Open loop transfer function of a closed loop control system is defined as:

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  1. Actuating signal / feedback signal
  2. Output / feedback signal
  3. Output / actuating signal
  4. Feedback signal / actuating signal

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Option 3 : Output / actuating signal
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Closed-loop control system:

These are the systems in which the control action depends on the output. These systems have a tendency to oscillate.

Ex: Temperature controllers, speed control of the motor, systems having sensors, Human eye, etc.

The closed-loop control system can be described by a block diagram as shown in the figure below.

F1 Harish Madhu 17.06.21  D1

Where, R(s) is Reference Input,

Actuating Signal E(s) = R(s) - C(s)

G(s) is unity feedback open loop gain.

H(s) is Feedback gain.

C(s) is the Output and it is given as a feedback signal to input through the feedback gain function H(s)

From the above figure, we can find out closed-loop transfer function.

CLTF = C(s) / R(s)

From this open-loop transfer function is calculated as,

\(OPLT = \dfrac{CLTF}{1-CLTF}=\dfrac{\frac {C(s)}{R(s)}}{1-\frac {C(s)}{R(s)}}\)

\(OLTF=\dfrac{C(s)}{R(s)-C(s)}=\dfrac{C(s)}{E(s)}\)

OLTF = Output / actuating signal

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