How Do You Factor Transfer Functions in S-Plane Analysis?

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In summary, the conversation discusses confusion regarding factoring transfer functions in S-plane analysis and how it relates to simple algebra. The original link provided is not accurate as it incorrectly simplifies the transfer function H(s). The correct method is to factor out 2 from the numerator, rather than dividing the numerator by 2 and multiplying the denominator by 2. The individual is seeking clarification on this concept.
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FrankJ777
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Hi all. I'm trying to relearn S-plane analysis and filter transfer functions. What I'm having problems with is simple algebra i think, because it's been a while. Right now I've been reading http://www.ee.up.ac.za/main/_media/en/undergrad/subjects/eli220/polezero.pdf. What I'm confused about, among other things, is factoring the transfer function H(s).
In their example:

H(s) = [itex]\frac{2s + 1}{(s^2 + 5S + 6)}[/itex]

factored

H(s) = [itex]\frac{1}{2}[/itex] [itex]\frac{s+1/2}{(s+3)(s+2)}[/itex]

I don't understand how they get that. The way I see it, because:
2s+1 = 2(s+1/2)
and
[itex]s^{2}[/itex]+5s+6 = (s+3)(s+2)
so

H(s) = [itex]\frac{2s + 1}{(s^2 + 5S + 6)}[/itex] = [itex]\frac{2}{1}[/itex] [itex]\frac{s+1/2}{(s+3)(s+2)}[/itex]

Also It seems that:

[itex]\frac{2s + 1}{(s^2 + 5S + 6)}[/itex] ≠ [itex]\frac{1}{2}[/itex] [itex]\frac{s+1/2}{(s+3)(s+2)}[/itex]

So I guess what I don't understand is why it seems that instead of factoring out 2 from the numerator, we are dividing the numerator by 2 and multiplying the denominator by 2.

Can someone please set me straight. I know I did this a few years ago and it seemed to make more sense then, than it does now.

Thanks a lot.
 
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  • #2
Hi FrankJ777. The explanation is quite simple: you are right and they are wrong. :smile:
 
  • #3
Really? I hope that's the case. Too bad I wasted several study hours trying to get it.

Thanks
 

FAQ: How Do You Factor Transfer Functions in S-Plane Analysis?

What is factoring transfer functions?

Factoring transfer functions is the process of breaking down a complex mathematical equation (transfer function) into smaller, simpler parts that can be more easily understood and manipulated. This is often used in the field of control systems engineering to analyze and design control systems.

Why is factoring transfer functions important?

Factoring transfer functions is important because it allows us to better understand and analyze complex systems. By breaking down a transfer function into smaller parts, we can identify key components and their individual effects on the overall system. This can help us design more efficient and effective control systems.

How is factoring transfer functions done?

There are various methods for factoring transfer functions, including the pole-zero cancellation method, partial fraction expansion, and the Hurwitz stability criterion. These methods involve manipulating the transfer function algebraically to break it down into smaller, simpler parts.

What are the benefits of factoring transfer functions?

Some benefits of factoring transfer functions include improved system understanding, easier analysis and design of control systems, and the ability to identify and troubleshoot potential issues in a system. It can also help with simplifying mathematical calculations and reducing complexity in system models.

Are there any limitations to factoring transfer functions?

While factoring transfer functions can be a useful tool, it does have its limitations. It may not always be possible to completely factor a transfer function or the resulting factors may not accurately represent the behavior of the original system. Additionally, factoring can become more difficult with more complex systems and may require advanced mathematical techniques.

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