Using a Velocimeter 39
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assumes that high transmission rates can be used without problems, i.e. that the cable connecting
the computer to the instrument is short. A higher baud rate may reduce the download time, but note
that the baud rate is limited to the operating system of the PC, the serial port, and the length of the
USB cable. If you experience communication issues after changing the baud rate, try changing it
back to the default.
The baud rate setting can be changed if you upgrade in-situ using long cables. The Vectrino verifies
the received head file and firmware upgrade files before they are allowed to replace the existing head
and firmware files, hence, using the wrong transmission speed will not cause trouble.
The table below shows the highest permissible sampling rate for a given baud rate (Vectrino).
Check the transducers
1. Fill a bucket with water and a little sound-scattering material ("Seeding").
2. Click Data collection > Start Data Collection. While the transducers are in the air, the velocity
measurement will look like random noise.
3. Immerse the transducers in the water, and observe the velocity, the standard deviation, and the
amplitude in counts. Note the change in the graphical view of the velocity when the probe is
lowered into the water. In the air the graphs are noisy; in water they should be smooth. Noisy
velocity graphs: If the velocity graphs remain noisy when the probe is immersed in water, try
varying the position of the probe, or add some seeding like dirt or small particles to the water.
4. Designed to act as a measurement quality assurance tool, the Probe Check function in the
Vectrino software lets you inspect the region where the Vectrino makes its measurements by
showing how the signal varies with range. You can use it to diagnose and correct problems and to
optimize data collection. Click Data Collection > Probe Check to start the Probe Check.
2.2.4 Configuring a Vectrino
The Deployment Planning dialog contains all parameters required to specify the operation of the
instrument. The Deployment planning frame on the right hand of the dialog displays performance
parameters that are automatically updated as you change the parameter settings. It is
recommended to use the Help file that is available within the instrument software for a complete
description for each of the setup parameters available.
For general recommendations for sampling in specific environments, check out these sections:
Things to Consider, Applications and Common Configuration Scenarios.
Sampling rate
When it comes to sampling rate, the general recommendation is that you will need to sample at
least twice as fast as your signal of interest in order to unambiguously resolve it (i.e. the Nyquist
sampling criteria). You will need to make a few estimates of what time scales and processes are of
interest and select a sample rate appropriate for those.
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