220 appendix software calibration the first command

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Unformatted text preview: ow. The Guide Box will give you directions and tasks to perform. It will also tell you when to select a command in the Command Panel. After selecting a command, it will “gray out” and the next command will become available. You can also print and/or quit from the Command Panel or abort your analysis and try again. The primary data output you get is by generating pdf files of your results, so be careful not to quit without printing pdf files or exporting your data to be emailed amongst your lab group. 220 APPENDIX: SOFTWARE Calibration The first command is to calibrate the Magnetic Field Sensor. Before selecting this command, you need to set the probe to the 6.4mT setting. After selecting the "Calibrate Probe" command, you will be asked to do two tasks. First, you will need to choose the quantity on the x-axis of your data graph. This is accomplished by moving the cursor over to the word "meter" in the red-colored area (shown below) and then pressing the mouse button. You should get a list of choices as shown to the right. By selecting any of these units, you will be making a choice about what you wish to measure. For example, if you choose to use "cm”, you will make a graph of magnetic field strength as a function of distance (B vs. x). It is likely you will want to choose a small unit (cm’s or mm’s) to measure the distance in, since many magnetic fields are not very strong over long distances Selecting "degree" will make a plot of magnetic field strength as a function of angle (B vs. ). Click "OK" when you are ready to proceed. Second, you will need to eliminate the effect of the background magnetic fields. This process is called "zeroing the Hall probe" in the Guide Box. Place the magnetic field sensor wand in the position you would like to take your measurement, but be sure that there are no magnets nearby. Note that power supplies and computers generate magnetic fields, so it is a good idea to keep away from them! When you are ready, select the "Set Probe Zero" as shown below. Then select the “Done” button. The calibration process is now complete. 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 221 APPENDIX: SOFTWARE something, but only if you stop to think about the discrepancies or similarities between your prediction and the results. In order to enter your prediction, you first need to decide on your coordinate axes and scale (units) for your measurements. Record these in your lab journal. Next, 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 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 or use the AutoScale feature (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. Exploration After you have entered your prediction, you can explore the limitations of your magnetic field sensor before you take data. The value of the magnetic field strength is displayed directly under the Guide Box. When you are ready to take data, select Acquire Data from the Command Panel. Data Acquisition Collecting data requires that you enter the x-axis data before the computer reads in a value for the magnetic field strength. You enter this data using the panel shown. For every x-axis data value you enter, the analysis program will record the magnetic field strength in gauss on the y-axis of the "Plot". Press "OK" to collect the next data point. 222 APPENDIX: SOFTWARE 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 or use the AutoScale feature (see Finding Data below). 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 a...
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