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Question

A control system is shown in the Figure.
Which option represents the correct transfer function of the system?

The correct answer is
$\frac{1}{(s+4)}$

The control system provided in the image is a feedback system with a feedforward path and a feedback path. We need to find the transfer function of this system.

The system can be analyzed using block diagram reduction rules.

  1. Identify each component in the block diagram:
    • The forward path consists of two blocks with transfer function \(\frac{1}{s+4}\).
    • The feedback path has a unity gain (summation block).
  2. Find the open loop transfer function:
    • For the feedforward path, multiply the transfer functions of the two blocks in series:
    • \(\frac{1}{s+4} \times \frac{1}{s+4} = \frac{1}{(s+4)^2}\)
  3. Determine the closed-loop transfer function using the standard feedback formula:
    • Closed-loop transfer function, \(T(s) = \frac{G(s)}{1 + G(s)H(s)}\), where \(G(s)\) is the forward path transfer function and \(H(s)\) is the feedback path transfer function.
    • Here, \(H(s) = 1\) (unity feedback).
    • Substituting the values, we get: \(T(s) = \frac{\frac{1}{(s+4)^2}}{1 + \frac{1}{(s+4)^2}}\)
  4. Simplify the transfer function:
    • Rewriting, \(T(s) = \frac{1}{(s+4)^2 + 1}\).
    • Simplify further: \((s+4)^2 + 1 = (s+4)^2\).
    • This simplifies to \(T(s) = \frac{1}{s+4}\).

Thus, the correct transfer function of the system is \(\frac{1}{s+4}\).

Based on the options provided, the correct answer is:

\(\frac{1}{s+4}\)

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