Bode plot with given transfer function

[gfd43tg]

Homework Statement

Homework Equations

The Attempt at a Solution

Hello,

I am having serious problems being able to draw bode plots. At first the professor said to put everything into standard form with an (ω/ω_c)...and then there is also a table in the textbook with standard forms that don't all include an ω_c, and he retracted his statement. So now I am just so confused how to draw these things.

I am working on the first transfer function in the image, and with two poles at 50 and 100, I'm not sure how to represent that.

 

[gfd43tg]

Here is what I have for my magnitude plot


I don't see anything in this table that looks like this transfer function anyway, leaving me even more confused

 

[rude man]

Your Bode gain plot needs help. But you have the right idea.

It's OK (flat) until you get to w=2, then a -20dB/decade fall from w=2 to w=10 is still OK, but then for some reason you give it a +40dB/decade rise when it should be just +20 dB. So make that correction and try again to finish the plot.

 

[donpacino]

I would recommend you get some semi-log paper. It will make things much easier

 

[donpacino]

Your Bode gain plot needs help. But you have the right idea.

It's OK (flat) until you get to w=2, then a -20dB/decade fall from w=2 to w=10 is still OK, but then for some reason you give it a +40dB/decade rise when it should be just +20 dB. So make that correction and try again to finish the plot.

To add to what Rude man said the slope is a running total

 

[gfd43tg]

Should the paper be log scale on horizontal axis and linear on vertical axis? I found a website that I can print semi log paper, thanks for the suggestion

 

[donpacino]

horizontal.
log base 10

here is an example
http://lpsa.swarthmore.edu/Bode/eqs/BodePaper1.gif

 

[psparky]

Should the paper be log scale on horizontal axis and linear on vertical axis? I found a website that I can print semi log paper, thanks for the suggestion

The gain and frequency are both logrithmic if referring to gain. If referring to dB, then only the horizontal is logrithmic.

Keep in mind that your transfer function will give you the exact gain and phase angle for any value of omega. So if you ever get confused, start plugging in your limits for 0 and infinity to see where your gain sits. Then plug in other values of interest, the break frequencys for sure. If there is an "s" in your transfer function, simply substiture "jω" for "s" and solve for that frequency. You will always get a vector with magnitude (gain) and an angle (phase).

If you plug in 0, 2, 10, 50 and 100 and infinity for omega, you can never miss.

And if you are "guessing" with the zeros and poles...at least you can back check your guess.