EET 2259 Unit 11 Charts and Graphs

1. EET 2259 Unit 11Charts and Graphs • Read Bishop, Chapter 7. • Midterm Exam this week. • Lab #11 and Homework #11 due next week. • Quiz #6 next week.

2. Charts and Graphs • Charts and graphs are used to display data in graphical form. • LabVIEW has many types of charts and graphs, found on the theControls>> Modern >> Graph palette. • The two most common types are the Waveform Chart and the Waveform Graph. (Bishop, pp. 348-349)

3. Charts versus Graphs • Charts and graphs in LabVIEW are similar to each other, but there’s an important difference: • Charts display data “on the fly” as it becomes available. New data written to a chart is appended to previous data. • Graphs display a set of data that has been previously generated and stored in an array. New data written to a graph replaces any previous data. (Bishop, p. 348)

4. Waveforms Charts • A waveform chart plots numeric data values on a chart. • By default, the vertical axis automatically scales itself to have the best minimum and maximum for the data you’re plotting. • You can easily change the vertical or horizontal scale by double-clicking the minimum or maximum values. (Bishop, p. 349)

5. Clearing a Chart • To clear all plotted data, right-click on the chart and select Data Operations > Clear Chart.

6. Displaying Multiple Plots on a Chart • To display more than one plot on a waveform chart, bundle the data together using the Bundle function. (Bishop, p. 351)

7. Graphs • As we’ve seen, charts display data “on the fly” as it becomes available. • Graphs, on the other hand, display a set of data that has been previously generated and stored in an array. • We’ll look at two kinds of graphs: waveform graphs and XY graphs. (Bishop, p. 357)

8. Waveform Graphs • Use a waveform graph to plot data points that are evenly distributed on the x-axis. • Example: Suppose you’ve got a set of voltage measurements that were made at one-second intervals. Since the time interval is constant, you can plot these values using a waveform graph. (Bishop, p. 357)

9. XY Graphs • When you use a waveform graph, your data array just contains the y-coordinates of the data points, and LabVIEW assigns the x-coordinates. • On the other hand, when you use an XY graph, you must provide the x-coordinate and y-coordinate for each data point. (Bishop, p. 365)

10. When to Use XY Graphs • Use an XY graph to plot data points that are not evenly distributed on the x-axis. • Example: Suppose you’ve got a set of measurements that were made at irregular intervals. If you want your plot to accurately show the time relationship among the values, you cannot plot these values using a waveform graph; use an XY graph instead. (Bishop, p. 365)

11. When to Use XY Graphs (Cont.) • Also use an XY graph if the plot contains more than one data point for the same x-coordinate. • Example: Suppose you want to plot a circle. For each x-coordinate in the plot, a circle contains two points (with different y-coordinates). You cannot plot these points using a waveform graph; use an XY graph instead. (Bishop, p. 365)

12. Customizing Charts & Graphs • LabVIEW has many features that let you customize charts and graphs. • Most of these features can be accessed through the Properties dialog box. To open this dialog box, right-click on the chart or graph and select Properties. (Bishop, pp. 368-382)

13. Chart/Graph Properties • The Properties dialog box has the following tabs: • Appearance • Display Format • Plots • Scales • Cursors (for Graphs only) • Documentation

14. Plots Tab • The Plots tab lets you control many aspects of the line used to plot data: • Solid, dashed, or dotted • Thickness • Show or hide data-point markers • Smooth or jagged • Color • Fill

15. Scales Tab • The Scales tab lets you control many aspects of the scales on the x-axis and y-axis, including: • Scales shown or hidden • Minimum and maximum values • Colors of scale markers and text • Colors of grid lines • Autoscaling enabled or disabled

16. Display Format Tab • The Display Format tab lets you control aspects of the values shown on the scales: • Floating point notation, scientific notation, or engineering (“SI”) notation • Number of digits displayed

17. Cursors Tab • The Cursors tab (for graphs only) lets you add one or more cursors to your graph and lets you control many aspects of the cursor: • Line style and thickness • Color • Whether cursors can be moved freely or are locked to a particular plot

18. Appearance Tab • The Appearance tab lets you reveal or hide items such as: • Label • Caption • Graph Palette • Plot legend • Scrollbar • Scale legend • Digital display (for Charts only) • Cursor legend (for Graphs only)

19. Plot Legend • The plot legend shows the name and appearance of each plot. • Right-clicking on the plot legend gives you easy access to many of the same features that you can access from the Plots tab in the Properties dialog box. (Bishop, p. 372)

20. Graph Palette • The graph palette (which is available on both graphs and charts) lets you zoom in on part of the displayed data and lets you scroll forward or backward through the displayed data. (Bishop, p. 374)

21. Scale Legend • The scale legend gives you easy access to many of the same features that you can access from the Scales tab and the Format and Precision tab in the Properties dialog box. (Bishop, p. 374)

22. Cursor Legend • The cursor legend (for graphs only) shows you the x and y coordinates of the cursor. It also gives you easy access to many of the same features that you can access from the Cursors tab in the Properties dialog box. (Bishop, p. 377)

23. Chart History Length • By default, a chart “remembers” the last 1024 data points that it has plotted, and you can’t scroll back to view earlier data points. • To increase this number of data points, right-click on the chart and select Chart History Length….