Control system miscellaneous


Control system miscellaneous

  1. The input x(t) and output y(t) of a system are related as The system is









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    Since y(t) and x(t) are related with some function of time, so they are not time-invariant.
    Let x(t) be bounded to some finite value k.

    y(t) is also bounded. Thus system is stable.

    Correct Option: B


    Since y(t) and x(t) are related with some function of time, so they are not time-invariant.
    Let x(t) be bounded to some finite value k.

    y(t) is also bounded. Thus system is stable.


  1. The matrix [A] =
    2
    1
    4
    -1

    is decomposed into a product of a lower triangular matrix [L] and an upper triangular matrix [U]. The properly decomposed [L] and [U] matrices respectively are









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    By Dolittle’s decomposition,

    2
    1
    =
    1
    0
    u11
    u12
    4
    -1
    l21
    1
    0
    u22

    We have u11 = 2, u12 = 1
    l21 u11 = 4
    ⇒ l21 = 2
    and l 21u12 + u22 = – 1
    ⇒ u22 = – 1 – l 21u12 = – 3
    then ,
    2
    1
    =
    1
    0
    2
    1
    .......(A)
    4
    -1
    2
    1
    0
    -3

    eqn (A) does not signfy any choice
    Now, from crout’s decomposition,
    2
    1
    =
    l11
    0
    1
    u12
    4
    -1
    l21
    l22
    0
    1

    We get, l11 = 2, l11 u12 = 1
    u12 =
    1
    = 0.5
    2

    and, l 21 = 4 , l21 u12 + l22 = – 1
    ⇒ l22 = – 3
    Then ,
    2
    1
    =
    2
    0
    1
    0.5
    4
    -1
    4
    -3
    0
    1

    Hence the choice is (d).

    Correct Option: D

    By Dolittle’s decomposition,

    2
    1
    =
    1
    0
    u11
    u12
    4
    -1
    l21
    1
    0
    u22

    We have u11 = 2, u12 = 1
    l21 u11 = 4
    ⇒ l21 = 2
    and l 21u12 + u22 = – 1
    ⇒ u22 = – 1 – l 21u12 = – 3
    then ,
    2
    1
    =
    1
    0
    2
    1
    .......(A)
    4
    -1
    2
    1
    0
    -3

    eqn (A) does not signfy any choice
    Now, from crout’s decomposition,
    2
    1
    =
    l11
    0
    1
    u12
    4
    -1
    l21
    l22
    0
    1

    We get, l11 = 2, l11 u12 = 1
    u12 =
    1
    = 0.5
    2

    and, l 21 = 4 , l21 u12 + l22 = – 1
    ⇒ l22 = – 3
    Then ,
    2
    1
    =
    2
    0
    1
    0.5
    4
    -1
    4
    -3
    0
    1

    Hence the choice is (d).



  1. If the electrical circuit of Fig.(b) is an equivalent of the coupled tank system of Fig.(a), then










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    C1 = capacity of tank (1)
    C2 = capacity of tank (2)
    h1, h2 = heights of water
    Q1, Q2 = flow rates
    R1, R2 = resistances of flow

    Q1 = Q2 + C1
    dh1
    dt

    Q2 = Q3 + C2
    dh2
    dt

    ∴ Q2 =
    h1 - h2
    , Q3 =
    h2
    R1R2

    Equivalent circuit :

    ∴ A, C = capacitance
    B, D = resistances

    Correct Option: D


    C1 = capacity of tank (1)
    C2 = capacity of tank (2)
    h1, h2 = heights of water
    Q1, Q2 = flow rates
    R1, R2 = resistances of flow

    Q1 = Q2 + C1
    dh1
    dt

    Q2 = Q3 + C2
    dh2
    dt

    ∴ Q2 =
    h1 - h2
    , Q3 =
    h2
    R1R2

    Equivalent circuit :

    ∴ A, C = capacitance
    B, D = resistances