EET 2259 Unit 11 Charts and Graphs Read Bishop, Chapter 7. Lab #11 and Homework #11 due next week.

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 Controls >> Modern >> Graph palette. The three most common types are the Waveform Chart, the Waveform Graph, and the XY Graph. -Collecting large amounts of data is easy, but interpreting it is more difficult. Charts and graphs can help. -As example of 3D graph, go to example finder, search for 3D, and open 3D Graph Properties - Torus.vi

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)

Waveform Charts and Waveform Graphs Waveform charts and waveform graphs look similar on the front panel. By default, waveform charts have the background grid turned off and waveform graphs have the grid turned on, but this is just a cosmetic difference that you can easily change. The more important difference is the one mentioned on the previous slide.

Waveforms Charts A waveform chart plots numeric data values on a chart. You can easily change the vertical or horizontal scale by double-clicking the minimum or maximum values. (Bishop, p. 349) -Place a chart on front panel, change its X scale from 100 to 20 pts. -On block diagram, generate random numbers in a While Loop with a 0.1 s delay.

Auto-Scaling By default, the vertical axis automatically scales itself to have the best minimum and maximum for the data you’re plotting. You can disable auto-scaling if you wish. -Modify previous example to multiply the random values by 10, and run again; note that new data is appended to the old, and the vertical scale automatically changes. -Demo turning off autoscale and adding an X scrollbar.

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

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) -Demo by modifying existing VI to display random numbers and random numbers x 10.

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)

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, and you wish to make a plot of voltage (on the vertical axis) versus time (on the horizontal axis). Since the time interval is constant, you can use a waveform graph. (Bishop, p. 357) -Create new VI with a waveform graph on front panel. Show that you get an error if you try to wire a random number to it. -Instead, place random number inside a For loop (with n=20), and then wire the output to waveform graph. Run it. Then clear the graph, and use execution highlighting to show how all 20 points are entered into array before any data passes to waveform graph. -Demo with WaveformGraphExample.vi on H drive. Then change function to sin(x/2).

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) -Tell them to keep existing example using waveform graph so we can come back to it later.

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 voltage measurements that were made at irregular intervals, and you wish to make a plot of voltage (on the vertical axis) versus time (on the horizontal axis). Since the time interval is not constant, if you want your plot to accurately show the time relationship among the values, you cannot use a waveform graph; use an XY graph instead. (Bishop, p. 365) -Demo with XYGraphExample.vi on H drive. -Reiterate that for waveform graphs and waveform charts the data points will be evenly distributed on the x-axis.

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)

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) -Before going into this, review the difference between waveform charts, waveform graphs, and xy graphs. -Place a waveform chart & a waveform chart. Look quickly at Properties of each, noting absence of Cursors tab on chart. Delete the chart, and write code to send 20 random numbers to the graph.

Chart/Graph Properties The Properties dialog box has the following tabs: Appearance Display Format Plots Scales Cursors (for Graphs) Documentation Data Binding -Demo with the waveform graph.

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 Colors Fill

Scales Tab The Scales tab lets you control many aspects of the scales on the x- and y-axes: Show or hide scales Autoscaling? Min and max values Colors -Demo

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

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, thickness Color Whether cursors can be moved freely or are locked to a particular plot -Demo on a waveform graph (doesn’t seem to work on xy graph). -You’ll probably want to turn on the cursors legend if you’re using a cursor.

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)

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) -Demo

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) -Demo the hand tool -Demo the zoom in and zoom out tools (last two tools under the magnifying glass icon).

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)

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)

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….