# How to measure the transfer function in Simulink?

1. Nov 24, 2012

### jean28

Let's say I simulate a simple filter in simulink and I want to see the transfer function graph (bode plot) of it. What do I do to get Vout/ Vin? I tried using the "PS Divide" Block and divide the output voltage and the input voltage, but that didn't work. Could anyone help me out here?

This is what I tried:

http://i1226.photobucket.com/albums/ee410/jean28x/bode1.jpg

This is the graph I got:

http://i1226.photobucket.com/albums/ee410/jean28x/bode2.jpg

Thank you all very much.

2. Nov 24, 2012

The scale on your scope is way of. Hit the button next to the printer and uncheck the box saying something like "save only last 1000 data points". Simulate again and hit the button with the binoculars. Does the result seem to be correct now? Check with your analytical answer!

If no results appear, check the Matlab command window for warnings and errors. A divide block can cause problems for certain inputs.

Also this setup does not create the bode plot of the system. A bode plot is the frequency response, here you got only one frequency.

Further hints: A system can create a phase shift between the input and output. Comparing the input and output at the same instant of time gives no true information about the attenuation. How is this done in your model...

3. Nov 24, 2012

### jean28

Ok thanks a lot! One more quick question. I am trying to simulate this circuit (quite complicated) and I can't seem to get an output signal that seems sinusoidal. I think it has something to do with the Refine factor, because when I simulate simpler circuits I DO get a good sine wave. Do you have any idea why this would act this way?

Circuit:

http://i1226.photobucket.com/albums/ee410/jean28x/finalproyect.jpg

Graph I get (instead of Sine Wave):

4. Nov 25, 2012