Find out transfer function in control system

In summary, the conversation discusses using Laplace to solve for a transfer function in the form TF = C(s) / R(s), with the given equation being 3s C(s) + C(s) = R(s) e-3s. There is confusion about the correct answer, with the book providing answer B but the participants pointing out errors in the wording and possible incorrect answers. It is suggested that the textbook being used may have errors and the forum is a helpful resource for clarification.
  • #1
jaus tail
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Homework Statement


upload_2018-2-4_12-5-23.png


Homework Equations


Using Laplace
TF = C (s) / R (s)

The Attempt at a Solution


Laplacing the equation:
3s C(s) + C(s) = R(s) e-3s
So C(s) / R(s) = e-3s / (1 + 3s)
Book answer is B
I know ramp input is At. Do I laplace it as: A/s2?
I'm not sure where I'm wrong
 

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  • #2
The wording is wrong.
The transfer function is in fact 1/(3s+1). A transfer function is output/input and so is not a function of the particular input.
What they might have meant is the Laplace transform of the output, but if r(t-3) is a ramp t delayed by 3 sec. then again none of the proffered answers is correct. It would be e-3s/{s2(3s+1)} as I think you surmised.
 
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  • #3
@jaus tail , you seem to be using textbooks that have many errors. I hope that as you advance, you will get access to better quality teaching materials.
 
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  • #4
anorlunda said:
@jaus tail , you seem to be using textbooks that have many errors. I hope that as you advance, you will get access to better quality teaching materials.
Yeah but exam is very near and I cannot study from another book now. I'll get more confused.
This forums is very helpful.
 

1. How do I find the transfer function in a control system?

The transfer function in a control system is the ratio of the output of the system to the input of the system in the Laplace domain. In order to find the transfer function, you will need to take the Laplace transform of the differential equation that describes your system. This will give you the transfer function in terms of the Laplace variable, s.

2. What is the significance of the transfer function in control system analysis?

The transfer function is an important tool in control system analysis as it allows us to understand the relationship between the input and output of the system. It can help us determine the stability, performance, and response of the system to different inputs. It also allows us to design controllers and tune the system for desired behavior.

3. Can the transfer function be derived using other methods besides the Laplace transform?

Yes, the transfer function can also be derived using other methods such as the state-space representation or frequency response analysis. However, the Laplace transform is the most commonly used method as it simplifies the analysis of dynamic systems.

4. How do I analyze the stability of a system using the transfer function?

To analyze the stability of a system using the transfer function, you can use the Routh-Hurwitz stability criterion or the Nyquist stability criterion. These methods use the transfer function to determine the stability of the system based on the poles and zeros of the transfer function.

5. Can the transfer function be used for non-linear systems?

No, the transfer function is only applicable for linear systems. For non-linear systems, other methods such as state-space representation or Lyapunov stability analysis are used for analysis and design.

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