AE/ME 201-- Procedure -- Lab: Tank Draining Instrumentation and ...

AE/ME 201 – Spring 2005
the multi-meter in frequency mode and measure
the frequency provided.
2. The bridge excitation should be set to approximately:
±2VAC @ 5000Hz
3. Wire the bridge circuit including the immersion
probe.
4. Place the multimeter leads on the bridge output.
Set the multi-meter to AC function using
the voltage setting and switching the function
button (it looks like a little sine wave) on the
left side. The liquid crystal display should show
that AC is being measured.
5. Place the immersion probe in the water in the
tank and use the meter stick to measure the
liquid level.
6. Balance the bridge by adjusting the trim potentiometer,
P1, in the bridge ciruit. Zero may
not be obtained but the AC reading on the voltmeter
should be minimized.
7. Connect the output cable from ports J8 and
J12 to the BNC port labeled ACH5 on the NA-
TIONAL INSTRUMENTS interface.
Calibration
1. Insure that the drain will run into a bucket and
not onto the floor.
2. Launch the LabVIEW Vi, and press the run
arrow in the upper left corner of the screen.
You should see a sine wave displayed in one of
the plots and a voltage in the digital display in
the upper left hand portion of the screen.
3. Measure the initial water level.
4. Record the voltage shown in the display on
LABVIEW VI. The current voltage is displayed
in the ”liquid level” text box in the upper left
hand corner of the acquisition window.
5. Slowly drain a small amount of water into the
catch bucket. Measure the new water level.
6. Repeat steps 4 and 5 until the immersion probe
is nearly uncovered.
Tank Draining Test
1. Insure that the drain will run into a bucket and
not onto the floor.
2. Open the drain valve briefly and a small
amount to insure the trap is filled
3. Start the data acquisition routine by pressing
the run arrow in the upper left hand corner of
the screen. The output should appear in the
upper plot and a Fourier transformed version
of the output appears in the middle plot as a
spike at 5kHz. The lower plot will appear when
you begin storing the data.
4. To begin the data acquisition click the toggle
switch or button beneath the liquid level indicator
text box. Allow the system to acquire a
few seconds worth of data and then open the
drain valve fully to begin draining the tank.
5. Close the drain valve when the probe reading
reaches approximately 0.1V or the water
level drops below the bottom of the immersion
probe.
6. Stop the data acquisition by clicking the toggle
switch again, or by clicking the stop button,
and save the data onto disk. Your data file will
contain two columns: time and voltage.
7. Refill the tank to the starting level and repeat
the test procedure with the valve half open.
Software
A LabVIEW virtual instrument titled “Tank Draining”
is available within the “MAE Lab Software”
folder on the desktop for use with this experiment.
Tasks:
1. Plot the calibration data: the immersion probe
depth as a function of the voltage. Be sure to
include error bars on your data.
2. Perform a least squares fit of the calibration
curve to obtain a calibration formula and plot
a sample curve onto the plot of Task 1 to show
the quality of your data. NOTE: the calibration
curve is not linear, so you should use either an
exponential or a polynomial least squares fit.
3. Use the calibration curve formula to convert
voltage data to immersion probe depth. Plot
your calibrated data as a function of time.
4. Compute the derivative dh/dt to obtain the
draining velocity and construct a plot of the
velocity as a function of time.
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