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Question

Given the transfer function $G(S) = \frac{1}{S^2+3S+2}$, Find the response y(t) to the input r(t)=5u(t).

The correct answer is

$y(t) = \left[\frac{5}{2} - 5e^{-t} + \frac{5}{2}e^{-2t}\right]\mu(t)$

To find the response \(y(t)\) for the given transfer function \(G(S) = \frac{1}{S^2+3S+2}\) with the input \(r(t)=5u(t)\), we will perform the following steps:

The first step is to express the transfer function \(G(S)\) as a partial fraction:

  1. \(\frac{1}{S^2+3S+2} = \frac{1}{(S+1)(S+2)}\)

We expect it to be of the form:

  1. \(\frac{A}{S+1} + \frac{B}{S+2}\)

Equating and solving for constants \(A\) and \(B\):

  1. \(1 = A(S+2) + B(S+1)\)

By substituting suitable values:

  • If \(S = -1\), then \(1 = A(1)\) ⇒ \(A = 1\).
  • If \(S = -2\), then \(1 = -B\) ⇒ \(B = -1\).

The next step is to find the Laplace Transform of the input \(r(t) = 5u(t)\):

  1. \(\mathcal{L}\{r(t)\} = \frac{5}{S}\)

Now, calculate \(Y(S) = G(S) \cdot R(S)\):

  1. \(Y(S) = \left(\frac{1}{S+1} - \frac{1}{S+2}\right) \cdot \frac{5}{S}\)

Resulting in:

  1. \(Y(S) = \frac{5}{S(S+1)} - \frac{5}{S(S+2)}\)

Taking the inverse Laplace transform:

  1. \(y(t) = [\frac{5}{2} - 5e^{-t} + \frac{5}{2}e^{-2t}]\mu(t)\)

Thus, the response to the input \(r(t) = 5u(t)\) is:

  • The correct option is: \(y(t) = \left[\frac{5}{2} - 5e^{-t} + \frac{5}{2}e^{-2t}\right]\mu(t)\)
  • Other options don't satisfy the calculated expression.
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Important Questions from Controllers and Compensators

  1. Given below are two statements:

    Statement I: In proportional control, the actuating signal for the control action in a control system is proportional to the error signal

    Statement II: It is desirable that control system be over damped for the point of view of quick response

    In the light of the above statements, choose thecorrectanswer from the options given below:

  2. Which of the following controllers improves the transient response of a system?

  3. The transfer function of the lead compensator is:

  4. Which of the following terms is responsible for noise measurement in the PID controller?

  5. The overall transfer function of a control system is given by the following equation. Find out the value of Derivative rate feedback constant K t. (Consider the Damping ratio 0.9)

    \(\dfrac{C(s)}{R(s)}= \dfrac{36}{s^2+3.6s+36}\)

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