Measurement alters circuit's behavior

Discussion in 'The Projects Forum' started by jocasa, May 16, 2010.

  1. jocasa

    Thread Starter New Member

    May 16, 2010
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    Hi!

    Do you know Chua's circuit? It is a simple circuit which exhibits chaotic dynamics as the value of a variable resistor is changed. As it happens with all chaotic systems it is very sensitive to small changes in its parameters.

    As the simulations with pspice show, the signal (voltage) I would like to measure ranges from -10V to 10V approximately. My data acquisition system is Arduino, whose analog inputs allow a voltage range of [0V, 5V]. So I thought of adding a voltage divider to scale the signal to [-2.5V, 2.5V] and then add to it 2.5V with a non-inverting summer (using an op-amp) to move the range to [0V, 5V].

    When simulating Chua's circuit with this addition the behavior of the circuit is very much affected. Have you any idea of how to implement this in a way that it's 'invisible' to the circuit?

    I guess the answer has to do with impedances, but about it I know almost nothing. I can post the circuit if you want.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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  3. jocasa

    Thread Starter New Member

    May 16, 2010
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    Sorry to say I don't get your point. Do you mean to save the signal of interest in a device, and treat it later in that external device? What kind of device can do that?
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    Sorry for the misunderstanding. My use of "buffer" means to use a high impedance op amp in follower configuration to present the signal to another circuit that will alter the appearance to suit your needs. The buffer is effectively invisible to the original circuitry. It will need +/- voltage supplies to work, though.

    Something like an OPA134PA would work very well as the buffer amp.
     
  5. jocasa

    Thread Starter New Member

    May 16, 2010
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    Thanks beenthere.

    Simulations now are much better than before. The presence of the follower opamp can be noticed, though. The signal still differs from the original circuit one. But I think yours may be a solution to my problem, as long as the overall characteristics of the original circuit are not severely modified.

    Perhaps the opamp that pspice uses is a not very high impedance one. What circuits simulation program would you recommend me?
     
  6. beenthere

    Retired Moderator

    Apr 20, 2004
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