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Unformatted text preview: s time display. 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 X-axis and Y-axis 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 Y-axis" and "AutoScale X-Axis" 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.

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