Nortek Vector Comprehensive Manual

Also see for Vector: Quick start guide

Contents

Nortek Vector Comprehensive Manual Manual pdf 16 page image

Comprehensive Manual16© 2018 Nortek ASFigure: The Vectrino/Vectrino Profiler and Vector XYZ coordinate system s and beam num bering asdefined relative to the probes. Beam 1 of the Vectrino has a red m arking, a black m arking defines beam 1for 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 w ith theright-hand rule.For the interested reader: For the Vector probe (see illustration third to the left, lower part), one maynotice that the X component is predominantly measured by beam 1 with nearly equal contributionsfrom beam 2 and beam 3. This makes sense since the XYZ coordinate system is aligned with Xpointing along one receiver arm. Beams 2 and 3 are at some angle α to the X-axis and measure acomponent of X proportional to cosα. For the Y-component, beam 1 contributes to zero (or very nearzero) because the Y-component is perpendicular to beam 1. Finally, the Z component is an equalcombination of all three beams since the Z-axis is aligned with the central transducer and eachbeam is at the same angle to the Z-axis. Note that this concept applies to the other probes as well.1.7 Signal StrengthTo be confident about the quality of the data and allow proper calculation of the velocities, thereceived echo (reflected by particles) need to be over a certain level. Signal strength (amplitude) is ameasure of the magnitude of the acoustic reflection from the water, and is a function of type andamount of particles in the water. If the echo is weak, the calculation will be statistically "noisy" andthe velocity data will show significant short-term variability. Signal strength is outputted by theinstrument and can be used to assess data quality.The signal strength is accessed as raw signal amplitude (using dimensionless unit called Counts) oras a "Signal-to-Noise ratio", SNR (in dB).CountsFor signal strength, Nortek frequently make use of the word counts, which obviously seem to beconnected to the decibel term, but how and why?Inside the velocimeters there are circuitries for the amplification of input signals. The number ofcounts is an indicator of how much gain we must apply to a signal – the less gain needed, thehigher the input signal level is. The number of counts is inversely proportional to the logarithm of thegain setting, which means that a higher number of counts reflects a need for less amplification thana 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.