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Question

The transfer function of a system is given by,

\(\frac{{{V_0}\left( s \right)}}{{{V_i}\left( s \right)}} = \frac{{1 - s}}{{1 + s}}\)

Let the output of the system be \({v_0}\left( t \right) = {V_m}\sin \left( {\omega t + \phi } \right)\) for the input, \({v_i}\left( t \right) = {V_m}\sin \left( {\omega t} \right)\). Then the lower and upper limiting values of the continuous unwrapped phase as ω ranges from 0 to infinity of ϕ (in radians) are respectively

The correct answer is

\(- \pi \;and\;0\)

The magnitude is unity and \(\phi(\omega)=\arg(1-j\omega)-\arg(1+j\omega)=-2\tan^{-1}\omega\). It tends from 0 at zero frequency to −π as frequency tends to infinity. Thus the lower and upper limiting phases are −π and 0.

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Important Questions from Closed Loop Control Systems

  1. In a closed loop automatic control system, the sequence of operations is as follows :

    (i) Controlling unit
    (ii) Correcting unit
    (iii) Impact on the process
    (iv) Measurement of process parameters

  2. The block diagram of a control system in given below

    A. The root of characteristics equation is 6

    B. The root of characteristics equation is -6

    C. The root of characteristics equation is 5

    D. The root of characteristics equation is -10

    E. The root of characteristics equation is -5

    Choose the most appropriate answer from the options given below :

  3. The location of closed loop poles of a LTI system is given as shown in the figure :

    The system will be

  4. A negative feedback control system whose open loop transfer function G(S) has feedback transfer function H(S) can be replaced by a single block with transfer function :

  5. The effect of Tachometer feedback in a control system is to reduce -

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