# Find the plant zeros

1. Jan 9, 2009

### ohmatlab

Good afternoon. I want to ask a question. If we knew the data X through the plant H, and the output is Y. All we have is measurement data Y. Can we find the zeros of the plant H from the output data Y?
Thanks and have a nice weekend.
01/09/2009

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Hi! Friends, I apologize for unclear descriptive, and thanks for remind me.
I just consider a engineer design question. For a plant, if the numerator have the zeros not strictive located on the left hand side s-plane ( maybe on the right hand side s-plane or just on jw axis ), we can said this plant is non-minimum phase. And it will be unstable. Therefore, for normal situation, from the knwledge of the plant, we can define this plant is stable or not.

Now I consider another problem, sometimes we can not get the plant details. Maybe I just only get the measurement data Y. Y is the output data from unknow plant or channel " H ". I assumed the input data X through the unknown plant or channel H, and only knowkedge we have is just measurement data Y. Because we don't have any knowledge of the plant H, therefore, we can not define if this plant stable or unstable from its poles and zeros. Only information we have is just output data Y.

Now, my question is that if I only have data Y. I just knew data Y is the output from a unknow plant H. reagrding this limited information, do any betters know how to find the zeros of the plant to define the plant atable or not?

I thought one immature idea. If I " fft " the Y. Setting Yfft=fft( Y). Then I set Y1=abs(Yfft). Therefore, every value of the Y1 must be greater or equal the " 0 ". Only value=0 is when meeting the plant zeros. So I can find zeros of the plant. I tried to do this, but I meet difficulties. Do any betters have any better idea?

Thanks Brewong and Danger reply my message. Have a nice weekend.

01/10/2009

Last edited: Jan 10, 2009
2. Jan 9, 2009

### brewnog

I don't really understand the question. Could you be a bit more descriptive? Are you talking about a manufacturing process with its input and output?

3. Jan 9, 2009

### Danger

I'm not as articulate are Brewnog, so I'm just going to say