In a positive feedback system if the open loop gain is -100 and the feedback factor 1/10, calculate the closed loop gain.

This question was previously asked in
HPCL Engineer Instrumentation 11 Aug 2021 Official Paper
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  1. 11.11
  2. 9.09
  3. -11.11
  4. -9.09

Answer (Detailed Solution Below)

Option 4 : -9.09
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Detailed Solution

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Concept

The open loop gain is given by G(s) 

The feedback factor is given by H(s)

Hence the closed loop transfer function is given by \(\frac{G(s)}{1+G(s)H(s)}\)

The transfer function of the closed-loop transfer function, with a positive value of feedback gain, is given by,

\(\frac{{G\left( s \right)H\left( s \right)}}{{1 - G\left( s \right)H\left( s \right)}}\)

Calculation

Given G(s)  = -100

H(s) = 1/10

The closed-loop transfer function is given by: 

\(\frac{-100}{1-(-100)0.1} =-\frac{100}{11}\) = -9.09

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