personal computer to control the motor controllers would make it possible to vary
the speed of the pumps during an experiment, for example to better approximate
the time-varying longshore current magnitude generated from irregular wave
forcing. This may be attempted in future experiments. However, at the present
time, all pump speeds are constant during an experiment. The method of
manually controlling the pump speed with the human interface modules has
proven to require minimal time and effort. Therefore, the serial communication
modules are not presently used. For further information on the serial
communication modules, see Allen-Bradley (1995).
Data Acquisition System for Flow Meters
A third computer in the LSTF control room is dedicated to data acquisition
and real-time display of data obtained from the in-line flow sensors. As
discussed previously, these flow sensors are used to measure discharge rates from
the 20 vertical turbine pumps in the longshore current recirculation system. This
data acquisition system is a completely independent system and is not integrated
into the MTS control and data acquisition system. The manufacturer of the flow
sensors developed the software used for data acquisition and display.
The real-time display software allows the operator to visualize the cross-
shore distribution of flow rates through the 20 pump-and-piping systems. These
data are displayed as a bar graph with Pumps No. 1 to 20 along the x-axis and
flow rate in liters per second along the y-axis. The flow rate measured with each
sensor also is displayed numerically below each vertical bar in the graph. The
data acquisition software was configured to output time-averaged values (every
30 sec) of the flow rate measured with each of the 20 flow sensors. The output
file is an ASCII file consisting of 20 columns of data, one for each flow sensor.
The files are then imported into a spreadsheet, and the average flow rate for the
sampling interval (several minutes) is computed. The procedure used for
obtaining the required pump settings using the manual iteration method, based on
the measured flow sensor data, is discussed in Chapter 7.
Data Acquisition System for Sediment Traps
A fourth computer is dedicated to data acquisition and real-time display of
data obtained from the sediment trapping system. Individual cables are used to
connect the 60 load cells, which support the 20 sediment traps to the data
acquisition system housed in the LSTF control room. This system is completely
independent from the MTS control and data acquisition system.
The data acquisition and display software was developed at ERDC, via
Visual Basic, to acquire and display measured data. The software includes two
general options for displaying the data. The first option allows the operator to
visualize the gradual increase (or trend) in the quantity of sand in a single trap.
These data are displayed as an X-Y line plot, with time on the x-axis and weight
on the y-axis. Four time series are plotted, the weight of sand recorded by each
of the three load cells and the total weight of sand in the trap. The second option
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Chapter 6
Experiment Control, Data Acquisition, and Analysis Packages
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