BodePlotGui

• Overview
• Freq Domain
• Why Bode?
• Asymptotic plots
• Making Plot
• Examples
• BodePlotGui
• Rules Table
• Printable

A Tool for Generating Piecewise Linear Asymptotic Bode Diagrams

Back

BodePlotGui is a graphical user interface written in the MATLAB® programming language.  It takes a transfer function and splits it into its constituent elements, then draws the piecewise linear asymptotic approximation for each element.  It is hoped that the BodePlotGui program will be a versatile program for teaching and learning the construction of Bode diagrams from piecewise linear approximations. 

Files for the program are found here

Use of program.

>>MySys=tf(1000*[1 0],[1 10]);   %define Xfer function 
>>BodePlotGui(MySys)        %Invoke GUI

 Starting in the upper left and going counterclockwise, the windows show:

1. The magnitude plot, both the piecewise linear approximation for all three terms as well as the asymptotic plot for the complete transfer function and the exact Bode diagram for magnitude. Also shown is a zero reference line.

2. The phase plot.

3. The legend identifying individual terms on the plot.

4. A box that shows elements excluded from the plot. This box is empty in this display because the diagram displays all three elements of the transfer function.

5. A 'Legend' box that shows elements displayed in the plot.

6. Above the legend box is a check-box that determines whether or not to display the asymptotic plot for the complete transfer function; sometimes it gets in the way of seeing the other plots, so you may want to hide it.

7. Several check-boxes that allow the user to display how the plots are displayed.

8. Two buttons that allow the user to close the GUI, or to go to a web page (this one) that describes Bode Plots.

Also shown in the upper right hand corner is the transfer function, H(s).

Modifying what is displayed

The function displayed can be manipulated term by term to illustrate the effect of each term. For example, the zero at the origin can be excluded simply by clicking on it in the lower left hand box. The figure below shows the result.

Note that the zero at the origin is no longer included in the plot.  Each term can be likewise included or excluded by simply clicking on it.

The next plot shows the plot modified to have thicker lines, a grid, phase in radians and without the asymptotic plot of the complete transfer function.  In the previous graph, the phase of the asymptotic plot obscured that of the real pole; this is an example when it is convenient not to show the asymptotic approximation.

Underdamped terms

Underdamped poles (and zeros) present a difficulty because they cause a peak (dip) in the magnitude plot.  The program show this with a simple circle showing the peak height.  For example the transfer function

yields the output shown below.  The peak due to the underdamped pole is clearly shown.

Limitations of the software:

The software has known limitations. It does not calculate the phase associate with a time delay. It only decomposes transfer functions with up to 20 separate terms (a limit only of the number of colors used). Repeated poles and zeros are treated as a single term (i.e., it is not possible to move only one pole of a repeated pair from the “Elements included in plot” window to the “Elements excluded from plot” window of the GUI). 

Back                          Get the files