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When you first start the application you will need to click the “DAQ START” button to start
226 APPENDIX: SOFTWARE streaming the probe readings. You will use the “DAQ STOP” to freeze the data screen for
taking measurements. A green indicator is used to indicate whether the interface is running
or not. The vertical axis is a measure of the potential
difference (voltage) between the two leads of
the voltage probe.
The horizontal axis
measures time. You should also notice that
the display has a grid on it. The scale of each
axis is shown at the bottom of the display.
As you might suspect, it is possible to change
the grid size of each axis. To change the scale
of the axis, simply click on the highest or
lowest number on that axis and type in a new
value. The axis will automatically adjust to
create even increments over the newly
defined range.
The red and blue lines that are on the display are movable simply by putting your mouse
pointer over one of the lines. When the mouse pointer changes shape, hold the mouse button 227 APPENDIX: SOFTWARE down and drag the lines to mark a voltage or time as shown. The lines mark the voltage and
time boundaries of the data that will be considered for analysis.
If you are unable to see the lines, it is possible that you changed the axes scale and “zoomed
in” too far. Try changing the axes to “zoom out” again, and determine if you can locate the
blue and red lines. Move the lines to within the values of the new scale, and they should
remain visible on the screen when you zoom in.
Predictions
This type of analysis relies on your graphical skills to interpret the data. You should be
familiar with both appendices, A Review of Graphs and Accuracy, Precision and
Uncertainty.
The first task is to enter your prediction of the mathematical function you expect to represent
your data. Making a prediction before taking data is the best way to determine if anything is
going wrong (remember Murphy’s Law). It’s also a good way to make sure you have learned
something, but only if you stop to think about the discrepancies or similarities between your
prediction and the results.
You will need to select the generic equation, u(x),
which describes the graph you expect for the data.
Clicking the equation currently showing in the box
will bring up a list of equations to choose from; see
the diagrams to the right.
After selecting your generic equation, you next
need to enter your best approximation for the
parameters A, B, C, and/or D. These values
should come directly from your prediction
equation you did for class. As you enter these
values, you should see the red line in the "Plot"
box changing. Once you have selected an equation and the values of the constants are entered, your
prediction equation is shown on the graph on the computer screen. If you do not see the
curve representing your prediction, change the scale of the graph axes (see Finding Data
below). When you are satisfied, select the Accept Prediction option from the Command
Panel. Once you have done this you cannot change your prediction except by starting over. 228 APPENDIX: SOFTWARE Exploration
After you have entered your prediction, you can explore the limitations of your voltage
probe sensor before you take data. The value of the voltage is displayed directly on the
voltage vs. time display. When you are ready to take data, select Acquire Data from the
Command Panel.
Data Acquisition
Collecting data requires that you position the
moveable red and blue lines on the voltage vs.
time display. The blue lines will generate
potential difference data and the red lines will
generate time/period data. The data values
are shown in the data box. The data box
appears once you have selected “Acquire Data”
from the Command Panel. Press "OK" to
collect each data point. Each data point should
appear on the graph on the computer screen as
you take it. If it doesn’t, adjust the scales of
your graph axes. If you are satisfied with your
data, choose Analyze Data from the Command
Panel.
Finding Data on the Graph
You can find your data on the graph by adjusting the scales of your Xaxis and Yaxis plots
manually. This scaling is accomplished by entering values into the legend of the graph.
Click on the upper or lower legend value and enter a new value, then hit enter. If you cannot
locate your data, you can select both "AutoScale Yaxis" and "AutoScale XAxis" to let the
program find the data for you. You can then adjust your axis scales to give you a convenient
graph for analysis. Be careful, the AutoScale option will often set the scales in such a way
that small fluctuations in the data are magnified into huge fluctuations.
Data Fits
Deciding which equation best fits your data is the most important part of using this analysis
program. While the actual mechanics of choosing the equation and parameters are similar to
what you did for your predictions, fitting data is somewhat more complicated.
By looking at the b...
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This document was uploaded on 02/23/2014 for the course MANAGMENT 2201 at University of Michigan.
 Spring '14

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