Strain Measurement Circuit

Discussion in 'The Projects Forum' started by Richi Nixon, Dec 22, 2015.

  1. Richi Nixon

    Thread Starter New Member

    Dec 8, 2015
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    Hi,

    I have designed the strain measurement circuit with instrumentation amplifier and RC low pass filter.
    Gain =10, Vsin = 2 v, input Freq = 2 kHz, cut off frequency fc = 15.9 kHz. The circuit is working efficiently until the frequency of the input is varied to 6 kHz but beyond these value the output is unpredictable that is amplitude is decreasing.

    Please find the attachment of the circuit screen shot and Lt Spice model is attached.

    Thanks and Regards,
    Richi Nixon V
     
  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    It says opamp2 undefined. When I tried it with LT1007 the -3dB bandwidth was roughly 6kHz. AC analysis is much better for analysing bandwidth than transient.
     
  3. Richi Nixon

    Thread Starter New Member

    Dec 8, 2015
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    Yes, even with LM741 I am able to get 6kHz and I tried with AC analysis too.

    Thank you
     
  4. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    When you delete the second stage you get that ~15kHz corner. However when you stack two stages together without any buffer they infulence each other and the corner shifts, in this case lower.
     
  5. Richi Nixon

    Thread Starter New Member

    Dec 8, 2015
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    Indeed it's happening the way suggested..
    Any work around! What if incase use of Bessel filter
     
  6. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    You can use whatever filter you want, but you need to calculate it properly. If you change the values to get the required corner everything should be fine with the simple one.
     
  7. Richi Nixon

    Thread Starter New Member

    Dec 8, 2015
    17
    0
    Ok...will look into it, many thanks again.
     
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