundaries may appear in the profiles.
Multiple echos from the bottom reflecting off the surface can also appear in the Probe Check data.
These will typically be at roughly integer multiples of the actual bottom check distance. Depending
on the acoustic path length, an echo closer than the actual boundary position may result.
If there are no obstructions and multiple bottom echos have been ruled out, there may be damage
to the probe head. If there are any signs of damage to your instrument, such as a bent receiver
arm, a bent probe stem for rigid probes, a damaged cable for cabled probes, or damage at the
bulkhead connector on either end of the electronics case, please check the Troubleshooting Guide
for further suggestions.
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