Laboratory Three. Waveform Generation and Sub-VI s.

Transcription

1 M.E. 401 Mechatronics Laboratory Three Waveform Generation and Sub-VI s. Required Materials Hardware P.C. Multi-Function data acquisition board One LED Software Measurement and Automation explorer (MAX) LabVIEW Study Material Course Text LabVIEW Manual Purpose To generate a variety of waveforms, including white and random noise. The topic of sub-vi s will be addressed and a Fourier series will be developed to approximate a square waveform. Introduction LabVIEW includes a large variety of VI s that allow for the generation and analysis of many different waveforms. Today you will gain experience in LabVIEW with square waveforms, observing their behavior and adding to them the above two types of noise. Fourier Series are a series of sine and cosine terms that can be used in a variety of practical applications to approximate general periodic functions. Fourier series are an important tool that can be used to solve problems involving ordinary and partial differential equations. In Part Three, we will use a Fourier series to approximate a square wave, observing how the accuracy of the approximation increases as we add terms to the series.

2 Part 1: Create VI Purpose: Generate a square wave and output this waveform to a waveform chart. Lab Procedure: 1. Create a new VI with an On-Off switch in LABView as was done in Lab 1 and Create While Loop Square Wave a. Right Click in the block diagram to bring up the Functions Panel, and select While Loop from the Structures subpalette. Click and drag cursor in the block diagram to place and size the structure. b. Wire the Boolean Control to the Loop condition located in the while loop. i. Add a Square waveform vi from the waveform generation from Signal processing subpalette of the Functions menu. ii. Now right click on the frequency terminal of sine waveform and go to create and select control. Notice the changes in front panel. iii. Follow the same procedure for amplitude and sampling info terminals on sine waveform. iv. Wire the offset terminal to the amplitude terminal. v. Now go to front panel and bring up the control menu by right click. Go to modern subpalette and select the waveform chart from graphs subpalette. Place the waveform chart by left click on the front panel. vi. Again, right click to bring up the control menu in front panel. Go to modern subpalette and select the vertical fill slide under numeric subpalette. Place it near to waveform chart in front panel. Rename it as volt. If there is an error, change it to an indicator. vii. Notice the waveform chart vi and volt vi in the block diagram. Place it inside the while loop near to the sine wave vi. viii. Wire the signal output terminal of the Square waveform vi to both waveform chart.vi and volt.vi Your Block Diagram should look something like this so far

3 Now we need to create a sub.vi Part 2: Create a sub-vi that adds two types of noise to the square waveform in Part 1. Procedure: 1. Open a new vi and save it as mysubvi.vi. 2. Right Click in the block diagram to bring up the Functions Panel, and select Case structure from the Structures subpalette. Click and drag cursor in the block diagram to place and size the structure. 3. Again, right click to bring up the control menu in front panel. Go to modern subpalette and select the Radio button under Boolean subpalette. 4. Rewrite the Radio Button as shown in figure

4 5. Now move to Block diagram and Wire the Radio button to the Case Structure by attaching the T/Fbox to the case selector located on the case structure frame. Notice the changes in the frame names of case structure. 6. Inside the Uniform white, Default frame of the case structure, add a Uniform white noise waveform.vi from the waveform generation subpalette of the Signalprocessing subpalette of Function menu. 7. Now right click on the amplitude terminal of Uniform white noise waveform.vi and go to create and select control. Notice the changes in front panel. Follow the same procedure for sampling info terminal. Note: Amplitude and Sampling Info should be outside of the case structure in order that the same controls be used for both cases. 8. Go to front panel and bring up the control menu by right click. Go to modern subpalette and select the waveform chart from graphs subpalette. Place the waveform chart by left click on the front panel. 9. Wire the waveform chart in the block diagram with the signal out terminal of the Uniform white noise waveform.vi 10. Following the same procedure, add Periodic Radom Noise Waveform.vi in frame periodic random of case structure. Your Front Panel and Block Diagram should look like this for sub.vi

5 Configuring the Sub.vi to accept inputs and outputs 1. Return to the front panel and look for icon panel in the upper right hand corner. 2. Right click on this pane and select show connector. The pane should be broken into empty blocks. 3. Click on a connector pane block and then the Boolean control. Click on a second block and then your amplitude control. Click on a third block and then your sampling information cluster. Click on the last block and then on the waveform chart. Your sub-vi is now configured to accept inputs and return outputs. Save this sub-vi if you haven t already. dealing with subvi) (Don t get confused, note that we are Back to Part 1 VI 1. Open your VI form Part 1 and in the functions palette find the select a vi subpalette. Choose the name of your sub-vi and place it in the block diagram.

6 2. Now right click on the amplitude terminal of your sub.vi and go to create and select control. Notice the changes in front panel. Follow the same procedure for sampling info and radio buttons terminal. 3. Rename the amplitude and sampling info terminals into noise amplitude and noise sampling info, respectively. As they will represent the noise waveform. 4. Bring up the function menu by right click. Go to programming subpalette; select the Waveform scale and offset.vi from analog waveform, which is under waveform subpalette. Place the Waveform scale and offset.vi by left click on the Block diagram right of your sub.vi. 5. Go to front panel and bring up the control menu by right click. Go to modern subpalette and select the waveform chart from graphs subpalette. Place the waveform chart by left click on the front panel. Rename to noise waveform chart. 6. Wire the waveform chart terminal of sub.vi waveform in terminal of Waveform scale and offset.vi and the waveform out terminal of Waveform scale and offset.vi to noise waveform chart. 7. Also, wire the offset terminal of Waveform scale and offset.vi to the noise amplitude. Configuring the sound output 1. Bring up the function menu by right click. Go to programming subpalette and select the Graphics and sound subpalette. Select Sound output write.vi from Output subpalette, which is under Sound subpalette. 2. Again, bring up the function menu by right click. Go to programming subpalette and select the Graphics and sound subpalette. Select Sound output configure.vi from Output subpalette, which is under Sound subpalette. Place the sound output configure.vi left to Sound output write.vi 3. Wire the task id terminal of Sound output write.vi to the task id terminal of Sound output configure.vi 4. Now go to front panel and bring up the control menu by right click. Go to modern subpalette and select the waveform chart from graphs subpalette. Place the waveform chart by left click on the front panel. Rename to noise plus waveform chart. 5. Bring up the function menu by right click. Go to mathematics subpalette and select add from numeric subpalette. Place it middle of the blockdiagram. 6. Wiring all the terminals:

7 i) Wire the x terminal of Add to signal out of the square waveform (also wired to the volt and waveform chart). ii) Wire the y terminal of Add to wire joining the noise waveform chat and signal out terminal of waveform scale and output.vi iii) Wire the x+y terminal of Add to the data terminal of Sound output write.vi. iv) Finally wire the noise plus waveform chart to the wire joining the x+y terminal of Add to the data terminal of Sound output write.vi. 7. Configure Time constant: i. Right Click in the block diagram to bring up the Functions Panel and select Timing=>Wait (ms). Then Right Click on the wait milliseconds (left-hand) terminal and Create=>Constant. Set the constant to 100 by double clicking in each frame You should now be ready to run your program. Execute the vi and observe how the noise affects the signal in the waveform chart and through the speaker. You can check your work using the example program below. Here is an image of Part 1 Front Panel and Block Diagram with sub.vi

8 Plot your results Describe how your code works (pay attention in explaining sub VI s.) What phenomenon you have seen or heard? Lab report s format should be the same as before.