LABVIEW HANDOUT 2
CHAPTER 2: THE FOR LOOP AND THE WAVEFORM GRAPH
Open a Blank VI. Place a For Loop on the Block Diagram:
Functions Palette>>Programming >>Structures>>For Loop
The initial value of the Loop Iteration Terminal
iteration. The Loop Count Terminal
is zero, and increments by one integer each
resides in the upper left-hand corner. The loop
terminates when i = N − 1. Place a Waveform Graph on the Front Panel:
View>>Controls Palette>>Modern>>Graph>>Waveform Graph
Change the x-axis label to x (radians) and the y-axis label to sin(x). On the Block Diagram,
move the Waveform Graph outside of the For Loop. Place a Sine Function icon in the For
Loop. Wire the Loop Iteration Terminal to the input of the Sine Function. Eliminate the red
Coercion Dot on the Sine Function input. Divide the Loop Iteration output (Sine Function
input) by 5. Create a constant for the input of the Loop Count Terminal equal to 100. Wire the
output of the Sine Function to the Waveform Graph.
Notice that the output wire of the For Loop is thick and orange, denoting a one-dimensional
array of double precision floating point numbers. A small box on the edge of the For Loop is
called the Auto-Indexed Tunnel. This accumulates the array of values. When the For Loop
completes its last iteration, it sends the array of numbers to the Waveform Graph. Run the
program.
Insert a Bundle Function on the wire that connects the For Loop and the Waveform Graph:
Right-Click>>Insert>>All Palettes>>Programming>>Cluster, Class, & Variant>>Bundle
Broken wires can be deleted by typing CTRL-B. Resize the Bundle to have three inputs by
pulling down on its lower edge.
Copy the constant 5 box by left-click highlighting the constant and then typing CTRL-C. Place
the cursor close to the Bundle and left-click. Then paste the constant using CTRL-V. Wire
constants to the top and middle inputs with values 0 and 0.2, respectively. Wire the output of the
For Loop to the bottom input of the Bundle. Wire the output of the Bundle to the Waveform
Graph. Notice the color of the output wire of the bundle has changed to pink. Use Show
Context Help to determine the meaning of the color and the inputs for the Waveform Graph.
Run the program.
Change the For Loop to a While Loop:
Right-Click>>Replace with While Loop
Insert a logical comparison function on the Block Diagram:
Functions Palette>>Programming>>Comparison>>Equal?
Bring the constant (100) into the While Loop and compare it to the Loop Iteration Terminal
using the Equal? Function. Wire the output of the Equal? Function to the Loop Condition
Terminal. This will stop the While Loop after 101 iterations.
Place an Array Indicator on the output wire of the While Loop:
Right-Click>>Create>>Indicator
Rerun the program. Resize the Array Indicator and examine the contents.
Place probes on several wires using the Probe Data Function:
View>>Tools Palette>>Probe Data
Rerun the program and observe the data. Delete the probes. On the Tools Palette, click on
Automatic Tool Selection. Change the constant 100 to 5. Press the Highlight Execution button
on the Block Diagram.
Rerun the program. Notice how the array of Sine Function data is stored at the Auto-Indexed
Tunnel at the edge of the While Loop until the iterations are complete.
Clean up the appearance of the Block Diagram and make it as compact as possible. Place your
name on the Front Panel. Print out the program using Microsoft Word by taking a screen shot of
the Front Panel and Block Diagram.