YSI ADV6600 - Manual (Page 50)

Section 4. Calibration and Diagnostics
ADV6600
Y S I
Environmental
Page 40
4-2.4. Viewing a Recorded Beam Check File
At the top of the Beam Check screen are buttons used during program operation to view a recorded
file:
Pause
Temporarily halts the display of data.
Start Starts regular updating of the data screen.
Stop Ends the display of a recorded Beam Check data file.
Playback Speed Adjusts the speed at which data is updated on the screen. Update interval
is user-selectable. Click on the arrow and move it up or down to adjust
the playback speed.
Averaging Averages pings together from the ADV to produce smoother data.
4-2.5. Interpreting Your Laboratory Beam Check Data
While it is not necessary to be an expert in Doppler technology to acquire good velocity data with
the ADV6600, it is important for all users to understand the output of a Beam Check test at a very
basic level. The key is to remember that the “amplitude” parameter shown on the y-axis of the
Beam Check plots represents the signal strength of returned signal for each of the receivers and the
“samples” on the x-axis represents the time it takes for the acoustic pulse to get from the scatterers
in the water back to the receiver. This time between scatterer and receiver can also be translated
into the distance between the scatterer and the receiver since the speed of sound in water is well
known.
To understand the Beam Check data it is also important to be acquainted with the concept of the
“sampling volume” of the Doppler sensor. As shown in the diagram below, because of the
geometry of the receiver arms, return Acoustic pulses are only detected from suspended scatterers in
a relatively small volume which is in the middle of the receiver arms and about 10 cm away from
the transmitter. Acoustic pulses will also be reflected so strongly from solid surfaces, for example
the bottom of the bucket in the tests above, that some signal will be detected even though the solid
surface is not in the sampling volume itself.