control systems <tons of questions>

Discussion in 'Homework Help' started by MegaMan, Oct 1, 2009.

  1. MegaMan

    Thread Starter Member

    Sep 25, 2009
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    Hi , getting control systems < studying Mechatronics Engineering , i will post a question from time to time >

    the professor said that the feedback should be negative , why ?

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  2. Papabravo

    Expert

    Feb 24, 2006
    10,140
    1,790
    It must be negative because otherwise the system and the amp would continue in the same direction until the amplifer reached it's limit and destroyed itself or the system began to oscillate. The purpose of feedback is to reduce the error at the output of the summation block (aka the summing junction).
     
  3. rjenkins

    AAC Fanatic!

    Nov 6, 2005
    1,015
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    Clue: One way you increase the error, the other way you decrease the error...
     
  4. MegaMan

    Thread Starter Member

    Sep 25, 2009
    53
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    i understand , thanks .
     
  5. hgmjr

    Moderator

    Jan 28, 2005
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    The only way to drive the error term to zero is to subtract two quantities. Hence negative feedback.

    hgmjr
     
  6. MegaMan

    Thread Starter Member

    Sep 25, 2009
    53
    0
    the proffessor said that there are certain cases where its +ve , case of oscilators ? , why ?
     
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