Comprehensive Manual16
© 2018 Nortek AS
Figure: The Vectrino/Vectrino Profiler and Vector XYZ coordinate systems and beam num bering as
defined relative to the probes. Beam 1 of the Vectrino has a red marking, a black marking defines beam 1
for the Vector (not show n here). For the Vector, beam 1 is also the arm opposite of the engraved head ID.
Beam 1 point in the direction of positive X-axis. The Y direction can be found in accordance with the
right-hand rule.
For the interested reader: For the Vector probe (see illustration third to the left, lower part), one may
notice that the X component is predominantly measured by beam 1 with nearly equal contributions
from beam 2 and beam 3. This makes sense since the XYZ coordinate system is aligned with X
pointing along one receiver arm. Beams 2 and 3 are at some angle α to the X-axis and measure a
component of X proportional to cosα. For the Y-component, beam 1 contributes to zero (or very near
zero) because the Y-component is perpendicular to beam 1. Finally, the Z component is an equal
combination of all three beams since the Z-axis is aligned with the central transducer and each
beam is at the same angle to the Z-axis. Note that this concept applies to the other probes as well.
1.7 Signal Strength
To be confident about the quality of the data and allow proper calculation of the velocities, the
received echo (reflected by particles) need to be over a certain level. Signal strength (amplitude) is a
measure of the magnitude of the acoustic reflection from the water, and is a function of type and
amount of particles in the water. If the echo is weak, the calculation will be statistically "noisy" and
the velocity data will show significant short-term variability. Signal strength is outputted by the
instrument and can be used to assess data quality.
The signal strength is accessed as raw signal amplitude (using dimensionless unit called Counts) or
as a "Signal-to-Noise ratio", SNR (in dB).
Counts
For signal strength, Nortek frequently make use of the word counts, which obviously seem to be
connected to the decibel term, but how and why?
Inside the velocimeters there are circuitries for the amplification of input signals. The number of
counts is an indicator of how much gain we must apply to a signal – the less gain needed, the
higher the input signal level is. The number of counts is inversely proportional to the logarithm of the
gain setting, which means that a higher number of counts reflects a need for less amplification than
a lower number of counts will do.
Strong signals have a higher noise immunity and they correlate much better than weak signals do.
For the Vector, 1 count ~ 0.4– 0.45 dB.
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