Find out transfer function in control system

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Discussion Overview

The discussion revolves around finding the transfer function in a control system context, specifically using Laplace transforms. Participants are addressing a homework problem that involves deriving the transfer function from a given equation and clarifying the implications of different types of inputs.

Discussion Character

  • Homework-related
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant presents an attempt at a solution using Laplace transforms, stating that the transfer function is C(s) / R(s) and deriving it as e-3s / (1 + 3s).
  • Another participant contests the initial claim, asserting that the correct transfer function should be 1/(3s+1) and emphasizes that a transfer function is defined as output/input, independent of the specific input type.
  • A further clarification is made regarding the Laplace transform of a ramp input, suggesting that it should be represented as e-3s/{s2(3s+1)} if considering a ramp delayed by 3 seconds.
  • One participant expresses concern about the quality of their textbooks and the potential confusion caused by studying from them, while acknowledging the helpfulness of the forum.

Areas of Agreement / Disagreement

Participants exhibit disagreement regarding the correct form of the transfer function and the interpretation of the input types. No consensus is reached on the correct approach or solution.

Contextual Notes

There are indications of missing assumptions regarding the nature of the input and the specific context of the problem, as well as potential errors in the textbooks referenced by participants.

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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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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@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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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.
 

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