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Temperature Analysis VI

Module by: National Instruments

Summary: To graph and analyze data.

Problem 1
Complete the following steps to build a VI that measures temperature every 0.25 seconds for 10 seconds. During the acquisition, the VI displays the measurements in real time on a waveform chart. After the acquisition is complete, the VI plots the data on a graph and calculates the minimum, maximum, and average temperatures. The VI displays the best fit of the temperature graph.

1.a) Front Panel

  1. Open a blank VI and build the front panel shown in Figure 1.
    Figure 1
    1. Set the point style of the waveform chart plot to a small xx.
    2. Hide the plot legend of the waveform chart.
    3. Change the label of the waveform chart to Temperature Chart.
    4. Change the label of the waveform graph to Temperature Graph.
    5. Right-click Temperature Chart and select Properties from the shortcut menu. On the Scales tab, change the x-axis multiplier to 0.25. On the Format and Precision tab, change the Digits of Precision to 2. The data for Temperature Graph will be formatted on the block diagram.
    6. Resize the plot legend of the waveform graph to show two plots.
    7. Change the name of Plot 0 to Temp and Plot 1 to Fitted.
    8. Set the point style of the waveform graph Temp plot to a small square.
    9. Do not create the Mean, Max, andMinindicators yet. They will be created from the block diagram.

1.b) Block Diagram

  1. Build the block diagram Figure 2.
    Figure 2
    1. Place the Thermometer VI on the block diagram. Select Functions>>All Functions>>Select a VI and navigate to C:\Exercises\LabVIEW Basics I\Thermometer.vi. This subVI returns one point of temperature data.
    2. Place the Wait Until Next ms Multiple function, located on the Functions>>All Functions>>Time & Dialog palette, on the block diagram. This function causes the For Loop to execute every 0.25seconds 0.25 seconds ( 250ms 250 ms ).
    3. Place the Array Max & Min function, located on the Functions>>All Functions>>Array palette, on the block diagram. This function returns the maximum and minimum temperature.
    4. Place the Mean VI, located on the Functions>>All Functions>>Analyze>>Mathematics>>Probability and Statistics palette, on the block diagram. This subVI returns the average of the temperature measurements.
    5. Right-click the output terminals of the Array Max & Min function and Mean VI and select Create>>Indicator from the shortcut menu to create the Max, Min, and Mean indicators.
    6. Place the General Polynomial Fit VI, located on the Functions>>All Functions>>Analyze>>Mathematics>>Curve Fitting palette, on the block diagram. This subVI returns an array that is a polynomial fit to the temperature array.
    7. Place the Bundle function, located on the Functions>>All Functions>>Cluster palette, on the block diagram. This function assembles the plot elements into a single cluster. Press the <Ctrl> key while you drag the function to copy it. The elements include the initial xx value (0), the Δx Δ x value (0.25), and the yy array of temperature data. The Δx Δ x value of 0.25 is required so that the VI plots the temperature array points every 0.250.25 seconds on the waveform graph.
    8. Place the Build Array function, located on the Functions>>All Functions>>Array palette, on the block diagram. This function creates an array of clusters from the temperature cluster and the best fit cluster.
    9. Complete the block diagram as shown.
  2. Save the VI as Temperature Analysis.vi in the C:\Exercises\LabVIEW Basics I directory.

1.c) Run the VI

  1. Display the front panel and run the VI. The graph displays both the temperature data and best fit curve of the temperature waveform.
  2. Try different values for the polynomial order constant on the block diagram and run the VI again.
  3. Change the appearance of the plots by modifying the plot styles and fill styles.
    1. Right-click the Temp plot display in the plot legend and select Common Plots>>Scatter Plot from the shortcut menu, the top middle option.
    2. Right-click the Fitted plot display in the plot legend, select Bar Plots from the shortcut menu, and select the second option in the middle row. The waveform graph should appear similar to the front panel in Figure 3.
      Figure 3
  4. Save and close the VI.

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